What is Hydrolethalus Syndrome?

Hydrolethalus syndrome is an inherited disease caused by harmful genetic changes (mutations) in the HYSF1 gene. The HYSF1 gene plays an important role in fetal development. Hydrolethalus syndrome causes severe brain abnormalities. These can include missing portions of the brain and extra fluid surrounding the brain (hydrocephalus). The opening at the base of the skull (foramen magnum) has an atypical key shape. Affected infants display differences in the face and skull (craniofacial malformations), including a small jaw (micrognathia) and a notched (cleft) lip and roof of mouth (palate). Other findings include extra digits of the fingers and toes (polydactyly), heart defects, narrowing of the airway, and malformation of the lungs (unilobular lungs).

The condition may be detected by an ultrasound scan around the thirteenth to fifteenth week of pregnancy due to the malformations of the brain and other organs. Extra amniotic fluid (polyhydramnios) is typically present in the later parts of the pregnancy.

How common is Hydrolethalus Syndrome?

Hydrolethalus syndrome is most common in individuals of Finnish descent, with an estimated incidence of approximately 1 in 10,000. It is extremely rare in individuals of other ethnicities.

How is Hydrolethalus Syndrome treated?

At this time, there are no cures or treatment options for individuals with hydrolethalus syndrome.

What is the prognosis for a person with Hydrolethalus Syndrome?

Unfortunately, the prognosis for an infant with hydrolethalus syndrome is poor. Most individuals are either stillborn or die shortly after birth. There have been rare cases where infants with hydrolethalus syndrome have lived for several months.

Other names for
hydrolethalus syndrome

  • HLS
  • HLS1
  • Hydrolethalus syndrome
  • Hydrolethalus syndrome 1
  • Salonen-Herva-Norio syndrome


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