LATE-ONSET FRIEDREICHS-DISEASE - CLINICAL-FEATURES AND MAPPING OF MUTATION TO THE FRDA LOCUS

Twenty two patients from 17 families with Friedreich's disease phenoty pe but with onset ranging from the ages of 21 to 36 are described. Com parison with ''typical'' Friedreich's disease with onset before 20 yea rs of age showed only a lower occurrence of skeletal deformities. The peripheral and central neurophysiological findings, sural nerve biopsy , and the neuroradiological picture did not allow the differentiation between ''late onset'' and ''typical'' Friedreich's disease. Duration of disease from onset to becoming confined to a wheelchair was five ye ars longer in late onset patients. Sixteen patients and 25 healthy mem bers from eight families were typed with the chromosome 9 markers MLS1 , MS, and GS4 tightly linked to the FRDA locus. All families showed po sitive led scores with a combined value of 5.17 at a recombination fra ction of theta = 0.00. It is concluded that ''late onset'' Friedreich' s disease is milder than the ''typical'' form and that it maps to the same locus on chromosome 9.