Huntington’s disease is an autosomal dominant, progressive neurological disorder that is characterized by motor disturbance, cognitive dysfunction, and psychiatric symptomatology. 1 Although some of these symptoms have been attributed to subcortical dysfunction (eg, striatum) and the connecting circuitry with the frontal lobes, 2, 3 most studies have examined the relationships with cognitive and motor symptoms. For example, executive dysfunction on cognitive tasks (ie, set shifting, response inhibition) has been linked with the dorsolateral-subcortical circuit4 and dorsolateral prefrontal cortex deficits. 5 Motor deficits in Huntington’s disease have also been related with abnormalities of the fronto-subcortical circuits. 5, 6 Unfortunately, the behavioral manifestations of this suspected frontalsubcortical dysfunction have been less widely examined in patients with Huntington’s disease. The current paper focuses on four examples of behaviors in Huntington’s disease that could be associated with this affected frontal circuitry: apathy, executive dysfunction, disinhibition, and decreased awareness. In the limited empirical studies of manifest Huntington’s disease, apathy, which includes problems with initiation, spontaneity, loss of interest, and decreased concern about self-care, appears to be a prevalent symptom. 7–10 For example, Paulsen et al. 11 reported that 56% of Huntington’s disease patients presented with this symptom. Apathy has also been correlated with other symptoms of Huntington’s disease (eg, motor, cognition), 7, 8 suggesting that apathy might be another hallmark symptom of the disease. Executive dysfunction, including problems with working memory, planning, and problem solving, appears to be another relatively prominent symptom in Huntington’s disease, although its impairments have largely been defined with neuropsychological measures2, 5 as opposed to self-reported behaviors. Fewer studies have examined disinhibition in Huntington’s disease, which includes impulsivity, hyperactivity, emotional lability, and “acting out,” and they have not found this symptom to be particularly prominent in these patients. 9, 12 One final example of frontal behaviors that might be relevant in Huntington’s disease is decreased awareness or loss of insight. Although anecdotal evidence of decreased awareness of symptoms has been reported in Huntington’s disease, few studies have investigated this clinical lore. In one, Snowden et al. 13 found that patients with diagnosed Huntington’s disease poorly identified their chorea compared to objective neurological examinations. Similarly, Hoth et al. 14 found that patients with manifest Huntington’s disease had impaired awareness across a range of abilities (eg, motor, cognition, emotional control) when compared to companion ratings and objective testing. Two other studies15, 16 found significant discrepancies between patient and companion reports on rating scales, which could be interpreted as decreased insight. Taken together, there is a growing body of literature that documents behavioral manifestations of frontal dysfunction in patients diagnosed with Huntington’s disease.

It is unclear from the existing literature, however, just how early these behavioral manifestations of frontal dysfunction occur in Huntington’s disease. With the availability of a genetic test, it is possible to identify individuals who have trinucleitide repeat expansion for Huntington’s disease but are not yet showing sufficient motor signs for diagnosis (ie, pre-Huntington’s disease). Several studies have found subtle motor, cognitive, psychiatric, and neuroimaging abnormalities occuring in Huntington’s disease years before diagnosis. 17–26 …