- 1 in 20,000 births.
- Decreased interorbital diameter <5th percentile.
- Hypotelorism is part of the midline migration defects together with holophrosecephaly (which is almost always present). The degree of hypotelorism can be extreme as in cyclopia.
- Chromosomal abnormalities, mainly trisomy 13, are found in 50% of cases.
- Genetic syndromes are very frequent and the most common is Meckel-Gruber syndrome (autosomal recesive, lethal condition characterized by occipital encephalocele, multicystic kidneys and post-axial polydactyly).
- Detailed ultrasound examination, including neurosonography.
- Invasive testing for karyotyping and array.
- Follow-up should be standard.
- Standard obstetric care and delivery.
- Part of trisomy 13: lethal.
- Normal karyotype: high risk of neurodevelopmental delay depending on the degree of holoprosencephaly.
- Isolated: no increased risk.
- Part of trisomy 13: 1%.
- Part of an autosomal recessive condition: 25%.