a single gene defect causes a clinically significant block in a metabolic pathway resulting either in accumulation of substrate behind the block or deficiency of the product IEM arises from a damaged gene which leads to abnormal enzyme. May be autosomal or sex-linked. May be recessive or dominant in expression. Heterozygote will have both normal and abnormal alleles. But homozygote will have two alleles the same on each chromosome. An accumulation of the substrate before the enzyme defect*. A decrease in the amount of the product is observed. An increased concentration of the alternative metabolites*. A decrease or absence of the enzyme activity. Screening for IEM who do not have the symptoms Investigations of the patient with symptoms of the IEM It is the process of detecting a patient with an IEM before they show overt symptoms of the disease. › Allow the treatment to begin › Counseling to be given Screening is done for high risk group which includes All newborn infants Family of affected children Expectant mothers who have history of affected children. (prenatal diagnosis) Suitable treatment for disease Life threatening disease High incidence of disease A suitable test is available Acceptable cost. › PKU › Congenital hypothyroidism Test to identify carriers of the disease Failure to thrive Poor feeding Persistent vomiting Unexplained jaundice Unexplained hypoglycemia Ketosis Lactic acidosis Convulsions and coma Lethargy Hypotonia hyperventilation Some may present later (within first few years) › Abnormal liver function tests › Mental retardation Front line tests Plasma › › › › › › Electrolytes Acid base balance Blood gases Glucose Liver function tests calcium Plasma › Insulin › Lactic acid › Ammonia › Ketones Urine › Amino acids › Organic acids › Sugars History of affected individual › Amniocentesis (15th week of gestation -20th week) fibroblast extracted from amniotic fluid. fibroblasts are cultured and specific enzyme studies are done Cvs (9th week completed within 10 days) › › › › DNA analysis (cystic fibrosis) Down syndrome Hemoglobinopathies Tay sachs disaease Autosomal recessive disorder 1 in 15,000 live births in America. Deficiency of phenylalanine hydroxylase Deficiency May be carried out in three stages: a. Diagnosis of Broad Category: Saudubray et al (2002)* suggested a battery of simple and routine tests for identification of the broad category of the disorders. These tests include plasma electrolytes, ABGs, blood ammonia and lactic acid etc. *Saudubray JM, Nasoogne MC, Lonlay PD, Touati G. Clinical approach to inherited metabolic disorders in neonates: an overview. Smin Neonatol 2002; 7: 3-15. May be carried out in three stages: b. Diagnosis of the exact disorder • It requires very sophisticated equipment e.g. HPLC, tandem mass spectrometry, GC-MS and ion exchange chromatography. May be carried out in three stages: b. Diagnosis of the exact disorder (cont) • These techniques also require elaborate infrastructure of trained manpower, proper back-up service for the instruments and regular supply of reagents. May be carried out in three stages: b. Diagnosis of the exact disorder (cont) • AKU hospital has taken an initiative to establish the first-ever lab in the country for the pin-point diagnosis of some of the IEM. May be carried out in three stages: c. Determination of deficient enzyme or protein Although a few laboratories in the world provide this facility, this is only of academic and research interest. Diagnosis of the genetic defect provides another promising pathway for some of these disorders.