Mapping the genetic landscape of treatable inherited metabolic disorders in a large Middle Eastern biobank.

PURPOSE: To date, approximately 1400 inherited metabolic disorders (IMDs) have been described, some of which are treatable. It is estimated that 2% to 3% of live births worldwide are affected by treatable IMDs. Roughly 80% of IMDs are autosomal recessive, leading to a potentially higher incidence in regions with high consanguinity. METHODOLOGY: The study utilized genome sequencing data from 14,060 adult Qatari participants who were recruited by the Qatar Biobank and sequenced by the Qatar Genome Program. The genome sequencing data were analyzed for 125 nuclear genes known to be associated with 115 treatable IMDs. RESULTS: Our study identified 253 pathogenic/likely pathogenic single-nucleotide variations associated with 69 treatable IMDs, including 211 known and 42 novel predicted loss-of-function variants. We estimated that approximately 1 in 13 unrelated individuals (8%) carry a heterozygous pathogenic variant for at least 1 of 46 treatable IMDs. Notably, phenylketonuria/hyperphenylalaninemia and homocystinuria had among the highest carrier frequencies (1 in 68 and 1 in 85, respectively). CONCLUSION: Population-based studies of treatable IMDs, particularly in globally under-studied populations, can identify high-frequency alleles segregating in the community and inform public health policies, including carrier and newborn screening.

Assessing the genetic burden of familial hypercholesterolemia in a large middle eastern biobank.

BACKGROUND: The genetic architecture underlying Familial Hypercholesterolemia (FH) in Middle Eastern Arabs is yet to be fully described, and approaches to assess this from population-wide biobanks are important for public health planning and personalized medicine. METHODS: We evaluate the pilot phase cohort (n = 6,140 adults) of the Qatar Biobank (QBB) for FH using the Dutch Lipid Clinic Network (DLCN) criteria, followed by an in-depth characterization of all genetic alleles in known dominant (LDLR, APOB, and PCSK9) and recessive (LDLRAP1, ABCG5, ABCG8, and LIPA) FH-causing genes derived from whole-genome sequencing (WGS). We also investigate the utility of a globally established 12-SNP polygenic risk score to predict FH individuals in this cohort with Arab ancestry. RESULTS: Using DLCN criteria, we identify eight (0.1%) 'definite', 41 (0.7%) 'probable' and 334 (5.4%) 'possible' FH individuals, estimating a prevalence of 'definite or probable' FH in the Qatari cohort of ~ 1:125. We identify ten previously known pathogenic single-nucleotide variants (SNVs) and 14 putatively novel SNVs, as well as one novel copy number variant in PCSK9. Further, despite the modest sample size, we identify one homozygote for a known pathogenic variant (ABCG8, p. Gly574Arg, global MAF = 4.49E-05) associated with Sitosterolemia 2. Finally, calculation of polygenic risk scores found that individuals with 'definite or probable' FH have a significantly higher LDL-C SNP score than 'unlikely' individuals (p = 0.0003), demonstrating its utility in Arab populations. CONCLUSION: We design and implement a standardized approach to phenotyping a population biobank for FH risk followed by systematically identifying known variants and assessing putative novel variants contributing to FH burden in Qatar. Our results motivate similar studies in population-level biobanks - especially those with globally under-represented ancestries - and highlight the importance of genetic screening programs for early detection and management of individuals with high FH risk in health systems.

Functional Characterization of the MYO6 Variant p.E60Q in Non-Syndromic Hearing Loss Patients.

