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Background: Cockayne syndrome (CS) is a rare autosomal recessive disorder caused by mutations in ERCC6/CSB or ERCC8/CSA that participate in the transcription-coupled nucleotide excision repair (TC-NER) of UV-induced DNA damage. CS patients display a large heterogeneity of clinical symptoms and severities, the reason of which is not fully understood, and that cannot be anticipated in the diagnostic phase. In addition, little data is available for affected siblings, and this disease is largely undiagnosed in North Africa., Methods: We report here the clinical description as well as genetic and functional characterization of eight Tunisian CS patients, including siblings. These patients, who belonged to six unrelated families, underwent complete clinical examination and biochemical analyses. Sanger sequencing was performed for the recurrent mutation in five families, and targeted gene sequencing was done for one patient of the sixth family. We also performed Recovery RNA Synthesis (RRS) to confirm the functional impairment of DNA repair in patient-derived fibroblasts., Results: Six out of eight patients carried a homozygous indel mutation (c.598_600delinsAA) in exon 7 of ERCC8, and displayed a variable clinical spectrum including between siblings sharing the same mutation. The other two patients were siblings who carried a homozygous splice-site variant in ERCC8 (c.843+1G>C). This last pair presented more severe clinical manifestations, which are rarely associated with CSA mutations, leading to gastrostomy and hepatic damage. Impaired TC-NER was confirmed by RRS in six tested patients., Conclusions: This study provides the first deep characterization of case series of CS patients carrying CSA mutations in North Africa. These mutations have been described only in this region and in the Middle-East. We also provide the largest characterization of multiple unrelated patients, as well as siblings, carrying the same mutation, providing a framework for dissecting elusive genotype-phenotype correlations in CS., (© 2022. The Author(s).)

Background: Deficient nucleotide excision repair (NER) activity causes a variety of autosomal recessive diseases including xeroderma pigmentosum (XP) a disorder which pre-disposes to skin cancer, and the severe multisystem condition known as Cockayne syndrome (CS). In view of the clinical overlap between NER-related disorders, as well as the existence of multiple phenotypes and the numerous genes involved, we developed a new diagnostic approach based on the enrichment of 16 NER-related genes by multiplex amplification coupled with next-generation sequencing (NGS)., Methods: Our test cohort consisted of 11 DNA samples, all with known mutations and/or non pathogenic SNPs in two of the tested genes. We then used the same technique to analyse samples from a prospective cohort of 40 patients. Multiplex amplification and sequencing were performed using AmpliSeq protocol on the Ion Torrent PGM (Life Technologies)., Results: We identified causative mutations in 17 out of the 40 patients (43%). Four patients showed biallelic mutations in the ERCC6(CSB) gene, five in the ERCC8(CSA) gene: most of them had classical CS features but some had very mild and incomplete phenotypes. A small cohort of 4 unrelated classic XP patients from the Basque country (Northern Spain) revealed a common splicing mutation in POLH (XP-variant), demonstrating a new founder effect in this population. Interestingly, our results also found ERCC2(XPD), ERCC3(XPB) or ERCC5(XPG) mutations in two cases of UV-sensitive syndrome and in two cases with mixed XP/CS phenotypes., Conclusions: Our study confirms that NGS is an efficient technique for the analysis of NER-related disorders on a molecular level. It is particularly useful for phenotypes with combined features or unusually mild symptoms. Targeted NGS used in conjunction with DNA repair functional tests and precise clinical evaluation permits rapid and cost-effective diagnosis in patients with NER-defects.

Background: Bardet-Biedl Syndrome (BBS) is a genetically heterogeneous ciliopathy with clinical cardinal features including retinal degeneration, obesity and renal dysfunction. To date, 20 BBS genes have been identified with BBS10 being a major BBS gene found to be mutated in almost 20 percent of all BBS patients worldwide. It codes for the BBS10 protein which forms part of a chaperone complex localized at the basal body of the primary cilium. Renal dysfunction in BBS patients is one of the major causes of morbidity in human patients and is associated initially with urinary concentration defects related to water reabsorption impairment in renal epithelial cells. The aim of this study was to study and compare the impact of a total Bbs10 inactivation (Bbs10 (-/-)) with that of a specific renal epithelial cells inactivation (Bbs10  (fl/fl) ; Cdh16-Cre (+/-))., Results: We generated the Bbs10 (-/-) and Bbs10  (fl/fl) ; Cadh16-Cre (+/-) mouse model and characterized them. Bbs10 (-/-) mice developed obesity, retinal degeneration, structural defects in the glomeruli, polyuria associated with high circulating arginine vasopressin (AVP) concentrations, and vacuolated, yet ciliated, renal epithelial cells. On the other hand, the Bbs10  (fl/fl) ; Cadh16-Cre (+/-)mice displayed no detectable impairment., Conclusions: These data highlight the importance of a systemic Bbs10 inactivation to trigger averted renal dysfunction whereas a targeted absence of BBS10 in the renal epithelium is seemingly non-deleterious.