A novel homozygous HPDL variant in Japanese siblings with autosomal recessive hereditary spastic paraplegia: case report and literature review.

Biallelic variants of 4-hydroxyphenylpyruvate dioxygenase-like (HPDL) gene have been linked to neurodegenerative disorders ranging from severe neonatal encephalopathy to early-onset spastic paraplegia. We identified a novel homozygous variant, c.340G > T (p.Gly114Cys), in the HPDL gene in two siblings with autosomal recessive hereditary spastic paraplegia (HSP). Despite sharing the same likely pathogenic variant, the older sister had pure HSP, whereas her brother had severe and complicated HSP, accompanied by early-onset mental retardation and abnormalities in magnetic resonance imaging. Given the clinical heterogeneity and potential for treatable conditions in HPDL-related diseases, we emphasize the importance of genetic testing for the HPDL gene.