Dopa-responsive dystonia (DRD) includes several sub-types, and specific genes are believed to be responsible for most of these sub-types
The most common form of DRD—often referred to as DYT5 dystonia—is a dominantly inherited condition caused by mutations in the GTP cyclohydrolase 1 gene (GTP-CH1). A dominantly inherited disorder means that only one parent need have the gene mutation in order for a child to inherit the disorder. Individuals with DYT5 DRD often have a parent who also has the mutation, with or without symptoms. The GTP-CH1 mutation has variable penetrance, meaning that not everyone who inherits the mutated gene will develop symptoms. Children of a parent with the GTP-CH1mutation have a 50% chance of inheriting the mutation. At this time, there is no way to predict whether a person with the mutation will ever develop symptoms
About 40% of DRD patients do not carry the mutation in the GTP-CH1 gene associated with DYT5 dystonia. Other known inherited metabolic conditions may cause DRD including a mutation in the recessively inherited tyrosine hydroxylase gene (hTH), autosomal recessive deficiencies of GTP-CH1 and aromatic L-amino acid decarboxylase, and other defects of tetrahydrobiopterin metabolism
At this time, genetic testing for DRD is usually reserved for research studies, and not widely commercially available. Prenatal testing and preimplantation genetic diagnosis may be available through select centers
