Phenylketonuria (pku) case study essay

Phenylketonuria (pku) case study essay

Case Study 1:

who they name A young married couple, John and Katrina Smith, have just given birth to their first baby, a girl Catalina. In the hospital a blood test is performed on the baby and the parents are informed that Amelia has phenylketonuria (PKU). They are surprised since neither of them have this disease. Phenylketonuria (pku) case study essay.


Please answer the following:

–       What is PKU?

–       How can the child have PKU if both parents do not have it?

–       What is the pathophysiology of PKU?

–       What is the treatment for PKU?



Protein metabolism disorders are some of the most common conditions among metabolic disorders that are inherited. Phenylketonuria (PKU), a disorder that is relatively common and responds well to treatment, is an inherited autosomal recessive condition that is inherited which is caused by phenylalanine hydroxylase deficiency. This paper discusses PKU, its pathophysiology and treatment based on the case study of a young married couple named Katrina and John Smith who had just given birth to their first baby girl named Catalina. The couple was surprised that although none of them had PKU, a blood test that was performed on the baby revealed that she had phenylketonuria (PKU). Phenylketonuria (pku) case study essay.

What is PKU?

Phenylketonuria, also known as PKU is an inherited genetic disorder which causes a buildup of phenylalanine, an amino acid in the body. Amino acids are known to be proteins building blocks. Phenylketonuria usually results from a defect in the PAH genes which assist in the creation of the enzyme required in the breaking down of phenylalanine.  This enzyme is called phenylalanine hydroxylase (Brown & Lichter-Konecki, 2016). The body usually needs this enzyme in order to convert phenylalanine tyrosine required in the creation of neurotransmitters. When PEH enzyme becomes unavailable, the body’s inability to break down phenylalanine increases, and this causes accumulation(Brown & Lichter-Konecki, 2016) Phenylketonuria (pku) case study essay.

            Phenylketonuria was first discovered by Ivar Asbjorn Folling in the year 1934. In the United States, babies are often screened for phenylketonuria some hours after birth to detect it. This is attributed to the fact that its severe signs and symptoms can rarely be detected through physical assessments. According to the statistics provided by the CDC, phenylketonuria is not common in the US. It occurs in 1 out of 10,000-15,000 newborns annually and the highest rates have been noted among Caucasians (Brown & Lichter-Konecki, 2016).  However, if left untreated, it is linked with an abnormal phenotype which gives rise to poor pigmentation of the skin, growth failure, severe intellectual development, microcephaly and a global delay in developmental milestones Phenylketonuria (pku) case study essay. In other cases, since it causes a buildup of amino acids in the body, it can lead to a musty smell and a lighter skin (Borrajo, 2016).  It is worth noting that, infants who are born to mothers with phenylketonuria that is poorly managed are at high risk of low birth weight, heart problems, and a small head, which are also the classical signs and symptoms of phenylketonuria. It is notable that males and females are equally affected by phenylketonuria.

How the Child Can Have PKU Even If Both Parents Do Not Have It

Phenylketonuria is a genetic disorder that is autosomal recessive. It occurs primarily as a result of phenylalanine hydroxylase chromosome mutationds. This means that it is a homozygous recessive for the trait of phenylketonuria. Therefore, it can only be inherited in the recessive form which has to be inherited from both parents (Blau, 2016).

However, in such a case where none of the parents had the disorder, it is certain that they were either heterozygous of PKU or gene carriers. In this context, heterozygous refers to an individual who has a single dominant gene for PKU and another recessive gene (Blau, 2016) Phenylketonuria (pku) case study essay. Therefore, in such heterozygous individuals, the gene that is dominant tends to completely mask that which is recessive which makes an individual to reveal no signs or symptoms of the disorder. This can possibly be explained by the following punnet square where the father is heterozygous genotype is shown on the left and the mothers at the top. For instance, the higher two squares show that the father will give the infant “P” gene which is the dominant gene. In the squares below, the mother will give the infant the recessive “p” gene. Therefore, “P” represents the gene that is dominant for PKU and “p” represents the gene that is recessive. Therefore, a baby with PKU born to a heterozygous parent will have a genetic makeup of “Pp”; one gene that is dominant and the other that is recessive. On the other hand, their phenotype or outward characteristics will be that of a non-PKU person. In comparison, for those with PKU, they have a genotype of “pp”; which are two recessive genes and a PKU phenotype.

