Novel THAP1 sequence variants in primary dystonia

Abstract

Background: THAP1 encodes a transcription factor (THAP1) that harbors an atypical zinc finger domain and regulates cell proliferation. An exon 2 insertion/deletion frameshift mutation in THAP1 is responsible for DYT6 dystonia in Amish-Mennonites. Subsequent screening efforts in familial, mainly early-onset, primary dystonia identified additional THAP1 sequence variants in non-Amish subjects.

Objective: To examine a large cohort of subjects with mainly adult-onset primary dystonia for sequence variants in THAP1.

Methods: With high-resolution melting, all 3 THAP1 exons were screened for sequence variants in 1,114 subjects with mainly adult-onset primary dystonia, 96 with unclassified dystonia, and 600 controls (400 neurologically normal and 200 with Parkinson disease). In addition, all 3 THAP1 exons were sequenced in 200 subjects with dystonia and 200 neurologically normal controls.

Results: Nine unique melting curves were found in 19 subjects from 16 families with primary dystonia and 1 control. Age at dystonia onset ranged from 8 to 69 years (mean 48 years). Sequencing identified 6 novel missense mutations in conserved regions of THAP1 (G9C [cervical, masticatory, arm], D17G [cervical], F132S [laryngeal], I149T [cervical and generalized], A166T [laryngeal], and Q187K [cervical]). One subject with blepharospasm and another with laryngeal dystonia harbored a c.-42C>T variant. A c.57C>T silent variant was found in 1 subject with segmental craniocervical dystonia. An intron 1 variant (c.71+9C>A) was present in 7 subjects with dystonia (7/1,210) but only 1 control (1/600).

Conclusions: A heterogeneous collection of THAP1 sequence variants is associated with varied anatomical distributions and onset ages of both familial and sporadic primary dystonia.

Figure 1 Detection of THAP1 sequence variants with high-resolution melting Normalized and temperature-shifted high-resolution melting curves (A) and difference plots (B) of exon 1 differentiate 4 sequence variants from 1 normal control (each in duplicate).

Figure 2 THAP1, THAP1, and localization of mutations in primary dystonia (A) Genomic structure of THAP1 and contiguous regions (NT 007995), 3-exon transcript (NM 018105), and translated protein (NP 060575) along with the locations of sequence variants. NLS = nuclear localization signal; Pro = proline-rich region; THAP = thanatos-associated protein. (B) Alignment of exon 1 and the 5′ portion of intron 1 in human, mouse, and rat. Sequence variants are highlighted in yellow (missense) or turquoise. Exonic nucleotides, uppercase; intronic nucleotides, lowercase. (C) Alignment of THAP1 homologues with ClustalW2: AVFPMILW, red (small + hydrophobic including aromatic − Y); DE, blue (acidic); RK, magenta (basic); STYHCNGQ, green (hydroxyl + amine + basic + Q). ClustalW2 generates the following symbols denoting the degree of conservation observed in each column: asterisk (*) means that residues in that column are identical in all sequences, period (.) means that conserved substitutions have been observed, and colon (:) means that semiconserved substitutions are observed. Sequence variants are highlighted.

Figure 3 Partial pedigrees of multiplex families with missense mutations in THAP1 Genotypes confirmed by sequencing are shown below individual family members.