4 NOVEL PEPD ALLELES CAUSING PROLIDASE DEFICIENCY

Mutations at the PEPD locus cause prolidase deficiency (McKusick 17010 0), a rare autosomal recessive disorder characterized by iminodipeptid uria, skin ulcers, mental retardation, and recurrent infections. Four PEPD mutations from five severely affected individuals were characteri zed by analysis of reverse-transcribed, PCR-amplified (RT-PCR) cDNA. W e used SSCP analysis on four overlapping cDNA fragments covering the e ntire coding region of the PEPD gene and detected abnormal SSCP bands for the fragment spanning all or part of exons 13-15 in three of the p robands. Direct sequencing of the mutant cDNAs showed a G --> A, 1342 substitution (G448R) in two patients and a 3-bp deletion (Delta E452 o r Delta E453) in another. In the other two probands the amplified prod ucts were of reduced size. Direct sequencing of these mutant cDNAs rev ealed a deletion of exon 5 in one patient and of exon 7 in the other. Intronic sequences flanking exons 5 and 7 were identified using invers e PCR followed by direct sequencing. Conventional PCR and direct seque ncing then established the intron-exon borders of the mutant genomic D NA revealing two splice acceptor mutations: a G --> C substitution at position -1 of intron 4 and an A --> G substitution at position -2 of intron 6. Our results indicate that the severe form of prolidase defic iency is caused by multiple PEPD alleles. In this report we attempt to begin the process of describing these alleles and cataloging their ph enotypic expression.