Huntington's disease-like

Huntington's disease-like (HDL) is a group of related neurological conditions. As the name suggests, HDLs resembles Huntington's disease. HDLs and Huntington's disease are both characterized by uncontrolled movements, emotional problems, and loss of thinking ability. In both conditions these signs and symptoms worsen over time. HDLs occurs in people with the characteristic features of Huntington's disease who do not have a variant (also called mutation) in the gene typically associated with that disorder. Researchers have described four HDLs that are designated Huntington's disease-like 1 (HDL1) through Huntington's disease-like 4 (HDL4). Sometimes, HDL4 is also known as spinocerebellar ataxia type 17 (SCA17).

HDL1, HDL2, and HDL4 usually begin in early to mid-adulthood, although they can start earlier or later. The first signs and symptoms of these conditions often include irritability, emotional problems, small involuntary movements (dyskinesia), poor coordination, and trouble learning new information or making decisions. Many people with an HDL develop involuntary jerking or twitching movements known as chorea. Over time, these abnormal movements worsen. Affected individuals may develop problems with walking (bradykinesia), speaking (dysarthria), and swallowing (dysphagia). People with these disorders also experience changes in personality and a decline in thinking and reasoning abilities (dementia). Individuals with an HDL syndrome can live for 10 to 20 years after signs and symptoms begin, though this can vary between the types of HDL syndromes.

HDL3 begins much earlier in life than the other HDLs (usually around age 3 or 4). Affected children experience a decline in thinking ability, difficulties with movement and speech, and seizures. Because HDL3 has some different signs and symptoms and a different pattern of inheritance, researchers are unsure whether it belongs in the same category as the other HDLs.