Hereditary hearing loss (HHL) is a common genetic disorder accounting for at least 60% of pre-lingual deafness in children, of which 70% is inherited in an autosomal recessive pattern. The long tradition of consanguinity among the Qatari population has increased the prevalence of HHL, which negatively impacts the quality of life. Here, we functionally validated the pathogenicity of the c.178G>C, p.E60Q mutation in the MYO6 gene, which was detected previously in a Qatari HHL family, using cellular and animal models. In vitro analysis was conducted in HeLa cells transiently transfected with plasmids carrying MYO6WT or MYO6p.E60Q, and a zebrafish model was generated to characterize the in vivo phenotype. Cells transfected with MYO6WT showed higher expression of MYO6 in the plasma membrane and increased ATPase activity. Modeling the human MYO6 variants in zebrafish resulted in severe otic defects. At 72 h post-injection, MYO6p.E60Q embryos demonstrated alterations in the sizes of the saccule and utricle. Additionally, zebrafish with MYO6p.E60Q displayed super-coiled and bent hair bundles in otic hair cells when compared to control and MYO6WT embryos. In conclusion, our cellular and animal models add support to the in silico prediction that the p.E60Q missense variant is pathogenic and damaging to the protein. Since the c.178G>C MYO6 variant has a 0.5% allele frequency in the Qatari population, about 400 times higher than in other populations, it could contribute to explaining the high prevalence of hearing impairment in Qatar.

Identification of mutation resistance coldspots for targeting the SARS-CoV2 main protease.

Mutations in the novel coronavirus SARS-CoV2 are the major concern as they might lead to drug/vaccine resistance. In the host cell, the virus largely depends on the main protease (Mpro ) to regulate infection hence it is one of the most attractive targets for inhibitor design. However, >19,000 mutations in the Mpro have already been reported. The mutations encompassing 282 amino acid positions and these "hotspots" might change the Mpro structure, activity and potentially delay therapeutic strategies targeting Mpro . Thus, here we identified 24 mutational "coldspots" where mutations have not been observed. We compared the structure-function relationship of these coldspots with several SARS-CoV2 Mpro X-ray crystal structures. We found that three coldspot residues (Leu141, Phe185, and Gln192) help to form the active site, while seven (Gly2, Arg4, Tyr126, Lys137, Leu141, Leu286, and Leu287) contribute to dimer formation that is required for Mpro activity. The surface of the dimer interface is more resistant to mutations compared to the active site. Interestingly, most of the coldspots are found in three clusters and forms conserved patterns when compared with other coronaviruses. Importantly, several conserved coldspots are available on the surface of the active site and at the dimer interface for targeting. The identification and short list of these coldspots offers a new perspective to target the SARS-CoV2 Mpro while avoiding mutation-based drug resistance.

In silico and in vivo models for Qatari-specific classical homocystinuria as basis for development of novel therapies.

Homocystinuria is a rare inborn error of methionine metabolism caused by cystathionine ß-synthase (CBS) deficiency. The prevalence of homocystinuria in Qatar is 1:1,800 births, mainly due to a founder Qatari missense mutation, c.1006C>T; p.R336C (p.Arg336Cys). We characterized the structure-function relationship of the p.R336C-mutant protein and investigated the effect of different chemical chaperones to restore p.R336C-CBS activity using three models: in silico, ΔCBS yeast, and CRISPR/Cas9 p.R336C knock-in HEK293T and HepG2 cell lines. Protein modeling suggested that the p.R336C induces severe conformational and structural changes, perhaps influencing CBS activity. Wild-type CBS, but not the p.R336C mutant, was able to restore the yeast growth in ΔCBS-deficient yeast in a complementation assay. The p.R336C knock-in HEK293T and HepG2 cells decreased the level of CBS expression and reduced its structural stability; however, treatment of the p.R336C knock-in HEK293T cells with betaine, a chemical chaperone, restored the stability and tetrameric conformation of CBS, but not its activity. Collectively, these results indicate that the p.R336C mutation has a deleterious effect on CBS structure, stability, and activity, and using the chemical chaperones approach for treatment could be ineffective in restoring p.R336C CBS activity.

Hypertrophic cardiomyopathy-linked variants of cardiac myosin-binding protein C3 display altered molecular properties and actin interaction.

