NONSENSE MUTATION IN THE PHOSPHOFRUCTOKINASE MUSCLE SUBUNIT GENE ASSOCIATED WITH RETENTION OF INTRON-10 IN ONE OF THE ISOLATED TRANSCRIPTS IN ASHKENAZI-JEWISH PATIENTS WITH TARUI DISEASE

Mutations in the human phosphofructokinase muscle subunit gene (PFKM) are known to cause myopathy classified as glycogenosis type VII (Tarui disease). Previously described molecular defects include base substitutions altering encoded amino acids or resulting in abnormal splicing. We report a mutation resulting in phosphofructokinase deficiency in three patients from an Ashkenazi Jewish family, Using a reverse transcription PCR assay, PFKM subunit transcripts differing by length were detected in skeletal muscle tissue of all three affected subjects, In the longer transcript, an insertion of 252 nucleotides totally homologous to the structure of the 10th intron of the PFKM gene,vas found separating exon 10 from exon 11, In addition, two single base transitions were identified by direct sequencing: [exon 6; codon 95; (C) under bar GA (Arg) to (T) under bar GA (stop)] and [exon 7; codon 172; AC (C) under bar (Thr) to AC (T) under bar (Thr)] in either transcript, Single-stranded conformational polymorphism and restriction enzyme analyses confirmed the presence of these point substitutions in genomic DNA and strongly suggested homozygosity for the pathogenic allele. The nonsense mutation at codon 95 appeared solely responsible for the phenotype in these patients, further expanding genetic heterogeneity of Tarui disease. Transcripts with and without intron 10 arising from identical mutant alleles probably resulted from differential pre-mRNA processing and may represent a novel message from the PFKM gene.