A SYSTEMATIC ANALYSIS OF THE MUTATIONS OF THE UROPORPHYRINOGEN-III SYNTHASE GENE IN CONGENITAL ERYTHROPOIETIC PORPHYRIA

Congenital erythropoietic porphyria (CEP) or Gunther's disease is an i nborn error of heme biosynthesis, transmitted as an autosomal recessiv e trait and characterized by a profound deficiency of uroporphyrinogen III synthase activity (UROIIIS). The molecular defects observed in CE P are mainly heterogeneous, except for one missense mutation, C73R (Cy s to Arg substitution at codon 73) which represents nearly 40% of the disease alleles, A convenient strategy was designed to establish a rap id diagnosis at the genetic level in samples from patients with CEP. A s a first step, the most frequent mutation is searched for by restrict ion analysis from genomic DNA amplified by PCR, Next, the nine coding exons and intron-exon boundaries are sequenced from genomic DNA. As an alternative, the mutation can be determined by sequencing the UROIIIS cDNA of the patient, using the RT-PCR technique on RNAs when a lympho blastoid cell line can be established, Finally, for each new mutation in UROIIIS coding sequence, the corresponding mutant protein is expres sed in Escherichia coli, in order to demonstrate the pathological sign ificance of the mutation. This work describes the analysis of UROIIIS gene mutations in IO new families with CEP and summarizes the data fro m 20 unrelated families studied in our laboratory. Three new missense mutations of UROIIIS coding sequence (H173Y, Q187P and P248Q) have bee n observed together with 8 known mutations. The significance of three intronic base changes (476 -31 T-->C; 562 -4 A --> T; 562 -23 A-->G) i s discussed, In 6 alleles out of 40 (15%), the mutation remains undete rmined.