Exome sequencing establishes diagnosis of Alström syndrome in an infant presenting with non-syndromic dilated cardiomyopathy

Genotype-phenotype associations in Alström syndrome: a systematic review and meta-analysis

BACKGROUND

Alström syndrome (ALMS; #203800) is an ultrarare monogenic recessive disease. This syndrome is associated with variants in the ALMS1 gene, which encodes a centrosome-associated protein involved in the regulation of several ciliary and extraciliary processes, such as centrosome cohesion, apoptosis, cell cycle control and receptor trafficking. The type of variant associated with ALMS is mostly complete loss-of-function variants (97%) and they are mainly located in exons 8, 10 and 16 of the gene. Other studies in the literature have tried to establish a genotype-phenotype correlation in this syndrome with limited success. The difficulty in recruiting a large cohort in rare diseases is the main barrier to conducting this type of study.

METHODS

In this study we collected all cases of ALMS published to date. We created a database of patients who had a genetic diagnosis and an individualised clinical history. Lastly, we attempted to establish a genotype-phenotype correlation using the truncation site of the patient's longest allele as a grouping criteria.

RESULTS

We collected a total of 357 patients, of whom 227 had complete clinical information, complete genetic diagnosis and meta-information on sex and age. We have seen that there are five variants with high frequency, with p.(Arg2722Ter) being the most common variant, with 28 alleles. No gender differences in disease progression were detected. Finally, truncating variants in exon 10 seem to be correlated with a higher prevalence of liver disorders in patients with ALMS.

CONCLUSION

Pathogenic variants in exon 10 of the ALMS1 gene were associated with a higher prevalence of liver disease. However, the location of the variant in the ALMS1 gene does not have a major impact on the phenotype developed by the patient.

Alström's Syndrome, Leber's Hereditary Optic Neuropathy, or Retinitis Pigmentosa? A Case of Misdiagnosis

A case of a patient with the Alström syndrome (AS) that was misdiagnosed as Leber's hereditary optic neuropathy or retinitis pigmentosa for 13 years is presented. AS is a rare genetic disorder caused by mutations in the ALMS1 gene. AS may lead to abnormal ciliary formation and function. AS affects metabolism, and symptomatology includes type 2 diabetes mellitus (T2DM), obesity, hypogonadism and gynecomastia in males, progressive bilateral sensorineural hearing loss, cardiomyopathy, nonalcoholic fatty liver disease (NAFLD), cirrhosis, and chronic progressive kidney disease. The onset of the above symptoms may vary significantly. The ophthalmic manifestation is early onset cone-rod dystrophy that starts as progressive vision loss, photophobia, and nystagmus in the first months of life. An accurate diagnosis may enable specialists to facilitate a significantly positive effect in the everyday life of a patient. Genetic counseling may also be recommended for these patients. Diagnosis was confirmed by DNA testing, thus highlighting its necessity in everyday practice.

Mitochondrial Dysfunction in Cardiac Diseases and Therapeutic Strategies

Mitochondria are the main site of intracellular synthesis of ATP, which provides energy for various physiological activities of the cell. Cardiomyocytes have a high density of mitochondria and mitochondrial damage is present in a variety of cardiovascular diseases. In this paper, we describe mitochondrial damage in mitochondrial cardiomyopathy, congenital heart disease, coronary heart disease, myocardial ischemia-reperfusion injury, heart failure, and drug-induced cardiotoxicity, in the context of the key roles of mitochondria in cardiac development and homeostasis. Finally, we discuss the main current therapeutic strategies aimed at alleviating mitochondrial impairment-related cardiac dysfunction, including pharmacological strategies, gene therapy, mitochondrial replacement therapy, and mitochondrial transplantation. It is hoped that this will provide new ideas for the treatment of cardiovascular diseases.

Molecular Diagnosis of Hypertrophic Cardiomyopathy (HCM): In the Heart of Cardiac Disease

Hypertrophic cardiomyopathy (HCM) is an inherited myocardial disease with the presence of left ventricular hypertrophy (LVH). The disease is characterized by high locus, allelic and phenotypic heterogeneity, even among members of the same family. The list of confirmed and potentially relevant genes implicating the disease is constantly increasing, with novel genes frequently reported. Heterozygous alterations in the five main sarcomeric genes (MYBPC3, MYH7, TNNT2, TNNI3, and MYL2) are estimated to account for more than half of confirmed cases. The genetic discoveries of recent years have shed more light on the molecular pathogenic mechanisms of HCM, contributing to substantial advances in the diagnosis of the disease. Genetic testing applying next-generation sequencing (NGS) technologies and early diagnosis prior to the clinical manifestation of the disease among family members demonstrate an important improvement in the field.

