huntington's disease-like syndrome huntington's disease-like syndrome 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. huntington's disease-like syndromeother nameshdl syndromespecialtyneurology 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. 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. 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. 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, 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. a huntington's disease-like presentation may also be caused by acquired causes.