VAMP1 mutation causes dominant hereditary spastic ataxia in Newfoundland families

Abstract

Our group previously described and mapped to chromosomal region 12p13 a form of dominantly inherited hereditary spastic ataxia (HSA) in three large Newfoundland (Canada) families. This report identifies vesicle-associated membrane protein 1 (VAMP1), which encodes a critical protein for synaptic exocytosis, as the responsible gene. In total, 50 affected individuals from these families and three independent probands from Ontario (Canada) share the disease phenotype together with a disruptive VAMP1 mutation that affects a critical donor site for the splicing of VAMP1 isoforms. This mutation leads to the loss of the only VAMP1 isoform (VAMP1A) expressed in the nervous system, thus highlighting an association between the well-studied VAMP1 and a neurological disorder. Given the variable phenotype seen in the affected individuals examined here, we believe that VAMP1 should be tested for mutations in patients with either ataxia or spastic paraplegia.

Figure 1

VAMP1, from the Gene to Its Encoded Protein (A) A chromatogram of the variant chr12: g.6574054T>G from an affected individual is compared to that from a control. (B) Representation of the three annotated VAMP1 isoforms. The wider boxes are exons, the medium boxes are UTRs, and the lines are introns. The variant position and the insert localization are indicated. (C) A zoomed-in view of the variant region, including the amino acid sequences of the annotated isoforms and the mutated sequence caused by the variant.

Figure 2

Testing Splicing with RNA from Transfected COS7 Cells (A) Agarose-gel result of RT-PCR on RNA extracted from COS7 cells transfected with a VAMP1 minigene. The allele present in the insert is indicated above the corresponding lane. (B) Representation of the plasmid portion relevant for RT-PCR. The beta-globin exons are in gray, the splicing events are represented by blue lines, and the variant position is indicated by the red dashed line. The insert, in red, has introns (lines) and an exon (wider box). The medium-sized box represents the nucleotides added by the abnormal splicing. The presented sequence represents the sequence of the insert; the mutated T is highlighted in red, and the alternatively used donor site is highlighted in yellow.