Ocular findings and genetic test in Alström syndrome in childhood

This study aimed to investigate the mutation spectrums and ocular features of Alström syndrome (AS) patients. Six AS patients from five unrelated families were included. Ocular and systemic examinations were performed in all subjects. Whole-exome sequencing (WES) was performed in the probands, and Sanger sequencing was performed for mutation validation and segregation analysis. Among the six patients, the first symptoms included nystagmus, poor fixation, and photophobia. Five patients had high hyperopia, four of whom (80%) were initially diagnosed with amblyopia before referral with prescribed corrective lenses and amblyopia treatment, but no improvement was obtained. Optical coherence tomography (OCT) revealed progressive damage to the photoreceptor layer, including blurred ellipsoid zone (EZ) and lack of interdigitation zone (IZ) within the macula, and thorough loss of photoreceptor layer in the peripheral retina. Electroretinograms (ERG) demonstrated severely diminished cone and rod responses. WES identified biallelic variants of ALMS1 in all the six patients, including two novels, c.3892C > T (p.Gln1298*) and c.2888_2897del (p.Ser963Thrfs*15) and five knowns, c.10819C > T (p.Arg3607Trp), c.2090C > A (p.Ser697*), c.4891C > T (p.Gln1631*), c.10825C > T (p.Arg3069*) and c.6430C > T (Arg2146*). In conclusion, this study expanded the ocular features and genotypic spectrum of AS. High hyperopia is a significant and common feature of AS. OCT and ERG are essential accessory techniques for the diagnosis of AS. If a patient had high hyperopia with a noneffective response to amblyopic treatment, the diagnosis of AS should be suspected, and detailed ocular examination, systemic evaluation, and genetic testing recommended.

Genetics in Familial Intrahepatic Cholestasis: Clinical Patterns and Development of Liver and Biliary Cancers: A Review of the Literature

The family of inherited intrahepatic cholestasis includes autosomal recessive cholestatic rare diseases of childhood involved in bile acids secretion or bile transport defects. Specific genetic pathways potentially cause many otherwise unexplained cholestasis or hepatobiliary tumours in a healthy liver. Lately, next-generation sequencing and whole-exome sequencing have improved the diagnostic procedures of familial intrahepatic cholestasis (FIC), as well as the discovery of several genes responsible for FIC. Moreover, mutations in these genes, even in the heterozygous status, may be responsible for cryptogenic cholestasis in both young and adults. Mutations in FIC genes can influence serum and hepatic levels of bile acids. Experimental studies on the NR1H4 gene have shown that high bile acids concentrations cause excessive production of inflammatory cytokines, resistance to apoptosis, and increased cell regeneration, all risk conditions for developing hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA). NR1H4 gene encodes farnesoid X-activated receptor having a pivotal role in bile salts synthesis. Moreover, HCC and CCA can emerge in patients with several FIC genes such as ABCB11, ABCB4 and TJP2. Herein, we reviewed the available data on FIC-related hepatobiliary cancers, reporting on genetics to the pathophysiology, the risk factors and the clinical presentation.

A deleterious mutation in the ALMS1 gene in a naturally occurring model of hypertrophic cardiomyopathy in the Sphynx cat

BACKGROUND

Familial hypertrophic cardiomyopathy is a common inherited cardiovascular disorder in people. Many causal mutations have been identified, but about 40% of cases do not have a known causative mutation. Mutations in the ALMS1 gene are associated with the development of Alstrom syndrome, a multisystem familial disease that can include cardiomyopathy (dilated, restrictive). Hypertrophic cardiomyopathy has not been described. The ALMS1 gene is a large gene that encodes for a ubiquitously expressed protein. The function of the protein is not well understood although it is believed to be associated with energy metabolism and homeostasis, cell differentiation and cell cycle control. The ALMS1 protein has also been shown to be involved in the regulation of cell cycle proliferation in perinatal cardiomyocytes. Although cardiomyocyte cell division and replication in mammals generally declines soon after birth, inhibition of ALMS1 expression in mice lead to increased cardiomyocyte proliferation, and deficiency of Alstrom protein has been suggested to impair post-natal cardiomyocyte cell cycle arrest. Here we describe the association of familial hypertrophic cardiomyopathy in Sphynx cats with a novel ALMS1 mutation.

