ABSTRACT
Monozygotic (MZ), 46-year-old, male twins, carrying the same Huntington disease (HD) mutation, presented with a different clinical course. In one of the twins, the disease process started at the age of 32 years with chorea, dysarthria, and a depressed mood. Over 14 years, the disease progressed to total functional dependence. The second twin presented at age 35 with gait disturbances. His behavior became aggressive with an obsessive pattern, whereas the motor features included hypokinesia, rigidity, gait unsteadiness, and dysarthria. This is the first report of genetic identity associated with different age of disease onset as well as a different motor and behavioral phenotype. Postzygotic events are a likely explanation for the observed differences of phenotype in these genetically identical twins.
