Holoprosencephaly is a birth defect of the brain, but it can also affect the patient’s facial features. It occurs when the embryonic forebrain fails to divide sufficiently into the cerebral hemispheres’ double lobes. It is classified as alobar, lobar, or semilobar. Understanding the genetics of holoprosencephaly will help both patients and healthcare providers best treat this condition.
This birth defect is relatively common and occurs shortly after the baby is conceived. Prevalence is approximately one in 250 during the early stage of embryo development and one in 10,000 to 20,000 at term.
The symptoms of this condition vary in severity. Several deformities, specifically facial deformities, are possible. Symptoms include:
- Small head
- Different degrees of mental retardation
- Endocrine abnormalities
- Organ abnormalities, such as abnormalities of the cardiovascular system, genitourinary system, skeletal system, and gastrointestinal system
- Excessive fluid in the brain
- Facial abnormalities
- Flat, single-nostril nose
- Cleft palate or lip
- Teeth problems
- Close set eyes
- Having just one eye
- Missing facial features
- Nose located on the forehead
There is no standard or specific treatment plan for this condition. The focus of treatment is supportive and symptomatic. For most patients, the prognosis is poor. There are some medications that can be used to treat specific symptoms.
Patients who experience gastroesophageal reflux disease can benefit from certain heartburn medications, such as Nexium, Prilosec, or Zantac. These medications can help to reduce all GERD-related symptoms. However, these medications may put children at a higher risk of developing respiratory or intestinal infections.
Anticonvulsant medications can help to treat epilepsy. Patients will take this type of drug once a day to reduce the risk of having seizures. Valproic acid and phenobarbital are the most commonly prescribed.
Botox may also be beneficial for some patients. Some children will develop increased muscle tone due to spasticity and Botox can help with this. This drug will be directly injected to any spastic muscles to help stop the muscle from twitching.
Esophageal surgery can help when the patient is having difficulty breathing or feeding as the result of esophageal muscle problems. The complications that are associated with this surgery are very serious, so this surgery is only done when absolutely necessary.
Several different genes have been shown to play a role in causing this condition. The genetics of holoprosencephaly include an inheritance pattern that is autosomal, autosomal dominant, and x-linked recessive. A chromosomal abnormality known as trisomy 13 is associated with this condition. The following genes have been found to play a role in causing this condition: HPE1 at 21q22.3, HPE3 at 7q36, and HPE2 at 2p21.
National Human Genome Research Institute. (2010). Learning About Holoprosencephaly. Retrieved on August 30, 2010 from the National Human Genome Research Institute: https://www.genome.gov/12512735
The Carter Centers. (2010). Information About Holoprosencephaly. Retrieved on August 30, 2010 from Stanford University: https://hpe.stanford.edu/about/