D-Bifunctional protein deficiency or D-BP deficiency can be caused by mutations in homozygous or compound heterozygous in the HSD17B4 gene, located on chromosome 5q23.1, which encodes the D-bifunctional protein (D-BP).
D-BP deficiency is a disorder of beta-oxidation of peroxisomal fatty acids.
It has been classified into 3 subtypes depending on the activity of the deficient enzyme:
- Type I: 2-enoyl-CoA hydratase deficiency and 3-hydroxyacyl-CoA dehydrogenase deficiency.
- Type II: deficiency of hydrazone activity.
- Type III: deficiency of dehydrogenase activity.
Clinical features include neonatal hypotonia, early-onset seizures, severe developmental delay, and abnormal facial features. Most of the patients die before age 2.
The diagnosis of D-BP deficiency is based on the accumulation of very long chain fatty acids (VLCFA), dihydroxy and trihydroxy-costic acid (DHCA and THCA) and pristanic and phytanic acid in plasma. In addition, brain magnetic resonance imaging may help in the diagnosis of patients with D-BP deficiency, especially in cases that do not manifest plasma abnormalities or these abnormalities are mild.