ABSTRACT
The study comprised four cases; two cases of Marfan syndrome and two cases of homocystinuria. The studied cases with Marfan syndrome clinically presented with myopia, tall stature, mild joint laxity, scoliosis, long slender limbs and arachnodactyly. One case was familial with father affected while the other case was sporadic. The two cases of homocystinuria were from two different families with affected sibs and positive parental consanguinity. The two probands of homocystinuria presented mainly with ectopia lentis, mental retardation, kyphosis and thrombo - embolic manifestations were noted. Utrastructural studies of pulp and gingiva in the Marfan syndrome cases showed active fibroblast cells, collagen fibers with accumulation of precollagen material and increased elastic fibers which showed degenerative changes. In Homocystinuria we noted accumulation of finely granular and fibrillar material between elastic and collagen fibers and in the nerve endings. Few elastic and pre - elastic fibers were seen. The precollagen material formed meshwork of fine filaments and granules. Collagen fibers were twisted, frayed, fragmented, split with increased density. The normal periodicity of collagen was lost in many areas. We can conclude that gingival and pulpal biopsies could be a reflection of molecular differences in the two disorders