CMT-DHX9

DHX9 | 2023

What Is CMT-DHX9?

CMT-DHX9 is a type of CMT caused by autosomal dominant mutations in the DHX9 gene. This gene provides instructions for making a helicase enzyme that unwinds DNA and RNA structures to support normal gene transcription in cells throughout the body. Mutations in the DHX9 gene disrupt nerve cell function, leading to impaired nerve signal transmission.

CMT-DHX9 is autosomal dominant, meaning that just one of the gene’s two copies needs a mutation to cause this subtype.

Clinical Features

The age of symptom onset in CMT-DHX9 is variable, ranging from childhood to adulthood. Symptoms typically begin in the lower extremities and progress over time to involve the upper limbs. Nerve conduction studies usually show somewhat slowed conduction velocities and reduced amplitudes, consistent with an axonal form of CMT.

CMT-DHX9 symptoms may include:

  • Weakness in the feet and lower legs
  • Muscle atrophy
  • Foot drop
  • Reduced or absent reflexes
  • Reduced sensation
  • A steppage-style walking pattern
  • Foot deformities, including high arches, and hammertoes (clawed toes)
  • Progressive involvement of the hands and forearms
  • Difficulty with fine motor skills and manual dexterity
  • Additional symptoms not listed here

Disease Course

CMT-DHX9 shows wide variability in severity and progression. Some individuals are mildly affected, while others develop a more severe disease. Disease progression is generally slow, and life expectancy is not reduced.

Clinical Basics

Subtype
CMT-DHX9

Classification
Unclassified Subtypes

Neuropathy Type
Axonal

Inheritance Pattern
autosomal dominant

Genetic Context

HGNC-Approved Gene Symbol
DHX9

Gene Full Name
Dexh-Box Helicase 9

HGNC Gene Alias(es)
LPK, DDX9

Chromosome
1q25.3

Zygosity of Responsible Variant
Heterozygous

Variant Mechanism

Unknown

Details

Mechanistic basis:
Unresolved

Confidence:
Low

Prediction:
The literature does not resolve a mechanism for CMT-DHX9: dominant monoallelic missense variants in the DHX9 helicase cause the disease, but the limited functional evidence from the original cohort does not distinguish haploinsufficiency from a dominant-negative or gain-of-function effect, so the CMT-specific mechanism is unresolved.

Rationale:
Dominant DHX9 helicase-domain missense alleles could act by a dominant-negative or gain-of-function effect, suggested by the missense-versus-loss genotype split, but the single 2023 cohort's data cannot exclude haploinsufficiency, so the mechanism remains unresolved at low confidence.

ClinVar Pathogenic Variants

View CMT-DHX9 ClinVar Variants

DHX9 OMIM Entry

DHX9 OMIM

More Info

CMT-DHX9 Research Opportunity

CMT Natural History Study

Original Discovery Publication

Publication Title

Monoallelic variation in DHX9, the gene encoding the DExH-box helicase DHX9, underlies neurodevelopment disorders and Charcot-Marie-Tooth disease

Authors

Calame, D. G., Guo, T., Wang, C., Garrett, L., Jolly, A., Dawood, M., Kurolap, A., Henig, N. Z., Fatih, J. M., Herman, I., Du, H., Mitani, T., Becker, L., Rathkolb, B., Gerlini, R., Seisenberger, C., Marschall, S., Hunter, J. V., Gerard, A., Heidlebaugh, A., Chalman, T., Spillman, R. C., Jhangiani, S. N., Coban-Akdemir, Z., Lalani, S., Liu, L., Revah-Politi, A., Iglesias, A., Guzman, E., Baugh, E., Boddaert, N., Rondeau, S., Ormieres, C., Barcia, G., Tan, Q. K. G., Thiffault, I., Pastinen, T., Sheik, K., Biliciler, S., Mei, D., Melani, F., Shashi, V. Yaron, Y., Steele, M., Wakeling, E., Ostergaard, E., Nazaryan-Peterson, L., Undiagnosed Disease Network, Millan, F., Santiago-Sim, T., Thevenon, J., Bruel, A., Thauvin-Robinet, C., Popp, D., Platzer, K., Gawlinski, P., Wiszniewski, W., Marafi, D., Pehlivan, D., Posey, J. E., Gibbs, R. A., Gailus-Durner, V., Guerrini, R., Fuchs, H., Hrabe de Angelis, M., Holter, S. M., Cheung, H-H., Gu, S., Lupski, J. R.

Publication Date
July 18, 2023

DOI
10.1016/j.ajhg.2023.06.013

Updated: July 18, 2026 | By: K. Raymond

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