Deep intronic mutation in OFD1, identified by targeted genomic next-generation sequencing, causes a severe form of X-linked retinitis pigmentosa (RP23).

X-linked retinitis pigmentosa (XLRP) is genetically heterogeneous with two causative genes identified, RPGR and RP2. We previously mapped a locus for a severe form of XLRP, RP23, to a 10.71 Mb interval on Xp22.31-22.13 containing 62 genes. Candidate gene screening failed to identify a causative mutation, so we adopted targeted genomic next-generation sequencing of the disease interval to determine the molecular cause of RP23. No coding variants or variants within or near splice sites were identified. In contrast, a variant deep within intron 9 of OFD1 increased the splice site prediction score 4 bp upstream of the variant. Mutations in OFD1 cause the syndromic ciliopathies orofaciodigital syndrome-1, which is male lethal, Simpson-Golabi-Behmel syndrome type 2 and Joubert syndrome. We tested the effect of the IVS9+706A>G variant on OFD1 splicing in vivo. In RP23 patient-derived RNA, we detected an OFD1 transcript with the insertion of a cryptic exon spliced between exons 9 and 10 causing a frameshift, p.N313fs.X330. Correctly spliced OFD1 was also detected in patient-derived RNA, although at reduced levels (39%), hence the mutation is not male lethal. Our data suggest that photoreceptors are uniquely susceptible to reduced expression of OFD1 and that an alternative disease mechanism can cause XLRP. This disease mechanism of reduced expression for a syndromic ciliopathy gene causing isolated retinal degeneration is reminiscent of CEP290 intronic mutations that cause Leber congenital amaurosis, and we speculate that reduced dosage of correctly spliced ciliopathy genes may be a common disease mechanism in retinal degenerations.

C1q but not mannose-binding lectin (Mbl-2) gene polymorphisms are associated with type 2 diabetes in the genetically homogeneous population of the island of Crete in Greece.

AIM: To investigate the role of mannose-binding lectin 2 (MBL2) and C1q gene polymorphisms on the susceptibility to type 2 diabetes (T2D), that may contribute to increased risk of infections in the genetically homogeneous Greek population of the island of Crete. METHODS: Ninety five patients with T2D and 333 healthy controls, all local Cretans were genotyped for the MBL-2 rs11003125 (C>G) and C1q rs292001 (G>A) single-nucleotide polymorphisms (SNPs) by the restriction fragment length polymorphism approach. RESULTS: The A/A genotype and the minor allele A of C1q SNP (P=0.0001 in both cases) were observed more frequently in T2D than in healthy controls. In contrast, the minor allele G of the rs11003125 MBL2 gene did not show any statistically significant difference between T2D patients and controls. The present study represents the first attempt to implicate the role of MBL2 and C1q gene polymorphisms in the susceptibility to T2D. CONCLUSIONS: The study has shown that the rs292001 C1q but not the rs11003125 MBL2 SNP are associated with increased risk for T2D susceptibility in the Cretan population.