Identification of a novel genetic locus underlying tremor and dystonia

Five affected individuals with syndromic tremulous dystonia, spasticity, and white matter disease from a consanguineous extended family covering a period of over 24 years are presented. A positional cloning approach utilizing genome-wide linkage, homozygozity mapping and whole exome sequencing was used for genetic characterization. The impact of a calmodulin-binding transcription activator 2, (CAMTA2) isoform 2, hypomorphic mutation on mRNA and protein abundance was studied using fluorescent reporter expression cassettes. Human brain sub-region cDNA libraries were used to study the expression pattern of CAMTA2 transcript variants.

Linkage analysis and homozygozity mapping localized the disease allele to a 2.1 Mb interval on chromosome 17 with a LOD score of 4.58. Whole exome sequencing identified a G>A change in the transcript variant 2 5'UTR of CAMTA2 that was only 6 bases upstream of the translation start site (c.-6G > A) (NM_001171166.1) and segregated with disease in an autosomal recessive manner. Transfection of wild type and mutant 5'UTR-linked fluorescent reporters showed no impact upon mRNA levels but a significant reduction in the protein fluorescent activity implying translation inhibition.

Mutation of CAMTA2 resulting in post-transcriptional inhibition of its own gene activity likely underlies a novel syndromic tremulous dystonia.