Hydrolethalus syndrome is a condition that causes improper fetal development. Multiple malformations along the body's midline, such as heart and brain defects, a cleft lip or palate, an abnormally shaped nose or jaw, and incomplete lung development result from this syndrome. The birth defects are typically extreme enough to cause stillbirth or death within a few days of birth. A less common name for hydrolethalus syndrome is Salonen-Herva-Norio syndrome, after the Finnish researchers who first described it in 1981.
Hydrolethalus syndrome is passed on through an autosomal recessive pattern of inheritance. Autosomal means that the syndrome is not carried on a sex chromosome, while recessive means that both parents must carry the gene mutation in order for their child to have the disorder. Some cases of hydrolethalus syndrome have been observed in cases where the parents are related by blood (consanguineous). Parents with one child affected by hydrolethalus syndrome have a 25% chance that their next child will also be affected with the disease.
Each parent passes 23 chromosomes, or units of genetic information, to the infant. Structurally, each chromosome has a short segment or "arm," called the p arm, and a long arm, called the q arm, extending from a central region called the centromere. Along each arm the chromosome is further divided by numbering the bands down the arm according to their appearance under a microscope. Each band corresponds to specific genes. Based on studies of genetic material from affected and non-affected families, studies in 1999 assigned the gene location for hydrolethalus syndrome to 11q23-25, or somewhere between the 23rd and 25th band of the q arm of chromosome 11.
The majority of cases of hydrolethalus syndrome have been reported in people of Finnish ancestry. In Finland the incidence of hydrolethalus syndrome is estimated at one in every 20,000. Less than twenty cases have been reported outside of Finland.
Hydrolethalus syndrome affects fetal development in the womb and is a syndrome of infants only, due to the extremely serious birth defects caused by the disorder. No cases of survival into childhood or adulthood have been reported. The syndrome appears to affect both males and females with equal probability.
Signs and symptoms
After birth, the following conditions may be observed as a result of hydrolethalus syndrome:
- fluid in the skull and swelling leading to an abnormally large head (hydrocephalus)
- defects in the structure of the heart
- incomplete development of the lungs
- the presence of extra fingers and toes (polydactyly), especially an extra big toe or little finger
- a cleft lip or palate
- a small lower jaw (micrognathia)
- abnormal eye and nose formation
- a keyhole-shaped defect at the back of the head
- abnormal genitalia
Hydrolethalus syndrome can be diagnosed prenatally by ultrasound scanning in as early as the eleventh week of gestation. After birth, the presence of multiple malformations, especially the extreme swelling of the skull and other brain and spinal cord defects, can confirm the diagnosis. A family history and genetic testing may be useful in making the diagnosis certain.
Treatment and management
There is no treatment for hydrolethalus syndrome other than management of the specific medical conditions of the infant. Genetic counseling is particularly important in the prenatal treatment and management of hydrolethalus syndrome. This is because the severity of symptoms almost always causes death of the infant within a few days of birth, even if the fetus survives to full term.
The prognosis for infants with hydrolethalus syndrome is extremely poor. Most affected infants are still-born or die within the first day of life. Only a handful of cases of survival past the neonatal period have been reported and the longest survival period was 44 days.
Visapaa, Ilona, et al. "Assignment of the locus for hydrolethalus syndrome to a highly restricted region on 11q23-25." American Journal of Human Genetics (September 1999): 1086-95.
March of Dimes Birth Defects Foundation. 1275 Mamaroneck Ave., White Plains, NY 10605. (888) 663-4637. email@example.com. <http://www.modimes.org>.
National Organization for Rare Disorders (NORD). PO Box 8923, New Fairfield, CT 06812-8923. (203) 746-6518 or (800) 999-6673. Fax: (203) 746-6481 <http://www.rarediseases.org>.
"Entry 236680: Hydrolethalus syndrome." OMIM—Online Mendelian Inheritance in Man. <http://www.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?236680> (April 20, 2001).
Jeanty, Philippe, and Sandra Silva. "Hydrolethalus syndrome." TheFetus.Net. <http://www.thefetus.net> (April 20, 2001).
Paul A. Johnson