- 1 in 10,000 births.
- There is a spectrum of midline abnormalities of the nose in association with holoprosencephaly, including: arhinia (complete absence of the nasal structures), proboscis (soft tissue appendage projecting from just below the forehead) and single nostril (usually central).
- Chromosomal abnormalities, mainly trisomy 13, are found in 40% of cases.
- Holoprosencephaly in all cases. Genetic syndromes are found in 20% of cases.
- Detailed ultrasound examination, including neurosonography.
- Invasive testing for karyotyping and array.
- If pregnancy continues, follow-up should be standard.
- Standard obstetric care and delivery.
- Very poor due to the associated holoprosencephaly and chromosomal abnormalities.
- Isolated: 6%
- Part of trisomy 13: 1%
- Part of genetic syndromes: 25% to 50%.