Mental retardation, now called as intellectual disability is neuropsychiatric disorder which may be present in children and newly youths. It is more common in males then in females because it is due to mutation in numerous genes on X chromosome. The male female ratio may be 1.3-1.9: 1.3. The affected individual often shows speech delay, slow performance and behavioral problems in them. The diagnosis of the MR/ID can be properly done before 18 years. The affected person of mental retardation has IQ level less than or equal to 70. The individuals affected with intellectual disability may be recognized by the certain characteristics like less performance at school, inability to take care of oneself and also showing inability to ensure self-safety. The IQ greater than 85 is considered as normal while individual IQ level b/w 71 to 84 is at border line. IQ level is more suitable for children having age more than 5 years. Despite more developments in investigation methods the etiological studies of mental retardation remain unclear in 30-50% cases. Mental retardation can be prenatal or postnatal. Less IQ level show more severity of the disease and vice versa. Mental retardation can be divided into four major types which can be described in the following lines to differentiate them from one another. Mild mental retardation is one in which affected person have IQ level 50-55 to 70, moderate MR/ID, IQ level is 35-40 to 50-55, severe intellectual disability or MR, IQ level is 20-25 to 35-40 while it is recommended that individual will be considered patient of profound mental retardation if his/her IQ level is lower than 20-25. The common causes of MR/ID may be chromosomal disorders, acquired CNS infections, fetal exposure to radiations, in October 2013 some 1149 genetic disorders have been identified to be associated with MR/ID. In this study four families from different areas of Baluchistan have been selected with two affected individuals ranging in age from 7-26 years. Pedigrees were drawn by the usage of Cyrillic software along with tests and blood samples were collected, DNA extraction was carried out by inorganic method. DNA was amplified by Polymerase Chain Reaction (PCR). DNA sequencing was done to confirm any genetic defect in selected families. Bioinformatics tools like BioEdit and SeqMan was used for the sequence analysis of gene TM4SF20 to check any mutation in selected families, but no mutation in the selected families was found and it was concluded that there may be any other candidate gene responsible for mutation resulting in mental retardation in affected families.