Prenatal Etiology

Genetic factors have been shown to be one of the most common causes of mental retardation. Chromosomal abnormalities are either heritable mutations or variations of genetic material. Advances in medical technology have furthered our knowledge of the role of genetic transmission of many conditions, including mental retardation. Chromosomal abnormalities may involve either single gene disorders (autosomal-dominant syndromes or autosomal-recessive syndromes) or disorders of the sex chromosomes. Chromosomal disorders that can lead to varying degrees of mental retardation and other cognitive and behavioral characteristics include phenylketonuria (PKU), Turner's syndrome, Lesch-Nylan syndrome, Tay-Sachs disease, maple syrup urine disease, cri du chat syndrome, and Klinefelter syndrome.

Numerous agents can have significant deleterious effects on the fragile central nervous system of a child in utero. Such teratogens are nongenetic, nonchromosomal agents that are major causes of mental sub-normality. These include poor nutrition, toxic substances, maternal disease or infection, blood incompatibility, drugs and alcohol exposure, and cigarettes.

For example, maternal alcohol abuse during pregnancy can result in fetal alcohol syndrome (FAS) or fetal alcohol effects (FAE). The dangers of ingestion of alcohol during pregnancy have been well-known for years. The teratogenic effects of alcohol and other illicit substances impact the developing, vulnerable brain and cause an interruption in the developmental stages of the body organs, most often the central nervous system. If a child meets all diagnostic criteria, as discussed later, he or she is said to have FAS. A child whose mother drank with some moderation during pregnancy, however, may have a typical physical appearance and milder cognitive impairments with accompanied learning and behavioral problems. Such a child would be noted to have FAE.

The prevalence of FAS is not known; however, it is clearly one of the major causes of mental retardation in the United States. It is estimated that 5000 children are born in the United States with FAS each year, with rates of 1-3 cases of FAS per 1000 births. As a whole, alcohol ingestion while a woman is pregnant has been associated with a spectrum of physical and neurode-velopmental effects on the developing child. The criteria for a diagnosis of FAS include pre- and postnatal growth retardation (e.g., low birth weight), central nervous system abnormalities (e.g., mental retardation), and craniofacial malformations (e.g., microcephaly).

Specifically, 80% of children with FAS are born low birth weight, 70% have feeding problems as infants, and most of the children are thin and short in stature. Characteristic physical features include microcephaly, widely space eyes with narrow eyelids, short and upturned noses, thin upper lips, large low-set ears, and a flattened philtrum. Vision problems, such as strabismus or nystagmus, also may be present. In addition to the noted physical and cognitive abnormalities, about two-thirds of children with FAS manifest significant behavioral and emotional problems, including oppo-sitional and defiant behaviors, inappropriate response to social cues, social withdrawal, mood instability, and other overt (e.g., aggression) and covert (e.g., lying and stealing) psychopathology.

Alcohol No More

Alcohol No More

Do you love a drink from time to time? A lot of us do, often when socializing with acquaintances and loved ones. Drinking may be beneficial or harmful, depending upon your age and health status, and, naturally, how much you drink.

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