A variant in the HS1-BP3 gene is associated with familial essential tremor

Abstract

Background: Genetic linkage studies have identified two susceptibility loci for essential tremor (ET) on chromosomes 3q13 (ETM1) and 2p24.1 (ETM2). Linkage disequilibrium studies in separate population samples from the United States and Singapore suggest an association between ET and loci at ETM2.

Methods: Fine mapping studies were conducted on multiplex and singleton US families linked to ETM2 using newly detected loci within the candidate interval to establish the minimal critical region (MCR) harboring an ET gene. The genes and transcripts within this interval were systematically analyzed by single-strand conformational polymorphism analysis and DNA sequencing.

Results: A 464-kb region between loci D2S2150 and etm1231 was defined as the MCR. The coding regions and flanking intronic splice sites of two genes and seven transcripts in this interval were evaluated for mutations. A missense mutation (828C-->G) in the transcript FLJ14249 (HS1-BP3) was identified in one US family. This mutation was found in another apparently unrelated US family with ET and was absent in 150 control samples (300 chromosomes). The 828C-->G mutation causes a substitution of a glycine for an alanine residue in the HS1-BP3 protein. The HS1-BP3 protein binds to proteins that are highly expressed in motor neurons and Purkinje cells and regulate the Ca2+/calmodulin-dependent protein kinase activation of tyrosine and tryptophan hydroxylase.

Conclusions: A rare variant in the HS1-BP3 gene that is associated with essential tremor (ET) in two families is reported. This finding will facilitate research on the functional role of this gene and related genes in the pathogenesis of ET.

Figure 1

Fine mapping studies in two families with essential tremor and the 828C→G mutation in the HS1-BP3 gene. Six loci including D2S2150, rs3732149, rs11680700, etm1240, etm1231, and etm1234 were used in the analysis. (A) Haplotype analysis of the first family that was identified with 828C→G mutation in the HS1-BP3 gene. The dark bar represents the affected alleles inherited from Individual I-2. Individual II-1 shows a recombination at the first locus D2S2150. Individual II-6 shows a recombination at the fifth locus etm1231. The gray bar represents the affected alleles inherited from Individual I-1. Individual II-1 shows a recombination at either the fourth (etm1240) or the fifth (etm1231) locus. No other recombinants are found telomeric to these loci on the ETM2 candidate contig. (B) Haplotype analysis of the second family with the 828C→G mutation in the HS1-BP3 gene. The white bar represents the alleles shared by Individuals II-3 and III-4. The extended haplotype for the six loci are different from the haplotypes in the family members shown in figure 1A. Black circles (females) and squares (males) represent affected individuals with essential tremor. Unaffected individuals are not shaded. Each generation is represented by Roman numerals to the left of the pedigrees. An individual is identified by generation number and the numbers below the symbols. The pedigree and individual identifiers in figure 1A are the same as in figure 2B. The pedigree and individual identifiers in figure 1B are the same as figure 2C.

Figure 2

Characterization of the 828C→G variant (Gen-Bank accession no. NM_106552) in exon 7 of the HS1-binding protein 3 gene (HS1-BP3) in two families with essential tremor. (A) Direct sequencing of PCR products. (Left) The HS1-BP3 sequence between nucleotide (nt) 824 and 831 from a normal individual without tremor. (Right) An 828C→G substitution in an affected individual from the family in figure 1A. Above the nucleotide sequence is the amino acid sequence. The variant results in a substitution of a glycine (G) residue for an alanine (A) residue at codon 265 of the HS1-BP3 protein (NP_567825) (A265G). (B) A 1% agarose/0.1% ethidium bromide gel showing the BseYI restriction enzyme analysis of HS1-BP3 exon 7 in the family shown in figure 1A. The PCR products of normal individuals (open circles and squares) are cleaved by BseYI and show an upper band of 228 bp representing the wild-type allele. Affected individuals (shaded circles and squares) show a lower band of 170 bp, representing a mutant allele. Individual I-2 is homozygous for the mutant allele. (C) Affected Individuals II-3 and III-4 from the family shown in figure 1B with the presence of the 170-bp mutant allele.