Rhythmic rocking, head-banging, incessant arm movements—so-called rhythmias or movement stereotypies—are observed in the majority of those who are severely and moderately severely impaired. These movements are maintained hour after hour without fatigue and may be accompanied by breathing sounds, squeals, and other exclamations. A number of them tend to be particularly common in certain forms of developmental delay: hand-flapping in autism, handwringing in Rett syndrome, and hand-waving in Down syndrome and other disorders. Self-stimulation, even hurtful—such as striking the forehead or ears or biting the fingers and forearms—seems to be compulsive or perhaps to provide some sort of satisfaction. It is not that these rhythmias are by themselves abnormal, for some of them occur for brief periods in normal babies, but that they persist. Nevertheless, many moderately delayed persons, when assigned to a simple task such as putting envelopes in a box, can continue this activity under supervision for several hours.
In the least-severe types of retardation, all the mental activities are intact but subnormal. The point to be made is that all aspects of intellectual life, personality, and deportment are affected in slightly differing degrees and that these effects have a neurologic basis. There is more than a hint that in particular diseases, because of their anatomy, the cognitive experience, affective life, and behavior are affected in special ways.
The group of moderately delayed, like the severely affected ones, is divisible into groups with somatic systemic and neurologic abnormalities, although the proportions are not the same. There are fewer of the dysmorphic type and more of the nondysmorphic, nonneurologic group.
Etiology of Severe Developmental Delay
From Table 37-1 it is obvious that many diseases can blight the development and maturation of the brain. Some of these are acquired and some are congenital and hereditary. Some affect all parts of the organism, giving rise to associated dermal, skeletal, and visceral abnormalities, while others affect only the nervous system in particular patterns. With respect especially to the milder degrees of developmental delay, in all populations thus far studied, infants of extremely low birth weight are more likely to have disabilities, brain abnormalities, and poorer language development and scholastic achievement (see Chap. 27). Mild developmental delay also tends to correlate with lower social status, which must relate in some manner to biological factors, as pointed out in the Scottish Low-Birthweight Study. Viral and spirochetal infections and parturitional accidents are other common causes. They act acutely and are theoretically preventable.
The factor of malnutrition during the fetal or infantile period of life as a cause of severe developmental delay has received considerable attention because it is a worldwide problem. Animal experiments by Winick and others demonstrated that severe undernutrition in early life leads to behavioral abnormalities and biochemical and morphologic changes in the brain, which may be permanent (see Chap. 40). Galler studied a group of infants in Barbados who were severely malnourished during the first year of life and then given an adequate diet. These children were followed to adulthood and compared with normally nourished siblings. No effect was observed on physical growth, but there were persistent attention deficits in 60 percent of the undernourished group and in only 15 percent of controls. The IQ scores of the former were also lower. Unfortunately, genetic factors could not be completely controlled for. In general, it may be said that the data showing developmental delay to be caused by malnutrition, while suggestive, are far from convincing.
Severe protein-calorie malnutrition in the first 8 months of life, which induces kwashiorkor, has been reported to retard mental development. However, such patients are said to regain mental function when fed. The authors have been impressed with the ability of the nervous system to withstand the effects of nutritional deficiency, perhaps better than any other organ.