Mutational screening of the POLG gene. a, Pedigree of the family. Affected members with an adult onset mitochondrial ataxia syndrome are shown by solid symbols. The segregation pattern of the changes identified and the ages of the pedigree members under study are indicated. b, Identification of mutations in the POLG gene in two patients with mitochondrial ataxia syndrome. Electropherograms are shown indicating the nucleotide changes identified. c, Amino acid sequence alignments of PolGA that contain the residues D122, K601 and Y837 in which novel substitutions were identified, and the common polymorphism Q1236H are shown.