Nov 14 2004
Numerous studies have documented IQ deficits in children with fetal alcohol syndrome (FAS). Little research, however, has found IQ deficits in children with alcohol-related neurodevelopmental disorder (ARND), who generally exhibit less severe neurobehavioral deficits than children with FAS.
A study in the November issue of Alcoholism: Clinical & Experimental Research examines the relationship between selected variables and prenatal alcohol exposure on subsequent IQ. Results indicate that maternal age and first-trimester drinking by mothers with a history of drinking problems can have substantial effects on IQ.
"FAS is characterized by growth retardation, central nervous system impairment, and a distinctive pattern of craniofacial anomalies," said Sandra W. Jacobson, a professor in the department of psychiatry and behavioral neurosciences at Wayne State University School of Medicine, and first author of the study. "ARND refers to nonsyndromal individuals with confirmed heavy prenatal alcohol exposure who exhibit measurable, but generally subtler neurobehavioral deficits than those seen with FAS. Whereas FAS is well established and easier to diagnose, it is not generally recognized that a child can be adversely affected by prenatal alcohol exposure without the characteristic facial features and growth deficits. Nonetheless, alcohol-exposed children with attention deficits or poor social judgment who lack the pattern of facial dysmorphic features may suffer from a similar set of problems that interfere with their academic and social performance."
"There is as of yet little public awareness or understanding of the behavioral teratologic sequelae of fetal alcohol exposure, such as the cognitive deficits found here in children who do not exhibit the physical markers of FAS," concurred Lynn T. Singer, Deputy Provost and Vice President for Academic Programs at Case Western Reserve University. "This study is seminal in that it demonstrates that what was interpreted in prior studies as a lack of any IQ effects in nonsyndromal, alcohol-exposed children was really due to a differential effect of exposure related to several risk/protective factors studied by these researchers."
"The incidence and severity of FAS and ARND vary considerably among children with similar prenatal exposures," added Jacobson. "Despite extensive interest in the differential susceptibility attributed to influences ranging from genetic predisposition to nutritional inadequacy, there has been relatively little systematic empirical investigation of the factors that may determine which children are affected."
Researchers administered the Wechsler Intelligence Scales for Children-III (WISC-III) to 337 inner-city African American children at 7.5 years of age whose mothers were recruited prenatally. (The WISC-III is the most commonly used standardized test of IQ administered to children ages 6 - 17 years.) Alcohol exposure was assessed using a timeline, follow-back interview that was administered to the mothers at every prenatal clinic visit. Numerous potential confounding variables were examined, including maternal education and IQ, smoking and illicit drug use, quality of parenting, maternal depression and psychopathology, and current maternal drinking. Researchers also used the Michigan Alcoholism Screening Test (MAST) to assess severity of psychosocial and physical alcohol-related problems.
"This study is the first to demonstrate substantial effects on IQ among children with ARND born to older or MAST-positive mothers, particularly in relation to first trimester drinking," said Jacobson. "When we looked specifically at the children born to women 30 years or older, we found an alcohol effect on Full Scale IQ and five of the seven composite IQ scores. Similarly, we found IQ effects in children born to MAST-positive mothers. For every two additional drinks consumed by the mother per day during pregnancy, we found a three-point decrease in Full Scale IQ and a five and a half point decrement on Freedom from Distractibility. These findings suggest that there are subgroups of more vulnerable and severely affected children with ARND, whose IQ scores and performance are compromised."
"Prior to this study," said Singer, "we had been unable to explain why children with similar prenatal alcohol exposure levels vary so much in the incidence and severity of negative outcomes, such as lower IQ and learning problems. This study shows that the wide variability in child outcomes is related to the fact that some children are more susceptible than others to the effects of alcohol exposure, namely, those whose mothers are older than 30 years, those whose mothers have alcohol dependence, those whose parents provide a less stimulating environment, and those whose mothers reported drinking during the time of conception. In fact, for those children, even when they do not have FAS, there are strongly negative effects of alcohol exposure on verbal IQ and working memory, both important for learning and school success."
Both Jacobson and Singer noted that one very important implication of these findings is that a moderate-to-heavy drinking mother who has given birth to an unaffected child when she was younger needs to be warned that, if she drinks while pregnant, her risk of having an adversely affected child increases as she grows older. This risk is also greater if she has a long-term drinking problem. "Women in these high-risk groups should be urged to abstain from drinking before becoming pregnant," said Jacobson.
Jacobson said that her group's future research will attempt to identify the underlying neural substrates that mediate the effects of alcohol exposure on behavior. "For example, we are beginning to study effects of alcohol exposure on components of arithmetic and number processing which have been linked to specific brain regions," she said. "We plan to use innovative neuroimaging procedures to help target when and where the damage occurs. By also identifying critical moderators of the relation between alcohol exposure and outcome, we hope to improve the ability to identify affected individuals and thus better understand the specific damage and mechanism by which this damage occurs. We have also collected data on a genetic polymorphism involved in maternal alcohol metabolism that appears to protect some children from the adverse effects of fetal alcohol exposure. Ultimately, the goal is to improve diagnosis and treatment of the full range of FASD and better identify women at high risk of having children with FASD."