C9orf72 expansion as a possible genetic cause of Huntington disease phenocopy syndrome

Huntington disease (HD), the most common inherited cause of chorea, is an autosomal dominant disorder, caused by an expanded trinucleotide CAG repeat (> 39) in the HTT gene on chromosome 4p16.3. Among patients diagnosed as HD solely on clinical grounds, a certain number was negative on genetic testing for HD. Therefore, HD-like disorders comprised a number of genetic causes of chorea, that may be indistinguishable from HD (e.g. HD phenocopy syndrome). Recent data suggested that the C9orf72 expansion may be the most common genetic cause of HD phenocopy presentations. In continuation with this observation, we analyzed a small cohort of 39 patients with HD phenocopy syndrome and detected the C9orf72 expansion in one female patient (2.6 %) with two-year lasting mild generalized chorea and severe oro-bucco-lingual dyskinesia, who complained on forgetfullness (neuropsychological testing revealed dysexecutive syndrome with preserved episodic memory and recognition), unexplainable fears and increased appetite. Our results confirmed a possible role of the C9orf72 expansion in the genetic background of HD phenocopy syndrome.