Final answer:
Severe symptoms of holoprosencephaly include cyclopia with proboscis, midfacial clefts including cleft palate, severe cognitive impairment, and a range of abnormal facial features.
Step-by-step explanation:
The severe symptoms of holoprosencephaly include various developmental delays and phenotypic effects due to the abnormal development of the brain. Some of the critical symptoms are:
- Cyclopia (one eye) and a primitive nasal structure (proboscis), which are significant indicators of severe holoprosencephaly.
- Midfacial clefts, including cleft palate and sometimes cleft lip, stemming from a failure in the fusion of facial structures during embryonic development.
- Severe cognitive impairment can be a consequence of improper brain development and may occur alongside other symptoms.
- Abnormal facial features that can include below-average head circumference, smaller eye openings, low nasal bridge, and smaller midface size.
These symptoms significantly affect individuals both physically and cognitively, often requiring specialized care and interventions.