Phenotype of CNTNAP1: a study of patients demonstrating a specific severe congenital hypomyelinating neuropathy with survival beyond infancy

A cross-sectional survey on the health status of patients with Charcot-Marie-Tooth disease in a Chinese national patient group

BACKGROUND

Charcot-Marie-Tooth disease (CMT) is a rare inherited peripheral neuropathy, and the health status of CMT patients in China is not well understood without a national disease registry system. We aimed to obtain the related epidemiological data to support effective work on CMT.

METHODS

The online cross-sectional study included patients definitively diagnosed with CMT nationwide. Descriptive analyses were conducted on CMT's disease characteristics, diagnostic results, walking condition, rehabilitation status, comorbidities, family history, etc. RESULTS: CMT1A, CMT2A, CMTX1, CMT2S, CMT1E, and CMT1B were the top six types accounting for 64.4% of the 523 eligible patients. PMP22, MFN2, GJB1, MPZ, GDAP1, and IGHMBP2 ranked as the top six genes among the collected 44 pathogenic genes. The median ages of symptom onset and diagnosis were 7.3 and 18.7 years, respectively, with a median interval of 3.8 years between symptom onset and genetic confirmation. Only 8.3% exhibited unaffected walking speed and balance, the remaining experienced varying degrees of motor impairment, and 42.1% employed rehabilitation. Moreover, 26.8% experienced initial misdiagnosis, and 47.0% were estimated to suffer from depression. Of comorbidities complained by the 94 patients, gastrointestinal was most common (17/94) followed by hypertension (13/94), and hiatal hernia (2/94) was first reported. Family history was documented in 35.2% of the surveyed patients.

CONCLUSION

Chinese patients with CMT were in complicated and poor health status with predominant disease types and pathogenic genes generally as anticipated. A national CMT registry system is highly wanted to collect comprehensive information to guide further research and improve patients' health status.

Paranode length in the prefrontal cortex of subjects with major depression and rats under chronic unpredictable stress

Experimental studies of major depressive disorder (MDD) and stress reveal connectivity disturbances of the prefrontal cortex (PFC) that may involve molecular and morphological changes in myelin and the axons it enwraps. These alterations may also affect the nodes of Ranvier (NR), myelin-bare axon stretches along myelin sheaths necessary for action potential propagation, as well as the paranodes, specialized regions of the myelin sheath flanking NRs. Thus, we investigated whether paranode length and the labeling of paranode marker CASPR in PFC white matter (WM) differed in MDD subjects and chronic stress-exposed rats, as compared to their respective controls. Histological sections were obtained from postmortem PFC blocks of 11 subjects with MDD diagnosis and 11 non-psychiatric controls as well as from 6 rats subjected to chronic unpredictable stress (CUS) and 6 non-stressed controls. NRs and paranodes were detected by immunofluorescence with specific antibodies to paranodal protein CASPR. Differences in paranode length and CASPR immunoreactivity were assessed by analysis of covariance and t-tests. In MDD, both paranode length and overall CASPR immunoreactivity were significantly lower than in non-psychiatric controls, while paranode length and CASPR labeling were positively correlated with age. However, those variables did not statistically differ between CUS-exposed and non-exposed rats. Shorter paranodes and lower CASPR immunoreactivity in MDD subjects suggest alterations in paranodal myelin, which may contribute to depression-related connectivity changes. However, without comparable changes in CUS-exposed rats, mechanisms other than the stress response cannot be ruled out as contributors to paranode alterations in MDD.

Novel CNTNAP1 gene variant identified in congenital hypomyelinating neuropathy-3: A case report

Contactin-associated protein (CNTNAP1) gene mutations have been reported in cases of congenital hypomyelinating neuropathy (CHN), a rare hereditary neuropathy. We present a case of a term male infant born at 39 weeks 4 days with respiratory distress, impaired swallow function, and hypotonia. Neurological workup for structural, autoimmune, neuromuscular, and metabolic etiologies was negative and whole exome sequencing revealed a novel mutation in the CNTNAP1 gene, consistent with a diagnosis of CHN3. While CHN3 cases with mutations in the same domain have required long-term respiratory support, our patient, now 2 years old, has not required respiratory support since his initial birth hospitalization. Neurologically, he now has central hypotonia with hypertonia in the bilateral extremities and global developmental delay. This case adds to a growing number of identified pathological CNTNAP1 mutations and their heterogenous clinical phenotypes and highlights a rare neurological etiology for respiratory distress in newborns.

