LAMA2 gene mutation update: Toward a more comprehensive picture of the laminin-α2 variome and its related phenotypes

Atypical Presentation of Congenital Muscular Dystrophy: A LAMA2 Related Muscular Dystrophy

The congenital muscular dystrophies are a group of inherited disorders that present in infancy or early childhood with generalized weakness and hypotonia as well as a wide range of other clinical manifestations. Merosin-deficient congenital muscular dystrophy, also referred to as LAMA2-related muscular dystrophy, is caused by biallelic pathogenic variants in the LAMA2 gene and can present with both an early-onset infantile and late-onset childhood form. Patients with the most severe phenotype typically present within the first few months of life with severe weakness and hypotonia and can develop contractures, scoliosis, dysphagia, as well as peripheral nerve and central nervous system abnormalities. We report a case of an infant that presented with focal weakness of his upper extremities that was initially thought to be due to cervical spinal abnormality or brachial plexus injury but was ultimately found to have Merosin-deficient congenital muscular dystrophy. This case highlights an atypical presentation of congenital muscular dystrophy and demonstrates the importance of having a low threshold for testing for congenital muscular dystrophies in infants with abnormalities in strength or tone.

A Spectrum of Pathogenic Variants in the LAMA2 Gene in the Russian Federation

LAMA2-associated muscular dystrophy is a rare genetic disorder caused by pathogenic or likely pathogenic variants in the LAMA2 gene. The aim of this study is to characterize the spectrum of pathogenic/likely pathogenic variants in the LAMA2 gene among Russian patients, identify frequent pathogenic variants specific to this population, and estimate the prevalence of this disorder in Russia. Data were collected and analyzed from patients with confirmed diagnoses of LAMA2-associated muscular dystrophy using various molecular genetic methods in research centers from 2008 to 2024. Data were obtained from 90 unrelated patients with LAMA2-associated muscular dystrophy, out of which 83 presented with the more severe form, MDC1A1, while seven had milder form of LAMA2-associated muscular dystrophy. The most common pathogenic variants identified were nonsense mutations (40% of cases), followed by frameshift variants (29.3%), splicing variants (21.4%), gross deletions (5.3%), and missense variants (4%). It is worth noting that missense variants were found exclusively in patients with the milder form of LAMA2-associated muscular dystrophy. The most prevalent identified pathogenic variant was c.7536del (15%), characteristic of Slavic populations with an established founder effect. Additionally, a common pathogenic variant, c.8245-2A>G, was found predominantly in Kazan Tatars. The estimated prevalence of LAMA2-associated muscular dystrophy in Russia is approximately 1 in 117,700.

Noncoding variants are a rare cause of recessive developmental disorders in trans with coding variants

PURPOSE

Identifying pathogenic noncoding variants is challenging. A single protein-altering variant is often identified in a recessive gene in individuals with developmental disorders (DD), but the prevalence of pathogenic noncoding "second hits" in trans with these is unknown.

METHODS

In 4073 genetically undiagnosed rare-disease trio probands from the 100,000 Genomes project, we identified rare heterozygous protein-altering variants in recessive DD-associated genes. We identified rare noncoding variants on the other haplotype in introns, untranslated regions, promoters, and candidate enhancer regions. We clinically evaluated the top candidates for phenotypic fit and performed functional testing where possible.

RESULTS

We identified 3761 rare heterozygous loss-of-function or ClinVar pathogenic variants in recessive DD-associated genes in 2430 probands. For 1366 (36.3%) of these, we identified at least 1 rare noncoding variant in trans. Bioinformatic filtering and clinical review, revealed 7 to be a good clinical fit. After detailed characterization, we identified likely diagnoses for 3 probands (in GAA, NPHP3, and PKHD1) and candidate diagnoses in a further 3 (PAH, LAMA2, and IGHMBP2).

CONCLUSION

We developed a systematic approach to uncover new diagnoses involving compound heterozygous coding/noncoding variants and conclude that this mechanism is likely to be a rare cause of DDs.

On RNA-programmable gene modulation as a versatile set of principles targeting muscular dystrophies

The repurposing of RNA-programmable CRISPR systems from genome editing into epigenome editing tools is gaining pace, including in research and development efforts directed at tackling human disorders. This momentum stems from the increasing knowledge regarding the epigenetic factors and networks underlying cell physiology and disease etiology and from the growing realization that genome editing principles involving chromosomal breaks generated by programmable nucleases are prone to unpredictable genetic changes and outcomes. Hence, engineered CRISPR systems are serving as versatile DNA-targeting scaffolds for heterologous and synthetic effector domains that, via locally recruiting transcription factors and chromatin remodeling complexes, seek interfering with loss-of-function and gain-of-function processes underlying recessive and dominant disorders, respectively. Here, after providing an overview about epigenetic drugs and CRISPR-Cas-based activation and interference platforms, we cover the testing of these platforms in the context of molecular therapies for muscular dystrophies. Finally, we examine attributes, obstacles, and deployment opportunities for CRISPR-based epigenetic modulating technologies.

Phenotype-genotype spectrum of a cohort of congenital muscular dystrophies: a single-centre experience from India

Congenital Muscular Dystrophies (CMD) are phenotypically and genotypically heterogenous disorders with a prevalence of 0.68 to 2.5/100,000, contributing to significant morbidity and mortality. We aimed to study the phenotype-genotype spectrum of genetically confirmed cases of CMD. This was retrospective & descriptive study done at a quaternary care referral centre in south India. Genetically confirmed cases of CMDs seen between 2010 to 2020 were recruited. Detailed clinical history, including pedigree, MRI brain/muscle, next generation sequencing results of 61 CMD cases were collected. Collagen VI-related dystrophy (COL6-RD) (36%) was the most common subtype with variants frequently seen in COL6A1 gene. Other CMDs identified were LAMA2-RD (26%), alpha-dystroglycan-RD (19%), LMNA-RD (8%), CHKB-RD (7%) and SEPN1-RD (3%). Similar to previous cohorts, overall, missense variants were common in COL-6 RD. Variants in triple helical domain (THD) of COL6-RD were seen in 11/22 patients, 5 of whom were ambulatory contrary to previous literature citing severe disease with these variants. However, our follow-up period was shorter. In the LAMA2-RD, 2/16 patients were ambulatory & all 16 carried truncating variants. Among dystroglycanopathies, FKRP-RD was the commonest. Milder phenotype of FKRP- RD was observed with variant c.1343C > T, which was also a recurrent variant in our cohort. p.Arg249Trp variant in LMNA-CMD associated with early loss of ambulation was also identified in 1/5 of our patients who expired at age 2.8 years. The current retrospective series provides detailed clinical features and mutation patterns of genetically confirmed cases of CMD from a single center in India.

Genetic profile of Brazilian patients with LAMA2-related dystrophies

LAMA2-related dystrophies (LAMA2-RD) constitute a rare neuromuscular disorder with a broad spectrum of phenotypic severity. Our understanding of the genotype-phenotype correlations in this condition remains incomplete, and reliable clinical data for clinical trial readiness is limited. In this retrospective study, we reviewed the genetic data and medical records of 114 LAMA2-RD patients enrolled at seven research centers in Brazil. We identified 58 different pathogenic variants, including 21 novel ones. Six variants were more prevalent and were present in 81.5% of the patients. Notably, the c.1255del, c.2049_2050del, c.3976 C>T, c.5234+1G>A, and c.4739dup variants were found in patients unable to walk and without cortical malformation. In contrast, the c.2461A>C variant was present in patients who could walk unassisted. Among ambulatory patients, missense variants were more prevalent (p < 0.0001). Although no specific hotspot regions existed in the LAMA2, 51% of point mutations were in the LN domain, and 88% of the missense variants were found within this domain. Functional analysis was performed in one intronic variant (c.4960-17C>A) and revealed an out-of-frame transcript, indicating that the variant creates a cryptic splicing site (AG). Our study has shed light on crucial phenotype-genotype correlations and provided valuable insights, particularly regarding the Latin American population.

Polymerizing laminins in development, health, and disease

Polymerizing laminins are multi-domain basement membrane (BM) glycoproteins that self-assemble into cell-anchored planar lattices to establish the initial BM scaffold. Nidogens, collagen-IV and proteoglycans then bind to the scaffold at different domain loci to create a mature BM. The LN domains of adjacent laminins bind to each other to form a polymer node, while the LG domains attach to cytoskeletal-anchoring integrins and dystroglycan, as well as to sulfatides and heparan sulfates. The polymer node, the repeating unit of the polymer scaffold, is organized into a near-symmetrical triskelion. The structure, recently solved by cryo-electron microscopy in combination with AlphaFold2 modeling and biochemical studies, reveals how the LN surface residues interact with each other and how mutations cause failures of self-assembly in an emerging group of diseases, the LN-lamininopathies, that include LAMA2-related dystrophy and Pierson syndrome.

