Mental retardation (MR) is one of the main causes of handicap among children and young people, with a prevalence of about 2–3% in general population. However, despite extensive investigations most persons with MR do not have accurate genetic diagnosis. Mutations in X-linked genes have long been considered to be an important cause of MR, proceeding from the observation that MR is 30–50% more common in males than in females; furthermore, compared with the autosomes, the X chromosome contains a significantly higher number of genes that, when mutated, cause mental impairment. This article presents a short summary of the most frequent X-linked MR syndromes: fragile X, Rett, Coffin-Lowry, Aarskog-Scott, ATR-X, West, and Partington syndrome, X-linked infantile spasms or other forms of epilepsy, Xlinked cleft-lip-palate and L1CAM gene mutation. Also, we present already known correlations of autism with X-linked MR. Large changes in DNA are usually detected with regular cytogenetic analysis, but for detecting small aberrations, more sensitive methods are needed. It is very important for clinical genetic diagnostics and for human genetic research to develop new methods that are sufficiently sensitive and flexible to detect small (<3Mb) chromosomal mutations. At present, several techniques are available for detecting copy number changes of various sizes, each with limitations in resolution and cost.
The methodology developed by us, called array multiplex amplifiable probe hybridization (array-MAPH), allows accurate and reliable determination of changes in copy number in complex genomes, certain chromosomes or loci. Array-MAPH is the result of further development of the principle of MAPH, a relatively simple method based on hybridization and PCR. The purpose of our study is to screen Estonian people with familial MR using array-MAPH.