Niemann: Pick's Disease Essay

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Niemann: Pick's Disease Niemann Pick disease consists of a group of genetic disorders in which the common feature is a varying degree of sphingomyelin storage in certain tissues of the body. According to the current classification based on the enzymatic defect underlying these disorders, two main groups are distinguished. The first group, which comprises type A, which is characterized by a severe deficiency in acid sphingomyelinase activity, includes infantile neuronopathic form; and type B, an adult chronic form without neurologic symptoms. In the second heterogeneous group called type C, neuro-visceral involvement is massive and lipid metabolism is affected. The sphingomyelin that accumulates in the lysosomes of the…show more content…
The reason for this significant difference in neurological involvement is not clear, but it may be consistent with the level of residual sphingomyelinase activity. Fibroblasts from normal individuals and patients with Niemann- Picks disease types A and B, synthesize the sphingomyelinase polypeptide having the same molecular mass 110 Kilo Daltons (KDa) and in the same degree of abundance, during further processing the 110 KDa polypeptide is processed to a lower molecular weight 84 KDa. Deficiency of sphingomyelinase is due to intragenic defects. Experiments done so far, suggest that specific defects could be small inframe deletions or additions or point mutations. The differences in clinical course of types A and B suggest that mutations are different. Sphingomyelinase follows the same intracellular targeting and post-translational processes as the majority of the lysosomal hydrolases. However, unlike any other enzyme there are two differently sized polypeptides which are differentially distributed in tissues. In tissues like brain the smaller polypeptide (molecular weight = 80 KDa) is found, whereas kidney contains both the polypeptides (110 and 80 KDa). There is no precise explanation for the occurrence of single differently sized polypeptides in some tissues, and the presence of both forms in tissues

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