Fatal Case of Exercise Collapse Associated with Sickle Cell Trait with Novel Underlying LAMA2 Mutation

ABSTRACT

Sickle cell trait is typically thought to be an asymptomatic carrier state, but it is rarely associated with exertional rhabdomyolysis in cases termed Exercise Collapse Associated with Sickle Cell Trait (ECAST). In a subset of these cases, underlying disease contributes to the development and/or severity of the ensuing medical complications. We describe the first ever case of ECAST reported in a previously asymptomatic, multiply deployed, highly physically active service member with an underlying heterozygous LAMA2 mutation. Moreover, the mutation identified via whole exome sequencing is a novel, likely pathogenic variant that has yet to be described in the literature.

A novel deep intronic variant in LAMA2 identified by RNA sequencing

LAMA2-related muscular dystrophy is caused by pathogenic variants of the alpha2 subunit of Laminin. This common form of muscular dystrophy is characterized by elevated CK >1000IU/L, dystrophic changes on muscle biopsy, complete or partial absence of merosin staining, and both central and peripheral nervous system involvement. Advancements in genomic testing using NGS and wider application of RNA sequencing has expanded our knowledge of novel non-coding pathogenic variants in LAMA2. RNA sequencing is an increasingly utilized technique to directly analyze the transcriptome, through creation of a complementary DNA (cDNA) from the transcript within a tissue sample. Here we describe a homozygous deep intronic variant that produces a novel splice junction in LAMA2 identified by RNA sequencing analysis in a patient with a clinical phenotype in keeping with LAMA2-related muscular dystrophy. Furthermore, in this case merosin staining was retained suggestive of a functional deficit.

Exploring Splice-Site Mutations in LAMA2-Related Muscular Dystrophies: A Comprehensive Analysis of Genotypic and Phenotypic Patterns

LAMA2-related muscular dystrophies (LAMA2-RDs) constitute the most prevalent subtype of congenital muscular dystrophies (CMDs). The clinical spectrum of LAMA2-RDs exhibits considerable diversity, particularly in motor development and disease progression. Phenotypic variability ranges from severe, early-onset presentation, known as merosin-deficient CMD type 1A, to milder, late-onset presentations, including limb-girdle muscular dystrophy-like phenotype. In this study, whole exome sequencing (WES) was applied to a family with a single proband affected by severe muscular dystrophy. The identified causative mutation was a biallelic splice-site mutation in intron 58 of the LAMA2 gene, leading to a premature termination codon in the critical G domain of laminin-α2 and resulting in a severe phenotype. Additionally, we summarized previously reported splice-site mutations to investigate the clinical and transcription consequences of these mutations. Our findings conclude that splice-site mutations predominantly lead to severe MDC1A, whether in a homozygous or heterozygous state, often associated with another loss-of-function mutation. Besides, splice-site mutations with available analysis of their transcriptional consequences were found to be responsible for exon skipping in most cases and the loss of the reading frame. These findings revealed the importance of WES in identifying disease-causing mutations, particularly in highly diversified pathologies like LAMA2-RDs. The results also underscore the importance of transcriptional analysis in determining the impact of splice-site mutations and the phenotype of LAMA2-RDs on patients.

An Extremely Rare LAMA2 Gene Variant c.442C>T (p.Arg148Trp) Causing Late-Onset LAMA2-Related Dystrophy

Mutations in the alpha-2 subunits of the laminin gene (LAMA2) cause an autosomal recessive congenital muscular dystrophy (CMD) subtype known as laminin a2-related muscular dystrophies (LAMA2-RD). LAMA2-RD can present with a wide range of phenotypes ranging from severe infantile congenital muscular dystrophy to milder adult-onset limb-girdle muscular dystrophy. This case describes a 28-year-old Indian gentleman having childhood-onset focal seizures, gradually progressive proximal predominant lower-limb weakness for the past three years, elevated creatinine phosphokinase levels, and MRI brain suggestive of diffuse symmetrical periventricular white matter hyperintensities. The whole exome sequencing revealed a rare homozygous missense variant in exon 4 of the LAMA2 gene on chromosome 6 (c.442C>T[p.Arg148Trp]). Adult-onset limb-girdle muscular dystrophy with white matter imaging abnormalities, hyperCKemia, and seizures should evoke suspicion of LAMA2-RD. This case brings forth an ultra-rare genetic mutation that has not been previously reported in individuals of South Asian ethnicity leading to LAMA2-RD. More cases of late-onset LAMA2-RD from various ethnicities need to be reported to expand our understanding of the clinical-genetic spectrum of the disease.

Clinical Reasoning: A 19-Month-Old Girl With Infantile-Onset Myopathy and White Matter Changes

We describe the case of a 19-month-old girl presenting with gross motor delays, hypotonia, diminished deep tendon reflexes, hyperCKaemia, extensive white matter changes on MRI brain, and electromyography studies consistent with myopathy. The differential diagnosis for infantile-onset hypotonia and muscle weakness is broad. It includes numerous subtypes of genetic disorders, including congenital muscular dystrophies, congenital myopathies, congenital myasthenic syndromes, spinal muscular atrophy, single-gene genetic syndromes, and inborn errors of metabolism. We outline our clinical approach leading to the diagnosis of a distinctive genetic neuromuscular condition essential for neurologists and geneticists working with patients of all ages to recognize.

Genetic blueprint of congenital muscular dystrophies with brain malformations in Egypt: A report of 11 families

Congenital muscular dystrophies (CMDs) are a group of rare muscle disorders characterized by early onset hypotonia and motor developmental delay associated with brain malformations with or without eye anomalies in the most severe cases. In this study, we aimed to uncover the genetic basis of severe CMD in Egypt and to determine the efficacy of whole exome sequencing (WES)-based genetic diagnosis in this population. We recruited twelve individuals from eleven families with a clinical diagnosis of CMD with brain malformations that fell into two groups: seven patients with suspected dystroglycanopathy and five patients with suspected merosin-deficient CMD. WES was analyzed by variant filtering using multiple approaches including splicing and copy number variant (CNV) analysis. We identified likely pathogenic variants in FKRP in two cases and variants in POMT1, POMK, and B3GALNT2 in three individuals. All individuals with merosin-deficient CMD had truncating variants in LAMA2. Further analysis in one of the two unsolved cases showed a homozygous protein-truncating variant in Feline Leukemia Virus subgroup C Receptor 1 (FLVCR1). FLVCR1 loss of function has never been previously reported. Yet, loss of function of its paralog, FLVCR2, causes lethal hydranencephaly-hydrocephaly syndrome (Fowler Syndrome) which should be considered in the differential diagnosis for dystroglycanopathy. Overall, we reached a diagnostic rate of 86% (6/7) for dystroglycanopathies and 100% (5/5) for merosinopathy. In conclusion, our results provide further evidence that WES is an important diagnostic method in CMD in developing countries to improve the diagnostic rate, management plan, and genetic counseling for these disorders.

Orthopedic manifestations of congenital muscular dystrophy subtypes in children: Emerging signatures need consolidation: a scoping review

Our objective was to screen the literature on congenital muscular dystrophy (CMD) children/adolescents regarding the extent/nature of reporting orthopedic manifestations/deformities and to assess its appropriateness in informing clinical practice/research. We searched PubMed for original research on orthopedic surgical/non-surgical manifestations of CMD. Eligible articles needed to focus on orthopedic manifestations/deformities as one of the study objectives with no restrictions on study designs/types or search period. Eight hundred and thirty articles were initially identified and screened. Following the exclusion of 501 articles for disagreeing titles/abstracts, 329 were available for eligibility assessment. Two hundred and fifty-five articles were excluded for reasons. Of one hundred articles, 15 were captured manually and 11 through pre-submission searches, with 1078 patients included in the final analysis. The most common subtype was Laminin alpha-2 (LAMA2)-relatedCMD. Orthopedic manifestations of CMD are generally underreported and insufficiently detailed. There is reliable evidence that accurate reporting of orthopedic manifestations can be a valuable clinical supplement to the complex differential diagnosis process in collagen VI-related CMD, LAMA2-related-CMD, LMNA-related-CMD, and SEPN1-related CMD (SELENON). For alpha dystroglycan-related CMD, there is insufficient information to delineate a subtype-specific pattern. There is emerging evidence that reporting spine surgery outcomes may facilitate orthopedic decision making. The greatest clinical/research utility was provided by articles with longitudinal, comprehensive, and correlative reporting of larger cohorts. Detailed reporting of the orthopedic phenotype of CMD in future research may further uncover its diagnostic potential.

