Oculopharyngeal muscular dystrophy: a point mutation which mimics the effect of the PABPN1 gene triplet repeat expansion mutation.
BACKGROUND
Oculopharyngeal muscular dystrophy (OPMD) is an autosomal dominant late onset neuromuscular disease characterised by proximal muscle weakness, ptosis, and swallowing difficulty. The only causative mutation described to date is a triplet repeat expansion consisting of two to seven additional base triplets in a repeat sequence in exon 1 of the polyadenine binding protein nuclear 1 (PABPN1) gene. This results in an increase in length of a polyalanine tract in the PABPN1 protein from 10 to 12-17 residues.


OBJECTIVE
Description of another mutation in a case of OPMD.


METHODS
Sequence analysis of exon 1 of the PABPN1 gene was undertaken on 202 patients referred for a possible diagnosis of OPMD but negative for the triplet repeat expansion mutation.


RESULTS
A case was identified with typical symptoms of OPMD, negative for the repeat expansion mutation but with a missense mutation in PABPN1 close to the 3' end of the normal polyalanine codon repeat sequence.


CONCLUSIONS
The single base mutation changes a glycine codon to an alanine codon and results in an increase in the number of contiguous polyalanine codons. This mimics the effect of the common triplet repeat expansion mutation and represents a previously undescribed mechanism of mutation.
Robinson
D O
DO
Wessex Regional Genetics Laboratory, Salisbury District Hospital, Salisbury, UK. david.robinson@salisbury.nhs.uk
Wills
A J
AJ
Hammans
S R
SR
Read
S P
SP
Sillibourne
J
J
D000368:Aged; D001483:Base Sequence; D004252:DNA Mutational Analysis; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D039141:Muscular Dystrophy, Oculopharyngeal / Q000175:diagnosis / Q000235:genetics*; D010375:Pedigree; D017354:Point Mutation; D039103:Poly(A)-Binding Protein II / Q000737:chemistry / Q000235:genetics*; D019680:Trinucleotide Repeat Expansion / Q000235:genetics
D039103:Poly(A)-Binding Protein II