RESULTS

A G/C variant was identified in exon 12 (human exon 13) of the ALMS1 gene in affected cats and was positively associated with the presence of hypertrophic cardiomyopathy in the feline population (p < 0.0001). The variant was predicted to change a highly conserved nonpolar Glycine to a positively charged Arginine. This was predicted to be a deleterious change by three in silico programs. Protein prediction programs indicated that the variant changed the protein structure in this region from a coil to a helix. Light microscopy findings included myofiber disarray with interstitial fibrosis with significantly more nuclear proliferative activity in the affected cats than controls (p < 0.0001).

CONCLUSION

This study demonstrates a novel form of cardiomyopathy associated with ALMS1 in the cat. Familial hypertrophic cardiomyopathy is a disease of genetic heterogeneity; many of the known causative genes encoding for sarcomeric proteins. Our findings suggest that variants in genes involved with cardiac development and cell regulation, like the ALMS1 gene, may deserve further consideration for association with familial hypertrophic cardiomyopathy.

A deleterious mutation in the ALMS1 gene in a naturally occurring model of hypertrophic cardiomyopathy in the Sphynx cat

Background

Familial hypertrophic cardiomyopathy is a common inherited cardiovascular disorder in people. Many causal mutations have been identified, but about 40% of cases do not have a known causative mutation. Mutations in the ALMS1 gene are associated with the development of Alstrom syndrome, a multisystem familial disease that can include cardiomyopathy (dilated, restrictive). Hypertrophic cardiomyopathy has not been described. The ALMS1 gene is a large gene that encodes for a ubiquitously expressed protein. The function of the protein is not well understood although it is believed to be associated with energy metabolism and homeostasis, cell differentiation and cell cycle control. The ALMS1 protein has also been shown to be involved in the regulation of cell cycle proliferation in perinatal cardiomyocytes. Although cardiomyocyte cell division and replication in mammals generally declines soon after birth, inhibition of ALMS1 expression in mice lead to increased cardiomyocyte proliferation, and deficiency of Alstrom protein has been suggested to impair post-natal cardiomyocyte cell cycle arrest. Here we describe the association of familial hypertrophic cardiomyopathy in Sphynx cats with a novel ALMS1 mutation.

Results

A G/C variant was identified in exon 12 (human exon 13) of the ALMS1 gene in affected cats and was positively associated with the presence of hypertrophic cardiomyopathy in the feline population (p < 0.0001). The variant was predicted to change a highly conserved nonpolar Glycine to a positively charged Arginine. This was predicted to be a deleterious change by three in silico programs. Protein prediction programs indicated that the variant changed the protein structure in this region from a coil to a helix. Light microscopy findings included myofiber disarray with interstitial fibrosis with significantly more nuclear proliferative activity in the affected cats than controls (p < 0.0001).

Conclusion

This study demonstrates a novel form of cardiomyopathy associated with ALMS1 in the cat. Familial hypertrophic cardiomyopathy is a disease of genetic heterogeneity; many of the known causative genes encoding for sarcomeric proteins. Our findings suggest that variants in genes involved with cardiac development and cell regulation, like the ALMS1 gene, may deserve further consideration for association with familial hypertrophic cardiomyopathy.

Prevalent ALMS1 Pathogenic Variants in Spanish Alström Patients

Alström syndrome (ALMS) is an ultrarare disease with an estimated prevalence lower than 1 in 1,000,000. It is associated with disease-causing mutations in the Alström syndrome 1 (ALMS1) gene, which codifies for a structural protein of the basal body and centrosomes. The symptomatology involves nystagmus, type 2 diabetes mellitus (T2D), obesity, dilated cardiomyopathy (DCM), neurodegenerative disorders and multiorgan fibrosis. We refined the clinical and genetic diagnosis data of 12 patients from 11 families, all of them from Spain. We also studied the allelic frequency of the different variants present in this cohort and performed a haplotype analysis for the most prevalent allele. The genetic analysis revealed 2 novel homozygous variants located in the exon 8, p.(Glu929Ter) and p.(His1808GlufsTer20) in 2 unrelated patients. These 2 novel variants were classified as pathogenic after an in silico experiment (computer analysis). On the other hand, 2 alleles were detected at a high frequency in our cohort: p.(Tyr1714Ter) (25%) and p.(Ser3872TyrfsTer19) (16.7%). The segregation analysis showed that the pathogenic variant p.(Tyr1714Ter) in 3 families is linked to a rare missense polymorphism, p.(Asn1787Asp). In conclusion, 2 novel pathological mutations have been discovered in homozygosis, as well as a probable founder effect in 3 unrelated families.