Uncovering Evolutionary Adaptations in Common Warthogs through Genomic Analyses

In the Suidae family, warthogs show significant survival adaptability and trait specificity. This study offers a comparative genomic analysis between the warthog and other Suidae species, including the Luchuan pig, Duroc pig, and Red River hog. By integrating the four genomes with sequences from the other four species, we identified 8868 single-copy orthologous genes. Based on 8868 orthologous protein sequences, phylogenetic assessments highlighted divergence timelines and unique evolutionary branches within suid species. Warthogs exist on different evolutionary branches compared to DRCs and LCs, with a divergence time preceding that of DRC and LC. Contraction and expansion analyses of warthog gene families have been conducted to elucidate the mechanisms of their evolutionary adaptations. Using GO, KEGG, and MGI databases, warthogs showed a preference for expansion in sensory genes and contraction in metabolic genes, underscoring phenotypic diversity and adaptive evolution direction. Associating genes with the QTLdb-pigSS11 database revealed links between gene families and immunity traits. The overlap of olfactory genes in immune-related QTL regions highlighted their importance in evolutionary adaptations. This work highlights the unique evolutionary strategies and adaptive mechanisms of warthogs, guiding future research into the distinct adaptability and disease resistance in pigs, particularly focusing on traits such as resistance to African Swine Fever Virus.

Myelin abnormalities in merosin-deficient congenital muscular dystrophy

INTRODUCTION/AIMS

Merosin is a protein complex located in the basement membrane of skeletal muscles and laminin α2-containing regions of the central and peripheral nervous systems. However, because of the prominence of muscle-related symptoms, peripheral neuropathy associated with merosin-deficient congenital muscular dystrophy type 1A (MDC1A) has received little clinical attention. This study aimed to present pathological changes in intramuscular nerves of three patients with MDC1A and discuss their relationship with electrophysiological findings to provide new evidence of peripheral nerve involvement in MDC1A.

METHODS

MDC1A was confirmed by clinical features, muscle biopsy, and genetic testing for variants in LAMA2. To clarify peripheral nerve involvement, we statistically evaluated electrophysiological and muscle pathology findings of intramuscular nerves. These findings were compared with those of age-matched boys with Duchenne muscular dystrophy (DMD) as controls with normal nerves. Nerve conduction studies (NCS) were performed before biopsy. Biopsied intramuscular nerves were examined with electron microscopy using g-ratio, which is the ratio of axon diameter to myelinated fiber diameter.

RESULTS

The myelin sheaths were significantly thinner in MDC1A patients than in age-matched DMD patients, with a mean g-ratio of 0.76 ± 0.07 in MDC1A patients and 0.65 ± 0.14 in DMD patients (p < .0001). No neuropathic changes were identified in muscle pathology. Low compound muscle action potential amplitudes, positive sharp waves and fibrillation potentials, and low-amplitude motor unit potentials with increased polyphasia indicated myopathic changes; no neurogenic changes were seen.

DISCUSSION

We postulate that the thin myelin associated with MDC1A reflects the role of merosin in myelin maturation.

Respiratory function in LAMA2-related muscular dystrophy and SELENON-related congenital myopathy, a 1.5-year natural history study

INTRODUCTION

LAMA2-related muscular dystrophy (LAMA2-MD) and SELENON(SEPN1)-related congenital myopathy (SELENON-RM) are rare neuromuscular diseases with respiratory impairment from a young age. Prospective natural history studies are needed for prevalence estimations, respiratory characterization, optimizing clinical care and selecting outcome measures for trial readiness.

METHODS

Our prospective 1.5-year natural history study included spirometry (forced vital capacity (FVC); difference between upright and supine vital capacity (dVC)), respiratory muscle strength tests (sniff nasal inspiratory pressure (SNIP)) (age≥5 years), and diaphragm ultrasound (thickness; thickening; echogenicity; all ages).

RESULTS

Twenty-six LAMA2-MD patients (M = 8, median 21 [9; 31] years) and 11 SELENON-RM patients (M = 8, 20 [10; 33] years) were included. At baseline, 17 (85 %) LAMA2-MD (FVC%: 59 % [33; 68]) and all SELENON-RM patients (FVC%: 34 % [31; 46]) had an impaired respiratory function (FVC%<80 %). Nine (35 %) LAMA2-MD and eight (73 %) SELENON-RM patients received mechanical ventilation at baseline, and two additional SELENON-RM patients started during follow-up. Contrarily to LAMA2-MD, SELENON-RM patients had severe diaphragm atrophy (diaphragm thickness z-score: 2.5 [-3.1; -2.1]) and dysfunction (diaphragm thickness ratio: 1.2 [1.0; 1.7]; dVC: 30 % [7.7; 41]). SNIP was low in both neuromuscular diseases and correlated with motor function. In SELENON-RM, respiratory function decreased during follow-up.

CONCLUSION

The majority of LAMA2-MD and all SELENON-RM patients had respiratory impairment. SELENON-RM patients showed lower respiratory function which was progressive, more prevalent mechanical ventilation, and more severe diaphragm atrophy and dysfunction than LAMA2-MD patients. Spirometry (FVC%, dVC) and respiratory muscle strength tests (SNIP) are useful in clinical care and as outcome measure in clinical trials.

CLINICAL TRIAL NUMBER

NCT04478981.

A Multicenter Cross-Sectional Study of the Swiss Cohort of LAMA2-Related Muscular Dystrophy

Background

LAMA2-related muscular dystrophy (LAMA2-RD) is an autosomal-recessive disorder and one of the most common congenital muscular dystrophies. Due to promising therapies in preclinical development, there is an increasing effort to better define the epidemiology and natural history of this disease.

Objective

The present study aimed to describe a well-characterized baseline cohort of patients with LAMA2-RD in Switzerland.

Methods

The study used data collected by the Swiss Registry for Neuromuscular Disorders (Swiss-Reg-NMD). Diagnostic findings were derived from genetics, muscle biopsy, creatine kinase-level and electrophysiological testing, as well as from brain MRIs. Further clinical information included motor assessments (CHOP INTEND, MFM20/32), joint contractures, scoliosis, ophthalmoplegia, weight gain, feeding difficulties, respiratory function, cardiac investigations, EEG findings, IQ and schooling.

Results

Eighteen patients with LAMA-RD were included in the Swiss-Reg-NMD as of May 2023 (age at inclusion into the registry: median age 8.7 years, range 1 month - 31 years F = 8, M = 10). Fourteen patients presented with the severe form of LAMA2-RD (were never able to walk; CMD), whereas four patients presented with the milder form (present or lost walking capability; LGMD). All patients classified as CMD had symptoms before 12 months of age and 11/14 before the age of six months. 15 carried homozygous or compound heterozygous pathogenic or likely pathogenic variants in LAMA2 and two were homozygous for a variant of unknown significance (one patient unknown). Brain MRI was available for 14 patients, 13 had white matter changes and 11 had additional structural abnormalities, including cobblestone malformations, pontine hypoplasia and an enlarged tegmento-vermial angle not reported before.

Conclusion

This study describes the Swiss cohort of patients with LAMA2-RD and gives insights into measuring disease severity and disease progression, which is important for future clinical trials, as well as for a better clinical understanding and management of patients with LAMA2-RD.

Artificial intelligence and the analysis of cryo-EM data provide structural insight into the molecular mechanisms underlying LN-lamininopathies

Laminins (Lm) are major components of basement membranes (BM), which polymerize to form a planar lattice on cell surface. Genetic alternations of Lm affect their oligomerization patterns and lead to failures in BM assembly manifesting in a group of human disorders collectively defined as Lm N-terminal domain lamininopathies (LN-lamininopathies). We have employed a recently determined cryo-EM structure of the Lm polymer node, the basic repeating unit of the Lm lattice, along with structure prediction and modeling to systematically analyze structures of twenty-three pathogenic Lm polymer nodes implicated in human disease. Our analysis provides the detailed mechanistic explanation how Lm mutations lead to failures in Lm polymerization underlining LN-lamininopathies. We propose the new categorization scheme of LN-lamininopathies based on the insight gained from the structural analysis. Our results can help to facilitate rational drug design aiming in the treatment of Lm deficiencies.

LAMA2-Related Muscular Dystrophy Across the Life Span: A Cross-sectional Study

Background and Objectives

LAMA2-related muscular dystrophy (LAMA2-MD) is a rare neuromuscular disease characterized by proximal and axial muscle weakness, rigidity of the spine, scoliosis, and respiratory impairment. No curative treatment options exist, yet promising preclinical studies are ongoing. Currently, there is a paucity on natural history data, and appropriate clinical and functional outcome measures are needed. We aim for deep clinical phenotyping, establishment of a well-characterized baseline cohort for prospective follow-up and recruitment for future clinical trials, improvement of clinical care, and selection of outcome measures for reaching trial readiness.