Integrating Genome Sequencing and Untargeted Metabolomics in Monozygotic Twins with a Rare Complex Neurological Disorder

Multi-omics approaches, which integrate genomics, transcriptomics, proteomics, and metabolomics, have emerged as powerful tools in the diagnosis of rare diseases. We used untargeted metabolomics and whole-genome sequencing (WGS) to gain a more comprehensive understanding of a rare disease with a complex presentation affecting female twins from a consanguineous family. The sisters presented with polymicrogyria, a Dandy-Walker malformation, respiratory distress, and multiorgan dysfunctions. Through WGS, we identified two rare homozygous variants in both subjects, a pathogenic variant in ADGRG1(p.Arg565Trp) and a novel variant in CNTNAP1(p.Glu910Val). These genes have been previously associated with autosomal recessive polymicrogyria and hypomyelinating neuropathy with/without contractures, respectively. The twins exhibited symptoms that overlapped with both of these conditions. The results of the untargeted metabolomics analysis revealed significant metabolic perturbations relating to neurodevelopmental abnormalities, kidney dysfunction, and microbiome. The significant metabolites belong to essential pathways such as lipids and amino acid metabolism. The identification of variants in two genes, combined with the support of metabolic perturbation, demonstrates the rarity and complexity of this phenotype and provides valuable insights into its underlying mechanisms.

Mouse models of human CNTNAP1-associated congenital hypomyelinating neuropathy and genetic restoration of murine neurological deficits

The Contactin-associated protein 1 (Cntnap1) mouse mutants fail to establish proper axonal domains in myelinated axons. Human CNTNAP1 mutations are linked to hypomyelinating neuropathy-3, which causes severe neurological deficits. To understand the human neuropathology and to model human CNTNAP1C323R and CNTNAP1R764C mutations, we generated Cntnap1C324R and Cntnap1R765C mouse mutants, respectively. Both Cntnap1 mutants show weight loss, reduced nerve conduction, and progressive motor dysfunction. The paranodal ultrastructure shows everted myelin loops and the absence of axo-glial junctions. Biochemical analysis reveals that these Cntnap1 mutant proteins are nearly undetectable in the paranodes, have reduced surface expression and stability, and are retained in the neuronal soma. Postnatal transgenic expression of Cntnap1 in the mutant backgrounds rescues the phenotypes and restores the organization of axonal domains with improved motor function. This study uncovers the mechanistic impact of two human CNTNAP1 mutations in a mouse model and provides proof of concept for gene therapy for CNTNAP1 patients.

Transcriptome-wide association study identifies novel candidate susceptibility genes for migraine

Genome-wide association studies (GWASs) have identified more than 130 genetic susceptibility loci for migraine; however, how most of these loci impact migraine development is unknown. To identify novel genes associated with migraine and interpret the transcriptional products of those genes, we conducted a transcriptome-wide association study (TWAS). We performed tissue-specific and multi-tissue TWAS analyses to assess associations between imputed gene expression from 53 tissues and migraine susceptibility using FUSION software. Meta-analyzed GWAS summary statistics from 26,052 migraine cases and 487,214 controls, all of European ancestry and from two cohorts (the Kaiser Permanente GERA and the UK Biobank), were used. We evaluated the associations for genes after conditioning on variant-level effects from GWAS, and we tested for colocalization of GWAS migraine-associated loci and expression quantitative trait loci (eQTLs). Across tissue-specific and multi-tissue analyses, we identified 53 genes for which genetically predicted gene expression was associated with migraine after correcting for multiple testing. Of these 53 genes, 10 (ATF5, CNTNAP1, KTN1-AS1, NEIL1, NEK4, NNT, PNKP, RUFY2, TUBG2, and VAT1) did not overlap known migraine-associated loci identified from GWAS. Tissue-specific analysis identified 45 gene-tissue pairs and cardiovascular tissues represented the highest proportion of the Bonferroni-significant gene-tissue pairs (n = 22 [49%]), followed by brain tissues (n = 6 [13%]), and gastrointestinal tissues (n = 4 [9%]). Colocalization analyses provided evidence of shared genetic variants underlying eQTL and GWAS signals in 18 of the gene-tissue pairs (40%). Our TWAS reports novel genes for migraine and highlights the important contribution of brain, cardiovascular, and gastrointestinal tissues in migraine susceptibility.

