A congenital anomaly is something unusual or different present at birth. Minor anomalies have no serious medical or cosmetic consequences, while major anomalies like cleft lip are of serious consequence. Mental retardation refers to below-average intelligence and adaptive functioning difficulties. It can be caused by infections, genetic or chromosomal abnormalities, trauma, malnutrition or toxic exposure. While impairments limit functioning, disabilities interfere with abilities, and handicaps disadvantage due to disabilities in adjusting to environments.