Glycyl tRNA synthetase mutations in Charcot-Marie-Tooth disease type 2D and distal spinal muscular atrophy type V

Abstract

Charcot-Marie-Tooth disease type 2D (CMT2D) and distal spinal muscular atrophy type V (dSMA-V) are axonal peripheral neuropathies inherited in an autosomal dominant fashion. Our previous genetic and physical mapping efforts localized the responsible gene(s) to a well-defined region on human chromosome 7p. Here, we report the identification of four disease-associated missense mutations in the glycyl tRNA synthetase gene in families with CMT2D and dSMA-V. This is the first example of an aminoacyl tRNA synthetase being implicated in a human genetic disease, which makes genes that encode these enzymes relevant candidates for other inherited neuropathies and motor neuron diseases.

Figure 1

Localization, organization, and expression of the GARS gene. A, The interval of human chromosome 7p14 harboring the CMT2D/dSMA-V gene(s) is defined by genetic markers 7p-3180 and D7S632, spans ∼980 kb, and contains the indicated 11 known genes (all with corresponding GenBank records). B, The GARS gene spans ∼40 kb and contains 17 exons. C, Northern analysis reveals that the ∼2.7-kb GARS transcript is ubiquitously expressed, with notable positive expression in the brain and spinal cord (arrows).

Figure 2

Characterization, localization, and conservation of GARS mutations. A, Representative sections of sequence chromatograms are shown for the regions encompassing the identified GARS mutations in the indicated families. Arrows denote each mutation (present in a heterozygous state), with the resulting amino acid changes depicted below along with an indication of their relative positions in the GARS protein. B, The known functional domains of the GARS protein are indicated in green (WHEP-TRS enzyme conjugation domain), red (core catalytic domain), and yellow (Gly-tRNA anticodon binding domain). C, For each of the four detected mutations, the variant amino acid is shown along with the flanking GARS sequence in multiple, evolutionarily diverse species. Note that each specific amino acid change is given at the top, with the relevant position depicted in red for the sequence in each species. Dashes indicate where sequence data were unavailable.

Figure 3

Segregation of GARS mutations with CMT2D/dSMA-V. A, Representative branch of family 1, showing segregation of the G240R mutation (amino acid change shown in red) with CMT2D. B, Sequence analysis of the G240R mutation in separated affected and unaffected copies of human chromosome 7 from family 1 (see text). Note that the 2094c allele (arrow) is present only on the affected chromosome (lower panel). C, Representative branch of family 4 showing segregation of the E71G mutation (amino acid change shown in red) with CMT2D/dSMA-V. D, Full pedigree of family 5. Note the autosomal dominant mode of inheritance and the presence of the G526R mutation in both individuals with dSMA-V (DNA from other family members was unavailable).