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Genetic prognosis in severe mental handicap
Insights
This study surveyed 698 children with severe mental handicap, finding a significant portion lacked a clear cause. Accurate diagnosis is crucial for effective genetic counseling and determining recurrence risks in families.
Area of Science:
- Medical Genetics
- Pediatrics
- Neurology
Background:
- Severe mental handicap affects a significant number of children.
- Understanding the etiology is vital for genetic prognosis and counseling.
- Previous studies highlighted the challenges in diagnosing the causes of mental retardation.
Purpose of the Study:
- To survey children with severe mental handicap for genetic prognosis.
- To determine the incidence of mental retardation in siblings of affected children.
- To emphasize the importance of etiological diagnosis for genetic counseling.
Main Methods:
- Survey of 698 children (under 16, IQ <50) admitted between 1956-1959.
- Categorization of cases by suspected etiology (environmental, Down's syndrome, genetic syndromes, hydrocephalus, unclassified).
- Tracing families of 660 children to assess sibling incidence of mental retardation.
Main Results:
- Etiological breakdown: 23.7% environmental, 50.9% unclassified, 16.2% Down's syndrome, 5.3% other genetic syndromes, 3.9% congenital hydrocephalus.
- Sibling incidence varied by etiology: 1.1% (environmental) to 11.5% (other genetic syndromes).
- A high proportion of cases remained without a definitive etiological diagnosis.
Conclusions:
- A significant proportion of severe mental handicap cases lack a clear etiological diagnosis.
- Accurate diagnosis is essential for providing reliable genetic counseling.
- Recurrence risk for unclassified cases, excluding specific familial patterns, is approximately 3%.
Abstract:
698 children below age sixteen years with severe mental handicap (below IQ50) who were admitted to hospital between 1956 and 1959 were surveyed for genetic prognosis. They were divided into 23.7% ascribed primarily to environmental factors, 50.9% unclassified aetiologically, 16.2% of Down's syndrome, 5.3% other genetic syndromes and 3.9% with congenital hydrocephalus. The incidence of a similar degree of mental retardation among the sibs of 660 whose families were traced, was 1.1% in the "environmental" group; 4.7% for the unclassified; 1.7% for Down's syndrome, 11.5% for other genetic syndromes and 4.3% for hydrocephalus with spina bifida. There were no affected sibs of the uncomplicated cases of congenital hydrocephalus. This survey underlines the fact that a high proportion of cases of mental handicap remain without aetiological diagnosis. It emphasises the value of such a diagnosis for genetic counselling. Advice given depends on the circumstances of the particular case which requires a detailed social history and sympathetic rapport by members of the team as well as appropriate clinical expertise (Kirman, 1971, 1972). When families with similarly affected new relative or previous severely mentally handicapped sibs are set aside, the recurrent risk for unclassified cases is reduced to three per cent.