Larger CAG expansions in skeletal muscle compared with lymphocytes in Kennedy disease but not in Huntington disease

The size of CAG repeats was compared in lymphocytes and skeletal muscle from nine patients with Huntingtan disease (HD) and two patients with Kennedy disease (KD). In HD, the number of CAG repeats did not differ between lymphocytes and skeletal muscle. In the two KD patients, however, the CAG expansion was larger in muscle than in lymphocytes. The difference in trinucleotide expansion between lymphocytes and muscle cells is not a universal phenomenon in trinucleotidc repeat disorders, but seems to occur in disorders primarily affecting the neuromuscular system.