Novel HSD17B4 Variants Cause Progressive Leukodystrophy in Childhood: Case Report and Literature Review

D-bifunctional protein (DBP) deficiency is a peroxisomal disorder with a high degree of phenotypic heterogeneity. Some patients with DBP deficiency develop progressive leukodystrophy in childhood. We report a 6-year-old boy with moderate hearing loss who presented with developmental regression. Brain magnetic resonance imaging demonstrated progressive leukodystrophy. However, very long chain fatty acids (VLCFAs) in the plasma were at normal levels. Whole-exome sequencing revealed compound heterozygous variants in HSD17B4 (NM_000414.3:c.[350A > T];[394C > T], p.[[Asp117Val]];[[Arg132Trp]]). The c.394C > T variant has been identified in patients with DBP deficiency and is classified as likely pathogenic, while the c.350A > T variant was novel and classified as uncertain significance. Although one of the two variants was classified as uncertain significance, an accumulation of phytanic and pristanic acids was identified in the patient, confirming type III DBP deficiency. DBP deficiency should be considered as a diagnosis in children with progressive leukodystrophy and hearing loss even if VLCFAs are within normal levels.