Objective: To present a case of childhood-onset dystonia with a new mutation in KMT2B gene.

Background: KMT2B-related dystonia (DYT-KMT2B) is an increasingly recognized cause of childhood onset generalized dystonia, with an autosomal dominant inheritance pattern. This disease usually presents with a progressive course, with variable severity, evolving from focal lower limb dystonia into a generalized dystonia with prominent cranial, bulbar, and cervical involvement. Chorea, myoclonus, psychomotor delay, intellectual disability, short stature and microcephaly can be additional features of the phenotype.

Method: Case report.

Results: A 50-year-old caucasian female, with unremarkable family history, was diagnosed with a writer’s cramp when she was eight years old. At the age of sixteen, she developed gait difficulties due to abnormal postures of her feet and noticed that her neck and trunk were bending to her right side. Since then, she reports that her symptoms have remained stable. Blood and urine work-up excluded secondary causes, such as Wilson’s disease. Brain MRI was normal. Finally, at the age of 49 years old, a NGS panel for genetic dystonia revealed a heterozygous new missense variant in KMT2B gene, classified as a variant of unknown significance. Currently, the patient presents a generalised dystonia phenotype, involving the neck, trunk, and limbs, combined with discrete choreic movements and mild intellectual disability. Under speech and physical therapy and trihexyphenidyl 12mg/day, there has been no symptomatic progression. Genetic consultation was ordered and the patient’s parents are currently waiting for their genetic test results.

Conclusion: With the advent of genetic testing, several new genes have been discovered as the cause of isolated or combined dystonia. KMT2B is an example of a new gene, discovered in 2016. However, more and more new variants of unknown significance are found with these genetic tests, sometimes being difficult to correlate them with the phenotype. In our case, we believe this new mutation can be the cause of the combined dystonia phenotype presented by our patient, given that it is similar to other cases reported in the literature. However, dystonia started as a writer’s cramp, which has been rarely described.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/childhood-onset-writers-cramp-evolving-to-generalised-dystonia-a-new-mutation-in-kmt2b-gene/