The most common inherited cardiac disorder, hypertrophic cardiomyopathy (HCM), is characterized by thickening of heart muscle, for which genetic mutations in cardiac myosin-binding protein C3 (c-MYBPC3) gene, is the leading cause. Notably, patients with HCM display a heterogeneous clinical presentation, onset and prognosis. Thus, delineating the molecular mechanisms that explain how disparate c-MYBPC3 variants lead to HCM is essential for correlating the impact of specific genotypes on clinical severity. Herein, five c-MYBPC3 missense variants clinically associated with HCM were investigated; namely V1 (R177H), V2 (A216T), V3 (E258K), V4 (E441K) and double mutation V5 (V3 + V4), all located within the C1 and C2 domains of MyBP-C, a region known to interact with sarcomeric protein, actin. Injection of the variant complementary RNAs in zebrafish embryos was observed to recapitulate phenotypic aspects of HCM in patients. Interestingly, V3- and V5-cRNA injection produced the most severe zebrafish cardiac phenotype, exhibiting increased diastolic/systolic myocardial thickness and significantly reduced heart rate compared with control zebrafish. Molecular analysis of recombinant C0-C2 protein fragments revealed that c-MYBPC3 variants alter the C0-C2 domain secondary structure, thermodynamic stability and importantly, result in a reduced binding affinity to cardiac actin. V5 (double mutant), displayed the greatest protein instability with concomitant loss of actin-binding function. Our study provides specific mechanistic insight into how c-MYBPC3 pathogenic variants alter both functional and structural characteristics of C0-C2 domains leading to impaired actin interaction and reduced contractility, which may provide a basis for elucidating the disease mechanism in HCM patients with c-MYBPC3 mutations.

The Role of Cardiac Myosin Binding Protein C3 in Hypertrophic Cardiomyopathy-Progress and Novel Therapeutic Opportunities.

Hypertrophic cardiomyopathy (HCM) is a common autosomal dominant genetic cardiovascular disorder marked by genetic and phenotypic heterogeneity. Mutations in the gene encodes the cardiac myosin-binding protein C, cMYBPC3 is amongst the various sarcomeric genes that are associated with HCM. These mutations produce mutated mRNAs and truncated cMyBP-C proteins. In this review, we will discuss the implications and molecular mechanisms involved in MYBPC3 different mutations. Further, we will highlight the novel targets that can be developed into potential therapeutics for the treatment of HMC. J. Cell. Physiol. 232: 1650-1659, 2017. © 2016 Wiley Periodicals, Inc.

Two patients with Canavan disease and structural modeling of a novel mutation.

Canavan disease (CD) is a rare fatal childhood neurological autosomal recessive genetic disease caused by mutations in the ASPA gene, which lead to catalytic deficiency of the ASPA enzyme, which catalyzes the hydrolysis of N-acetyl-L-aspartate (NAA) into aspartate and acetate. CD occurs frequently among Ashkenazi Jewish population, however it has been reported in many other ethnic groups with significantly lower frequency. Here, we report on two Egyptian patients diagnosed with CD, the first patient harbors five missense mutations (c.427 A > G; p. I143V, c.502C > T; p. R168C, c.530 T > C; p. I177T, c.557 T > C; p. V186D c.548C > T; p. P183L) and a silent mutation (c.693 C > T; p. Y231Y). The second patient was found to be homozygous for two missense mutations (c.427 A > G; p. I143V and c.557 T > A; p. V186D). Furthermore, molecular modeling of the novel mutation p. P183L provides an instructive explanation of the mutational impact on the protein structure that can affect the function of the ASPA. Here, the clinical, radiological, and biochemical profile of the two patients are reviewed in details.

Structural modeling of p.V31F variant in the aspartoacylase gene.