Methods

We performed a cross-sectional, single-center, observational study. This study included neurologic examination and functional measurements among others the Motor Function Measure 20/32 (MFM-20/32) as primary outcome measure, accelerometry, questionnaires, muscle ultrasound, respiratory function tests, electrocardiography and echocardiography, and dual-energy X-ray absorptiometry.

Results

Twenty-seven patients with genetically confirmed LAMA2-MD were included (21 ± 13 years; M = 9; ambulant = 7). Axial and proximal muscle weakness was most pronounced. The mean MFM-20/32 score was 42.0% ± 29.4%, with domain 1 (standing and transfers) being severely affected and domain 3 (distal muscle function) relatively spared. Physical activity as measured through accelerometry showed very strong correlations to MFM-20/32 (Pearson correlation, -0.928, p < 0.01). Muscle ultrasound showed symmetrically increased echogenicity, with the sternocleidomastoid muscle most affected. Respiratory function was impaired in 85% of patients without prominent diaphragm dysfunction and was independent of age. Ten patients (37%) needed (non)invasive ventilatory support. Cardiac assessment revealed QRS fragmentation in 62%, abnormal left ventricular global longitudinal strain in 25%, and decreased left ventricular ejection fraction in 14% of patients. Decreased bone quality leading to fragility fractures was seen in most of the patients.

Discussion

LAMA2-MD has a widely variable phenotype. Based on the results of this cross-sectional study and current standards of care for congenital muscular dystrophies, we advise routine cardiorespiratory follow-up and optimization of bone quality. We propose MFM-20/32, accelerometry, and muscle ultrasound for assessing disease severity and progression. For definitive clinical recommendations and outcome measures, natural history data are needed.

Clinical Trials Registration

This study was registered at clinicaltrials.gov (NCT04478981, 21 July 2020). The first patient was enrolled in September 2020.

En route towards a personalized medicine approach: Innovative therapeutic modalities for connective tissue disorders

Connective tissue disorders can be caused by pathogenic variants (mutations) in genes encoding extracellular matrix (ECM) proteins. Such disorders typically manifest during development or postnatal growth and result in significant morbidity and mortality. The development of curative treatments for connective tissue disorders is hampered in part by the inability of many mature connective tissues to efficiently regenerate. To be most effective, therapeutic strategies designed to preserve or restore tissue function will likely need to be initiated during phases of significant endogenous connective tissue remodeling and organ sculpting postnatally and directly target the underlying ECM protein mutations. With recent advances in whole exome sequencing, in-vitro and in-vivo disease modeling, and the development of mutation-specific molecular therapeutic modalities, it is now feasible to directly correct disease-causing mutations underlying connective tissue disorders and ameliorate their pathogenic consequences. These technological advances may lead to potentially curative personalized medicine approaches for connective tissue disorders that have previously been considered incurable. In this review, we highlight innovative therapeutic modalities including gene replacement, exon skipping, DNA/mRNA editing, and pharmacological approaches that were used to preserve or restore tissue function in the context of connective tissue disorders. Inherent to a successful application of these approaches is the need to deepen the understanding of mechanisms that regulate ECM formation and homeostasis, and to decipher how individual mutations in ECM proteins compromise ECM and connective tissue development and function.

Chain-specificity of laminin α1-5 LG45 modules in the recognition of carbohydrate-linked receptors and intramolecular binding

Laminins are a family of heterotrimers composed of α-, β-, and γ-chains in the basement membrane. Five α chains contain laminin globular (LG) domain consisting of five tandem modules (LG1-5 modules) at their C-terminus. Each LG45 modules is connected to a compact cloverleaf-shaped structure of LG1-3 through a flexible linker. Although the accumulated studies of the LG45 modules have suggested differences in each α chain regarding the binding of carbohydrate chain and intramolecular interaction, this remains unclear. In this study, to characterize their functions comparatively, we produced recombinant proteins of LG45 modules of human laminin α1-5 chains. Dystroglycan (DG) modified with matriglycan readily bound to the LG45 modules of α1 and α2 chains but not to the other α chains. In contrast, heparin bound to the LG45 modules of the α chains, except for α2. The binding of heparan sulfate/heparin-linked syndecans (SDCs) to LG45 modules was influenced by their core proteins. Furthermore, the α1 and α4LG45 modules bound to SDCs in a pH-dependent manner. A cell adhesion assay showed that HEK293 cells could readily adhere to the LG45 modules of α3-5 chains through a combination of SDCs and integrins. Moreover, α5LG45 modules bound to the E8 fragment, which includes the C-terminus of the laminin coiled-coil (LCC) domain and LG1-3 modules, but α2LG45 modules did not. The results suggested that although α5LG45 modules was fixed within the LG domain, α2LG45 modules was freely placed in the vicinity of LG1-3. Our findings provide information for investigation of the structural and functional diversity of basement membranes.

Case report: Novel frameshift mutation in LAMA2 gene causing congenital muscular dystrophy type 1A

Congenital muscular dystrophy type 1A (CMD1A) is a rare autosomal recessive disorder caused by mutations in the LAMA2 gene. CMD1A is characterized by peripheral hypotonia and muscle weakness from the first months of life, cerebral white matter abnormalities, and elevated creatine phosphokinase (CPK) levels. We describe an 8-year-old girl from Colombia with clinical features compatible with CMD1A, severe scoliosis corrected with surgery, and feeding difficulty corrected with a gastrostomy. Whole-exome sequencing identified two heterozygous variants: a reported nonsense variant (LAMA2 NM_000426.3:c.4198C>T) and a novel likely pathogenic variant (LAMA2 NM_000426.3:c.9227_9243dup). This is the first genetically confirmed case of CMD1A in Colombia and the first report of the c.9227_9243dup variant causing CMD1A.

Limb girdle muscular dystrophy 23 caused by compound heterozygous mutations of LAMA2 gene

Introduction

Mutations of LAMA2 gene are associated with congenital muscular dystrophy (CMD). The LAMA2-related CMD mainly consists of two diseases, merosin deficient congenital muscular dystrophies type 1A (MDC1A) and limb girdle muscular dystrophy 23 (LGMD23). LGMD23 is characterized by slowly progressive proximal muscle weakness, which primarily affects the lower limbs and results in gait difficulties. Additional clinical features include increased serum creatine kinase, abnormal electromyography with or without white matter abnormalities on brain imaging.

Methods

Clinical data were collected from a Chinese Han family. Whole-exome sequencing, Sanger sequencing, RT-PCR and TA clone sequencing were performed on the family members.

Results

Compound heterozygous mutations of LAMA2: c.1693C > T (p. Q565*) (maternally inherited) and c.9212-6T > G (paternally inherited) were identified and confirmed in the proband. The mutation c.1693C > T (p. Q565*) was classified as pathogenic according to American College of Medical Genetics and Genomics (ACMG) guidelines. By performing RT-PCR and TA clone sequencing, an insertion of 40-bp intronic sequence (intron 64) was found in the transcripts of the proband and her father, which resulted in a frameshift and premature truncation codon of the LAMA2. In particular, the variant truncated the LamG domain of the LAMA2. Therefore, the c.9212-6T>G was classified as likely pathogenic according to American College of Medical Genetics and Genomics (ACMG) guidelines.

Discussion

Our findings described two novel mutations in a girl with LGMDR23, which contributes to the genetic counseling of the family and expands the clinical and molecular spectrums of the rare disease.

Merosin-deficient congenital muscular dystrophy type 1a: detection of LAMA2 variants in Vietnamese patients

Background: Merosin-deficient congenital muscular dystrophy type 1A (MDC1A), also known as laminin-α2 chain-deficient congenital muscular dystrophy (LAMA2-MD), is an autosomal recessive disease caused by biallelic variants in the LAMA2 gene. In MDC1A, laminin- α2 chain expression is absent or significantly reduced, leading to some early-onset clinical symptoms including severe hypotonia, muscle weakness, skeletal deformity, non-ambulation, and respiratory insufficiency. Methods: Six patients from five unrelated Vietnamese families presenting with congenital muscular dystrophy were investigated. Targeted sequencing was performed in the five probands. Sanger sequencing was carried out in their families. Multiplex ligation-dependent probe amplification was performed in one family to examine an exon deletion. Results: Seven variants of the LAMA2 (NM_000426) gene were identified and classified as pathogenic/likely pathogenic variants using American College of Medical Genetics and Genomics criteria. Two of these variants were not reported in the literature, including c.7156-5_7157delinsT and c.8974_8975insTGAT. Sanger sequencing indicated their parents as carriers. The mothers of family 4 and family 5 were pregnant and a prenatal testing was performed. The results showed that the fetus of the family 4 only carries c.4717 + 5G>A in the heterozygous form, while the fetus of the family 5 carries compound heterozygous variants, including a deletion of exon 3 and c.4644C>A. Conclusion: Our findings not only identified the underlying genetic etiology for the patients, but also provided genetic counseling for the parents whenever they have an offspring.

