Genotype-phenotype correlation of 33 patients with maple syrup urine disease.

Maple syrup urine disease (MSUD) is a rare autosomal recessive inherited disorder due to defects in the branched-chain α-ketoacid dehydrogenase complex (BCKDC). MSUD varies in severity and its clinical spectrum is quite broad, ranging from mild to severe phenotypes. Thirty-three MSUD patients were recruited into this study for molecular genetic variant profiling and genotype-phenotype correlation. Except for one patient, all other patients presented with the classic neonatal form of the disease. Seventeen different variants were detected where nine were novel. The detected variants spanned across the entire BCKDHA, BCKDHB and DBT genes. All variants were in homozygous forms. The commonest alterations were nonsense and frameshift variants, followed by missense variants. For the prediction of variant's pathogenicity, we used molecular modeling and several in silico tools including SIFT, Polyphen2, Condel, and Provean. In addition, six other tools were used for the prediction of the conservation of the variants' sites including Eigen-PC, GERP++, SiPhy, PhastCons vertebrates and primates, and PhyloP100 rank scores. Herein, we presented a comprehensive characterization of a large cohort of patients with MSUD. The clinical severity of the variants' phenotypes was well correlated with the genotypes. The study underscores the importance of the use of in silico analysis of MSUD genotypes for the prediction of the clinical outcomes in patients with MSUD.

Identification of Novel CDH23 Variants Causing Moderate to Profound Progressive Nonsyndromic Hearing Loss.

Mutant alleles of CDH23, a gene that encodes a putative calcium-dependent cell-adhesion glycoprotein with multiple cadherin-like domains, are responsible for both recessive DFNB12 nonsyndromic hearing loss (NSHL) and Usher syndrome 1D (USH1D). The encoded protein cadherin 23 (CDH23) plays a vital role in maintaining normal cochlear and retinal function. The present study's objective was to elucidate the role of DFNB12 allelic variants of CDH23 in Saudi Arabian patients. Four affected offspring of a consanguineous family with autosomal recessive moderate to profound NSHL without any vestibular or retinal dysfunction were investigated for molecular exploration of genes implicated in hearing impairment. Parallel to this study, we illustrate some possible pitfalls that resulted from unexpected allelic heterogeneity during homozygosity mapping due to identifying a shared homozygous region unrelated to the disease locus. Compound heterozygous missense variants (p.(Asp918Asn); p.(Val1670Asp)) in CDH23 were identified in affected patients by exome sequencing. Both the identified missense variants resulted in a substitution of the conserved residues and evaluation by multiple in silico tools predicted their pathogenicity and variable disruption of CDH23 domains. Three-dimensional structure analysis of human CDH23 confirmed that the residue Asp918 is located at a highly conserved DXD peptide motif and is directly involved in "Ca2+" ion contact. In conclusion, our study identifies pathogenic CDH23 variants responsible for isolated moderate to profound NSHL in Saudi patients and further highlights the associated phenotypic variability with a genotypic hierarchy of CDH23 mutations. The current investigation also supports the application of molecular testing in the clinical diagnosis and genetic counseling of hearing loss.

First description of the molecular and clinical characterization of hereditary factor V deficiency in Saudi Arabia: report of four novel mutations.

Coagulation factor V plays a significant role in the blood coagulation cascade as part of the prothrombinase complex. Factor V deficiency (FVD) is a rare autosomal recessive bleeding disorder with a variable phenotypic expression which varies from being asymptomatic-to-severe bleeding episodes. The aim of this study was to perform molecular and clinical characterization of FVD in patients originating from Saudi Arabia. Eleven patients (two males and nine females) with confirmed FVD were recruited in the study with ages ranging between 5 and 53 years. A next-generation sequencing-based hematology panel encompassing 393 known genes was used. A total of six sequence variations in F5 gene were identified, including four missense mutations (p.Pro189Leu, p.Trp2004Arg, p.Met2148Thr, p. Arg2202Cys), a deletion (p.Arg872Lysfs*12) and a splicing variant (c.1118+5G>T). Four variants were identified for the first time in this study. Three patients were homozygous for their respective mutations and seven patients were heterozygous. We were not able to identify a pathogenic variant in one patient of the cohort. In-silico and three-dimensional structural analyses were performed to predict the possible impact and functional consequences of the identified variants. To our knowledge, this is the first study addressing factor V mutations in patients with Arab ancestry. Results have helped in providing a definitive diagnosis to the patients and carrier detection in extended family members. Overall, the hematology panel assay was an efficient platform, demonstrating a formidable approach for the molecular diagnosis of other suspected bleeding disorders.