A KMT2B Frameshift Variant Causing Focal Dystonia Restricted to the Oromandibular Region After Long-Term Follow-up

New insights from a Malaysian real-world deep brain stimulation cohort

BackgroundThe availability of deep brain stimulation (DBS), a highly efficacious treatment for several movement disorders, remains low in developing countries, with scarce data available on utilization and outcomes.ObjectiveWe characterized the DBS cohort and outcomes at a Malaysian quaternary medical center.MethodsA retrospective chart review was done on DBS-related surgery at the University of Malaya, including clinico-demographic, genetics, and outcomes data focusing on post-operative medication reduction and complications.Results149 Parkinson's disease (PD) patients underwent DBS targeting the subthalamic nucleus. Six had globus pallidus internus DBS (primarily for dystonia). Only 16.1% of patients were government-funded. Of the 133 PD patients operated in the past decade (2013-2022), 25 (18.8%) had disease duration <5 years. At 6-12 months post-DBS, median levodopa-equivalent daily dose (LEDD) reduction was 440.5 [418.9] mg/day, corresponding to a reduction of ≥50% and ≥30% in 42.2% and 69.8% of patients, respectively. LEDD reductions were larger in the early-onset and short-duration subgroups. Three patients (1.9% of 155) had symptomatic intracranial hemorrhage, resulting in stroke in two. Pathogenic monogenic or GBA1 variants were detected in 12/76 (16%) of patients tested, mostly comprising the "severe" GBA1 variant p.L483P (12%).ConclusionsThis is the largest report on DBS from Southeast Asia. The procedures were effective, and complication rates on par with international norms. Our study found a high frequency of GBA1-PD; and included a substantial number of patients with short-duration PD, who had good outcomes. It also highlights regional inequities in access to device-aided therapy.

Genetic Update and Treatment for Dystonia

A neurological condition called dystonia results in abnormal, uncontrollable postures or movements because of sporadic or continuous muscular spasms. Several varieties of dystonia can impact people of all ages, leading to severe impairment and a decreased standard of living. The discovery of genes causing variations of single or mixed dystonia has improved our understanding of the disease's etiology. Genetic dystonias are linked to several genes, including pathogenic variations of VPS16, TOR1A, THAP1, GNAL, and ANO3. Diagnosis of dystonia is primarily based on clinical symptoms, which can be challenging due to overlapping symptoms with other neurological conditions, such as Parkinson's disease. This review aims to summarize recent advances in the genetic origins and management of focal dystonia.

KMT2B-Related Dystonia in Indian Patients With Literature Review and Emphasis on Asian Cohort

OBJECTIVE

aaMutations in the KMT2B gene have been identified in patients previously diagnosed with idiopathic dystonia. Literature on KMT2B-related dystonia is sparse in the Indian and Asian populations.

METHODS

aaWe report seven patients with KMT2B-related dystonia studied prospectively from May 2021 to September 2022. Patients underwent deep clinical phenotyping and genetic testing by whole-exome sequencing (WES). A systematic literature search was performed to identify the spectrum of previously published KMT2B-related disorders in the Asian subcontinent.

RESULTS

aaThe seven identified patients with KMT2B-related dystonia had a median age at onset of four years. The majority experienced onset in the lower limbs (n = 5, 71.4%), with generalization at a median duration of 2 years. All patients except one had complex phenotypes manifesting as facial dysmorphism (n = 4), microcephaly (n = 3), developmental delay (n = 3), and short stature (n = 1). Magnetic resonance imaging (MRI) abnormalities were present in four cases. WES revealed novel mutations in the KMT2B gene in all patients except one. Compared to the largest cohort of patients with KMT2B-related disorders, the Asian cohort, comprising 42 patients, had a lower prevalence of female patients, facial dysmorphism, microcephaly, intellectual disability, and MRI abnormalities. Protein-truncating variants were more prevalent than missense variants. While microcephaly and short stature were more common in patients with missense mutations, facial dysmorphism was more common in patients with truncating variants. Deep brain stimulation, performed in 17 patients, had satisfactory outcomes.

CONCLUSION

aaThis is the largest series of patients with KMT2B-related disorders from India, further expanding the clinico-genotypic spectrum. The extended Asian cohort emphasizes the unique attributes of this part of the world.