ABSTRACT
Huntingtons disease is caused by a trinucleotide repeat expansion [CAG]n in the gene coding for Huntingtin [Htt] and is one of the several polyglutamine diseases. Its physical symptoms occur in a large range of ages, with a mean occurrence in a persons late 40s and early 50s. Almost all references indicated that if the age of onset is below 20 years then it is known as juvenile HD. Our case was an Iranian family with 4 affected siblings [2 sisters and 2 brothers]. In addition to 4 affected children, they had 5 normal male progenies. There was no any other case in their family history. The onset age of the disease in our case family was 20 to 25 years. Their parents were unaffected and nonconsanguineous. Analysis of the pathogenic [CAG]n repeat region of the HD gene for the affected members have showed an expansion allele with 46, 50, 46, and 44 repeats in 4 affected siblings. Our results indicated that the age of 20 years maybe is not a stable limit point for all cases of juvenile HD, and perhaps onset ages are related with the CAG repeat sizes in such individuals