Brain MRI Abnormalities, Epilepsy and Intellectual Disability in LAMA2 Related Dystrophy - a Genotype/Phenotype Correlation

BACKGROUND

LAMA2-related muscular dystrophy is a disorder that causes muscle weakness and varies in severity, from a severe, congenital type to a milder, late-onset form. However, the disease does not only affect the muscles, but has systemic involvement and can lead to alterations such as brain malformation, epilepsy and intellectual disability.

OBJECTIVE

Describe the frequency of cortical malformations, epilepsy and intellectual disability in LAMA2-RD in a Brazilian cohort and correlate the neurological findings to genetic and motor function.

METHODS

This is an observational study of 52 LAMA2-RD patients, who were divided into motor function subgroups and compared based on brain MRI findings, epilepsy, intellectual disability, and type of variants and variant domains.

RESULTS

44 patients (84.6%) were only able to sit, and 8 patients (15.4%) were able to walk. 10 patients (19.2%) presented with cortical malformations (polymicrogyria, lissencephaly-pachygyria, and cobblestone),10 patients (19.2%) presented with epilepsy, and 8 (15.4%) had intellectual disability. CNS manifestations correlated with a more severe motor phenotype and none of the patients able to walk presented with cortical malformation or epilepsy. There was a relation between gene variants affecting the laminin-α2 LG-domain and the presence of brain malformation (P = 0.016). There was also a relation between the presence of null variants and central nervous system involvement. A new brazilian possible founder variant was found in 11 patients (21,15%) (c.1255del; p. Ile419Leufs *4).

CONCLUSION

Cortical malformations, epilepsy and intellectual disability are more frequent among LAMA2-RD patients than previously reported and correlate with motor function severity and the presence of variants affecting the laminin-α2 LG domain. This brings more insight fore phenotype-genotype correlations, shows the importance of reviewing the brain MRI of patients with LAMA2-RD and allows greater attention to the risk of brain malformation, epilepsy, and intellectual disability in those patients with variants that affect the LG domain.

Dual transgene amelioration of Lama2-null muscular dystrophy

Null mutations of the Lama2-gene cause a severe congenital muscular dystrophy and associated neuropathy. In the absence of laminin-α2 (Lmα2) there is a compensatory replacement by Lmα4, a subunit that lacks the polymerization and α-dystroglycan (αDG)-binding properties of Lmα2. The dystrophic phenotype in the dy3K/dy3K Lama2-/- mouse were evaluated with transgenes driving expression of two synthetic laminin-binding linker proteins. Transgenic muscle-specific expression of αLNNd, a chimeric protein that enables α4-laminin polymerization, and miniagrin (mag), a protein that increases laminin binding to the receptor αDG, separately improved median mouse survival two-fold. The double transgenes (DT) improved mean survival three-fold with increases in overall body weight, muscle size, and grip strength, but, given absence of neuronal expression, did not prevent hindlimb paresis. Muscle improvements included increased myofiber size and number and reduced fibrosis. Myofiber hypertrophy with increased mTOR and Akt phosphorylation were characteristics of mag-dy3K/dy3K and DT-dy3K/dy3K muscle. Elevations of matrix-bound α4-, β1 and γ1 laminin subunits were detected in muscle extracts and immunostained sections in response to DT expression. Collectively, these findings reveal a complimentary polymerization and αDG-binding benefit to Lama2-/- mouse muscle largely mediated through modified laminin-411.

RNA analysis of intronic variants in the LAMA2 gene detected by whole genome sequencing confirms a rare dual diagnosis of incontinentia pigmenti with limb-girdle muscular dystrophy

We see that a multiple methods approach to diagnosis remains necessary in the era of whole genome sequencing. We also observe that reproductive risk genetic counseling can be a motivating factor for further testing along the diagnostic odyssey.

Estimating the Prevalence of LAMA2 Congenital Muscular Dystrophy using Population Genetic Databases

Background: Recessive pathogenic variants in LAMA2 resulting in complete or partial loss of laminin α2 protein cause congenital muscular dystrophy (LAMA2 CMD). The prevalence of LAMA2 CMD has been estimated by epidemiological studies to lie between 1.36–20 cases per million. However, prevalence estimates from epidemiological studies are vulnerable to inaccuracies owing to challenges with studying rare diseases. Population genetic databases offer an alternative method for estimating prevalence. Objective: We aim to use population allele frequency data for reported and predicted pathogenic variants to estimate the birth prevalence of LAMA2 CMD. Methods: A list of reported pathogenic LAMA2 variants was compiled from public databases, and supplemented with predicted loss of function (LoF) variants in the Genome Aggregation Database (gnomAD). gnomAD allele frequencies for 273 reported pathogenic and predicted LoF LAMA2 variants were used to calculate disease prevalence using a Bayesian methodology. Results: The world-wide birth prevalence of LAMA2 CMD was estimated to be 8.3 per million (95% confidence interval (CI) 6.27 –10.5 per million). The prevalence estimates for each population in gnomAD varied, ranging from 1.79 per million in East Asians (95% CI 0.63 –3.36) to 10.1 per million in Europeans (95% CI 6.74 –13.9). These estimates were generally consistent with those from epidemiological studies, where available. Conclusions: We provide robust world-wide and population-specific birth prevalence estimates for LAMA2 CMD, including for non-European populations in which LAMA2 CMD prevalence hadn’t been studied. This work will inform the design and prioritization of clinical trials for promising LAMA2 CMD treatments.

Rare Coding Variants in Patients with Non-Syndromic Vestibular Dysfunction

Vertigo due to vestibular dysfunction is rare in children. The elucidation of its etiology will improve clinical management and the quality of life of patients. Genes for vestibular dysfunction were previously identified in patients with both hearing loss and vertigo. This study aimed to identify rare, coding variants in children with peripheral vertigo but no hearing loss, and in patients with potentially overlapping phenotypes, namely, Meniere's disease or idiopathic scoliosis. Rare variants were selected from the exome sequence data of 5 American children with vertigo, 226 Spanish patients with Meniere's disease, and 38 European-American probands with scoliosis. In children with vertigo, 17 variants were found in 15 genes involved in migraine, musculoskeletal phenotypes, and vestibular development. Three genes, OTOP1, HMX3, and LAMA2, have knockout mouse models for vestibular dysfunction. Moreover, HMX3 and LAMA2 were expressed in human vestibular tissues. Rare variants within ECM1, OTOP1, and OTOP2 were each identified in three adult patients with Meniere's disease. Additionally, an OTOP1 variant was identified in 11 adolescents with lateral semicircular canal asymmetry, 10 of whom have scoliosis. We hypothesize that peripheral vestibular dysfunction in children may be due to multiple rare variants within genes that are involved in the inner ear structure, migraine, and musculoskeletal disease.

CRISPRa-induced upregulation of human LAMA1 compensates for LAMA2-deficiency in Merosin-deficient congenital muscular dystrophy

Merosin-deficient congenital muscular dystrophy (MDC1A) is an autosomal recessive disorder caused by mutations in the LAMA2 gene, resulting in a defective form of the extracellular matrix protein laminin-α2 (LAMA2). Individuals diagnosed with MDC1A exhibit progressive muscle wasting and declining neuromuscular functions. No treatments for this disorder are currently available. We previously showed that postnatal Lama1 upregulation, achieved through CRISPR activation (CRISPRa), compensates for Lama2 deficiency and prevents neuromuscular pathophysiology in a mouse model of MDC1A. In this study, we assessed the feasibility of upregulating human LAMA1 as a potential therapeutic strategy for individuals with MDC1A, regardless of their mutations. We hypothesized that CRISPRa-mediated upregulation of human LAMA1 would compensate for the lack of LAMA2 and rescue cellular abnormalities in MDC1A fibroblasts. Global transcriptomic and pathway enrichment analyses of fibroblasts collected from individuals carrying pathogenic LAMA2 mutations, compared with healthy controls, indicated higher expression of transcripts encoding proteins that contribute to wound healing, including Transforming Growth Factor-β (TGF-β) and Fibroblast Growth Factor (FGF). These findings were supported by wound-healing assays indicating that MDC1A fibroblasts migrated significantly more rapidly than the controls. Subsequently, we treated the MDC1A fibroblasts with SadCas9-2XVP64 and sgRNAs targeting the LAMA1 promoter. We observed robust LAMA1 expression, which was accompanied by significant decreases in cell migration and expression of FGFR2, TGF-β2, and ACTA2, which are involved in the wound-healing mechanism in MDC1A fibroblasts. Collectively, our data suggest that CRISPRa-mediated LAMA1 upregulation may be a feasible mutation-independent therapeutic approach for MDC1A. This strategy might be adapted to address other neuromuscular diseases and inherited conditions in which strong compensatory mechanisms have been identified.

