COMPARATIVE COST-ANALYSIS OF CYTOGENETIC AND MOLECULAR METHODS TO IDENTIFY GENETIC CAUSES OF MENTAL-RETARDATION

Mental retardation is sometimes due to chromosal abnormalities. Most f requent illnesses are Down syndrome and Fragile X syndrome. Using a co st analysis, we try to see what diagnosis method is the most relevant to find chromosomic causes for mental retardation in an institutionali zed male population. Two techniques are compared : cytogenetic techniq ue and molecular biology technique. Four diagnostic strategies are ide ntified. They all have the same effectiveness, but, costs vary. Result s depend on prevalence rates in the epidemiologic literature on Fragil e X syndrome and other chromosomic abnormalities. The least-cost diagn ostic strategy is molecular biology then constitutional caryotype in c ase of a negative result. This strategy costs about 600 FF1991 less co mpared with Fragile X caryotype and about 120 FF1991 less than when mo lecular biology is done in second, for fixed prevalence rates (i.e. Fr agile X prevalence rate between 4.5 and 10 % and other abnormalities b etween 2.2 and 25 %). Fragile X caryotype strategy has the highest cos t whatever the prevalence rates. Those results are discussed when intr oducing female population and delay to test results for prenatal diagn osis.