From the Punnet square, three combinations of genes can be obtained whereby, as seen in the upper left square, the infant is supplied with a gene that is dominant giving rise to a homozygous dominant child with no PKU. The infant will receive a dominant gene from the father and a recessive gene from her mother which results to a heterozygous infant as demonstrated in the upper right square. In this case, this child can pass PKU to their children. A child gets a recessive gene from the father and a dominant gene from the mother resulting to a heterozygous baby as illustrated in the lower left square. Lastly, in the lower right, the child tends to inherit a gene that is recessive from both the mother and father resulting in a child who is homozygous recessive with PKU. Phenylketonuria (pku) case study essay.

Pathophysiology of PKU

Mutations in the PAH gene usually lead to the production of phenylalanine hydroxylase enzyme with reduced catalytic activity or failure in the production of the PAH enzyme. As a result, the levels of phenylalanine in the blood usually increase which also increases the amount of phenylalanine transported to the brain. In patients with phenylketonuria, phenylalanine is in itself thought to be a direct and major cause of neurotoxicity (Schuck et al., 2015). Other mechanisms that can lead to neurotoxicity are a deficiency in brain neurotransmitters and reduced synthesis of proteins in the brain. During infancy and early childhood when the levels of phenylalanine in the blood become chronically elevated beyond a specific threshold, what results is microcephaly, abnormal myelination, a diminished IQ, delay in developmental milestones and seizures(Schuck et al., 2015) Phenylketonuria (pku) case study essay. The severity and length of duration of these adverse effects are closely related to the duration of phenylalanine blood elevation.  This is the function of the enzyme defects and the extent of control of metabolism among patients undergoing treatment.

When tyrosinase enzyme is inhibited by high levels of phenylalanine in untreated individuals, what results is a reduced synthesis of melanin leading to hypopigmentation.  Later in life, when the levels of phenylalanine in blood among patients with PKU rise acutely, a patient displays a lot of abnormalities in behavioral and cognitive function (Schuck et al., 2015). There are also EEG abnormalities, which can be reversed by controlling the levels of phenylalanine in the blood. In case blood phenylalanine levels persist for quite long, chronic toxicity that is irreversible can occur. Phenylketonuria (pku) case study essay Chronic toxicity is usually characterized by declined IQ, depression, anxiety, attention disorders, phobias and defects in executing simple tasks and functions (Schuck et al., 2015).

Treatment of PKU

            Patients with PKU are usually management pharmacologically and non-pharmacologically.  The Non-pharmacological management involves diet management where patients are restricted to maintain that is low in phenylalanine for the brain to develop optimally. Such foods include egg whites, shrimps, fish, nuts, soybeans, legumes, turkey, watercress and nuts. Start such as corn and potatoes are accepted but need to be controlled.

The levels of phenylalanine need to be strictly controlled since phenylalanine is important for protein synthesis and needed for proper growth (Al Hafid & Christodoulou, 2015) Phenylketonuria (pku) case study essay.  At a minimum, the Institute of Medicine recommends phenylalanine at 33mg/kg daily of among adults aged 19 years and older. For pediatric clients up to 10 years of age, 200-500mg/day is recommended (Al Hafid & Christodoulou, 2015).

Starting from infancy, protein and tyrosine supplements are often prescribed to ensure the provision of amino acids and other important nutrients that are likely to lack in diets with low-phenylalanine. It should be noted that diets that are low in phenylalanine with very low protein substitutes can fail to influence reduced levels of phenylalanine by triggering catabolism (Al Hafid & Christodoulou, 2015). When it comes to the pharmacologic management, sapropterin, which is a synthetic form of BH4, can be prescribed to reduce phenylalanine levels in blood in individuals whose levels are high.



Blau, N. (2016). Genetics of phenylketonuria: then and now. Human mutation, 37(6), 508-515.

Al Hafid, N., & Christodoulou, J. (2015). Phenylketonuria: a review of current and future treatments. Translational pediatrics, 4(4), 304.

Borrajo, G. J. (2016). Newborn screening for phenylketonuria: Latin American consensus guidelines. Journal of Inborn Errors of Metabolism and Screening, 4, 2326409816682764.

Schuck, P. F., Malgarin, F., Cararo, J. H., Cardoso, F., Streck, E. L., & Ferreira, G. C. (2015). Phenylketonuria pathophysiology: on the role of metabolic alterations. Aging and disease, 6(5), 390.

Brown, C. S., & Lichter-Konecki, U. (2016). Phenylketonuria (PKU): a problem solved?. Molecular genetics and metabolism reports, 6, 8-12. Phenylketonuria (pku) case study essay