Novel compound heterozygous mutations of LAMA2-limb-girdle muscular dystrophy: A case report and literature review

The laminin α2 (LAMA2) gene pathogenic variants can lead to limb-girdle muscular dystrophy (known as LGMDR23), which is rarely reported and characterized by proximal weakness in the limbs. We present the case of a 52-year-old woman who gradually developed weakness in both lower extremities since the age of 32 years. Magnetic resonance imaging (MRI) brain showed symmetrical sphenoid wings-like white matter demyelination in bilateral lateral ventricles. Electromyography showed quadriceps muscle damage on the bilateral lower extremity. Next-generation sequencing (NGS) found two loci variations in the LAMA2 gene, i.e., c.2749 + 2dup and c.8689C>T. This case highlights the importance of considering LGMDR23 in patients presenting with weakness and white matter demyelination on MRI brain and further expands the gene variants spectrum of LGMDR23.

Case report: Adult-onset limb girdle muscular dystrophy in sibling pair due to novel homozygous LAMA2 missense variant

Recessive pathogenic variants in the laminin subunit alpha 2 (LAMA2) gene cause a spectrum of disease ranging from severe congenital muscular dystrophy to later-onset limb girdle muscular dystrophy (LGMDR23). The phenotype of LGMDR23 is characterized by slowly progressive proximal limb weakness, contractures, raised creatine kinase, and sometimes distinctive cerebral white matter changes and/or epilepsy. We present two siblings, born to consanguineous parents, who developed adult-onset LGMDR23 associated with typical cerebral white matter changes and who both later developed dementia. The male proband also had epilepsy and upper motor neuron signs when he presented at age 72. Merosin immunohistochemistry and Western blot on muscle biopsies taken from both subjects was normal. Whole exome sequencing revealed a previously unreported homozygous missense variant in LAMA2 [Chr6(GRCh38):g.129297734G>A; NM_000426.3:c.2906G>A; p.(Cys969Tyr)] in the proband. The same homozygous LAMA2 variant was confirmed by Sanger sequencing in the proband's affected sister. These findings expand the genotypic and phenotypic spectrum of LGMDR23.

LAMA2-Related Muscular Dystrophy: The Importance of Accurate Phenotyping and Brain Imaging in the Diagnosis of LGMD

We report three siblings from a non-consanguineous family presenting with contractural limb-girdle phenotype with intrafamilial variability. Muscle MRI showed posterior thigh and quadriceps involvement with a sandwich-like sign. Whole-exome sequencing identified two compound heterozygous missense TTN variants and one heterozygous LAMA2 variant. Brain MRI performed because of concentration difficulties in one of the siblings evidenced white-matter abnormalities, subsequently found in the others. The genetic analysis was re-oriented, revealing a novel pathogenic intronic LAMA2 variant which confirmed the LAMA2-RD diagnosis. This work highlights the importance of a thorough clinical phenotyping and the importance of brain imaging, in order to orientate and interpret the genetic analysis.

Unique genotype-phenotype correlations within LAMA2-related limb girdle muscular dystrophy in Chinese patients

Background

LAMA2-related limb girdle muscular dystrophy (LGMD R23) is rare. The detailed clinical phenotypes and genetic information associated with LGMD R23 are unknown.

Methods

We conducted a retrospective cross-sectional and longitudinal study on 19 LGMD R23 patients.

Results

Normal early motor development was observed in 84.2% patients. Mild orthopedic complications were observed in 42.1% patients. 36.8% patients had seizures, which is unusually frequent in LGMD. Epilepsy was eventually diagnosed in 26.3% patients. 46.7% patients presented with motor neuropathy. Genetic analysis identified 29 pathogenic variants, with missense and frameshift variants being the most common. The mutant sites were mainly distributed in the N-terminal and G-like domains of laminin. The missense variants are distributed near the N-terminus (exons 3-11), whereas frameshift variants are distributed in exons 12-65. Five patients were diagnosed with epilepsy and all of them harbor at least one missense variants in exon 4. 71.4% variants of patients with motor neuropathy located in the LN domain.

Conclusions

Missense variants in exon 4 maybe correlated with epilepsy and variants in the LN domain maybe correlated with motor neuropathy in Chinese patients. Our study expands the clinical and genetic spectrum caused by LAMA2 variations and provides novel genotype-phenotype correlations of LGMD R23.

Mechanisms of Myofibre Death in Muscular Dystrophies: The Emergence of the Regulated Forms of Necrosis in Myology

Myofibre necrosis is a central pathogenic process in muscular dystrophies (MD). As post-lesional regeneration cannot fully compensate for chronic myofibre loss, interstitial tissue accumulates and impairs muscle function. Muscle regeneration has been extensively studied over the last decades, however, the pathway(s) controlling muscle necrosis remains largely unknown. The recent discovery of several regulated cell death (RCD) pathways with necrotic morphology challenged the dogma of necrosis as an uncontrolled process, opening interesting perspectives for many degenerative disorders. In this review, we focus on how cell death affects myofibres in MDs, integrating the latest research in the cell death field, with specific emphasis on Duchenne muscular dystrophy, the best-known and most common hereditary MD. The role of regulated forms of necrosis in myology is still in its infancy but there is increasing evidence that necroptosis, a genetically programmed form of necrosis, is involved in muscle degenerating disorders. The existence of apoptosis in myofibre demise will be questioned, while other forms of non-apoptotic RCDs may also have a role in myonecrosis, illustrating the complexity and possibly the heterogeneity of the cell death pathways in muscle degenerating conditions.

Establishment of a PBMC-derived induced pluripotent stem cell (NJUCMi001-A) from a patient with LAMA2-related congenital muscular dystrophy (MDC1A) carrying frameshift deletion c.3367delA in LAMA2 gene

LAMA2-related congenital muscular dystrophy (MDC1A), the most commonly recognized type of congenital muscular dystrophies, is a severe neonatal onset muscle disease caused by recessive mutations in the LAMA2 gene. Here, we established an induced pluripotent stem cell line from a MDC1A patient carrying a frameshift deletion c.3367delA in LAMA2 gene. The iPSC line expressed pluripotency markers, retained normal karyotype, showed capability of differentiating into three germ layers. The iPSC line will help to further elucidate the pathogenic mechanisms of LAMA2 mutation, and benefit treatment for congenital muscular dystrophies in the future.

Causative variants linked with limb girdle muscular dystrophy in an Iranian population: 6 novel variants

BACKGROUND

Limb-girdle muscular dystrophy (LGMD) is a non-syndromic muscular dystrophy caused by variations in the genes involved in muscle structure, function and repair. The heterogeneity in the severity, progression, age of onset, and causative genes makes next-generation sequencing (NGS) a necessary approach for the proper diagnosis of LGMD.

METHODS

In this article, 26 Iranian patients with LGMD criteria were diagnosed with disease variants in the genes encoding calpain3, dysferlin, sarcoglycans and Laminin α-2. Patients were referred to the hospital with variable distribution of muscle wasting and progressive weakness in the body. The symptoms along with biochemical and EMG tests were suggestive of LGMD; thus the genomic DNA of patients were investigated by whole-exome sequencing including flanking intronic regions. The target genes were explored for the disease-causing variants. Moreover, the consequence of the amino acid alterations on proteins' secondary structure and function was investigated for a better understanding of the pathogenicity of variants. Variants were sorted based on the genomic region, type and clinical significance.

RESULTS

In a comprehensive investigation of previous clinical records, 6 variations were determined as novel, including c.1354-2 A > T and c.3169_3172dupCGGC in DYSF, c.568 G > T in SGCD, c.7243 C > T, c.8662_8663 insT and c. 4397G > C in LAMA2. Some of the detected variants were located in functional domains and/or near to the post-translational modification sites, altering or removing highly conserved regions of amino acid sequence.

