HSD17B4 Gene

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.

Perrault syndrome is a rare condition that causes different patterns of signs and symptoms in affected males and females. A key feature of this condition is hearing loss, which occurs in both males and females. Affected females also have abnormalities of the ovaries. Neurological problems occur in some affected males and females.

In Perrault syndrome, the problems with hearing are caused by changes in the inner ear, which is known as sensorineural hearing loss. The impairment usually affects both ears and can be present at birth or begin in early childhood. Unless hearing is completely impaired at birth, the hearing problems worsen over time.

Females with Perrault syndrome have abnormal or missing ovaries (ovarian dysgenesis), although their external genitalia are normal. Severely affected girls do not begin menstruation by age 16 (primary amenorrhea), and most never have a menstrual period. Less severely affected women have an early loss of ovarian function (primary ovarian insufficiency); their menstrual periods begin in adolescence, but they become less frequent and eventually stop before age 40. Women with Perrault syndrome may have difficulty conceiving or be unable to have biological children (infertile).

Neurological problems in individuals with Perrault syndrome can include intellectual disability, difficulty with balance and coordinating movements (ataxia), and loss of sensation and weakness in the limbs (peripheral neuropathy). However, not everyone with this condition has neurological problems.