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Homeostasis of Dopamine
Published in Nira Ben-Jonathan, Dopamine, 2020
TH is a mixed function oxidase that uses L-tyrosine and molecular oxygen as substrates, and L-tetrahydrobiopterin (BH4) and ferrous iron (Fe2+) as cofactors [3]. Tyrosine is one of the 20 standard amino acids used by cells to synthesize proteins. It is a nonessential amino acid with a polar side chain group. Given its natural abundance, catecholamine levels are not influenced either by changing the dietary levels of tyrosine or by its parenteral administration, even at large amounts. Because of its essential role as a cofactor in TH enzymatic activity, a deficiency in BH4 can cause systemic deficiencies of catecholamines. One example of BH4 deficiency is the development of dopamine-responsive dystonia, characterized by increased muscle tone and Parkinsonian features. This condition can be treated with carbidopa/levodopa which directly restores dopamine levels within the brain.
Central nervous system: Adult-onset and psychiatric disorders
Published in Angus Clarke, Alex Murray, Julian Sampson, Harper's Practical Genetic Counselling, 2019
Primary torsion dystonia follows autosomal dominant inheritance in most cases, though with incomplete penetrance in some gene carriers and minimal expression in others; the disorder is more common in Ashkenazi Jews. A single mutation in a specific gene on chromosome 9 has been found to be responsible for almost all typical cases, Jewish and non-Jewish, including most sporadic early-onset cases. Late-onset dystonia is poorly understood, and most cases may not be genetic. Dystonia may also form part of other more general degenerative brain disorders. Dopamine-responsive dystonia, due to a specific molecular defect, is an important, treatable form to recognise, even though it is very rare.
Pharmacotherapy for the management of the symptoms of Machado-Joseph Disease
Published in Expert Opinion on Pharmacotherapy, 2022
Jessica Blanc Leite Oliveira, Alberto R.M. Martinez, Marcondes Cavalcante França Jr
Dystonia is another frequent movement disorder in SCA3/MJD, presenting either as a focal/segmental or a generalized manifestation. It may be very disabling, especially in patients with early disease onset and large (CAG) expansions [5,32–35]. SCA3/MJD-related dystonia is typically not dopa-responsive [36–38]. However, there are rare reports of dopamine-responsive dystonia, indicating that a levodopa trial should be considered for most patients with this phenotype [39–41].