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The following summary is from Orphanet, a European reference portal for information on rare diseases and orphan drugs.
Orpha Number: 255
Dopa-responsive dystonia (DRD) describes a group of neurometabolic disorders characterized by dystonia that typically shows diurnal fluctuations, that responds excellently to levodopa (L-dopa) and that is comprised of autosomal dominant dopa-responsive dystonia (DYT5a), autosomal recessive dopa-responsive dystonia (DYT5b) and dopa responsive dystonia due to sepiapterin reductase (SR) deficiency.
The estimated European prevalence of DRD ranges from 1/1,000,000-1/200,000.
DRD usually has a pediatric onset, typically with lower limb dystonia that leads to gait disturbances and that usually worsens during the course of the day and is improved in the morning after sleeping. Parkinsonism can develop at a later age in some patients. Anxiety, depression, sleep disturbances and obsessive-compulsive disorders have also been reported in a few patients with DYT5a. Rarer subtypes which are inherited in an autosomal recessive manner typically show a much more severe phenotype, with onset in the first year of life with additional manifestations of global developmental delay, axial hypotonia, oculogyric crises and encephalopathy. DRD responds dramatically and continuously to L-dopa therapy, and patients usually experience a significant improvement of symptoms once treatment is initiated. If untreated, patients can become wheelchair bound.
DRD is due to mutations in genes that encode proteins essential for the biosynthesis of dopamine. DYT5a is due to mutations in the GTP cyclohydrolase 1 ( GCH1 ) gene (14q22.1 to q22.2) which encodes an enzyme needed for the biosynthesis of tetrahydrobiopterin, the essential co-factor for tyrosine hydroxylase. DYT5b is caused by mutations in the tyrosine hydroxylase TH gene (11p15.5) encoding tyrosine hydroxylase, the enzyme responsible for catalyzing the conversion of tyrosine to L-dopa, the precursor of dopamine. Finally, DRD due to an SRD is due to mutations in the SPR gene (2p14-p12), encoding the enzyme sepiapterin reductase (SR), which is also required for the biosynthesis of tetrahydrobiopterin.
DRD can be inherited in an autosomal dominant or autosomal recessive manner, depending on the subtype. It can also occur due to de novo mutations.
Visit the Orphanet disease page for more resources.
Source: GARD Last updated on 05-01-20
When DRD is caused by mutations in the GCH1 gene, it is inherited in an autosomal dominant manner. This means that having a mutation in only one of the 2 copies of the gene is enough to cause signs and symptoms of the disorder. In some cases, an affected person inherits the mutation from an affected parent; other cases result from having a new (de novo) mutation in the gene. When a person with an autosomal dominant condition has children, each child has a 50% (1 in 2) chance to inherit the mutated gene. Some people who inherit a mutated GCH1 gene never develop features of DRD; this phenomenon is known as reduced penetrance.
When DRD is caused by mutations in the TH gene, it is inherited in an autosomal recessive manner. This means that a person must have mutations in both of their copies of the gene to be affected. The parents of a person with an autosomal recessive condition usually each carry one copy of the mutated gene and are referred to as carriers. Carriers typically do not have signs or symptoms. When parents who are both carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) chance to be affected, a 50% chance to be an unaffected carrier like each parent, and a 25% chance to be unaffected and not be a carrier.
When DRD is caused by mutations in the SPR gene, it can be inherited in an autosomal recessive or autosomal dominant manner.
Last updated on 05-01-20
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