Huntington disease (HD) is a neurodegenerative, dominantly inherited genetic disorder caused by the expansion
of a CAG triplet repeat (> 36 CAG) of the Huntington gene on chromosome 4p16.3. The
juvenile variant of the disorder is rare (5 to 7%) and shows a phenotype with myoclonic
jerks, seizures, behavioral disturbances, ataxia, dystonia, and parkinsonism. Choreatic
movements are rare.
We describe a case of a female patient from Ecuador who was diagnosed with HD at the
age of 10 years. The father's positive HD was not mentioned on presentation owing
to the daughter's negative genetic results. Progressive myoclonic epilepsy had been
suspected in Ecuador because of epilepsy and progressive myoclonic jerks in the presence
of only mild and unspecific MRT changes. Valproic acid and levetiracetam led to amelioration
of the epilepsy. However, the emergence and slow progression of other symptoms such
as dysarthria, saccadic eye movements, tremors, and ataxia leading to a loss of free
ambulation were also observed.
Owing to the suggestive clinical phenotype, it was decided to repeat the molecular
genetic assessment to verify or exclude HD. This showed a triple nucleotide repeat
expansion of 112 CAG repeats and confirmed the diagnosis, which was also double-checked
at a second laboratory. At the same time, all relevant differential diagnoses with
the leading symptom myoclonic epilepsy were considered and relevant diagnostic steps
taken.
This case report demonstrates that a positive diagnosis in a father is an important
hint regarding suspicion of juvenile HD in his child. Should a PCR-based test produce
a negative result, southern-blot analysis is a valuable alternative method.
