Mutations in DNMT1 cause autosomal dominant cerebellar ataxia, deafness and narcolepsy

Abstract

Autosomal dominant cerebellar ataxia, deafness and narcolepsy (ADCA-DN) is characterized by late onset (30-40 years old) cerebellar ataxia, sensory neuronal deafness, narcolepsy-cataplexy and dementia. We performed exome sequencing in five individuals from three ADCA-DN kindreds and identified DNMT1 as the only gene with mutations found in all five affected individuals. Sanger sequencing confirmed the de novo mutation p.Ala570Val in one family, and showed co-segregation of p.Val606Phe and p.Ala570Val, with the ADCA-DN phenotype, in two other kindreds. An additional ADCA-DN kindred with a p.GLY605Ala mutation was subsequently identified. Narcolepsy and deafness were the first symptoms to appear in all pedigrees, followed by ataxia. DNMT1 is a widely expressed DNA methyltransferase maintaining methylation patterns in development, and mediating transcriptional repression by direct binding to HDAC2. It is also highly expressed in immune cells and required for the differentiation of CD4+ into T regulatory cells. Mutations in exon 20 of this gene were recently reported to cause hereditary sensory neuropathy with dementia and hearing loss (HSAN1). Our mutations are all located in exon 21 and in very close spatial proximity, suggesting distinct phenotypes depending on mutation location within this gene.

Figure 1.

DNMT1 mutations in four kindreds with autosomal dominant ataxia, deafness and narcolepsy (ADCA-DN). (A) US pedigree. (B) Swedish pedigree previously reported by Melberg et al. (1). (C) Italian kindred with de novo mutation. (D) Second Italian pedigree. The amino acid changes are noted for each subject for whom we tested for the mutation in the genomic DNA sequence, either whole-exome sequencing (subjects in boxes, for details on exome sequencing results see Supplementary Material, Table S1) or Sanger sequencing. Age of each subject at the time of study, or age at death, is indicated next to each symbol. Black symbol indicates affected status, white indicates unaffected at the time of study. The asterisk denotes a subject with narcolepsy only, as documented by sleepiness and a positive MSLT with three sleep onset REM periods. For details on phenotypes and typical ages of onset for various symptoms, please refer to Table 1.

Figure 2.

(A) Protein structure of mouse DNMT1 (PDB accession number 3AV5, image generated with Jmol_S) and locations of newly identified amino acid substitutions (orange arrows) in the RFTS domain. Also shown are positions of amino acid changes reported by Klein et al. (4), in the TS domain of the protein (light green arrows). The substrate shown is S-adenosyl-l-homocystein. (B) Overview of the degree of conservation of the region containing the three novel mutations (orange boxes) and the two mutations previously reported by Klein et al. (4) (light green boxes).