Cerebro-oculo-facio-skeletal syndrome caused by the homozygous pathogenic variant Gly47Arg in ERCC2

DNA repair-related heritable photosensitivity syndromes: Mutation landscape in a multiethnic cohort of 17 multigenerational families with high degree of consanguinity

Inherited photosensitivity syndromes are a heterogeneous group of genetic skin disorders with tremendous phenotypic variability, characterized by photosensitivity and defective DNA repair, especially nucleotide excision repair. A cohort of 17 Iranian families with heritable photosensitivity syndromes was evaluated to identify their genetic defect. The patients' DNA was analyzed with either whole-exome sequencing or RNA sequencing (RNA-Seq). The interpretations of the genomic results were guided by genome-wide homozygosity mapping. Haplotype analysis was performed for cases with recurrent mutations. RNA-Seq, in addition to mutation detection, was also utilized to confirm the pathogenicity. Thirteen sequence variants, including six previously unreported pathogenic variants, were disclosed in 17 Iranian families, with XPC as the most common mutated gene in 10 families (59%). In one patient, RNA-Seq, as a first-tier diagnostic approach, revealed a non-canonical homozygous germline variant: XPC:c.413-9 T > A. The Sashimi plot showed skipping of exon 4 with dramatic XPC down-expression. Haplotype analysis of XPC:c.2251-1 G>C and XPC:1243 C>T in four families showed common haplotypes of 1.7 Mb and 2.6 Mb, respectively, denoting a founder effect. Lastly, two extremely rare cases were presented in this report: a homozygous UVSSA:c .1990 C>T was disclosed, and ERCC2-related cerebro-oculo-facio-skeletal (COFS) syndrome with an early childhood death. A direct comparison of our data with the results of previously reported cohorts demonstrates the international mutation landscape of DNA repair-related photosensitivity disorders, although population-specific differences were observed.

TFIIH central activity in nucleotide excision repair to prevent disease

The heterodecameric transcription factor IIH (TFIIH) functions in multiple cellular processes, foremost in nucleotide excision repair (NER) and transcription initiation by RNA polymerase II. TFIIH is essential for life and hereditary mutations in TFIIH cause the devastating human syndromes xeroderma pigmentosum, Cockayne syndrome or trichothiodystrophy, or combinations of these. In NER, TFIIH binds to DNA after DNA damage is detected and, using its translocase and helicase subunits XPB and XPD, opens up the DNA and checks for the presence of DNA damage. This central activity leads to dual incision and removal of the DNA strand containing the damage, after which the resulting DNA gap is restored. In this review, we discuss new structural and mechanistic insights into the central function of TFIIH in NER. Moreover, we provide an elaborate overview of all currently known patients and diseases associated with inherited TFIIH mutations and describe how our understanding of TFIIH function in NER and transcription can explain the different disease features caused by TFIIH deficiency.

Uridine Treatment of the First Known Case of SLC25A36 Deficiency

SLC25A36 is a pyrimidine nucleotide carrier playing an important role in maintaining mitochondrial biogenesis. Deficiencies in SLC25A36 in mouse embryonic stem cells have been associated with mtDNA depletion as well as mitochondrial dysfunction. In human beings, diseases triggered by SLC25A36 mutations have not been described yet. We report the first known case of SLC25A36 deficiency in a 12-year-old patient with hypothyroidism, hyperinsulinism, hyperammonemia, chronical obstipation, short stature, along with language and general developmental delay. Whole exome analysis identified the homozygous mutation c.803dupT, p.Ser269llefs*35 in the SLC25A36 gene. Functional analysis of mutant SLC25A36 protein in proteoliposomes showed a virtually abolished transport activity. Immunoblotting results suggest that the mutant SLC25A36 protein in the patient undergoes fast degradation. Supplementation with oral uridine led to an improvement of thyroid function and obstipation, increase of growth and developmental progress. Our findings suggest an important role of SLC25A36 in hormonal regulations and oral uridine as a safe and effective treatment.

Severe Form of ßIV-Spectrin Deficiency With Mitochondrial Dysfunction and Cardiomyopathy-A Case Report

ßIV-spectrin is a protein of the spectrin family which is involved in the organization of the cytoskeleton structure and is found in high quantity in the axon initial segment and the nodes of Ranvier. Together with ankyrin G, ßIV-spectrin is responsible for the clustering of KCNQ2/3-potassium channels and NaV-sodium channels. Loss or reduction of ßIV-spectrin causes a destabilization of the cytoskeleton and an impairment in the generation of the action potential, which leads to neuronal degeneration. Furthermore, ßIV-spectrin has been described to play an important role in the maintenance of the neuronal polarity and of the diffusion barrier. ßIV-spectrin is also located in the heart where it takes an important part in the structural organization of ion channels and has also been described to participate in cell signaling pathways through binding of transcription factors. We describe two patients with a severe form of ßIV-spectrin deficiency. Whole-exome sequencing revealed the homozygous stop mutation c.6016C>T (p.R2006^*) in the SPTBN4 gene. The phenotype of these patients is characterized by profound psychomotor developmental arrest, respiratory insufficiency and deafness. Additionally one of the patients presents with cardiomyopathy, optical nerve atrophy, and mitochondrial dysfunction. This is the first report of a severe form of ßIV-spectrin deficiency with hypertrophic cardiomyopathy and mitochondrial dysfunction.