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XL PCR for the detection of large trinucleotide expansions in juvenile Huntington's disease

Juvenile Huntington's disease (HD) becomes clinically manifest before 20 years of age. The diagnosis of HD is based on family history, characteristic clinical findings, and the detection of an expansion of a CAG polyglutamine tract in the Huntingtin gene. Juvenile HD is characterized by paternal anticipation and large CAG expansions that may be missed using routine molecular analysis. We have developed an easy, rapid, and reliable modified PCR method using XL (Extra Long) PCR that allowed us to diagnose one of the youngest children reported with juvenile HD. Without this innovation we would not have been able to demonstrate the large CAG expansion. This assay could become part of a standard protocol for HD testing in molecular diagnostic laboratories.