Revealing modifier variations characterizations for elucidating the genetic basis of human phenotypic variations

A novel mutation in the UBAP1 gene causing hereditary spastic paraplegia: A case report and overview of the genotype-phenotype correlation

Hereditary Spastic Paraplegia (HSP) is considered to be one of the common neurodegenerative diseases with marked genetic heterogeneity. Recently, the mutations in ubiquitin-associated protein 1 (UBAP1) have been described in patients with HSP, known as spastic paraplegias 80 (SPG80). Here, we reported a Chinese HSP family presenting a frameshift mutation in the UBAP1 gene leading to complex HSP. Their clinical features encompassed spastic paraparetic gait, exaggerated patellar tendon reflexes, bilateral Babinski signs, and hyperactive Achilles tendon reflex. The proband also had severe urinary incontinence and a dermoid cyst at the lumbar 4–5 spinal cord, which rarely occurs in HSP patients. Following whole-exome sequencing, a novel heterozygous mutation (c.437dupG, NM_016,525) was identified in the UBAP1 that segregated with the family’s phenotype and resulted in truncating UBAP1 protein (p.Ser146ArgfsTer13). Moreover, we reviewed the genotypes of UBAP1 and the phenotypic variability in 90 HSP patients reported in the literature. We found that the age of onset in UBAP1-related patients was juvenile, and there were population differences in the age of onset. The main complications were lower extremity spasticity, hyperreflexia, and the Babinski sign. Exon 4 of UBAP1 was identified as a mutation hotspot region. Our study expands the knowledge of UBAP1 mutations, which will aid in HSP patient counseling. Further molecular biological research is needed to explore the genotype-phenotype correlations of UBAP1-related HSP.