The Friedreich ataxia critical region spans a 150-kb interval on chromosome 9q13.

By analysis of crossovers in key recombinant families and by homozygosity analysis of inbred families, the Friedreich ataxia (FRDA) locus was localized in a 300-kb interval between the X104 gene and the microsatellite marker FR8 (D9S888). By homology searches of the sequence databases, we identified X104 as the human tight junction protein ZO-2 gene. We generated a large-scale physical map of the FRDA region by pulsed-field gel electrophoresis analysis of genomic DNA and of three YAC clones derived from different libraries, and we constructed an uninterrupted cosmid contig spanning the FRDA locus. The cAMP-dependent protein kinase gamma-catalytic subunit gene was identified within the critical FRDA interval, but it was excluded as candidate because of its biological properties and because of lack of mutations in FRDA patients. Six new polymorphic markers were isolated between FR2 (D9S886) and FR8 (D9S888), which were used for homozygosity analysis in a family in which parents of an affected child are distantly related. An ancient recombination involving the centromeric FRDA flanking markers had been previously demonstrated in this family. Homozygosity analysis indicated that the FRDA gene is localized in the telomeric 150 kb of the FR2-FR8 interval.