Huntington disease-like (HDL) syndromes are conditions that resemble Huntington disease, but are not caused by the same mutant huntingtin gene. There are four types of HDL syndromes: HDL1, HDL2, HDL3, and HDL4. HDL syndromes are extremely rare; they are less common than Huntington disease.
HDL3 is most likely inherited in an autosomal recessive pattern. It is characterized by early-onset mental deterioration, dysarthria, dystonia, pyramidal signs, ataxia, and gait impairment. The age of onset is around 3-4 years. Affected children experience a decline in thinking ability, difficulties with movement and speech, and seizures. HDL3 has been found in only one family from Saudi Arabia.