Mental Retardation ; Molecular Cytogenetic Techniques Used for Diagnosis ; a Literature Survey

INTRODUCTION the chromosomes of the probands by investigating Mental retardation (MR) affects approximately 1-3 % of chromosome numbers and or chromosomal the general population in the United States (Higgins et abnormalities. If karyotype is normal then fragile X al., 2004) but this figure would be higher in developing testing is performed. Afterward, on the basis of clinical countries because of high rate of consanguinity. evaluation, chromosome analysis and fragile X 3 screening results, copy number analysis, microdeletions Prevalence of MR in male is higher (30% excess than and duplications analysis, inversion and translocation female with a 1.4-1.6:1 ratio of affected male to female mapping, homozygosity and linkage analysis for and this is mainly because of X specific MR genes and 4 mutations in the responsible genes are carried out. There presence of single X chromosome . Intellectual or are varieties of cytogenetic techniques for screening of cognitive functioning of an individual can be assess by whole genome to look for the aberration. These include ‘‘Intelligence Quotient’’ (IQ) so on the basis of IQ score conventional and spectral karytyping, interphase FISH, mental retardation is subcategorized as. comparative genomic hybridization (CGH), primed in situ Ÿ Mild (IQ level: 50-55 to 70), labeling (PRINS), multiplex amplifiable probe Ÿ Moderate (IQ level:35-40 to 50-55), 5 hybridization (MAPH), chromosome microdissection, Ÿ Severe (IQ level:20-25 to 35-40) and microarray. Ÿ Profound (IQ level: below 20-25) (American Psychiatric Association, fourth edition and 6 Conventional Karyotyping ICD-10 classification . This technique is used for assessing the number and appearance of chromosomes in a cell. In this Molecular cytogenetics is the combination of molecular methodology, size, position of centromere, differences biology and cytogenetics. Their utility has increased the between sex chromosomes and other characteristics are resolution and diagnostic utility in the field of MR. A considered and the result is presented in the standard number of cytogenetic techniques and their advanced format termed as karyogram or ideogram. During version are introduced every year. The prime and initial karyotyping the chromosomes are visualized by different step of molecular diagnosis is karyotyping i.e analysis of staining methodologies G-banding followed by digestion MENTAL RETARDATION; MOLECULAR CYTOGENETIC TECHNIQUES USED FOR DIAGNOSIS; A LITERATURE SURVEY