In order to simplify the process of identifying informative linked markers for SCA3/MJD PGT-M in future prospective couples, we developed a single-tube assay for the simultaneous genotyping of multiple highly polymorphic microsatellites lying within 1 Mb upstream and downstream of the ATXN3 CAG repeat. The gene discussed is ATXN3; the disease is Spinocerebellar ataxia type 3.