# A Novel Frameshift Variant in the SPAST Gene Causing Hereditary Spastic Paraplegia in a Bulgarian–Turkish Family

## TL;DR

A new genetic mutation in the SPAST gene was found to cause hereditary spastic paraplegia in a Bulgarian-Turkish family.

## Contribution

A novel frameshift variant in SPAST is identified as a cause of HSP in an underrepresented population.

## Key findings

- A novel SPAST frameshift variant (c.339delG) was identified in two affected siblings.
- The variant is predicted to cause nonsense-mediated decay and loss of key spastin domains.
- The variant is absent from major population and variant databases and is classified as likely pathogenic.

## Abstract

Background: Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous group of neurodegenerative disorders characterized by progressive lower-limb spasticity and weakness. SPAST mutations are the most common cause of autosomal dominant HSP (SPG4). However, many pathogenic SPAST variants are unique and genetic data from underrepresented communities remain limited. Methods: Whole-exome sequencing (WES) was performed on the index patient with HSP. Variant annotation tools included Ensembl VEP, LOFTEE, CADD, SIFT, PolyPhen-2, MutationTaster, and SpliceAI. Variant interpretation followed ACMG/AMP guidelines. Clinical evaluation and family history supported phenotypic correlation and segregation. Results: A novel heterozygous frameshift variant in SPAST (c.339delG; p.Glu114Serfs*47) was identified. The variant was predicted to cause nonsense-mediated decay, resulting in loss of the microtubule-interacting and AAA ATPase domains of spastin. It was absent from population databases (gnomAD, TOPMed, 1000 Genomes) and public variant repositories (ClinVar, HGMD). The variant segregated with disease in two affected siblings and could be classified as likely pathogenic. Conclusions: This novel SPAST frameshift variant expands the mutational spectrum of SPG4-HSP and highlights the importance of including isolated or minority communities in genomic research to improve variant interpretation.