Alu Deletions in LAMA2 and CDH4 Genes Are Key Components of Polygenic Predictors of Longevity

Longevity is a unique human phenomenon and a highly stable trait, characterized by polygenicity. The longevity phenotype occurs due to the ability to successfully withstand the age-related genomic instability triggered by Alu elements. The purpose of our cross-sectional study was to evaluate the combined contribution of ACE*Ya5ACE, CDH4*Yb8NBC516, COL13A1*Ya5ac1986, HECW1*Ya5NBC182, LAMA2*Ya5-MLS19, PLAT*TPA25, PKHD1L1*Yb8AC702, SEMA6A*Yb8NBC597, STK38L*Ya5ac2145 and TEAD1*Ya5ac2013 Alu elements to longevity. The study group included 2054 unrelated individuals aged from 18 to 113 years who are ethnic Tatars from Russia. We analyzed the dynamics of the allele and genotype frequencies of the studied Alu polymorphic loci in the age groups of young (18-44 years old), middle-aged (45-59 years old), elderly (60-74 years old), old seniors (75-89 years old) and long-livers (90-113 years old). Most significant changes in allele and genotype frequencies were observed between the long-livers and other groups. The search for polygenic predictors of longevity was performed using the APSampler program. Attaining longevity was associated with the combinations LAMA2*ID + CDH4*D (OR = 2.23, PBonf = 1.90 × 10-2) and CDH4*DD + LAMA2*ID + HECW1*D (OR = 4.58, PBonf = 9.00 × 10-3) among persons aged between 18 and 89 years, LAMA2*ID + CDH4*D + SEMA6A*I for individuals below 75 years of age (OR = 3.13, PBonf = 2.00 × 10-2), LAMA2*ID + HECW1*I for elderly people aged 60 and older (OR = 3.13, PBonf = 2.00 × 10-2) and CDH4*DD + LAMA2*D + HECW1*D (OR = 4.21, PBonf = 2.60 × 10-2) and CDH4*DD + LAMA2*D + ACE*I (OR = 3.68, PBonf = 1.90 × 10-2) among old seniors (75-89 years old). The key elements of combinations associated with longevity were the deletion alleles of CDH4 and LAMA2 genes. Our results point to the significance for human longevity of the Alu polymorphic loci in CDH4, LAMA2, HECW1, SEMA6A and ACE genes, involved in the integration systems.

LAMA2-related muscular dystrophy mimicking multiple sclerosis

Laminin-alpha2-related muscular dystrophy (LAMA2-MD) is a genetic condition due to reduced LAMA2, a protein found throughout the nervous system. Late-onset LAMA2-MD may present with proximal muscle weakness, joint contractures, neuropathy, epilepsy and/or cardiorespiratory issues, and is less common than the neonatal form. We describe a novel phenotype of LAMA2-MD with progressive myelopathy and spinal cord abnormalities.A woman was referred for evaluation of multiple sclerosis (MS) with progressive gait difficulty and abnormal neuroimaging showing white matter abnormalities in the brain and spinal cord. Ancillary testing was not consistent with primary neuroinflammatory disorders, systemic autoimmunity or infection. Metabolic workup revealed low cyanocobalamin. Genetic testing identified two LAMA2-MD variants.Genetic disorders can mimic treatable neurological conditions. Chronic progressive course, involvement of the peripheral and central nervous systems, and confluent white matter abnormalities should be investigated with molecular testing that includes LAMA2 sequencing to ensure proper diagnosis and management.

Evidence of Two Novel LAMA2 Variants in a Patient With Muscular Dystrophy: Facing the Challenges of a Certain Diagnosis

Background

Benefits and challenges resulting from advances in genetic diagnostics are two sides of the same coin. Facilitation of a correct and timely diagnosis is paralleled by challenges in interpretation of variants of unknown significance (VUS). Focusing on an individual VUS-re-classification pipeline, this study offers a diagnostic approach for clinically suspected hereditary muscular dystrophy by combining the expertise of an interdisciplinary team.

Methods

In a multi-step approach, a thorough phenotype assessment including clinical examination, laboratory work, muscle MRI and histopathological evaluation of muscle was performed in combination with advanced Next Generation Sequencing (NGS). Different in-silico tools and prediction programs like Alamut, SIFT, Polyphen, MutationTaster and M-Cap as well as 3D- modeling of protein structure and RNA-sequencing were employed to determine clinical significance of the LAMA2 variants.

Results

Two previously unknown sequence alterations in LAMA2 were detected, a missense variant was classified initially according to ACMG guidelines as a VUS (class 3) whereas a second splice site variant was deemed as likely pathogenic (class 4). Pathogenicity of the splice site variant was confirmed by mRNA sequencing and nonsense mediated decay (NMD) was detected. Combination of the detected variants could be associated to the LGMDR23-phenotype based on the MRI matching and literature research.

Discussion

Two novel variants in LAMA2 associated with LGMDR23-phenotype are described. This study illustrates challenges of the genetic findings due to their VUS classification and elucidates how individualized diagnostic procedure has contributed to the accurate diagnosis in the spectrum of LGMD.

LAMA2 Nonsense Variant in an Italian Greyhound with Congenital Muscular Dystrophy

A 4-month-old, male Italian Greyhound with clinical signs of a neuromuscular disease was investigated. The affected dog presented with an abnormal short-strided gait, generalized muscle atrophy, and poor growth since 2-months of age. Serum biochemistry revealed a marked elevation in creatine kinase activity. Electrodiagnostic testing supported a myopathy. Histopathology of muscle biopsies confirmed a dystrophic phenotype with excessive variability in myofiber size, degenerating fibers, and endomysial fibrosis. A heritable form of congenital muscular dystrophy (CMD) was suspected, and a genetic analysis initiated. We sequenced the genome of the affected dog and compared the data to that of 795 control genomes. This search revealed a private homozygous nonsense variant in LAMA2, XM_022419950.1:c.3285G>A, predicted to truncate 65% of the open reading frame of the wild type laminin α2 protein, XP_022275658.1:p.(Trp1095*). Immunofluorescent staining performed on muscle cryosections from the affected dog confirmed the complete absence of laminin α2 in skeletal muscle. LAMA2 loss of function variants were shown to cause severe laminin α2-related CMD in humans, mouse models, and in one previously described dog. Our data together with current knowledge on other species suggest the LAMA2 nonsense variant as cause for the CMD phenotype in the investigated dog.

A Mosaic Mutation in the LAMA2 Gene in a Case of Merosin-deficient Congenital Muscular Dystrophy

Merosine deficient congenital muscular dystrophy is one of the most common forms of congenital muscular dystrophy. This disease is caused by a primary deficiency or a functionally inactive form of the protein merosin in muscle tissue. The type of inheritance of this disease is autosomal recessive. De novo variants with this type of inheritance are rare, and it is quite possible that the de novo variant may hide a mosaic form in the parent of an affected child. We present a birth family with two affected children who inherited a previously undescribed pathogenic variant c.1755del from their mother and a previously described pathogenic variant c.9253C > T in the LAMA2 gene from their mosaic father. LAMA2 gene mutation analysis was performed by mass parallel sequencing and direct sequencing of genomic DNAs.

Muscle magnetic resonance imaging in patients with LAMA2-related muscular dystrophy

LAMA2-related muscular dystrophy (LAMA2-MD) is classified into congenital muscular dystrophy type 1A (MDC1A) and autosomal recessive limb-girdle muscular dystrophy-23 (LGMDR23). The purpose of this study was to identify the involvement pattern of thigh muscles of LAMA2-MD patients on magnetic resonance imaging. Fourteen MDC1A and 3 LGMDR23 patients were included, with 21 known and 8 novel LAMA2 disease-causing variants. In LAMA2-MD, the gluteus maximus, anterior (quadriceps femoris) and posterior (adductor magnus and biceps femoris) thigh muscles were extensively and severely affected with fatty infiltration, with relatively sparing of the adductor longus. The pattern of muscle involvement was similar between MDC1A and LGMDR23, but more severe in MDC1A, as well as in LAMA2-MD patients without ambulation. The rather peculiar pattern of the adductor magnus and long head of the biceps femoris first and severely affected in the mid-thigh level was found in LGMDR23. Strong correlation between fatty infiltration and age as well as disease duration was observed for the adductor longus in MDC1A. Edema and atrophy selectively involved in some muscles. The pattern of fatty infiltration on thigh muscle MRI of LAMA2-MD could provide important information for the diagnosis, differential diagnosis and assessment of clinical severity.

Diagnostic interest of whole-body MRI in early- and late-onset LAMA2 muscular dystrophies: a large international cohort

BACKGROUND

LAMA2-related muscular dystrophy (LAMA2-RD) encompasses a group of recessive muscular dystrophies caused by mutations in the LAMA2 gene, which codes for the alpha-2 chain of laminin-211 (merosin). Diagnosis is straightforward in the classic congenital presentation with no ambulation and complete merosin deficiency in muscle biopsy, but is far more difficult in milder ambulant individuals with partial merosin deficiency.

