Alobar holoprosencephaly is the most severe of the four types of holoprosencephaly, a condition in which the brain doesn’t properly divide into the left and right hemispheres. Holoprosencephaly can also affect the development of the face and head.
The four types of holoprosencephaly, in order of severity, are alobar, semi-lobar, lobar, and middle interhemispheric variant (MIHV). As a general rule, the severity of any facial defects will depend on the severity of the brain abnormality.
Alobar holoprosencephaly sufferers tend to have one central eye (cyclopia) and a nasal structure shaped like a tube (proboscis) located somewhere above the eye. The less severe forms tend to have only partially divided brains. Their eyes are typically set very close together on their faces.
Other symptoms of the disorder can include intellectual disability and problems with the pituitary gland. But, these conditions only arise if the infant survives, as severe cases often do not live for very long.
Holoprosencephaly can arise due to at least 14 different gene mutations, chromosomal abnormalities, or teratogens. Teratogens are substances that can cause birth defects if a pregnant mother comes into contact with them. It can also come about in tandem with other co-occurring genetic syndromes. In a lot of cases, the exact cause of the condition is unknown.
Life expectancy and treatment options depend on the severity of the condition.
Symptoms Of Alobar Holoprosencephaly
Alobar holoprosencephaly occurs when the brain completely fails to divide into the left and right hemispheres as it should. This causes the midline structures of the brain and face to never develop, along with a fusion of the cavities of the brain. These cavities are called the lateral and third ventricles, and they’re usually separated.
Facial symptoms typically include either cyclopia (a single eye), anophthalmia (absent eyes), or microphthalmia (unusually small eyes). Other possibilities include a tubular-shaped nose called a proboscis, hypotelorism (closely-spaced eyes), a cleft lip in the middle (median cleft lip) or a bilateral cleft lip on both sides.
In some uncommon cases, the face may look virtually the same as other infants. This occurs especially in those with mutations in the ZIC2 gene.
Other symptoms can include neural tube defects, hydrocephalus, seizures, a short stature, difficulties feeding, pituitary dysfunction, and an instability of the heart rate, temperature, and respiration rate.
Other Information About Alobar Holoprosencephaly
What is the prognosis for alobar holoprosencephaly?
The prognosis for the infant depends on the sub-type of holoprosencephaly. Alobar holoprosencephaly is the most severe form. Most infants with it are stillborn, die shortly after birth, or within the first 6 months.
However, those with less severe forms of holoprosencephaly, and a few children with the more severe form, can still survive past the age of 12 months.
More than 50% of children with lobar or semi-lobar holoprosencephaly (and without significant abnormalities of other organs) are still alive 12 months after birth.