Aspartoacylase (ASPA) is an abundant enzyme in the brain, which catalyzes the conversion of N-acetylaspartate into acetate and aspartate, deficiency in its activity leads to degeneration of the white matter of the brain and is a recognized cause of Canavan disease (CD), which affect children. Although genotype-phenotype correlation have been reported for Canavan disease patients, this relationships is still not straightforward. In this communication, we use molecular modeling to address the structural consequences resulting from the missense variant p.V31F in the ASPA enzyme, which we previously reported in a homozygous form in an Egyptian patient with infantile CD. This modeling suggests that this variant brings significant changes to the catalytic core by introducing structural flexibility through neighbouring key residues. In particular, it provides a molecular explanation for the pathogenic effect of this variant and provides a meaningful genotype-phonotype relationships. The mutational impact appears to have an influence on the function of the protein and initiates molecular event for the mechanism of the disease.

Burden of Mendelian disorders in a large Middle Eastern biobank.

BACKGROUND: Genome sequencing of large biobanks from under-represented ancestries provides a valuable resource for the interrogation of Mendelian disease burden at world population level, complementing small-scale familial studies. METHODS: Here, we interrogate 6045 whole genomes from Qatar-a Middle Eastern population with high consanguinity and understudied mutational burden-enrolled at the national Biobank and phenotyped for 58 clinically-relevant quantitative traits. We examine a curated set of 2648 Mendelian genes from 20 panels, annotating known and novel pathogenic variants and assessing their penetrance and impact on the measured traits. RESULTS: We find that 62.5% of participants are carriers of at least 1 known pathogenic variant relating to recessive conditions, with homozygosity observed in 1 in 150 subjects (0.6%) for which Peninsular Arabs are particularly enriched versus other ancestries (5.8-fold). On average, 52.3 loss-of-function variants were found per genome, 6.5 of which affect a known Mendelian gene. Several variants annotated in ClinVar/HGMD as pathogenic appeared at intermediate frequencies in this cohort (1-3%), highlighting Arab founder effect, while others have exceedingly high frequencies (> 5%) prompting reconsideration as benign. Furthermore, cumulative gene burden analysis revealed 56 genes having gene carrier frequency > 1/50, including 5 ACMG Tier 3 panel genes which would be candidates for adding to newborn screening in the country. Additionally, leveraging 58 biobank traits, we systematically assess the impact of novel/rare variants on phenotypes and discover 39 candidate large-effect variants associating with extreme quantitative traits. Furthermore, through rare variant burden testing, we discover 13 genes with high mutational load, including 5 with impact on traits relevant to disease conditions, including metabolic disorder and type 2 diabetes, consistent with the high prevalence of these conditions in the region. CONCLUSIONS: This study on the first phase of the growing Qatar Genome Program cohort provides a comprehensive resource from a Middle Eastern population to understand the global mutational burden in Mendelian genes and their impact on traits in seemingly healthy individuals in high consanguinity settings.

Clinical, Genetic and Functional Characterization of a Novel AVPR2 Missense Mutation in a Woman with X-Linked Recessive Nephrogenic Diabetes Insipidus.

Nephrogenic diabetes insipidus (NDI) is a rare disorder characterized by renal unresponsiveness to the hormone vasopressin, leading to excretion of large volumes of diluted urine. Mutations in the arginine vasopressin receptor-2 (AVPR2) gene cause congenital NDI and have an X-linked recessive inheritance. The disorder affects almost exclusively male family members, but female carriers occasionally present partial phenotypes due to skewed inactivation of the X-chromosome. Here, we report a rare case of a woman affected with X-linked recessive NDI, presenting an average urinary output of 12 L/day. Clinical and biochemical studies showed incomplete responses to water deprivation and vasopressin stimulation tests. Genetic analyses revealed a novel heterozygous missense mutation (c.493G > C, p.Ala165Pro) in the AVPR2 gene. Using a combination of in-silico protein modeling with human cellular models and molecular phenotyping, we provide functional evidence for phenotypic effects. The mutation destabilizes the helical structure of the AVPR2 transmembrane domains and disrupts its plasma membrane localization and downstream intracellular signaling pathways upon activation with its agonist vasopressin. These defects lead to deficient aquaporin 2 (AQP2) membrane translocation, explaining the inability to concentrate urine in this patient.

