Our data demonstrate that ISCA2 deficiency leads to a hereditary mitochondrial neurodegenerative white matter disease in infancy.

Background - Childhood-onset cardiomyopathy (CMP) is a heterogenous group of conditions the etiology of which is largely unknown. The influence of consanguinity on the genetics of CMP has not been addressed at a large scale. Methods - To unravel the genetic etiology of childhood-onset CMP in a consanguineous population a categorized approach was adopted. Cases with childhood-onset CMP were consecutively recruited. Based on the likelihood of founder mutation and on the clinical diagnosis, genetic test was categorized to either: (i) Targeted Genetic Test (TGT) with: targeted mutation test, single gene test, or multi-gene panel for Noonan syndrome, or (ii) Untargeted genetic test with whole exome sequencing (WES) or whole genome sequencing (WGS). Several bioinformatics tools were used to filter the variants. Results - 205 unrelated probands with various forms of CMP were evaluated. The median age of presentation was 10 months. In 30.2% (n=62), TGT had a yield of 82.7% compared to 33.6% for WES/WGS (n=143) giving an overall yield of 53.7%. Strikingly, 96.4% of the variants were homozygous, 9% of which were found in 4 dominant genes. Homozygous variants were also detected in 7 novel candidates ( ACACB , AASDH , CASZ1 , FLII , RHBDF1 , RPL3L , ULK1 ). Conclusions - Our work demonstrates the impact of consanguinity on the genetics of childhood-onset CMP, the value of adopting a categorized population-sensitive genetic approach, and the opportunity of uncovering novel genes. Our data suggest that if a founder mutation is not suspected, adopting WES/WGS as a first-line test should be considered.

BackgroundFamilial dilated cardiomyopathy (DCM) is genetically heterogeneous. Mutations in more than 40 genes have been identified in familial cases, mostly inherited in an autosomal dominant pattern. DCM due to recessive mutations is rarely observed. In consanguineous families, homozygosity mapping and whole exome sequencing (WES) can be utilized to identify the genetic defects in recessively inherited DCM.MethodsIn a consanguineous family with four affected siblings with severe DCM, we combined homozygosity mapping, linkage analysis and WES, to uncover the genetic defect.ResultsA region of homozygosity (ROH) on chromosome 8q24.13–24.23 was found to be shared by all of the four affected siblings. WES detected ~47,000 variants that were filtered to a homozygous mutation (p.Gly243Arg) in the FBXO32 gene, located within the identified ROH. The mutation segregated with the phenotype, replaced a highly-conserved amino acid, and was not detected in 1986 ethnically-matched chromosomes. FBXO32, which encodes a muscle-specific ubiquitin ligase, has been implicated in the pathogenesis of cardiomyopathy through the ubiquitin proteasome system (UPS). In addition, FBXO32-knockout mice manifest with cardiomyopathy. Screening the index patient for all of the WES variants in 48 genes known to be implicated in hypertrophic and dilated cardiomyopathy was negative.ConclusionsOur data suggest that FBXO32 is a candidate gene for recessive DCM. Acting as a cardiac ubiquitin ligase, mutated FBXO32 could perturb the degradation of target proteins in the UPS, the impairment of which has been observed in cardiomyopathy. Our work proposes that genes encoding other ubiquitin ligases could also be implicated in familial cardiomyopathy.Electronic supplementary materialThe online version of this article (doi:10.1186/s12881-016-0267-5) contains supplementary material, which is available to authorized users.

Infantile-Onset Pompe Disease (IOPD) is an autosomal recessive disorder of glycogen metabolism resulting from deficiency of the lysosomal hydrolase acid α-glucosidase encoded by GAA gene. Affected infants present before the age of 12 months with hypotonia, muscle weakness, and hypertrophic cardiomyopathy. Enzyme replacement therapy (ERT) has been shown to improve survival, cardiac mass, and motor skills. In this work, we aim to illustrate the genotypes of IOPD and the outcome of ERT in our population. The medical records of infants with confirmed diagnosis of IOPD who received ERT were reviewed. Eighteen infants (7 males, 11 females) were included in the study. The median age at presentation was 2 months and the median age at the start of ERT was 4.5 months. Fifteen (83.3%) infants died with a median age at death of 12 months. The 3 alive infants (whose current ages are 6½ years, 6 years, and 10 years), who were initiated on ERT at the age of 3 weeks, 5 months, and 8 months respectively, has had variable response with requirement of assisted ventilation in one child and tracheostomy in another child. All infants were homozygous for GAA mutations except one infant who was compound heterozygous. All infants (n = 8) with truncating mutations died. Our work provides insight into the correlation of genotypes and outcome of ERT in IOPD in Saudi Arabia. Our data suggest that early detection of cases, through newborn screening, and immunomodulation before the initiation of ERT may improve the outcome of ERT in Saudi infants with IOPD.