The strength of association between fragile (X) chromosome presence and mental retardation

Area of Science:

• Genetics
• Medical Genetics
• Human Genetics

Background:

• The fragile X chromosome (fra(X)) is a known genetic marker associated with intellectual disability.
• Previous studies suggested a correlation between fra(X) and mental retardation (MR), but quantitative estimates were needed.

Purpose of the Study:

• To quantitatively assess the association between the fragile X chromosome (fra(X)) and mental retardation (MR).
• To evaluate the probability of fra(X) presence in both non-retarded and MR males.
• To determine the utility of fra(X) detection in prenatal diagnosis for families with a history of fra(X)-linked MR.

Main Methods:

• Analysis of existing data from male populations, categorized by intellectual status (retarded vs. non-retarded).
• Statistical evaluation of incidence rates of fra(X) in different groups.
• Examination of family data exhibiting a pattern of fra(X)-linked MR.

Main Results:

• The fragile X chromosome (fra(X)) occurs significantly less frequently in non-retarded males compared to males with mental retardation (MR).
• Despite this, existing data suggested a possibility of non-retarded males carrying fra(X).
• In families with fra(X)-linked MR, the probability of non-retarded male offspring having fra(X) was very low, while the probability for MR male offspring was very high.

Conclusions:

• The presence of the fragile X chromosome (fra(X)) is a strong indicator for mental retardation (MR).
• Prenatal diagnosis of fra(X) can provide accurate prognostic information, particularly in families with a known history of fra(X)-linked MR.