Dopa-responsive dystonia and phenotypes associated with TH gene variants: a systematic review and Mexican case series

Dopa-responsive dystonia (DRD) has a broad, clinical, and genetically heterogeneous spectrum; its manifestations include parkinsonism, dystonia, tremor, and other movement disorders. The severity of DRD ranges from mild to fatal encephalopathy. DRD is caused by recessive mutations in the TH gene.

This article is a systematic review (SR) of all reports of patients with DRD, including the first Mexican cases and other phenotypes associated with variants in the gene encoding tyrosine hydroxylase (TH), from its first description to the first quarter of 2024. The SR followed the PRISMA guidelines in five databases (Scopus, MEDLINE, PubMed Central, LILACS, and Scielo).

Sixty-two publications were selected. They included 179 patients with TH deficiency, but only 143 included clinical descriptions. The age of onset was infantile regardless of phenotype, and there was a delay in age at diagnosis (t = -7.139, P < 0.001). Encephalopathy was the earliest presentation, and psychomotor retardation was common in all forms of TH deficiency. Multiple motor manifestations may be present, including dystonia, parkinsonism, gait disturbances, and others. Response to dopaminergic replacement therapy (DRT) has been reported in 143 patients (good in 64.3%, moderate in 23.7%, and poor in 12%). The compound heterozygous genotype was the most common (61.45%) for the biallelic variants of the TH gene. In addition, data from 6 cases with heterozygous variants are described.

This is the most comprehensive review of TH deficiency cases and shows that these phenotypes are rare, have a wide neurological phenotypic variability, are often infantile-onset, and respond well to DRT.