ClinVar Genomic variation as it relates to human health

In affected members of 2 unrelated but consanguineous families of Arabian ancestry with Fanconi anemia of complementation group C (FANCC; 227645), Hartmann et al. (2010) identified a homozygous G-to-T transversion in intron 2 of the FANCC gene (165+1G-T), changing a highly conserved GT dinucleotide to TT at the 5-prime splice site. Two affected individuals from a family of mixed Arabian/British ancestry were compound heterozygous for the intron 2 mutation and a 250-bp deletion (613899.0010), resulting in the skipping of exons 2 and 3. The phenotype was relatively mild in the 2 Arabian families, but was severe in the 2 patients in the mixed Arabian/British family, who died at ages 13.5 and 16 years. RT-PCR analysis of the splice site mutation yielded 4 distinct products, including the wildtype product at 27% of the total transcripts. Functional analysis of the splice site mutation within splicing reporters showed that increasing complementarity to U1 snRNA could reconstitute splicing at the noncanonical TT dinucleotide, and that artificial TT-adapted U1 snRNA improved correct mRNA processing at the mutant TT splice site. These results were replicated in patient fibroblasts, with correctly spliced transcripts increasing from about 30% to 56-58%. Finally, Hartmann et al. (2010) demonstrated that use of lentiviral vectors as a delivery system to introduce expression cassettes for TT-adapted U1 snRNAs into primary FANCC patient fibroblasts allowed the continuous correction of the DNA damage-induced G2 cell-cycle arrest in these cells. These findings indicated an alternative transcript-targeting approach for genetic therapy of inherited splice site mutations. (less)