OBJECTIVE

To investigate the diagnostic utility of muscle imaging in LAMA2-RD using whole-body magnetic resonance imaging (WBMRI).

RESULTS

27 patients (2-62 years, 21-80% with acquisition of walking ability and 6 never ambulant) were included in an international collaborative study. All carried two pathogenic mutations, mostly private missense changes. An intronic variant (c.909 + 7A > G) was identified in all the Chilean cases. Three patients (two ambulant) showed intellectual disability, epilepsy, and brain structural abnormalities. WBMRI T1w sequences or T2 fat-saturated images (Dixon) revealed abnormal muscle fat replacement predominantly in subscapularis, lumbar paraspinals, gluteus minimus and medius, posterior thigh (adductor magnus, biceps femoris, hamstrings) and soleus. This involvement pattern was consistent for both ambulant and non-ambulant patients. The degree of replacement was predominantly correlated to the disease duration, rather than to the onset or the clinical severity. A "COL6-like sandwich sign" was observed in several muscles in ambulant adults, but different involvement of subscapularis, gluteus minimus, and medius changes allowed distinguishing LAMA2-RD from collagenopathies. The thigh muscles seem to be the best ones to assess disease progression.

CONCLUSION

WBMRI in LAMA2-RD shows a homogeneous pattern of brain and muscle imaging, representing a supportive diagnostic tool.

Identification of a compound heterozygous missense mutation in LAMA2 gene from a patient with merosin-deficient congenital muscular dystrophy type 1A

Background

Merosin‐deficient congenital muscular dystrophy type 1A (MDC1A) is occurred by mutations in LAMA2 gene that encodes the laminin α2 chain (merosin). MDC1A is a predominant subtype of congenital muscular dystrophy. Herein, we identified two missense mutations in LAMA2 gene in compound heterozygous status in an Iranian patient with MDC1A using whole‐exome sequencing (WES).

Methods

In the present study, we evaluated genetic alterations in an Iranian 35‐month‐old boy with MDC1A and his healthy family using WES method. The identified mutations further confirmed by Sanger sequencing method. Finally, in silico analysis was conducted to further evaluation of molecular function of the identified genetic variants.

Results

We identified two potentially pathogenic missense mutations in compound heterozygous state (c.7681G>A p.Gly2561Ser and c.4840A>G p.Asn1614Asp) in LAMA2 gene as contributing to the MDC1A phenotype. The healthy parents of our proband are single heterozygous for identified mutations. These variants were found to be pathogenic by in silico analysis.

Conclusions

In general, we successfully identified LAMA2 gene mutations in an Iranian patient with MDC1A using WES. The identified mutations in LAMA2 gene can be useful in genetic counseling, prenatal diagnosis, and predicting prognosis of MDC1A.

Derivation of human pluripotent stem cell line via CRISPR/Cas9 mediated deletion of exon 3 LAMA2 gene (DMBi001-A-1)

LAMA2-related muscular dystrophy (LAMA2-MD) results from mutations in LAMA2 gene, encoding laminin α-2. It is a congenital disease characterized by muscle wasting, with the most severe version being diagnosed within first few months after birth. To generate LAMA2-DM in vitro model, we excised exon 3 from the LAMA2 gene in our previously derived healthy human induced pluripotent stem cells (hiPSCs). Obtained hiPSCs show expression of pluripotency markers, differentiation capacity into all three germ layers, normal karyotype and lack of LAMA2 expression on mRNA and protein level after differentiation into skeletal myocytes. Accordingly, it may provide novel insight into the molecular basis of LAMA2-MD.

Laminin Polymerization and Inherited Disease: Lessons From Genetics

The laminins (LM) are a family of basement membranes glycoproteins with essential structural roles in supporting epithelia, endothelia, nerves and muscle adhesion, and signaling roles in regulating cell migration, proliferation, stem cell maintenance and differentiation. Laminins are obligate heterotrimers comprised of α, β and γ chains that assemble intracellularly. However, extracellularly these heterotrimers then assemble into higher-order networks via interaction between their laminin N-terminal (LN) domains. In vitro protein studies have identified assembly kinetics and the structural motifs involved in binding of adjacent LN domains. The physiological importance of these interactions has been identified through the study of pathogenic point mutations in LN domains that lead to syndromic disorders presenting with phenotypes dependent on which laminin gene is mutated. Genotype-phenotype comparison between knockout and LN domain missense mutations of the same laminin allows inferences to be drawn about the roles of laminin network assembly in terms of tissue function. In this review, we will discuss these comparisons in terms of laminin disorders, and the therapeutic options that understanding these processes have allowed. We will also discuss recent findings of non-laminin mediators of laminin network assembly and their implications in terms of basement membrane structure and function.

Epilepsy in LAMA2-related muscular dystrophy: A systematic review of the literature

Epilepsy is a common, often severe, feature of LAMA2-related muscular dystrophy (LAMA2-RD) and could represent its onset and main manifestation, even in the absence of overt muscle involvement. To date, there is no systematic characterization of epilepsy in LAMA2-RD, and its impact on neurodevelopment and on the clinical course remains poorly established. In view of this knowledge gap, we conducted a systematic review of the literature and, as an illustrative example, reported the clinical case of a boy with late-onset LAMA2-related limb-girdle muscular dystrophy presenting with severe epilepsy. Our analyses of the literature data revealed a mean age at first seizure of 8 years, with significant differences between early- versus late-onset disease (5.78 ± 4.11 and 9.00 ± 2.65 years, respectively; p = 0.0007), and complete versus partial merosin deficiency (5.33 ± 3.70 and 10.36 ± 5.49 years, respectively; p = 0.0176). A generalized onset was the most common seizure presentation, regardless of merosin expression levels or the timing of muscular distrophy onset. Cortical malformations were not significantly associated with an earlier epilepsy onset, and were found to be quasi-significantly associated with a greater incidence of focal, or focal and generalized, onset seizures. No clear conclusions could be reached on the electrophysiological and neurodevelopmental features of the disorder, or on the relative efficacy of anti-epileptic treatments; further research on these aspects is needed. This systematic review helps to show that epilepsy in LAMA2-RD may be more than an ancillary manifestation of the disease, but rather one of its core features. A targeted and prompt electroencephalographic and epilepsy assessment, in addition to the specific neuromuscular workup, is therefore mandatory in early clinical management to pursue the best possible outcome for affected children.

Natural history and genetic study of LAMA2-related muscular dystrophy in a large Chinese cohort

Background

LAMA2-related muscular dystrophy including LAMA2-related congenital muscular dystrophy (LAMA2-CMD) and autosomal recessive limb-girdle muscular dystrophy-23 (LGMDR23) is caused by LAMA2 pathogenic variants. We aimed to describe the natural history and establish genotype–phenotype correlations in a large cohort of Chinese patients with LAMA2-related muscular dystrophy.

Methods

Clinical and genetic data of LAMA2-related muscular dystrophy patients enrolled from ten research centers between January 2003 and March 2021 were collected and analyzed.

Results

One hundred and thirty patients (116 LAMA2-CMD and 14 LGMDR23) were included. LAMA2-CMD group had earlier onset than LGMDR23 group. Head control, independent sitting and ambulation were achieved in 76.3%, 92.6% and 18.4% of LAMA2-CMD patients at median ages of 6.0 months (range 2.0–36.0 months), 11.0 months (range 6.0–36.0 months), and 27.0 months (range 18.0–84.0 months), respectively. All LGMDR23 patients achieved independent ambulation at median age of 18.0 months (range 13.0–20.0 months). Motor regression in LAMA2-CMD mainly occurred concurrently with rapid progression of contractures during 6–9 years old. Twenty-four LAMA2-related muscular dystrophy patients died, mostly due to severe pneumonia. Seizures occurred in 35.7% of LGMDR23 and 9.5% of LAMA2-CMD patients. Forty-six novel and 97 known LAMA2 disease-causing variants were identified. The top three high-frequency disease-causing variants in Han Chinese patients were c.7147C > T (p.R2383*), exon 4 deletion, and c.5156_5159del (p.K1719Rfs*5). In LAMA2-CMD, splicing variants tended to be associated with a relatively mild phenotype. Nonsense variants were more frequent in LAMA2-CMD (56.9%, 66/116) than in LGMDR23 (21.4%, 3/14), while missense disease-causing variants were more frequent in LGMDR23 (71.4%, 10/14) than in LAMA2-CMD (12.9%, 15/116). Copy number variations were identified in 26.4% of survivors and 50.0% of nonsurvivors, suggesting that copy number variations were associated with lower rate of survival (p = 0.029).

Conclusions

This study provides better understandings of natural history and genotype–phenotype correlations in LAMA2-related muscular dystrophy, and supports therapeutic targets for future researches.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-01950-x.