Huntington's disease-like syndrome

Huntington's disease-like syndrome type 1
Synonyms	Huntington disease-like 1, HDL-1, HDL1, HD-like 1
Classification and external resources
OMIM	603218
DiseasesDB	33521
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Huntington's disease-like syndrome type 2
Synonyms	Huntington disease-like 2, HDL-2, HDL2, HD-like 2
Classification and external resources
OMIM	606438
DiseasesDB	33520
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Huntington's disease-like syndrome type 3
Synonyms	Huntington disease-like 3, HDL-3, HDL3, HD-like 3
Classification and external resources
OMIM	604802
DiseasesDB	34626
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The Huntington's disease-like syndromes (often abbreviated as HD-like 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.

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 is the commonest HD-like syndrome and is caused by GTC/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 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 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, .

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