CNTNAP1-encephalopathy: Six novel patients surviving the neonatal period

CNTNAP1 encodes CASPR1, involved in the paranodal junction. Thirty-three patients, with CNTNAP1 biallelic mutations have been described previously. Most of them had a very severe neurological impairment and passed away in the first months of life. We identified four patients, from two unrelated families, who survived over the neonatal period. Exome sequencing showed compound heterozygous or homozygous variants. Severe hypotonia was a constant feature. When compared to previous reports, the most important clinical differences observed in our patients were the absence of antenatal problems and, in two of them, the lack of respiratory distress. Less commonly reported characteristics such as epileptic seizures, dystonia, and impaired communication skills were also observed. MRIs revealed hypomyelination or abnormal white matter signal, cerebral or cerebellar atrophy. The present observations support a wider than initially reported clinical spectrum, including survival after the neonatal period and additional neurological features. They contribute to better delineate the phenotype-genotype correlations for CNTNAP1. In addition, we report one more family with two sibs who carry a missense variant of uncertain significance which we propose could be associated with a milder phenotype.

The effect of polyhydramnios degree on chromosomal microarray results: a retrospective cohort analysis of 742 singleton pregnancies

PURPOSE

To analyze the risk for clinically significant microarray aberrations in pregnancies with polyhydramnios.

METHODS

Data from all chromosomal microarray analyses (CMA) performed due to polyhydramnios between January 2013 and December 2019 were retrospectively obtained from the Ministry of Health Database. The rate of clinically significant (pathogenic and likely pathogenic) CMA findings in isolated and non-isolated polyhydramnios cohorts was compared to a local control group of 5541 fetuses with normal ultrasound, in which 78 (1.4%) abnormal results were demonstrated. Subgroup analyses were performed by the degree of polyhydramnios, week of diagnosis, maternal age, and the presence of additional sonographic anomalies.

RESULTS

In the isolated polyhydramnios cohort, 19/623 (3.1%) clinically significant CMA aberrations were noted, a significantly higher rate compared to the control population. However, the risk for abnormal CMA results in the 158 cases with mild polyhydramnios (AFI 25-29.9, or maximal vertical pocket 8-11.9 cm) did not significantly differ from pregnancies with normal ultrasound. Of 119 cases of non-isolated polyhydramnios (most frequently associated with cardiovascular (26.1%) and brain (15.1%) anomalies), 8 (6.7%) abnormal CMA findings were noted, mainly karyotype-detectable.

CONCLUSION

Mild polyhydramnios was not associated with an increased rate of clinically significant microarray results, compared to pregnancies with normal ultrasound. An extensive anatomical sonographic survey should be performed in pregnancies with polyhydramnios, with consideration of fetal echocardiography.

A CNTNAP1 Missense Variant Is Associated with Canine Laryngeal Paralysis and Polyneuropathy

Laryngeal paralysis associated with a generalized polyneuropathy (LPPN) most commonly exists in geriatric dogs from a variety of large and giant breeds. The purpose of this study was to discover the underlying genetic and molecular mechanisms in a younger-onset form of this neurodegenerative disease seen in two closely related giant dog breeds, the Leonberger and Saint Bernard. Neuropathology of an affected dog from each breed showed variable nerve fiber loss and scattered inappropriately thin myelinated fibers. Using across-breed genome-wide association, haplotype analysis, and whole-genome sequencing, we identified a missense variant in the CNTNAP1 gene (c.2810G>A; p.Gly937Glu) in which homozygotes in both studied breeds are affected. CNTNAP1 encodes a contactin-associated protein important for organization of myelinated axons. The herein described likely pathogenic CNTNAP1 variant occurs in unrelated breeds at variable frequencies. Individual homozygous mutant LPPN-affected Labrador retrievers that were on average four years younger than dogs affected by geriatric onset laryngeal paralysis polyneuropathy could be explained by this variant. Pathologic changes in a Labrador retriever nerve biopsy from a homozygous mutant dog were similar to those of the Leonberger and Saint Bernard. The impact of this variant on health in English bulldogs and Irish terriers, two breeds with higher CNTNAP1 variant allele frequencies, remains unclear. Pathogenic variants in CNTNAP1 have previously been reported in human patients with lethal congenital contracture syndrome and hypomyelinating neuropathy, including vocal cord palsy and severe respiratory distress. This is the first report of contactin-associated LPPN in dogs characterized by a deleterious variant that most likely predates modern breed establishment.

