Identification of 14 novel CTNS mutations and characterization of seven splice site mutations associated with cystinosis.

Cystinosis is an autosomal recessive disorder characterized by intra-lysosomal accumulation of cystine. Three disease forms exist, infantile, juvenile, and ocular nonnephropathic cystinosis, delineated on the basis of severity of symptoms and age of onset. Mutations in the causative gene, CTNS, which encodes cystinosin, the seven transmembrane domain lysosomal cystine transporter, have been identified in all forms confirming their allelic status. By screening for mutations in the CTNS exons and promotor region, we report 14 novel mutations associated with cystinosis: 11 underlying infantile cystinosis, two juvenile cystinosis, and one associated with an atypical form of the disease. These mutations, all situated in the exons or immediately flanking intronic sequences, comprise in-frame insertions and deletions, as well as missense, nonsense, and putative splice-site mutations. Furthermore, we confirmed the putative splice-site mutations we have reported to date (five novel and two previously reported) by isolation of RNA from the affected carriers and characterization of the resultant transcripts using RT-PCR. Since the cloning of CTNS, we have screened for mutations in 108 affected individuals, which has resulted in a high mutation detection rate of 95.8%. Interestingly, the few undetectable mono- or bi-allelic mutations segregated mostly in the noninfantile forms, suggesting that these individuals carry mutations either in the introns or in unidentified regulatory sequences.

Structure of the human type IV collagen gene COL4A3 and mutations in autosomal Alport syndrome.

Mutations in either the COL4A3 or the COL4A4 genes, encoding the alpha3 and alpha4 chains of type IV collagen, are responsible for the autosomal-recessive form of Alport syndrome, a progressive hematuric nephropathy characterized by glomerular basement membrane abnormalities. Reported here are the complete COL4A3 exon-intron structure and a comprehensive screen for mutations of the 52 COL4A3 exons in 41 unrelated patients diagnosed as having autosomal Alport syndrome. This resulted in the identification of 21 mutations that are expected to be causative. Furthermore, it is shown that heterozygous COL4A3 missense mutations, when symptomatic, can be associated with a broad range of phenotypes, from familial benign hematuria to the complete features of Alport syndrome nephropathy.