Mental retardation of unknown origin in male family members, related to each other via the female line.
X-Linked Mental Retardation, XLMR
Clinical Features
A prevalence of approximately 3% is reported for mental retardation. In about 25 to 35%, mental retardation is caused by genetic defects. Among them, most (5 – 18%) of the cases are caused by X-linked mental retardation which preferably affects males and which is caused by the fragile X syndrome in 15 to 20%. In the remainder of cases, syndromic and non-syndromic forms of X-linked retardation are known. Typical dysmorphic features are found in all affected family members in the syndromic forms. Family members affected by the non-syndromic forms do not show further dysmorphic features or neurological symptoms besides mental retardation. X-linked mental retardation should be considered if, consistent with X-linked inheritance, at least two family members are affected. The diagnostic procedures have to be discussed individually.
Genetic Information
X-linked mental retardation is caused by a large number of different genetic defects on the X chromosome.
Prevalence
1 : 500 in men
Diagnostic
Indication
Method
Linkage analysis using polymorphic microsatellite markers on the X chromosome. Blood samples of as many affected and non-affected family members as possible are required.
Sample Requirement
2 - 4 ml of EDTA blood
Duration
Depending on family size, upon agreement