Summary of Phenylketonuria
Phenylketonuria (PKU) is an uncommon inherited genetic disorder that results from the reduced metabolism of the amino acid called phenylalanine, causing a high build up the amino acid in the body. The disease arises from a mutation of the gene that helps in creating the enzyme (phenylalanine hydroxylase, PAH) necessary for the breakdown of the phenylalanine. The disorder can lead to several problems like intellectual disability, mental disorders, seizures, and behavioral problems if not treated. The disease is autosomal recessive, that is, both the copies of the genes must be mutated to develop the condition. The disease is in two different types, variant PKU and classic PKU, depending on if the enzyme of the function remains. The patients with a single mutation of the gene do not have symptoms.
When the patients with phenylketonuria eat foods containing proteins or aspartame, artificial sweetener, the phenylalanine will build up to a dangerous level, which can cause health complications. Patients for the rest of their lives are mandated to follow a diet that restricts the level of phenylalanine mostly found in pretentious foods. The screening for phenylketonuria happens at birth in hospitals in various countries. Identification of the disease from the onset will be advantageous in controlling it. However, due to the palatability of the diet, there are significant issues with nutritional compliance. Several factors are associated with dietetic therapy, including dietary deficiencies in vitamin D and B12 majorly (Al Hafid & Christodoulou, 2015). There are other methods including the practice of large neutral amino acids and glycomacrpeptides, gene therapy, and enzyme replacement or substitution therapy.
The diet for the PKU patient should include the phenylalanine free medical formula, which is said to be the low phenylalanine food pattern. The task is in the maintenance of the low phe therapy for the whole life. Low phe therapy should begin immediately after the diagnosis of the PKU. The main aim of nutritional management for these patients is providing a nutritionally complete diet to maintain plasma Phe concentration, which supports optimal growth, mental functioning, and development.
Nutritional management of PKU should be from an experienced team of health professionals. The dietary prescription considers first the age-specific requirement of energy and protein. The utilization of AAs effectively for the body protein synthesis is influenced by various factors, including the presence of all indispensable AA, protein digestion and AA blood absorption rates, energy intake adequacy, and nitrogen needed to support the metabolism for protein synthesis (Al Hafid & Christodoulou, 2015). An increase in the protein provided by an elemental AA based diet increases the protein requirement paralleled to intact protein owing to the faster absorption of AA, causing reduced use for protein synthesis. However, there is no increase in protein requirement for the adult with PKU, where the AA offers the majority of dietary protein.
Phe is indispensable for protein synthesis. Moreover, it should be in an appropriate amount that supports the growth in childhood, tissue repair, and turnover of proteins in adults as the plasma Phe concentration is kept within the commended levels. The minimum phe requirement for PKU patients is not different from those with ordinary PAH activities (Brown & Lichter-Konecki, 2016). However, the intake has to be in combination with tyrosine. The amount of the phe required should assess individually as the specific gene mutation in PAH, and the recycling will enhance the conversion of phe in tyrosine on phe requirement. The procedure would work for them as the guideline for the development of phe requirement for the individual. The obese people’s prescription should in consideration of the weight, height, and age because the needs for phe are proportionate to protein synthesis.
Tyrosine is vital for the PKU since they cannot hydroxylate Phe to tyrosine. Tyrosine initiates the thyroxine, melanin, and catecholamines, and the levels of plasma should be watched about the phe as numerous patients indicate small tyrosine levels. Nonetheless, the PKU phenotype is never corrected by the tyrosine alone (MacLeod & Ney, 2010). Tyrosine is provided in abundance in AA formulas. However, it is insoluble, and it may not be received enough by the individuals if not shaken before consumption. The best way to promote protein synthesis is through breast milk or the infant formula for the infants and then fruits, vegetables, and low protein products later in life. The diet for the individual with the PKU should not contain more than 25% of proteins from natural foods.
