Identifying the Fourth Patient With Spastic Paraplegia 90, Extending the Phenotype Spectrum

Spastic paraplegia 90 (SPG90; OMIM #620416, 620417) is a rare neurologic disease caused by monoallelic or biallelic variants in the serine palmitoyltransferase small subunit A (SPTSSA) gene. This syndrome is characterized by neurodevelopmental delay, sensorineural hearing loss, progressive motor impairment, and lower extremity spasticity. To date, only three patients have been reported. In this report, we present a 10-year-old female patient with global developmental delay, inability to walk, axial hypotonia, extremity spasticity, dystonia, distal renal tubular acidosis, recurrent urinary tract infections, nephrolithiasis, neurogenic bladder, and primary polydipsia. Exome sequencing revealed a heterozygous pathogenic variant (p.Thr51Ile), which was detected in two of the reported patients, suggesting a recurrent variant in this syndrome. The neurogenic bladder and primary polydipsia found in our patient are novel findings, and we propose that genitourinary problems may be a component of the syndrome.