ALDH18A1-related hereditary spastic paraplegia and developmental and epileptic encephalopathy with spike-wave activation in sleep: Expanding the clinical phenotype

Objective We present the cases of two sisters, both harboring the same ALDH18A1 gene mutations, who presented with a complex clinical phenotype characterized by spastic paraparesis with ataxia, epileptic encephalopathy, severe psychomotor deficits, and behavioral abnormalities. Methods Case description of two sisters with ALDH18A1 gene mutations. Results The older patient, a 12-year-old girl, exhibited spastic paraparesis with ataxia, microcephaly, facial dysmorphisms, and severe intellectual disability, with an absence of verbal language. An electroencephalogram (EEG) revealed marked spike-and-wave activation during sleep (SWAS), although no clinically documented seizures were observed. The younger sister, who was 9 years old, displayed a similar clinical presentation, including spastic paraparesis with ataxia, microcephaly, dysmorphisms, however, she displayed slightly more severe intellectual deficits and polymorphic seizures. EEG revealed a SWAS pattern in this case. Magnetic resonance imaging scans in both cases showed only a thin corpus callosum. Whole exome sequencing unveiled the presence of two likely pathogenic variants in compound heterozygosity within the ALDH18A1 gene. Specifically, these variants included the splice site variant c.88 + 1c.88+1G>A of paternal origin and the variant c.1364c.1364T>C (p.Leu455Ser) of maternal origin. Both sisters displayed normal blood levels of ammonia, ornithine, citrulline, arginine, and other amino acids. Interpretation These findings were compatible with ALDH18A1-related HSP complicated with a clinical and EEG pattern reminiscent of DEE-SWAS. We present the first report of DEE-SWAS in ALDH18A1-related HSP, expanding the clinical manifestations of this complex neurodevelopmental condition.