The plasma concentration of phe and tyrosine parallel to the phe intake should be monitored frequently for the adjustment of the dietary prescription for phe. The amount of phe prescription will increase the mass of the body when there is a peak growth, and the prescription will reduce with the growth rate decline (MacLeod & Ney, 2010). The ingestion of phe should be within the recommended target range. For the infants, the prescription may be required based on the growth and assessment of the concentration of the plasma phe.
Plasma phe concentration elevation may occur as a result of various reasons. Excessive intake of phe can be the reason for the elevation. Conversely, taking low phe, total energy, or protein concerning what is needed for growth spurt may also be the cause of the plasma phe concentration elevation due to the release of the proteins in the blood after the catabolism. For the women, the elevation occurs in the late luteal phase during menstruation (Giovannini et al., 2012). Moreover, infections and trauma may induce protein catabolism, causing an imbalance in nitrogen and thus and elevation in the plasma phe concentration. Immediate treatment is recommended to reduce prevent that catabolism and elevates the concentration of plasma phe. The treatment can be achieved through the increase in carbohydrates, and oral solution to provide the energy sipped through the day.
For the infants and early childhood, the AA formula that is phe free gives the most protein, nutrients, and energy for growth. Initially, the requirements are met through breast milk or infant formula. Later after the development of the feeding skills, the requirements can be obtained from the rice cereals, vegetables, and pureed fruits (Giovannini et al., 2012). Continued development of feeding skills, they can get their phe requirement from the table foods that have low protein
For the adolescents and the school-going children, the compliance may change because, at this point, children have a preference for what to eat and would not like the diet. However, children should be advised to adhere to the diet. Majorly here, the diet is related to the consumption of the formula based on AA (MacLeod & Ney, 2010). They may transition from formula 3 or 4 daily to once or twice, restricting the AA availability. Regular AA consumption during the day may cause stability in the concentration of plasma phe and increased tolerance as the protein synthesis and retention improves.
For the adults, the diet learned through childhood would likely be continued. If the diet was missed during childhood, the adult might try to reinstitute the diet, which will be difficult (MacLeod & Ney, 2010). Unlike other diseases like diabetes, an adult who stops compliance at adulthood may experience irritability and lack of concentration.
For the woman with PKU and becomes pregnant, maternal PKU, poor dietary compliance can have severe consequences. The fetus, when exposed to the high phe concentration, will cause microcephaly, intrauterine growth retardation, congenital heart defects, and learning disability (Brown & Lichter-Konecki, 2016). It is recommended that a woman attains the appropriate level of plasma phe concentration before conception. The key is the consumption of enough phe free AA formula as this would help solve the requirement of vitamins, proteins, and minerals during pregnancy.
Potential Problematic Nutrients and Foods
The potential risk is the deviation from the diet. The primary treatment for the PKU is through the consumption of a low protein diet. The patient should avoid completely high protein foods like meat, dairy products, and eggs and indulge in the consumption of cereals, fruits, and vegetables that are low in protein content (Rocha & MacDonald, 2016). Due to the high uncertainty in the consumption of a diet using the amino acid supplement, AA can help bridge the gap of choosing the foods and ensure the availability of the nutrients for growth and good health. However, it should be noticed that the deviation in the diet may cause an imbalance in the basic need leading to the elevation of plasma phe concentration. There is also some version of products for the PKU including flour pasta and rice
Al Hafid, N., & Christodoulou, J. (2015). Phenylketonuria: a review of current and future treatments. Translational Pediatrics, 4(4), 304.
Brown, C. S., & Lichter-Konecki, U. (2016). Phenylketonuria (PKU): a problem solved. Molecular genetics and metabolism reports, 6, 8-12.
Giovannini, M., Verduci, E., Salvatici, E., Paci, S., & Riva, E. (2012). Phenylketonuria: nutritional advances and challenges. Nutrition & metabolism, 9(1), 7.
MacLeod, E. L., & Ney, D. M. (2010). Nutritional management of phenylketonuria. Annales Nestlé (English ed.), 68(2), 58-69.Rocha, J. C., & MacDonald, A. (2016). Dietary intervention in the management of phenylketonuria: current perspectives. Pediatric health, medicine, and therapeutics, 7, 155.
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