Effect of trinucleotide repeat length and parental sex on phenotypic variation in spinocerebellar ataxia I

Am J Hum Genet. 1994 Jun;54(6):959-65.


Trinucleotide repeat expansion has been found in 64 subjects from 19 families: 57 patients with SCA1 and 7 subjects predicted, by haplotype analysis, to carry the mutation. Comparison with a large set of normal chromosomes shows two distinct distributions, with a much wider variation among expanded chromosomes. The sex of transmitting parent plays a major role in the size distribution of expanded alleles, those with > 54 repeats being transmitted by affected fathers exclusively. Our data suggest that alleles with > 54 repeats have a reduced chance of survival; these appear to be replaced in each generation by further expansion of alleles in the low- to medium-expanded repeat range, preferentially in male transmissions. Detailed clinical follow-up of a subset of our patients demonstrates significant relationships between increasing repeat number on expanded chromosomes and earlier age at onset, faster progression of the disease, and earlier age at death.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Base Sequence
  • Female
  • Humans
  • Male
  • Middle Aged
  • Molecular Sequence Data
  • Oligodeoxyribonucleotides
  • Parents
  • Phenotype
  • Polymorphism, Genetic*
  • Repetitive Sequences, Nucleic Acid*
  • Sex Factors
  • Spinocerebellar Degenerations / genetics*


  • Oligodeoxyribonucleotides