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Behavioural changes in an adopted teenager

© Author(s) (or their employer(s)) 2021. No commercial reuse. See rights and permissions. Published by BMJ. A 22yearold woman presented with an insidious progressive cognitive decline and a recent, although transient, period of illicit drug use. She had been normal until age 16 years but then had developed learning difficulties, a stiffening of posture and gait and occasional involuntary jerks. She had been adopted in early infancy, with no available birth history or family history. She had initially been referred to the psychiatric clinic and been treated for depressed mood with features of psychosis and suspected catatonia. Her mood had settled but the rigidity, posturing and gait abnormalities had persisted, prompting neurological referral. On examination, she had disturbed behaviour with poor eye contact and perseveration of speech. She had a stiff truncal posture, spastic gait, intermittent bilateral dystonic hand posturing, mild dysarthria, global rigidity and hyperreflexia. MR scan of the brain showed bilateral T2 FLAIR (T2weighted fluidattenuated inversion recovery) hyperintensities in the head of the caudate nuclei and putamina, but without enlargement of the frontal horns of the lateral ventricles (figure 1). Genetic testing confirmed an abnormal CAG repeat expansion within the HTT gene (with 67 repeats), confirming a diagnosis of juvenileonset Huntington disease. The juvenileonset form of Huntington disease is typically defined by onset of symptoms when aged ≤20 years and accounts for 2.4%–16% of all cases. 2 Huntington disease is an autosomal dominant neurodegenerative disease that shows anticipation, with successive generations acquiring greater numbers of CAG repeats and thereby an earlier age of onset. Its classical movement disorder is chorea, which is marked in older individuals; people with an earlier adult onset show more prominent cognitive and behavioural changes. When the CAG repeat expansion reaches a critical size, the disease manifests in younger people, with a hypokinetic rigid syndrome and substantial cognitive dysfunction, first described by Westphal in 1883. An intermediate CAG repeat (27–35) in the HTT gene of a father can expand to produce juvenile onset Huntington disease in his offspring, even