Only described in one family, it is caused by an eight-octapeptide repeat insertion in the PRNP gene.
More broadly, inherited prion diseases in general can mimic HD.
[1] HDL2 is the most common HD-like syndrome and is caused by CTG/CAG triplet expansions in the JPH3 gene encoding junctophilin-3.
The same study found that increasing repeat number is correlated with greater cognitive and behavioural impairment, but less chorea.
Others include mutations in C9orf72,[3][4] spinocerebellar ataxias type 1 and 3, neuroacanthocytosis, dentatorubral-pallidoluysian atrophy (DRPLA), brain iron accumulation disorders, Wilson's disease, benign hereditary chorea, Friedreich's ataxia and mitochondrial diseases.