A recessive variant in SIM2 in a child with complex craniofacial anomalies and global developmental delay.

Rare deletions and duplications on the long arm of Chromosome 21 have previously been reported in many patients with craniofacial and developmental phenotypes. However, this Down Syndrome Critical Region (DSCR) contains multiple genes, making identifying a single causative gene difficult. Here, we report a case of a boy with bicoronal craniosynostosis, facial dysmorphism, developmental delay, and intellectual impairment who was found by whole genome sequencing to have a homozygous missense mutation in the Single-Minded Homolog 2 (SIM2) gene (c.461 A > G, p.Tyr154Cys) within the DSCR. SIM2 encodes an essential bHLH and PAS domain transcription factor expressed during fetal brain development and acts as a master regulator of neurogenesis. This variant is globally very rare, segregates in the family, and is predicted to be highly deleterious by in silico analysis, 3D molecular modeling of protein structure, and functional analysis of zebrafish models. Zebrafish expressing the human SIM2p.Y154C variant displayed a progressed microcephaly-like phenotype and head shape abnormalities. When combined with careful phenotyping of the patient vis-à-vis previously reported cases harboring structural variants in this critical 21q22 region, the data support a pathogenic role of SIM2 in this complex syndrome and demonstrates the utility of next-generation sequencing in prioritizing genes in contiguous deletions/duplications syndromes and diagnosing microarray-negative patients in the craniofacial clinic.

A Neutrophil-Driven Inflammatory Signature Characterizes the Blood Transcriptome Fingerprint of Psoriasis.

Transcriptome profiling approaches have been widely used to investigate the mechanisms underlying psoriasis pathogenesis. Most researchers have measured changes in transcript abundance in skin biopsies; relatively few have examined transcriptome changes in the blood. Although less relevant to the study of psoriasis pathogenesis, blood transcriptome profiles can be readily compared across various diseases. Here, we used a pre-established set of 382 transcriptional modules as a common framework to compare changes in blood transcript abundance in two independent public psoriasis datasets. We then compared the resulting "transcriptional fingerprints" to those obtained for a reference set of 16 pathological or physiological states. The perturbations in blood transcript abundance in psoriasis were relatively subtle compared to the changes we observed in other autoimmune and auto-inflammatory diseases. However, we did observe a consistent pattern of changes for a set of modules associated with neutrophil activation and inflammation; interestingly, this pattern resembled that observed in patients with Kawasaki disease. This similarity between the blood-transcriptome signatures in psoriasis and Kawasaki disease suggests that the immune mechanisms driving their pathogenesis might be partially shared.

Next Generation Sequencing and Animal Models Reveal SLC9A3R1 as a New Gene Involved in Human Age-Related Hearing Loss.

Age-related hearing loss (ARHL) is the most common sensory impairment in the elderly affecting millions of people worldwide. To shed light on the genetics of ARHL, a large cohort of 464 Italian patients has been deeply characterized at clinical and molecular level. In particular, 46 candidate genes, selected on the basis of genome-wide association studies (GWAS), animal models and literature updates, were analyzed by targeted re-sequencing. After filtering and prioritization steps, SLC9A3R1 has been identified as a strong candidate and then validated by "in vitro" and "in vivo" studies. Briefly, a rare (MAF: 2.886e-5) missense variant c.539G > A, p.(R180Q) was detected in two unrelated male patients affected by ARHL characterized by a severe to profound high-frequency hearing loss. The variant, predicted as damaging, was not present in healthy matched controls. Protein modeling confirmed the pathogenic effect of p.(R180Q) variant on protein's structure leading to a change in the total number of hydrogen bonds. In situ hybridization showed slc9a3r1 expression in zebrafish inner ear. A zebrafish knock-in model, generated by CRISPR-Cas9 technology, revealed a reduced auditory response at all frequencies in slc9a3r1 R180Q/R180Q mutants compared to slc9a3r1 +/+ and slc9a3r1 +/R180Q animals. Moreover, a significant reduction (5.8%) in the total volume of the saccular otolith (which is responsible for sound detection) was observed in slc9a3r1 R180Q/R180Q compared to slc9a3r1 +/+ (P = 0.0014), while the utricular otolith, necessary for balance, was not affected in agreement with the human phenotype. Overall, these data strongly support the role of SLC9A3R1 gene in the pathogenesis of ARHL opening new perspectives in terms of diagnosis, prevention and treatment.

