Holoprosencephaly is a genetic disease affecting about 1 live birth every 10,000 worldwide. It affects the brain and presents 3 classical forms, with a gravity gradually greater. All three manifestations start from a defect in the separation of the cerebral hemispheres, but there is a strong clinical variability.

The three forms are:

• alobar holoprosencephaly. It is the most severe form of holoprosencephaly: the separation is completely absent and the thalami are fused. As a result the skull is smaller than average and roundish. Prenatal diagnosis is possible from the first trimester;
• Semilobar holoprosencephaly. The hemispheres are fused in the anterior area;
• lobar oloprosencephaly. This is the most difficult form to diagnose. The separation is almost complete, so the disease can go unnoticed during ultrasound.

In most cases, a correlation between disease severity and facial abnormalities is evident. The most severe form is often accompanied by craniofacial malformations. In the slightest form, however, the malformations are almost absent, even if there is a certain degree of mental retardation. Common symptoms are also motor deficit, food problems, epilepsy and endocrine disorders. Severe forms are often fatal due to brain malformations and associated defects.

Prenatal diagnosis usually occurs through ultrasound and imaging diagnostics. Current genetic tests are able to identify about 25% of the mutations related to the disease. The latter are especially recommended for women who have more than one risk factor, such as suspected familiarity and diabetes.
The prognosis of oloprosencephaly is variable and depends largely on the form of the disease and related complications.

Source: orpha.net