A rare birth defect known as homoloprosencephaly affects the development of both the brain and the face. During the early stages of pregnancy, the forebrain does not divide into two halves, which results in a single, large brain hemisphere instead of two separate ones. A person with holoprosencephaly may also have abnormal facial features, such as a small head, a cleft lip or palate, or a single eye.
The exact cause of holoprosencephaly is unknown, but it is believed to be related to genetic and environmental factors. Some of the possible causes are:
Mutations or deletions in certain genes that are involved in the formation of the brain and the face, such as SHH, ZIC2, SIX3, or TGIF. These genes can be inherited from one or both parents, or they can occur randomly in the developing fetus.
Chromosomal abnormalities, such as trisomy 13, trisomy 18, or triploidy, which affect the number or structure of the chromosomes in the cells. These abnormalities can also be inherited or occur randomly in the developing fetus.
Exposure to certain substances or infections during pregnancy, such as alcohol, drugs, mercury, rubella, or toxoplasmosis, which can interfere with the normal development of the brain and the face.
The symptoms of holoprosencephaly vary depending on the severity and the type of the condition. There are three main types of holoprosencephaly:
Alobar holoprosencephaly, which is the most severe type, where there is no division of the brain at all. This type usually causes severe intellectual disability, seizures, breathing problems, and death in infancy.
Semilobar holoprosencephaly, which is a moderate type, where there is some division of the brain, but not complete. This type usually causes mild to moderate intellectual disability, developmental delays, and craniofacial anomalies.
Lobar holoprosencephaly, which is the least severe type, where there is almost complete division of the brain, but some parts are still fused. This type usually causes mild intellectual disability, learning difficulties, and minor facial defects.
Some of the common symptoms of holoprosencephaly are:
Microcephaly, which is a small head size
Cleft lip or palate, which is a split in the upper lip or the roof of the mouth
Cyclopia, which is a single eye in the middle of the forehead
Ethmocephaly, which is a single nostril in the middle of the face
Cebocephaly, which is a small nose with a single nostril
Hypotelorism, which is a close-set or fused eyes
Anophthalmia or microphthalmia, which is the absence or small size of one or both eyes
Hypopituitarism, which is a deficiency of hormones produced by the pituitary gland, which can affect growth, metabolism, and sexual development
Diabetes insipidus, which is a disorder of water balance, causing excessive thirst and urination
The diagnosis of holoprosencephaly can be made before or after birth, based on the results of various tests and examinations. Some of the tests that can be used to diagnose or confirm holoprosencephaly are:
Ultrasound, which uses sound waves to produce images of the fetus in the womb, can detect holoprosencephaly as early as the first trimester of pregnancy.
The magnetic resonance imaging (MRI) scan generates detailed images of the brain and face using a strong magnetic field and radio waves. When ultrasound is inconclusive or unclear, MRI can provide additional information about the type and extent of holoprosencephaly.
For genetic testing, amniocentesis or chorionic villus sampling (CVS) involves taking samples of amniotic fluid or placental tissue. In addition to detecting mutations or chromosomal abnormalities associated with holoprosencephaly, these tests can also rule out other conditions that can produce similar symptoms.
Physical examination involves checking the baby's appearance and function after birth. Physical examination can confirm the severity of holoprosencephaly, as well as identify any complications or anomalies associated with it.
Holoprosencephaly has no cure, and treatment is mainly supportive and symptomatic. Treatment options depend on the type and severity of the condition, as well as the individual needs and preferences of the child.
It is possible to perform surgery to correct some of the facial defects, such as cleft lip or palate, or to relieve some of the brain pressure, such as placing a shunt to drain excess fluid. The child's appearance and quality of life can be improved by surgery, but it does not affect their brain development or function.
It is possible to control some of the symptoms with medication, such as seizures, infections, or hormonal imbalances. However, medication cannot prevent or reverse the damage to the brain.
The child can receive physical, occupational, speech, or behavioral therapy to develop their skills and abilities, such as motor, cognitive, language, or social skills. By receiving therapy, the child will be able to reach his or her full potential and improve self-esteem and independence.
A child and family may receive emotional, psychological, or practical support through counseling, education, or social services. In addition to helping the child and family cope with the challenges and the stress of living with holoprosencephaly, support can help them access resources and care.
There is no known way to prevent holoprosencephaly, as it is a complex condition that involves multiple factors. However, some measures that may help reduce the risk or the severity of holoprosencephaly are:
A prenatal care and genetic counseling program is recommended, especially if your family has a history of holoprosencephaly or other birth defects. Prenatal care can help monitor the health and the development of the fetus, and genetic counseling can help determine the chances and options of having a child with holoprosencephaly.
Avoiding harmful substances or infections during pregnancy, such as alcohol, drugs, mercury, rubella, or toxoplasmosis. The development of the brain and face can be hampered by these substances or infections, and holoprosencephaly or other complications can result.
Taking folic acid supplements before and during pregnancy, as recommended by the doctor. Folic acid plays a key role in the formation of the neural tube, the precursor to the brain and spinal cord. A deficiency of folic acid can result in neural tube defects, such as spina bifida and anencephaly, which are sometimes associated with holoprosencephaly as well.
