D-bifunctional protein deficiency

D-bifunctional protein deficiency is a disorder that causes deterioration of nervous system functions (neurodegeneration) beginning in infancy. Newborns with D-bifunctional protein deficiency have weak muscle tone (hypotonia) and seizures. Most babies with this condition never acquire any developmental skills. Some may reach very early developmental milestones such as the ability to follow movement with their eyes or control their head movement, but they experience a gradual loss of these skills (developmental regression) within a few months. As the condition gets worse, affected children develop exaggerated reflexes (hyperreflexia), increased muscle tone (hypertonia), more severe and recurrent seizures (epilepsy), and loss of vision and hearing. Most children with D-bifunctional protein deficiency do not survive past the age of 2. A small number of individuals with this disorder are somewhat less severely affected. They may acquire additional basic skills, such as voluntary hand movements or unsupported sitting, before experiencing developmental regression, and they may survive longer into childhood than more severely affected individuals.

Individuals with D-bifunctional protein deficiency may have unusual facial features, including a high forehead, widely spaced eyes (hypertelorism), a lengthened area between the nose and mouth (philtrum), and a high arch of the hard palate at the roof of the mouth. Affected infants may also have an unusually large space between the bones of the skull (fontanelle). An enlarged liver (hepatomegaly) occurs in about half of affected individuals. Because these features are similar to those of another disorder called Zellweger syndrome (part of a group of disorders called the Zellweger spectrum), D-bifunctional protein deficiency is sometimes called pseudo-Zellweger syndrome.