RESUMEN
<p><b>OBJECTIVE</b>To identify the type of a pedigree with spinocerebellar ataxia, and carry out asymptomatic carrier detection and prenatal diagnosis.</p><p><b>METHODS</b>The blood samples of two patients in the spinocerebellar ataxia pedigree were collected. Based on the clinical characteristics of the pedigree and the disease incidence in China, the regions containing the CAG repeat of the SCA1, SCA2 and SCA3/MJD genes were amplified by polymerase chain reaction (PCR). The numbers of CAG repeats in the normal and abnormal allele fragments were identified by using agarose gel electrophoresis and DNA sequencing. We further carried out tests on the children of the patients and fetus to identify the presence of the abnormal allele.</p><p><b>RESULTS</b>The numbers of CAG repeat in the SCA1 and SCA2 genes were in the normal range. The CAG repeat number in one allele of SCA3/MJD gene was in the normal range, while that in the other allele was in the abnormal range. One of the children of the patients and the fetus carried the abnormal allele.</p><p><b>CONCLUSION</b>It was confirmed that the pedigree was SCA3/MJD by gene diagnosis. One of the children of the patients was asymptomatic carrier and the fetus also carried the abnormal allele.</p>