Candidate variants in TUB are associated with familial tremor

Abstract

Essential tremor (ET) is the most common adult-onset movement disorder. In the present study, we performed whole exome sequencing of a large ET-affected family (10 affected and 6 un-affected family members) and identified a TUB p.V431I variant (rs75594955) segregating in a manner consistent with autosomal-dominant inheritance. Subsequent targeted re-sequencing of TUB in 820 unrelated individuals with sporadic ET and 630 controls revealed significant enrichment of rare nonsynonymous TUB variants (e.g. rs75594955: p.V431I, rs1241709665: p.Ile20Phe, rs55648406: p.Arg49Gln) in the ET cohort (SKAT-O test p-value = 6.20e-08). TUB encodes a transcription factor predominantly expressed in neuronal cells and has been previously implicated in obesity. ChIP-seq analyses of the TUB transcription factor across different regions of the mouse brain revealed that TUB regulates the pathways responsible for neurotransmitter production as well thyroid hormone signaling. Together, these results support the association of rare variants in TUB with ET.

Fig 1. Pedigree of the multiplex ET family.

Affected individuals are categorized in two different tiers. Tier 1, highlighted in red, are participants whom we are most certain have familial tremor (definite). They have all been diagnosed by a physician or neurologist and have clear symptoms of tremor that the age of onset was before their 65s. Tier 2, highlighted in blue, are participants who do state they have not been diagnosed with tremor by a physician, but describe clear symptoms of tremor in their questionnaires, with onset before their 65s. All have described the tremor interfering with their activities of daily living in some way. Individuals highlighted in yellow are Tier 3, whom the tremor is most unclear. Some are unsure if their symptoms are actually ET or not. The symptoms are generally very mild and, in many cases, intermittent. None have been diagnosed by a physician, and for some symptoms didn't onset until their 70s or later. Individuals highlighted in black are reported to have tremor, but these individuals are not participating. Controls, highlighted in green, are in their mid 50s or older and have no symptoms of tremor, according to their questionnaires. (Please note that this is a short version of the pedigree. (The full pedigree is shown in S1 Fig).

Fig 2. Sanger sequencing traces (ATG/ACT) showing the p.Val 431 Ile variant in exon 11 of the TUB gene (using sequencing primer 5`-AGCGAGTGGAAGAACAGCATTGCC-3`).

The segregation of this variant has been confirmed in 15 available DNA samples (six controls and 9 affected individuals) from this family.

Fig 3. Schematic of the coding sequence of TUB gene and p.Val 431 Ile variant within TUB.

The amino-acid sequence of TUB around (p.Val 431 Ile) colored according to the conservation scores. Conservation scores were calculated by ConSurf tool[49]. ConSurf estimates the evolutionary conservation of amino acid residues in a peptide based on the phylogenetic relations between homologous sequences as well as amino acid’s structural and functional importance.

Fig 4

A) Number of TUB binding sites across different regions of the mouse brain by ChIP-seq. B) The overlap of TUB binding sites across different regions of the mouse brain.

Fig 5

A. Genomic annotation of ChIP peaks across different regions of the mouse brain. B. Heatmap plot of ChIP binding sites to transcription start sites (TSS) regions.

Fig 6. KEGG pathway enrichment analyses of TUB binding sites.