Huntington's disease-like syndromes (HD-like syndromes, or HDL syndromes) are a family of inherited neurodegenerative diseases that closely resemble Huntington's disease (HD) in that they typically produce a combination of chorea, cognitive decline or dementia and behavioural or psychiatric problems.^[1]

Types

HDL1

HDL1 is an unusual, autosomal dominant familial prion disease. 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

HDL2 is the most common HD-like syndrome and is caused by CTG/CAG triplet expansions in the JPH3 gene encoding junctophilin-3. It is almost exclusively restricted to populations of African descent and is actually more common than Huntington's disease in Black South Africans.^[1]

HDL3

HDL3 is a rare, autosomal recessive disorder linked to chromosome 4p15.3. It has only been reported in two families, and the causative gene is unidentified.^[1]

Other

Other neurogenetic disorders can cause an HD-like or HD phenocopy syndrome but are not solely defined as HDL syndromes. The commonest is spinocerebellar ataxia type 17 (SCA-17), occasionally called HDL-4. Others include mutations in C9orf72,^[2][3] 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.^[1]

A Huntington's disease-like presentation may also be caused by acquired causes.^[1]