![]() ![]() The life expectancy of these affected individuals varies depending on the severity of symptoms. In the less severe forms, the brain is partially divided and the eyes are usually set close together (hypotelorism). Most babies with severe nonsyndromic holoprosencephaly die before birth or soon after. These affected individuals have one central eye (cyclopia) and a tubular nasal structure (proboscis) located above the eye. In the most severe forms of nonsyndromic holoprosencephaly, the brain does not divide at all. From most to least severe, the types are known as alobar, semi-lobar, lobar, and middle interhemispheric variant (MIHV). Nonsyndromic holoprosencephaly can be grouped into four types according to the degree of brain division. The severity of nonsyndromic holoprosencephaly varies widely among affected individuals, even within the same family. ![]() This condition is called nonsyndromic to distinguish it from other types of holoprosencephaly caused by genetic syndromes, chromosome abnormalities, or substances that cause birth defects (teratogens). Holoprosencephaly occurs when the brain fails to divide properly into the right and left hemispheres. Normally, the brain divides into two halves ( hemispheres ) during early development. Nonsyndromic holoprosencephaly is an abnormality of brain development that also affects the head and face. ![]()
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