Generation of an induced pluripotent stem cell line from an Alström Syndrome patient with ALMS1 mutation (c.3902C > A, c.6436C > T) and a gene correction isogenic iPSC line

To develop a disease model for the human Alström Syndrome (AS), we used the episomal reprogramming system and CRISPR/Cas9 technology to generate an induced pluripotent stem cell (iPSC) line with the compound heterozygous patient mutation (ALMS1 c.3902C > A, c.6436C > T) along with an isogenic gene-corrected control iPSC line. Both iPSC lines showed normal karyotype, expressed pluripotent markers, and differentiated into cells of three embryonic germ layer. These AS mutant and isogenic iPSC control line will be of great use in investigating the disease mechanisms, drug screening and treatment in patients.

Next Generation Sequencing and Bioinformatics Analysis of Family Genetic Inheritance

Mendelian and complex genetic trait diseases continue to burden and affect society both socially and economically. The lack of effective tests has hampered diagnosis thus, the affected lack proper prognosis. Mendelian diseases are caused by genetic mutations in a singular gene while complex trait diseases are caused by the accumulation of mutations in either linked or unlinked genomic regions. Significant advances have been made in identifying novel diseases associated mutations especially with the introduction of next generation and third generation sequencing. Regardless, some diseases are still without diagnosis as most tests rely on SNP genotyping panels developed from population based genetic analyses. Analysis of family genetic inheritance using whole genomes, whole exomes or a panel of genes has been shown to be effective in identifying disease-causing mutations. In this review, we discuss next generation and third generation sequencing platforms, bioinformatic tools and genetic resources commonly used to analyze family based genomic data with a focus on identifying inherited or novel disease-causing mutations. Additionally, we also highlight the analytical, ethical and regulatory challenges associated with analyzing personal genomes which constitute the data used for family genetic inheritance.

Genetic evaluation of cardiomyopathy: a clinical practice resource of the American College of Medical Genetics and Genomics (ACMG)

PURPOSE

The purpose of this document is to provide updated guidance for the genetic evaluation of cardiomyopathy and for an approach to manage secondary findings from cardiomyopathy genes. The genetic bases of the primary cardiomyopathies (dilated, hypertrophic, arrhythmogenic right ventricular, and restrictive) have been established, and each is medically actionable; in most cases established treatments or interventions are available to improve survival, reduce morbidity, and enhance quality of life.

METHODS

A writing group of cardiologists and genetics professionals updated guidance, first published in 2009 for the Heart Failure Society of America (HFSA), in a collaboration with the American College of Medical Genetics and Genomics (ACMG). Each recommendation was assigned to teams of individuals by expertise, literature was reviewed, and recommendations were decided by consensus of the writing group. Recommendations for family history, phenotype screening of at-risk family members, referral to expert centers as needed, genetic counseling, and cardiovascular therapies, informed in part by phenotype, are presented in the HFSA document.

RESULTS

A genetic evaluation of cardiomyopathy is indicated with a cardiomyopathy diagnosis, which includes genetic testing. Guidance is also provided for clinical approaches to secondary findings from cardiomyopathy genes. This is relevant as cardiomyopathy is the phenotype associated with 27% of the genes on the ACMG list for return of secondary findings. Recommendations herein are considered expert opinion per current ACMG policy as no systematic approach to literature review was conducted.

CONCLUSION

Genetic testing is indicated for cardiomyopathy to assist in patient care and management of at-risk family members.

Clinical, molecular genetics and therapeutic aspects of syndromic obesity

Obesity has become a major health problem worldwide. To date, more than 25 different syndromic forms of obesity are known in which one (monogenic) or multiple (polygenic) genes are involved. This review gives an overview of these forms and focuses more in detail on 6 syndromes: Prader Willi Syndrome and Prader Willi like phenotype, Bardet Biedl Syndrome, Alström Syndrome, Wilms tumor, Aniridia, Genitourinary malformations and mental Retardation syndrome and 16p11.2 (micro)deletions. Years of research provided plenty of information on the molecular genetics of these disorders and the obesity phenotype leading to a more individualized treatment of the symptoms, however, many questions still remain unanswered. As these obesity syndromes have different signs and symptoms in common, it makes it difficult to accurately diagnose patients which may result in inappropriate treatment of the disease. Therefore, the big challenge for clinicians and scientists is to more clearly differentiate all syndromic forms of obesity to provide conclusive genetic explanations and eventually deliver accurate genetic counseling and treatment. In addition, further delineation of the (functions of the) underlying genes with the use of array- or next-generation sequencing-based technology will be helpful to unravel the mechanisms of energy metabolism in the general population.

