Congenital erythropoietic porphyria: a novel uroporphyrinogen III synthase branchpoint mutation reveals underlying wild-type alternatively spliced transcripts.
Splicing mutations account for approximately 10% of lesions causing genetic diseases, but few branchpoint sequence (BPS) lesions have been reported. In 3 families with autosomal recessive congenital erythropoietic porphyria (CEP) resulting from uroporphyrinogen III synthase (URO-synthase) deficiency, sequencing the promoter, all 10 exons and the intron/exon boundaries did not detect a mutation. Northern analyses of lymphoblast mRNAs from 2 patients and reverse-transcribed polymerase chain reaction (RT-PCR) of lymphoblast mRNAs from all 3 patients revealed multiple longer transcripts involving intron 9 and low levels of wild-type message. Sequencing intron 9 RT-PCR products and genomic DNA in each case revealed homozygosity for a novel BPS mutation (c.661-31T-->G) and alternatively spliced transcripts containing 81, 246, 358, and 523 nucleotides from intron 9. RT-PCR revealed aberrant transcripts in both wild-type and CEP lymphoblasts, whereas BPS mutation reduced the wild-type transcript and enzyme activity in CEP lymphoblasts to approximately 10% and 15% of normal, respectively. Although the +81-nucleotide alternative transcript was in-frame, it only contributed approximately 0.2% of the lymphoblast URO-synthase activity. Thus, the BPS mutation markedly reduced the wild-type transcript and enzyme activity, thereby causing the disease. This is the first BPS mutation in the last intron, presumably accounting for the observed 100% intron retention without exon skipping.
Bishop
David F
DF
Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York, NY 10029-6574, USA.
Schneider-Yin
Xiaoye
X
Clavero
Sonia
S
Yoo
Han-Wook
HW
Minder
Elisabeth I
EI
Desnick
Robert J
RJ
D000293:Adolescent; D000328:Adult; D017398:Alternative Splicing / Q000235:genetics*; D015152:Blotting, Northern; D004252:DNA Mutational Analysis; D005091:Exons / Q000235:genetics; D005192:Family Health; D005260:Female; D006801:Humans; D007438:Introns / Q000235:genetics; D008214:Lymphocytes / Q000378:metabolism; D008297:Male; D008875:Middle Aged; D009154:Mutation; D017092:Porphyria, Erythropoietic / Q000201:enzymology / Q000235:genetics* / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014576:Uroporphyrinogen III Synthetase / Q000235:genetics*; D055815:Young Adult
D012333:RNA, Messenger; D014576:Uroporphyrinogen III Synthetase