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Abstract
Objective: To describe a novel mutation in TRK-fused gene (TFG) as a new cause of dominant axonal Charcot-Marie-Tooth disease (CMT) identified by exome sequencing and further characterized by in vitro functional studies.
Methods: Exome sequencing and linkage analysis were utilized to investigate a large Taiwanese family with a dominantly inherited adult-onset motor and sensory axonal neuropathy in which mutations in common CMT2-implicated genes had been previously excluded. Functional effects of the mutant gene products were investigated in vitro.
Results: Exome sequencing of 2 affected individuals in this family revealed a novel heterozygous mutation, c.806G>T (p.Gly269Val), in TFG that perfectly cosegregates with the CMT2 phenotype in all 27 family members. This mutation occurs at an evolutionarily conserved residue and is absent in the 1,140 ethnically matched control chromosomes. Genome-wide linkage study also supported its disease-causative role. Cell transfection studies showed that the TFG p.Gly269Val mutation increased the propensity of TFG proteins to form aggregates, resulting in sequestration of both mutant and wild-type TFG proteins and might thus deplete functional TFG molecules. The secreted Gaussia luciferase reporter assay demonstrated that inhibition of endogenous TFG compromised the protein secretion pathways, which could only be rescued by expressing wild-type TFG but not the p.Gly269Val altered proteins. TFG mutation was not found in 55 additional unrelated patients with CMT2, suggesting its rarity.
Conclusion: This study identifies a new cause of dominant CMT2 and highlights the importance of TFG in the protein secretory pathways that are essential for proper functioning of the human peripheral nervous system.
GLOSSARY
- CMT=
- Charcot-Marie-Tooth disease;
- dbSNP=
- Single Nucleotide Polymorphism Database;
- ER=
- endoplasmic reticulum;
- ERES=
- endoplasmic reticulum exit sites;
- Fluc=
- Firefly luciferase;
- Gluc=
- Gaussia luciferase;
- HMSN-P=
- hereditary motor and sensory neuropathy with proximal dominance;
- mRNA=
- messenger RNA;
- MTT=
- 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide;
- NHLBI=
- National Heart, Lung, and Blood Institute;
- siRNA=
- small interfering RNA;
- TDP-43=
- TAR DNA-binding protein 43;
- TFG=
- TRK-fused gene
Footnotes
Go to Neurology.org for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
↵* These authors contributed equally to this work.
Supplemental data at Neurology.org
- Received March 16, 2014.
- Accepted in final form May 28, 2014.
- © 2014 American Academy of Neurology
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