Cultivated skin fibroblasts from patients with I-cell disease and one patient's parents were investigated by light and electron microscopy. Abundant membrane-bound inclusions, apparently within lysosomes, were found in cultured skin fibroblasts obtained from both patients. Light and electron microscopy demonstrated that the inclusions were PAS positive, oil red O positive, metachromatic, and osmiophilic. The inclusions were comprised of multivesicular and pleomorphic membranes, as well as homogeneous electron dense and electron translucent material. Similar morphological abnormalities were noted occasionally in cells from the patient's father. These morphologic abnormalities, persisting after many cellular generations in vitro, appear to be characteristic features of the I-cell phenotype.
Hanai J, Leroy J, O'Brien JS. Ultrastructure of Cultured Fibroblasts in I-Cell Disease. Am J Dis Child. 1971;122(1):34-38. doi:10.1001/archpedi.1971.02110010070011