Genetic Evaluation of Cardiomyopathy-A Heart Failure Society of America Practice Guideline

This guideline describes the approach and expertise needed for the genetic evaluation of cardiomyopathy. First published in 2009 by the Heart Failure Society of America (HFSA), the guideline has now been updated in collaboration with the American College of Medical Genetics and Genomics (ACMG). The writing group, composed of cardiologists and genetics professionals with expertise in adult and pediatric cardiomyopathy, reflects the emergence and increased clinical activity devoted to cardiovascular genetic medicine. The genetic evaluation of cardiomyopathy is a rapidly emerging key clinical priority, because high-throughput sequencing is now feasible for clinical testing and conventional interventions can improve survival, reduce morbidity, and enhance quality of life. Moreover, specific interventions may be guided by genetic analysis. A systematic approach is recommended: always a comprehensive family history; an expert phenotypic evaluation of the proband and at-risk family members to confirm a diagnosis and guide genetic test selection and interpretation; referral to expert centers as needed; genetic testing, with pre- and post-test genetic counseling; and specific guidance as indicated for drug and device therapies. The evaluation of infants and children demands special expertise. The approach to managing secondary and incidental sequence findings as recommended by the ACMG is provided.

Recessive TAF1A mutations reveal ribosomopathy in siblings with end-stage pediatric dilated cardiomyopathy

Non-ischemic dilated cardiomyopathy (DCM) has been recognized as a heritable disorder for over 25 years, yet clinical genetic testing is non-diagnostic in >50% of patients, underscoring the ongoing need for DCM gene discovery. Here, whole exome sequencing uncovered a novel molecular basis for idiopathic end-stage heart failure in two sisters who underwent cardiac transplantation at three years of age. Compound heterozygous recessive mutations in TAF1A, encoding an RNA polymerase I complex protein, were associated with marked fibrosis of explanted hearts and gene-specific nucleolar segregation defects in cardiomyocytes, indicative of impaired ribosomal RNA synthesis. Knockout of the homologous gene in zebrafish recapitulated a heart failure phenotype with pericardial edema, decreased ventricular systolic function, and embryonic mortality. These findings expand the clinical spectrum of ribosomopathies to include pediatric DCM.

A Next Generation Sequencing custom gene panel as first line diagnostic tool for atypical cases of syndromic obesity: Application in a case of Alström syndrome

Obesity phenotype can be manifested as an isolated trait or accompanied by multisystem disorders as part of a syndromic picture. In both situations, same molecular pathways may be involved to different degrees. This evidence is stronger in syndromic obesity, in which phenotypes of different syndromes may overlap. In these cases, genetic testing can unequivocally provide a final diagnosis. Here we describe a patient who met the diagnostic criteria for Alström syndrome only during adolescence. Genetic testing was requested at 25 years of age for a final confirmation of the diagnosis. The genetic diagnosis of Alström syndrome was obtained through a Next Generation Sequencing genetic test approach using a custom-designed gene panel of 47 genes associated with syndromic and non-syndromic obesity. Genetic analysis revealed a novel homozygous frameshift variant p.(Arg1550Lysfs*10) on exon 8 of the ALMS1 gene. This case shows the need for a revision of the diagnostic criteria guidelines, as a consequence of the recent advent of massive parallel sequencing technology. Indications for genetic testing reported in these currently accepted diagnostic criteria for Alström syndrome, were drafted when sequencing was expensive and time consuming. Nowadays, Next Generation Sequencing testing could be considered as first line diagnostic tool not only for Alström syndrome but, more generally, for all those atypical or not clearly distinguishable cases of syndromic obesity, thus avoiding delayed diagnosis and treatments. Early diagnosis permits a better follow-up and pre-symptomatic interventions.

