The aim of the present study was to conduct a familial investigation and provide a genetic diagnosis to a family presenting with spastic paraplegia and clinically diagnosed with hereditary spastic paraplegia (HSP). Blood samples were obtained from the family, and mutations in the gene causing spinocerebellar ataxia type 3 (SCA3)/Machado-Joseph disease (MJD), known as MJD1, were analyzed using the polymerase chain reaction, 8% denaturing polyacrylamide gel electrophoresis, and T-vector ligation and sequencing. The trinucleotide repeat number of the mutant allele was 80, leading to a genetic diagnosis of SCA3/MJD. This suggests that patients with SCA3/MJD characteristically present with typical spastic paraplegia without evident manifestations of ataxia. For those families with HSP involving the nervous system and showing genetic anticipation, an MJD1 genetic diagnosis should be considered to assist in clinical diagnosis of HSP.
Keywords: CAG trinucleotide repeats; Machado-Joseph disease gene; genetic anticipation; hereditary spinocerebellar ataxia type 3; mutation analysis; spastic paraplegia.