What Is D-Bifunctional Protein Deficiency? D-bifunctional protein deficiency, also known as peroxisomal bifunctional enzyme deficiency, is an inherited disease causing severe biochemical abnormalities that are usually fatal within the first two years of life. D-bifunctional protein deficiency is the most severe among a group of diseases known as peroxisomal fatty acid oxidation disorders. Peroxisomes are structures within the cells of the body that are necessary for proper metabolism. D-bifunctional protein deficiency is caused by mutations in the HSD17B4 gene. Infants with D-bifunctional protein deficiency have poor muscle tone and typically experience seizures shortly after birth or within the first few months of life. They also demonstrate significant changes in brain structure, experience both vision and hearing impairment, and have severe developmental delays. Few infants with D-bifunctional protein deficiency achieve any developmental milestones. Children with D-bifunctional protein deficiency may also have enlargement of the liver and tend to share characteristic facial features. How Common Is D-Bifunctional Protein Deficiency? The estimated prevalence of D-bifunctional protein deficiency is 1 in 100,000 individuals. How Is D-Bifunctional Protein Deficiency Treated? There is no treatment for the underlying cause of D-bifunctional protein deficiency. Available treatments address the symptoms of the condition, such as the use of medications for seizures or placement of a feeding tube to ensure proper nutrition. What Is the Prognosis for a Person with D-Bifunctional Protein Deficiency? The prognosis for D-bifunctional protein deficiency is typically poor. Most children with the condition die within the first two years of life without achieving any developmental milestones. Other names forD-bifunctional protein deficiency DBP deficiency PBFE deficiency Peroxisomal bifunctional enzyme deficiency Pseudo-Zellweger syndrome Zellweger-like syndrome References Ferdinandusse et al., 2006, Am J Hum Genet, 78(1):112-24, PMID: 16385454 Ferdinandusse et al., 2006, Ann Neurol, 59(1):92-104, PMID: 16278854 Online Inheritance in Man, OMIM [#261515], 2014, http://omim.org/entry/261515 Vanderver et al., 2014, https://www.ncbi.nlm.nih.gov/books/NBK184570/