Diagnostic Yield of Whole Exome Sequencing in Pediatric Dilated Cardiomyopathy

Dilated cardiomyopathy (DCM) is a heritable, genetically heterogeneous disorder characterized by progressive heart failure. DCM typically remains clinically silent until adulthood, yet symptomatic disease can develop in childhood. We sought to identify the genetic basis of pediatric DCM in 15 sporadic and three affected-siblings cases, comprised of 21 affected children (mean age, five years) whose parents had normal echocardiograms (mean age, 39 years). Twelve underwent cardiac transplantation and five died with severe heart failure. Parent-offspring whole exome sequencing (WES) data were filtered for rare, deleterious, de novo and recessive variants. In prior work, we reported de novo mutations in TNNT2 and RRAGC and compound heterozygous mutations in ALMS1 and TAF1A among four cases in our cohort. Here, de novo mutations in established DCM genes—RBM20, LMNA, TNNT2, and PRDM16—were identified among five additional cases. The RBM20 mutation was previously reported in familial DCM. An identical unreported LMNA mutation was identified in two unrelated cases, both harboring gene-specific defects in cardiomyocyte nuclear morphology. Collectively, WES had a 50% diagnostic yield in our cohort, providing an explanation for pediatric heart failure and enabling informed family planning. Research is ongoing to discover novel DCM genes among the remaining families.

Whole genome sequencing identifies a novel ALMS1 gene mutation in two Chinese siblings with Alström syndrome

Background

Alström syndrome is a rare multi-systemic disorder with a broad spectrum of symptoms. This syndrome is characterized by childhood retinal degeneration; sensorineural hearing loss; obesity; type 2 diabetes mellitus; cardiomyopathy; systemic fibrosis; and pulmonary, hepatic, and renal failure.

Case presentation

A Chinese quartet family with two siblings predominantly affected by cone-rod dystrophy and short stature were recruited. The craniofacial dysmorphism and on-set age-of-cone-rod dystrophy in the proband showed a minor intrafamilial variability. Whole genome sequencing was performed to provide the full spectrum of the two siblings’ genetic variations. In this study, we present the patients’ clinical features and our interpretation of the whole genome sequencing data. After examining the data, we focus on two compound heterozygous mutations, (c.3902C > A, p.S1301X; c.6436C > T, p.R2146X) in ALMS1, which are shared by two siblings.

Conclusion

We reported a novel ALMS1 mutation. Whole genome sequencing is a powerful tool to provide the full spectrum of genetic variations for heterogeneous disorders such as Alström syndrome.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-017-0418-3) contains supplementary material, which is available to authorized users.

De novo RRAGC mutation activates mTORC1 signaling in syndromic fetal dilated cardiomyopathy

Idiopathic dilated cardiomyopathy (DCM) is a heritable, genetically heterogeneous disorder with variable age-dependent penetrance. We sought to identify the genetic underpinnings of syndromic, sporadic DCM in a newborn female diagnosed in utero. Postnatal evaluation revealed ventricular dilation and systolic dysfunction, bilateral cataracts, and mild facial dysmorphisms. Comprehensive metabolic and genetic testing, including chromosomal microarray, mitochondrial DNA and targeted RASopathy gene sequencing, and clinical whole exome sequencing for known cardiomyopathy genes was non-diagnostic. Following exclusion of asymptomatic DCM in the parents, trio-based whole exome sequencing was carried out on a research basis, filtering for rare, predicted deleterious de novo and recessive variants. An unreported de novo S75Y mutation was discovered in RRAGC, encoding Ras-related GTP binding C, an essential GTPase in nutrient-activated mechanistic target of rapamycin complex 1 (mTORC1) signaling. In silico protein modeling and molecular dynamics simulation predicted the mutation to disrupt ligand interactions and increase the GDP-bound state. Overexpression of RagC(S75Y) rendered AD293 cells partially insensitive to amino acid deprivation, resulting in increased mTORC1 signaling compared to wild-type RagC. These findings implicate mTORC1 dysregulation through a gain-of-function mutation in RagC as a novel molecular basis for syndromic forms of pediatric heart failure, and expand genotype-phenotype correlation in RASopathy-related syndromes.

Exome Sequencing Identifies Pathogenic and Modifier Mutations in a Child With Sporadic Dilated Cardiomyopathy

Background

Idiopathic dilated cardiomyopathy (DCM) is typically diagnosed in adulthood, yet familial cases exhibit variable age‐dependent penetrance and a subset of patients develop sporadic DCM in childhood. We sought to discover the molecular basis of sporadic DCM in an 11‐year‐old female with severe heart failure necessitating cardiac transplantation.

