perinatal insults, acquired childhood disease, and environmental and social factors (Table 10-7). Mild MR correlates with socioeconomic status, although profound MR does not. Although a single organic cause may be found, each individual’s performance should be considered a function of theinteraction of environmental influences with the individual’s organic substrate. Behavioral difficulties resulting from the MRitself and from the family’s reaction to the child and the condition are common. More severe forms of MR can be traced to biologic factors. The earlier the cognitive slowing is recognized,the more severe the deviation from normal is likely to be.
The first step in the diagnosis and management of a child with MR is to identify functional strengths and weaknesses for purposes of medical and habilitative therapies. A history and physical examination may suggest a diagnostic approach that, then, may be confirmed by laboratory testing and/or imaging. Frequently used laboratory tests include chromosomal analysis and magnetic resonance imaging of the brain. Almost one third of individuals with MR do not have readily identifiable reasons for their disability.
Significant visual impairment is a problem in many children. Partial vision (defined as visual acuity between 20/70 and 20/200) occurs in 1 in 500 school-age children in the United States. Legal blindness is defined as distant visual acuity of 20/200 or worse and affects about 35,000 children in the United States. Such impairment can be a major barrier to optimal development.
The most common cause of severe visual impairment in children is retinopathy of prematurity (see Chapter 61). Congenital cataracts may lead to significant amblyopia. Cataracts also are associated with other ocular abnormalities and developmental disabilities. Amblyopia is a pathologic alteration of the visual system characterized by a reduction in visual acuity in one or both eyes with no clinically apparent organic abnormality that completely accounts for the visual loss. Amblyopia is due to a distortion of the normal clearly formed retinal image (from congenital cataracts or severe refractive errors); abnormal binocular interaction between the eyes as one eye competitively inhibits the other (strabismus); or a combination of both mechanisms. Albinism, hydrocephalus, congenital cytomegalovirus infection, and birth asphyxia are other significant contributors to blindness in children.
Sporadic events affecting embryogenesis, usually a stable developmental challenge Chromosomal changes (e.g., trisomy 21 syndrome)
Prenatal influences (e.g., substance abuse, teratogenic medications, intrauterine TORCH infections) †
No definite issue is identified, or multiple elements present, none of which is diagnostic (may be multifactorial)
Dynamic influences, commonly associated with other challenges Deprivation (neglect) Parental mental illness Environmental intoxications (e.g., significant lead intoxication)*
Impingement on normal intrauterine development or delivery; neurologic abnormalities frequent, challenges are stable or occasionally worsening
Perinatal complications (e.g., prematurity, birth asphyxia, birth trauma)
Preconceptual origin, variable expression in the individual infant, multiple somatic effects, frequently a progressive or degenerative course
Inborn errors of metabolism (e.g., Tay-Sachs disease, Hunter disease, phenylketonuria)
Single-gene abnormalities (e.g., neurofibromatosis or tuberous sclerosis)
Other chromosomal aberrations (e.g., fragile X syndrome, deletion mutations such as Prader-Willi syndrome)
Acute modification of developmental status, variable potential for functional recovery Infections (all can ultimately lead to brain damage, but most significant are encephalitis and meningitis)
Cranial trauma (accidental and child abuse) Accidents (e.g., near-drowning, electrocution) Environmental intoxications (prototype is lead poisoning)