Approaches to Classification of the Causation of Mental Retardation

Approaches to Classification of the Causation of Mental Retardation

The prevalence of diagnosable (using current techniques) bio-medical causes of mental retardation varies with the degree of the disability. When the retardation is severe, a prenatal cause can be identified in 59 to 73% of patients, but in mild mental retardation such a cause can be identified in only 23 to 43% of patients.

Table 24.1 illustrates the most commonly employed clas-sification system of the etiology of mental retardation. It reflects

both the timing and the type of the causative process which will affect the development and function of the CNS (Wilska and Kaski, 1999). The goal of the etiological assessment is to eluci-date the earliest developmental cause as well as other coexisting causative factors because their effects are usually interactive and cumulative (McLaren and Bryson, 1987)

Phenomenology and Variations in Presentation

The clinical presentation of persons with mental retardation is in-fluenced by multiple factors, which can be grossly divided into biological (such as syndromes underlying the retardation), psycho-logical (the level of the person’s intellectual and adaptive function-ing), and environmental (such as cultural expectations and services received). Their mutual relationship is illustrated in Figure 24.1.

The more severe the mental retardation, the earlier the child will come to medical attention because the developmen-tal delay will be obvious earlier, and associated physical impair-ments will be more prevalent. Conversely, children with mild mental retardation may not be diagnosed until they reach school age, when they fail in academic learning. If the sociocultural en-vironment does not value and stress early academic learning and early education is not available, mild mental retardation might go undetected, especially if the person has relatively good adap-tive skills. A false-positive diagnosis of mental retardation can also occur, especially if psychological tests are not sensitive to cultural background, and there is a language barrier between the child and the tester.

The importance of the earliest diagnosis possible cannot be overstated because the prognosis will be much better if the in-tervention which results from the diagnostic knowledge is begun as early as possible.