Next-generation sequencing identified SPATC1L as a possible candidate gene for both early-onset and age-related hearing loss.

Hereditary hearing loss (HHL) and age-related hearing loss (ARHL) are two major sensory diseases affecting millions of people worldwide. Despite many efforts, additional HHL-genes and ARHL genetic risk factors still need to be identified. To fill this gap a large genomic screening based on next-generation sequencing technologies was performed. Whole exome sequencing in a 3-generation Italian HHL family and targeted re-sequencing in 464 ARHL patients were performed. We detected three variants in SPATC1L: a nonsense allele in an HHL family and a frameshift insertion and a missense variation in two unrelated ARHL patients. In silico molecular modelling of all variants suggested a significant impact on the structural stability of the protein itself, likely leading to deleterious effects and resulting in truncated isoforms. After demonstrating Spatc1l expression in mice inner ear, in vitro functional experiments were performed confirming the results of the molecular modelling studies. Finally, a candidate-gene population-based statistical study in cohorts from Caucasus and Central Asia revealed a statistically significant association of SPATC1L with normal hearing function at low and medium hearing frequencies. Overall, the amount of different genetic data presented here (variants with early-onset and late-onset hearing loss in addition to genetic association with normal hearing function), together with relevant functional evidence, likely suggest a role of SPATC1L in hearing function and loss.

A Strategy to Enhance Secretion of Extracellular Matrix Components by Stem Cells: Relevance to Tissue Engineering.

The ability of cells to secrete extracellular matrix proteins is an important property in the repair, replacement, and regeneration of living tissue. Cells that populate tissue-engineered constructs need to be able to emulate these functions. The motifs, KTTKS or palmitoyl-KTTKS (peptide amphiphile), have been shown to stimulate production of collagen and fibronectin in differentiated cells. Molecular modeling was used to design different forms of active peptide motifs to enhance the efficacy of peptides to increase collagen and fibronectin production using terminals KTTKS/SKTTK/SKTTKS connected by various hydrophobic linkers, V4A3/V4A2/A4G3. Molecular dynamic simulations showed SKTTKS-V4A3-SKTTKS (P3), with palindromic (SKTTKS) motifs and SKTTK-V4A2-KTTKS (P5), maintained structural integrity and favorable surface electrostatic distributions that are required for functionality. In vitro studies showed that peptides, P3 and P5, showed low toxicity to human adipose-derived stem cells (hADSCs) and significantly increased the production of collagen and fibronectin in a concentration-dependent manner compared with the original active peptide motif. The 4-day treatment showed that stem cell markers of hADSCs remained stable with P3. The molecular design of novel peptides is a promising strategy for the development of intelligent biomaterials to guide stem cell function for tissue engineering applications.

Impact of disease-causing mutations on inter-domain interactions in cMyBP-C: a steered molecular dynamics study.

The molecular interactions of the sarcomeric proteins are essential in the regulation of various cardiac functions. Mutations in the gene MYBPC3 coding for cardiac myosin-binding protein-C (cMyBP-C), a multi-domain protein, are the most common cause of hypertrophic cardiomyopathy (HCM). The N-terminal complex, C1-motif-C2 is a central region in cMyBP-C for the regulation of cardiac muscle contraction. However, the mechanism of binding/unbinding of this complex during health and disease is unknown. Here, we study possible mechanisms of unbinding using steered molecular dynamics simulations for the complex in the wild type, in single mutations (E258K in C1, E441K in C2), as well as in a double mutation (E258K in C1 + E441K in C2), which are associated with severe HCM. The observed molecular events and the calculation of force utilized for the unbinding suggest the following: (i) double mutation can encourage the formation of rigid complex that required large amount of force and long-time to unbind, (ii) C1 appears to start to unbind ahead of C2 regardless of the mutation, and (iii) unbinding of C2 requires larger amount of force than C1. This molecular insight suggests that key HCM-causing mutations might significantly modify the native affinity required for the assembly of the domains in cMyBP-C, which is essential for normal cardiac function.