Mutations of CNTNAP1 led to defects in neuronal development

Mutations of CNTNAP1 were associated with myelination disorders, suggesting the role of CNTNAP1 in myelination processes. Whether CNTNAP1 may have a role in early cortical neuronal development is largely unknown. In this study, we identified 4 compound heterozygous mutations of CNTNAP1 in 2 Chinese families. Using mouse models, we found that CNTNAP1 is highly expressed in neurons and is located predominantly in MAP2⁺ neurons during the early developmental stage. Importantly, Cntnap1 deficiency results in aberrant dendritic growth and spine development in vitro and in vivo, and it delayed migration of cortical neurons during early development. Finally, we found that the number of parvalbumin⁺ neurons in the cortex and hippocampus of Cntnap1^–/– mice is strikingly increased by P15, suggesting that excitation/inhibition balance is impaired. Together, this evidence elucidates a critical function of CNTNAP1 in cortical development, providing insights underlying molecular and circuit mechanisms of CNTNAP1-related disease.

Deficiency of CNTNAP1 causes severe cortical developmental deficits, leading to human lethal perinatal symptoms.

CNTNAP1 Mutations and Their Clinical Presentations: New Case Report and Systematic Review

Lethal congenital contracture syndrome type 7 (LCCS7) and congenital hypomyelinating neuropathy type 3 (CHN3) are rare autosomal recessive diseases, characterized by severe neonatal hypotonia, polyhydramnios, arthrogryposis, facial diplegia, and severe motor paralysis, leading to death in early infancy. They are related to mutations in the CNTNAP1 (contactin associated protein 1) gene, playing an important role in myelination. Recent studies have shown that both diseases could present with a wide phenotypic spectrum, with promising survival up to early childhood. We report on a 7-year-old boy from a nonconsanguineous Lebanese family presenting with neonatal hypotonia, respiratory distress, and arthrogryposis. Molecular analysis revealed the presence of a pathogenic variant in the CNTNAP1 gene leading to a premature stop codon: NM_003632.2:c.3361C>T p.(Arg1121^∗). A review of the literature is discussed.

Molecular organization and function of vertebrate septate-like junctions

Septate-like junctions display characteristic ladder-like ultrastructure reminiscent of the invertebrate epithelial septate junctions and are present at the paranodes of myelinated axons. The paranodal junctions where the myelin loops attach to the axon at the borders of the node of Ranvier provide both a paracellular barrier to ion diffusion and a lateral fence along the axonal membrane. The septate-like junctions constrain the proper distribution of nodal Na⁺ channels and juxtaparanodal K⁺ channels, which are required for the safe propagation of the nerve influx and rapid saltatory conduction. The paranodal cell adhesion molecules have been identified as target antigens in peripheral demyelinating autoimmune diseases and the pathogenic mechanisms described. This review aims at presenting the recent knowledge on the molecular and structural organization of septate-like junctions, their formation and stabilization during development, and how they are involved in demyelinating diseases.

Oligodendrocyte Neurofascin Independently Regulates Both Myelin Targeting and Sheath Growth in the CNS

Selection of the correct targets for myelination and regulation of myelin sheath growth are essential for central nervous system (CNS) formation and function. Through a genetic screen in zebrafish and complementary analyses in mice, we find that loss of oligodendrocyte Neurofascin leads to mistargeting of myelin to cell bodies, without affecting targeting to axons. In addition, loss of Neurofascin reduces CNS myelination by impairing myelin sheath growth. Time-lapse imaging reveals that the distinct myelinating processes of individual oligodendrocytes can engage in target selection and sheath growth at the same time and that Neurofascin concomitantly regulates targeting and growth. Disruption to Caspr, the neuronal binding partner of oligodendrocyte Neurofascin, also impairs myelin sheath growth, likely reflecting its association in an adhesion complex at the axon-glial interface with Neurofascin. Caspr does not, however, affect myelin targeting, further indicating that Neurofascin independently regulates distinct aspects of CNS myelination by individual oligodendrocytes in vivo.

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Single oligodendrocytes coordinate myelin targeting and growth at the same time

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Oligodendrocyte Neurofascin prevents myelination of cell bodies

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Oligodendrocyte Neurofascin promotes myelin sheath growth

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The neuronal binding partner of Neurofascin, Caspr, promotes myelin sheath growth