Methods and Results

Parental echocardiograms excluded asymptomatic DCM. Whole exome sequencing was performed on the family trio and filtered for rare, deleterious, recessive, and de novo variants. Of the 8 candidate genes identified, only 2 had a role in cardiac physiology. A de novo missense mutation in TNNT2 was identified, previously reported and functionally validated in familial DCM with markedly variable penetrance. Additionally, recessive compound heterozygous truncating mutations were identified in XIRP2, a member of the ancient Xin gene family, which governs intercalated disc (ICD) maturation. Histomorphological analysis of explanted heart tissue revealed misregistration, mislocalization, and shortening of ICDs, findings similar to Xirp2^−/− mice.

Conclusions

The synergistic effects of TNNT2 and XIRP2 mutations, resulting in perturbed sarcomeric force generation and transmission, respectively, would account for an early‐onset heart failure phenotype. Whereas the importance of Xin proteins in cardiac development has been well established in animal models, this study implicates XIRP2 as a novel modifier gene in the pathogenesis of DCM.

Evaluation of genetic causes of cardiomyopathy in childhood

Cardiomyopathy frequently has a genetic basis. In adults, mutations in genes encoding components of the sarcomere, cytoskeleton, or desmosome are frequent genetic causes of cardiomyopathy. Although children share these causes, ~30% of children have an underlying metabolic, syndromic, or neuromuscular condition causing their cardiomyopathy, making the aetiologies more diverse in children as compared with adults. Although some children present with obvious signs or symptoms of metabolic, syndromic, or neuromuscular disease, other cases may be quite subtle, requiring a high level of suspicion in order to diagnose them. In general, the younger the child, the more extensive the differential. Advantages of identifying the underlying genetic cause of cardiomyopathy in the paediatric population include confirming the diagnosis in ambiguous cases, facilitating appropriate surveillance and management of cardiac and extra-cardiac diseases, providing prognostic information, and establishing the genetic basis in the family, thereby allowing the identification of at-risk relatives and institution of appropriate family screening as indicated. For these reasons, genetic testing is increasingly recognised as standard of care, and guidelines for genetic counselling, testing, and incorporation of family-based risk assessment have been established. Therapies aimed at treating specific genetic aetiologies of cardiomyopathy are emerging and are exciting new developments that require increasingly sophisticated approaches to diagnosis. As genetic testing capabilities continue to expand technically, careful interpretation, knowledgeable clinical utilisation, and appropriate dissemination of genetic information are important and challenging components of clinical care.

Alström syndrome: current perspectives

Alström syndrome (ALMS) is a rare genetic disorder that has been included in the ciliopathies group, in the last few years. Ciliopathies are a growing group of diseases associated with defects in ciliary structure and function. The development of more powerful genetic approaches has been replaced the strategies to follow for getting a successful molecular diagnosis for these patients, especially for those without the typical ALMS phenotype. In an effort to deepen the understanding of the pathogenesis of ALMS disease, much work has been done, in order to establish the biological implication of ALMS1 protein, which is still being elucidated. In addition to its role in ciliary function and structure maintenance, this protein has been implicated in intracellular trafficking, regulation of cilia signaling pathways, and cellular differentiation, among others. All these progresses will lead to identifying therapeutic targets, thus opening the way to future personalized therapies for human ciliopathies.

Alström Syndrome: Mutation Spectrum of ALMS1

Alström Syndrome (ALMS), a recessive, monogenic ciliopathy caused by mutations in ALMS1, is typically characterized by multisystem involvement including early cone-rod retinal dystrophy and blindness, hearing loss, childhood obesity, type 2 diabetes mellitus, cardiomyopathy, fibrosis, and multiple organ failure. The precise function of ALMS1 remains elusive, but roles in endosomal and ciliary transport and cell cycle regulation have been shown. The aim of our study was to further define the spectrum of ALMS1 mutations in patients with clinical features of ALMS. Mutational analysis in a world-wide cohort of 204 families identified 109 novel mutations, extending the number of known ALMS1 mutations to 239 and highlighting the allelic heterogeneity of this disorder. This study represents the most comprehensive mutation analysis in patients with ALMS, identifying the largest number of novel mutations in a single study worldwide. Here, we also provide an overview of all ALMS1 mutations identified to date.