Phenotypic and Genetic Complexity in Pediatric Movement Disorders

A novel mutation in SETX and ATM causes ataxia in consanguineous Pakistani families

Background & Objectives

Ataxia is usually caused by cerebellar pathology or a decrease in vestibular or proprioceptive afferent input to the cerebellum. It is characterized by uncoordinated walking, truncal instability, body or head tremors, uncontrolled coordination of the hands, dysarthria, and aberrant eye movements. The objective of the current investigation was to identify the underlying genetic cause of the hereditary ataxia that affects the Pakistani population.

Methods

We studied numerous consanguineous Pakistani families whose members had ataxia-related clinical symptoms to varying degrees. The families were chosen from the Punjab province, and the neurophysician conducted a clinical examination. Peripheral blood samples from both sick and healthy members of the family were taken after obtaining informed consent. Genomic DNA was used to find potential variations in probands using whole exome sequencing. The study was carried out at the University Hospital of Tübingen, Germany, and Government College University in Faisalabad, Pakistan, during 2018-2023.

Results

The molecular analysis of these families identified different variants including SGCB: c.902C>T, c.668G>A, ATM: c.6196_6197insGAA, SPG11: c.5769del, SETX c.5525_5533del, and ATM: c.7969A>T. A noteworthy mutation in ATM and SETX was observed among them, and its symptoms were shown to cause ataxia in these families.

Conclusion

The current study broadens the mutation spectrum of several hereditary ataxia types and suggests the next generation sequencing in conjunction with clinical research for a more accurate diagnosis of overlapping phenotypes of this disorder in the Pakistani population.

Hyperkinetic Movement Disorder Caused by the Recurrent c.892C>T NACC1 Variant

BACKGROUND

Genetic syndromes of hyperkinetic movement disorders associated with epileptic encephalopathy and intellectual disability are becoming increasingly recognized. Recently, a de novo heterozygous NACC1 (nucleus accumbens-associated 1) missense variant was described in a patient cohort including one patient with a combined mitochondrial oxidative phosphorylation (OXPHOS) deficiency.

OBJECTIVES

The objective is to characterize the movement disorder in affected patients with the recurrent c.892C>T NACC1 variant and study the NACC1 protein and mitochondrial function at the cellular level.

METHODS

The movement disorder was analyzed on four patients with the NACC1 c.892C>T (p.Arg298Trp) variant. Studies on NACC1 protein and mitochondrial function were performed on patient-derived fibroblasts.

RESULTS

All patients had a generalized hyperkinetic movement disorder with chorea and dystonia, which occurred cyclically and during sleep. Complex I was found altered, whereas the other OXPHOS enzymes and the mitochondria network seemed intact in one patient.

CONCLUSIONS

The movement disorder is a prominent feature of NACC1-related disease.

Next-generation sequencing and bioinformatics in rare movement disorders

The ability to sequence entire exomes and genomes has revolutionized molecular testing in rare movement disorders, and genomic sequencing is becoming an integral part of routine diagnostic workflows for these heterogeneous conditions. However, interpretation of the extensive genomic variant information that is being generated presents substantial challenges. In this Perspective, we outline multidimensional strategies for genetic diagnosis in patients with rare movement disorders. We examine bioinformatics tools and computational metrics that have been developed to facilitate accurate prioritization of disease-causing variants. Additionally, we highlight community-driven data-sharing and case-matchmaking platforms, which are designed to foster the discovery of new genotype-phenotype relationships. Finally, we consider how multiomic data integration might optimize diagnostic success by combining genomic, epigenetic, transcriptomic and/or proteomic profiling to enable a more holistic evaluation of variant effects. Together, the approaches that we discuss offer pathways to the improved understanding of the genetic basis of rare movement disorders.