THAP1 is the first transcriptional factor involved in primary dystonia and the hypothesis of a transcriptional deregulation, which was primarily proposed for the X-linked dystonia-parkinsonism (DYT3 dystonia), provided thus a new way to investigate the possible mechanism underlying the development of dystonic movements.
A total of three nucleotide variants were detected, which include a reported missense mutation (c.427 A>G; p.Met143Val) in a juvenile onset generalized dystonia patient, a novel frameshift deletion mutation (c.208-209 ΔAA; p.K70VfsX15) in a juvenile onset cervical dystonia patient and a rare variant in 3' UTR of THAP1 (c.*157 T>C) in an adult-onset blepharospasm patient.
After excluding mutations in known primary dystonia genes (TOR1A, THAP1 and CIZ1), whole-exome sequencing identified a GNAL missense mutation (c.682G>T, p.V228F) in an African-American pedigree with clinical phenotypes that include cervical, laryngeal and hand-forearm dystonia.
Carriers were less likely to have dystonia restricted to a single site (11.11% in carriers vs. 65.9% in noncarriers; P < 0.01) and were less likely to have dystonia onset in cervical regions (25.9% of THAP1 carriers vs. 52.5% of noncarriers; P = 0.04).
Dystonias with known genes include DYT1 and DYT6dystonia, presenting as isolated torsion dystonia, as well as DYT5 (dopa-responsive dystonia), DYT11 (myoclonus-dystonia), and DYT12 (rapid-onset dystonia-parkinsonism), where dystonia occurs in conjunction with other types of movement disorders.
For this report, we screened 750 additional subjects for mutations in coding regions of THAP1 and interrogated all published descriptions of THAP1 phenotypes (gender, age of onset, anatomical distribution of dystonia, family history and site of onset) to explore the possibility of THAP1 genotype-phenotype correlations and facilitate a deeper understanding of THAP1 pathobiology.
Here, I review the clinical genetics and cell biology of three forms of inherited dystonia for which the causative mutation is known: DYT1 (TOR1A), DYT6 (THAP1), DYT25 (GNAL).
In contrast, affected individuals from the excluded families had a later age of onset (46.9 years vs. 16.1 years in the DYT6), and the dystonia was both more likely to be of focal distribution and begin in the cervical muscles.
Moreover, in the absence of family history and strong in silico or in vitro evidence of deleteriousness, the pathogenicity of novel SVs in THAP1 and other dystonia-associated genes can be indeterminate.