Molecular Characterization of Inherited Skeletal Deformities in Pakistani Families

Abstract

Genetic disorders of the skeleton are a large and heterogeneous group of diseases whose unifying features are malformation, disproportionate grO\vth, and deformation of the skeleton or of individual bones or a gro up of bones. Clini cal severity differs between individual, ranging from minor handi cap to death in the neonatal period. Both genetic and environmental factors contribute to the etiology of ske letal disorders. The genetic factor is mostly due to single gene mutation. More than 6000 human genetic diseases are caused by a mutation in a single gene resulting in a disorder that can be inherited through generations. Over 300 genetic conditions involve problems with the growth and development of the skeleton. To date, no data is available about the genetic contribution to skeletal deformities in Pakistani population . The consanguineous marri age pattern has sign ifi cant impli cati on for increased rate of recessive genetic disorders. Autosomal recessive diseases are more prevalent in endogenous and iso lated populations. Pakistan represents a true treasure for mol ecul ar dissection of geneti c disorder because 60% marrI ages are consanguineous and out of those approximately 80% are between first cousins. Present study was conducted to detect pathogenic variants in genes underlying skeletal deformiti es in Pakistani families. Three skeletal disorder famil ies (SD-1 , SD14 and SO-26), segregating as autosomal recessive, were identifi ed from Charsada District. Skeletal disorder family (SD-l) has the phenotype of club foot, characteri zed by medial rotation, inclined inward and pointed downward. Skeletal disorder- 14 (SD14) and skeletal disorder-26 (SD-26) families were dwarf, and was characterized by proportionate short strature. Genomic DNA was extracted using standard phenol/Chloroform extraction method. Conventional iinkage analysis was performed using mi erosatellie markers to refine the critical region and to identify the disease causing gene. WNT7A gene located on chromosome 3p2S, P1TXI gene located on chromosome Sq3 1 and Gli 3 gene on chromosome 7p 13 was excluded by genotyping tightly linked microsatellite markers in skeletal disorder- 1 (SD-1 ) famil y. Skeletal disorder family (SD- 14), was linked to mi crosatellite markers 01 7S944 (90.9 1cM), D17S 1290 (87.7ScM) and D17S792 (87 .7ScM) in the GHI gene interval. The exoni c sequences of the candidate gene (GHI ) were analyzed by direct sequenc ing, but no pathogenic mutation was detected . So it was concl uded that the VII mutation may be present in the promoter region of the GHl gene. The third skeletal disorder family (SD-26), showed linkage to microsatellite markers 07S2564 (42.92 cM), D7S22 52 (50.85 cM) and 07S817 (50.85 cM), ti ghtl y linked to GHRHR gene located on chromosome 7p1 4. So it is suggested that GHRHR gene will be sequenced for the purpose to find any pathogeni c variant involve in the disease.