Purpose: Inherited axonopathies (IA) are rare, clinically and genetically heterogeneous diseases that lead to length-dependent degeneration of the long axons in central (hereditary spastic paraplegia [HSP]) and peripheral (Charcot–Marie–Tooth type 2 [CMT2]) nervous systems. Mendelian high-penetrance alleles in over 100 different genes have been shown to cause IA; however, about 50% of IA cases do not receive a genetic diagnosis. A more comprehensive spectrum of causative genes and alleles is warranted, including causative and risk alleles, as well as oligogenic multilocus inheritance. Methods: Through international collaboration, IA exome studies are beginning to be sufficiently powered to perform a pilot rare variant burden analysis. After extensive quality control, our cohort contained 343 CMT cases, 515 HSP cases, and 935 non-neurological controls. We assessed the cumulative mutational burden across disease genes, explored the evidence for multilocus inheritance, and performed an exome-wide rare variant burden analysis. Results: We replicated the previously described mutational burden in a much larger cohort of CMT cases, and observed the same effect in HSP cases. We identified a preliminary risk allele for CMT in the EXOC4 gene (p value= 6.9 × 10-6, odds ratio [OR] = 2.1) and explored the possibility of multilocus inheritance in IA. Conclusion: Our results support the continuing emergence of complex inheritance mechanisms in historically Mendelian disorders.
Bibliographical noteFunding Information:
We thank the patients and their families for their participation. This study was supported by the National Institute of Neurological Disorders and Stroke (NINDS) (U54NS065712-12 to S.Z. as site principal investigator [PI], R01NS105755 to S.Z., R01NS072248 to S.Z.), the Charcot–Marie–Tooth Association, the Hereditary Neuropathy Foundation, and the Muscular Dystrophy Association. This work was done as a part of a Canadian collaboration to study HSP (CanHSP). The CanHSP cohort was funded by Canadian Institutes of Health Research (CIHR) Emerging Team Grant, in collaboration with the Canadian Organization for Rare Disorders (CORD), grant number RN127580–260005.
© 2020, American College of Medical Genetics and Genomics.
- Charcot–Marie–Tooth disease
- hereditary spastic paraplegia
- inherited axonopathy
- mutational burden
- oligogenic inheritance
PubMed: MeSH publication types
- Journal Article
- Research Support, N.I.H., Extramural
- Research Support, Non-U.S. Gov't