Towards developing a vaccine for rheumatic heart disease.

Rheumatic heart disease (RHD) is the most serious manifestations of rheumatic fever, which is caused by group A Streptococcus (GAS or Streptococcus pyogenes) infection. RHD is an auto immune sequelae of GAS pharyngitis, rather than the direct bacterial infection of the heart, which leads to chronic heart valve damage. Although antibiotics like penicillin are effective against GAS infection, improper medical care such as poor patient compliance, overcrowding, poverty, and repeated exposure to GAS, leads to acute rheumatic fever and RHD. Thus, efforts have been put forth towards developing a vaccine. However, a potential global vaccine is yet to be identified due to the widespread diversity of S. pyogenes strains and cross reactivity of streptococcal proteins with host tissues. In this review, we discuss the available vaccine targets of S. pyogenes and the significance of in silico approaches in designing a vaccine for RHD.

Targeted sequencing identifies novel variants involved in autosomal recessive hereditary hearing loss in Qatari families.

Hereditary hearing loss is characterized by a very high genetic heterogeneity. In the Qatari population the role of GJB2, the worldwide HHL major player, seems to be quite limited compared to Caucasian populations. In this study we analysed 18 Qatari families affected by non-syndromic hearing loss using a targeted sequencing approach that allowed us to analyse 81 genes simultaneously. Thanks to this approach, 50% of these families (9 out of 18) resulted positive for the presence of likely causative alleles in 6 different genes: CDH23, MYO6, GJB6, OTOF, TMC1 and OTOA. In particular, 4 novel alleles were detected while the remaining ones were already described to be associated to HHL in other ethnic groups. Molecular modelling has been used to further investigate the role of novel alleles identified in CDH23 and TMC1 genes demonstrating their crucial role in Ca2+ binding and therefore possible functional role in proteins. Present study showed that an accurate molecular diagnosis based on next generation sequencing technologies might largely improve molecular diagnostics outcome leading to benefits for both genetic counseling and definition of recurrence risk.

An Investigation of the Molecular Mechanism of Double cMyBP-C Mutation in a Patient with End-Stage Hypertrophic Cardiomyopathy.

Mutations in the gene coding for cardiac myosin binding protein-C (cMyBP-C), a multi-domain (C0-C10) protein, are a major causative factor for inherited hypertrophic cardiomyopathy. Patients carrying mutations in this gene have an extremely heterogeneous clinical course, with some progressing to end-stage heart failure. The cause of this variability is unknown. We here describe molecular modeling of a double mutation in domains C1 (E258K) and C2 (E441K) in a patient with severe HCM phenotype. The three-dimensional structure for the C1-motif-C2 complex was constructed with double and single mutations being introduced. Molecular dynamic simulations were performed for 10 ns under physiological conditions. The results showed that both E258K and E441K in isolation can predominantly affect the native domain as well as the nearby motif via conformational changes and result in an additive effect when they coexist. These changes involve important regions of the motif such as phosphorylation and potential actin-binding sites. Moreover, the charge reversal mutations altered the surface electrostatic properties of the complex. In addition, we studied protein expression, which showed that the mutant proteins were expressed and we can suppose that the severe phenotype was not due to haploinsufficiency. However, additional studies on human gene expression will need to confirm this hypothesis. The double mutation affecting the regulatory N-terminal of cMyBP-C have the potential of synergistically interfering with the binding to neighbouring domains and other sarcomeric proteins. These effects may account for the severe phenotype and clinical course observed in the complex cMyBP-C genotypes.