Scientists discovered that there is another mutation (on a different chromosome), which
causes HD-like symptoms and apparently develops in the same way. Since it's located in a different place, standard blood tests
will not reveal it as they check whether the extensive CAG repeats occur in the expected place.
There are a significant amount of examples of HD in the absence of a huntingtin (CAG)
n expansion, suggesting that mutations in other genes can provoke HD like disorders.
The identifications of genes responsible for these "phenocopies" may greatly improve the
reliability of genetic screens for HD and may provide further insight into neurodengerative disease.
We have examined.....this
reveals that this HD phenocopy is, in fact, a familial prion disease and that PrP repeat-expansion mutations can provoke an
HD "genocopy."
This observations raises the possibility that unknown number of HD phenocopies are, in fact, familial
prion diseases and argues that clinicians should consider screening for PrP mutations in individuals with HD-like diseases
in which that characteristic HD (CAG)n repeat expansions are absent.
In the HD phneonocopy pedigree described here,
chorea seems to have been a more prominent clinical feature, being present in 4 of 6 affected individuals.
