An inborn error of metabolism is a genetic error in which the production of a protein either is inhibited or gets altered in the body. This protein may also be an enzyme at times.
Enzymes are important in order to catalyse the reaction or metabolism to take place in our body. During the absence of an enzyme, the products do not get metabolised, accumulates and interferes with the functioning of other metabolic pathways within our body. These altered processes have adverse effects and might prove fatal at times.
Therefore, dietary and pharmaceutical management of these errors is to prevent the toxic accumulation of any metabolites in the body. In this article, we will understand some of the inborn errors of metabolism in which there is an inability to metabolise an amino acid, therefore, its dietary implication includes completely omitting or minimising the intake of such amino acid.
1. Phenylketonuria - Out of a total of nine amino acids, our body requires an amino acid called phenylalanine for new tissue synthesis. It also gets converted to another amino acid - tyrosine in the body, which is further utilised for our biochemical processes. For this conversion to take place, our body requires an enzyme called phenylalanine hydroxylase. Phenylketonuria inborn error is characterised by the impaired activity of this enzyme. Due to the lack of this enzyme, our body is unable to convert phenylalanine to tyrosine which causes its accumulation, eventually leading to brain damage. This error is generally seen among infants of 3-6 months, causes a delay in brain development, microcephaly, abnormal brain functioning and eczema. The transmission of neurotransmitters is also affected. This condition can be managed through diet and diet should contain foods low in phenylalanine amino acid. Opting for infant-formulas specifically formulated for this error is also a good alternative.
2. Tyrosinemia - This error occurs in two types - type I and II. In type I tyrosinemia, there is an impairment of an enzyme called fumarylacetoacetate hydrolase which is required for the breakdown of tyrosine. In type II tyrosinemia, the blood and urine concentration of tyrosine amino acid are abnormally high. People with this genetic disorder are prone to kidney damage, hypertension, liver disorders, vitamin D deficiency, corneal erosions and mental retardation. Dietary management includes consuming foods with low tyrosine and phenylalanine content. Foods like rice, bread, pasta, fruits, vegetables, potatoes, corn, peas and good fats should be used.
3. Maple Syrup Urine Disease (MSUD) - This genetic disorder is associated with the defect in the metabolism of branched-chain amino acids (BCAA) - leucine, isoleucine and valine. These amino acids are popularly used in the form of supplements by athletes and active people as BCAA are thought to promote muscle growth, minimise muscle damage, support recovery and enhance stamina. It occurs due to the deficiency of oxidative decarboxylase in the white blood cells. This blocks the removal of a carboxyl group and causes augmentation of BCAA leading to vomiting, lethargy, seizures, growth retardation and neurological impairment. The name of this error is due to the reason that the urine of people suffering from MSUD, smells like the odour of burnt maple syrup.
4. Homocystinuria - In this disorder, there is an error in the metabolism of amino acid - methionine. It occurs due to the deficiency of an enzyme cystathionine beta-synthase, which is needed for the conversion of homocysteine to cystathionine. This result in the accumulation of methionine and homocysteine. If left untreated, it can lead to skeletal disorders, osteoporosis, abnormal blood clotting and eye lens dislocation. Its dietary management includes administering doses of pyridoxine, folate and foods low in methionine like carrot, beetroot, tomatoes, brinjal, cabbage, lettuce, cucumber, onions, melons, apples, pears, berries, plums, peach, banana and mango.
5. Galactosemia - Galactosemia means the presence of galactose in the blood. This genetic error results from insufficiency to metabolise the sugar galactose due to the deficiency of any of these enzymes - galactokinase, Galactose-1-phosphate uridylyltransferase and galactose-4-epimerase. Patients with these disorders exhibit symptom of cataract, jaundice, liver cirrhosis, renal impairment, altered physical and mental growth. If left untreated, galactosemia might prove fatal. Dietary management includes avoiding foods containing galactose and lactose sugar.