Huntington disease-like syndrome

Huntington disease-like syndrome (HDL syndrome) is a group of rare neurodegenerative disorders that clinically resemble Huntington disease (HD) but are not caused by the characteristic CAG trinucleotide repeat expansion in the HTT gene. These conditions are sometimes collectively referred to as HD phenocopies or Huntington disease-like syndromes. Several distinct subtypes have been identified, including HDL1 (associated with PRNP gene mutations), HDL2 (caused by CTG/CAG repeat expansions in the JPH3 gene), HDL3 (mapped to chromosome 4p15.3 with autosomal recessive inheritance), and HDL4 (now recognized as spinocerebellar ataxia type 17, caused by TBP gene expansions). The grouping under Orphanet code 158266 encompasses these and potentially other phenocopies that share the core clinical presentation of HD without the classic genetic cause. The syndrome primarily affects the central nervous system, leading to progressive motor dysfunction including chorea (involuntary jerky movements), dystonia, rigidity, and bradykinesia. Psychiatric symptoms such as personality changes, depression, irritability, and psychosis are common and may precede motor symptoms. Cognitive decline progressing to dementia is a hallmark feature. Some subtypes may also present with cerebellar ataxia, seizures, or parkinsonism. Brain imaging typically reveals caudate nucleus atrophy and generalized cerebral atrophy similar to that seen in classic Huntington disease. There is currently no cure or disease-modifying treatment for Huntington disease-like syndromes. Management is symptomatic and supportive, paralleling the approach used in classic HD. Chorea may be treated with tetrabenazine or deutetrabenazine, psychiatric symptoms with appropriate psychotropic medications, and physical, occupational, and speech therapy can help maintain function. Genetic counseling is essential for affected families, as the inheritance pattern and recurrence risk vary depending on the specific subtype identified. Accurate molecular diagnosis is important to distinguish these conditions from classic HD and to guide appropriate genetic counseling.

Common questions about Huntington disease-like syndrome