Environmental factors may trigger the onset and severity of disease. It also depends upon the degree of accumulation of toxic substances before the metabolic block. Age of clinical presentation varies from child to child and the form of presentation is also variable according to age. There is no sex difference reported in the incidence of IMD. In one of the earlier studies in India, biochemical screening of 4400 cases of mental retardation revealed that 5.75% (256 cases) were due to various inherited metabolic disorders. India is a country with a very high birth-rate and the number of children born with IMD is also very high making it a problem of tremendous importance. There is an accelerating demographic switch from communicable diseases to genetic disorders. OADs were seen in some Western countries, for example in North Carolina, as reported by Frazier et al. There are also other studies which report a higher prevalence of OAD in India (Please see details mentioned below). In our previous paper, we have showed that organic acidurias (OAD) are quite common in our part of the world. However organic acidurias are comparatively rare in UK, USA and other Western countries. PKU is very common in USA, China, Taiwan, Turkey, Ireland, Italy, UK, British Columbia and other parts of Europe, whereas it is rare in India. In Western countries, aminoacidurias, especially phenylketonuria, are the most common IMD. Several studies have pointed out the main clinical and laboratory characteristics that lead to the suspicion of inborn error of metabolism especially OAD in critically ill children. Although individually rare, the conjunct frequency of OAD in preselected high-risk group may be up to 200 times higher than that identified in the general population. It is now known that along with amino acidurias, organic acidurias form the most important class of IMD in high-risk population and among severely-ill children. It leads to accumulation of organic acids in tissues and their subsequent excretion in urine. Organic acidurias (Organic acid disorders, OADs) are an important class of inherited metabolic disorders (IMD) arising due to defect in intermediary metabolic pathways of carbohydrate, amino acids and fatty acid oxidation.
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