[Juvenile form of Huntington's disease--diagnostic problems].
Variability of clinical manifestation is an important feature of Huntington's disease (HD). It is due to the high instability of CAG sequences within a coding region of IT15 gene. We present five pedigrees in which apart from the adult form of HD the juvenile form of the disease affected some of the patients--as a result of genetic anticipation. Molecular analysis confirmed the well known fact that anticipation, which manifests itself by earlier onset of the disease in the subsequent generations, is strongly correlated with the degree of amplification of (CAG)n repeats in IT15 gene. An interesting feature of the presented data is the fact, that expansion of CAG repeats occurred not only at the paternal but also at the maternal transmission of the mutation. Some children in the presented HD pedigrees presented other neurological disturbances which could be suspected of HD; a molecular analysis revealing normal number of CAG repeats, enabled us to avoid misdiagnosis. The presented data provide evidence that clinical diagnosis of HD, particularly in cases with not very characteristic clinical picture--is not possible without DNA analysis--even in the families undoubtfully affected with the disease.