ABSTRACT. This article reviews causes of cognitive impairment in children with a focus on those in developing countries. The number of children with cognitive limitations is increasing, and for the majority there is little access to professional expertise. Causes include malnutrition, genetic diseases, infectious diseases such as meningitis, parasites, and cerebral malaria, in utero drug and alcohol exposure, newborn asphyxia, low birth weight, head injuries, and endocrine disorders. Many of these are preventable; however, resources for prevention are limited in most developing areas of the world. The challenge for this century is to encourage community leaders and government officials to take on the prevention of cognitive impairment as the highest priority for society. This article proposes that specialists in child behavior and development work with United Nations agencies to develop a “world cognitive impairment watch” to assess and assist each country annually in terms of risk factors, prevention programs, and early intervention programs.
There is much publicity about the HIV/AIDS epidemic that is worsening in many parts of the world, 1 the spread of tuberculosis in association with the HIV/AIDS epidemic, 2 the increasing numbers of disasters, 3 and the hazards of anthrax. In terms of sheer numbers, the epidemic of neurodevelopmental insults affecting children and adults exceeds the total of these problems. This epidemic is escalating as the result of increasing population numbers, higher survival rates of children (who are surviving diseases or conditions that compromise brain development and that lead to cognitive sequelae), and limited resources for helping affected individuals. Given a world population of approximately 6.5 billion, of whom 5.3 billion live in developing countries, where half the population is aged less than 15 years, the estimated number of children with cognitive limitations is approximately 780 million. This includes 130 million children with impairments resulting from severe malnutrition in the first year of life (5% of all children living in developing countries), 260 million suffering iron-deficiency anemia in the first 2 years of life (10% of all children living in developing countries), 260 million with severe parasitic infections (10% of all children living in developing countries), and 130 million with other conditions causing brain impairment, including genetic and metabolic diseases. This is probably a low estimate, given estimates in the United States that at least 10% of children have learning disabilities and/or mental retardation. 4 In developing countries, there may be many more children at risk for cognitive impairments. An example of this might be those children who experienced 1 year of moderate malnutrition with associated iron-deficiency anemia as the result of hookworm disease or who experienced a combination of low birth weight (LBW) and iron-deficiency anemia. In the majority of countries, precise data are lacking regarding the incidence and prevalence of most child health problems, including cognitive and learning impairments. It is likely that conditions compromising brain development cause considerable lost human potential in the societies that can least absorb this loss. Not only may children have various brain insults leading to difficulties in information processing, but many live in environmental conditions that compound their limitations. Furthermore, for most children in the world, there is little access to professional expertise (i.e., teachers or child health specialists) to assist children who suffer cognitive impairment.
In the United States, the number of child behavior and development specialists, including child psychologists, behavioral-developmental pediatricians, and child psychiatrists, is approximately 8000. This amounts to one specialist for every 8500 children aged less than 18 years. Compare this with Uganda, where, in 2002, there were two child psychologists, no child psychiatrists, and no behavioral-developmental pediatricians for a population of 10 million children. In Saudi Arabia there is one behavioral pediatrician. In Laos and Afghanistan there are no child psychologists, no child psychiatrists, no behavioral pediatricians, and no special education programs. This is the norm in many developing countries where there is little recognition that some diseases, which affect children in the early years of life, may have long-term negative effects in terms of brain function.
This article reviews causes of cognitive impairment with a special focus on developing countries. Causes will be discussed in terms of specific conditions (Table 1) and environments or situations (Table 2) that put children at greater risk for some of those specific conditions. The brain insults may lead to specific learning disabilities, mental retardation, attentional problems, and/or problems with executive function. These problems may be manifested before and/or during the school years. This review also focuses on the implications of cause and prevalence data related to interventions and research needs.
Many of the hazards to early brain development are well known. They include head injury, newborn asphyxia, infections of the brain that occur in utero and in the first years of life, genetic defects, head injuries, lead poisoning, and malnutrition. More recently, the negative effects on the brain of micronutrient deficiencies such as iodine or iron deficiencies, genetic disorders such as fragile X syndrome, phenylketonuria (PKU), or myotonic dystrophy, HIV infection, hypoxia related to congenital heart disease, prenatal use of drugs and alcohol, sickle cell-related strokes, and late effects of chemotherapeutic agents used in treatment of childhood malignancies have been recognized. How any given society identifies causes or outcomes from early brain insults and how it copes with them may vary according to culture, availability of child health specialists, diagnostic resources, educational systems, and financial resources.