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Of 1007 patients with signs and symptoms compatible with a diagnosis of Huntington's disease,995 had an expanded CAG repeat that included from 36 to 121 repeats(median,44)(sensitivity,98.8 percent,95 percent confidence interval,97.7 to 99.4 percent).There were no significant differences among national and ethnic groups in the number of repeats.No CAG expansion was found in the 113 control subjects with other neuropsychiatric disorders (specificity,100 percent;95 percent confidence interval,95.2 to 100 percent).In 1581 of the 1595 control chromosomes(99.1 percent),the number of CAG repeats ranged from 10 to 29(median,18).In 12 control chromosomes, (0.75 percent),intermediate-sized CAG sequences with 30 to 35 repeats were found,and 2 normal chromosomes unexpectedly had expanded to CAG sequences, of 39 and 37 repeats.CAG trinucleotide expansion is the molecular basis of Huntington's disease worldwide and is a highly sensitive and specific marker for inheritance of the disease mutation. |
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