Introduction
Phenylketonuria (usually known as PKU) is a genetic disorder illustrated by the body’s failure to make use of phenylalanine an essential amino acid which is obtained from the diet. Phenylalanine is found in all natural proteins and some artificial sweeteners. Phenylketonuria is normally a Mendelian recessive error of metabolism. The crucial problem in this situation is abnormality of phenylalanine hydroxylase enzyme that leads to an increase in amino acid phenylalanine in the blood serum thus increasing phenylalanine level in the blood up to harmful levels which can cause severe health problems (Howell, 2000).
In a classic PKU, phenylalanine levels range between 6-80mg/dl whereas a normal phenylalanine level in blood is 1 mg/dl. If this disease is not identified and treated by consumption of low protein diets, then the amino acid phenylalanine accumulates in the blood leading to mental retardation and a serious brain damage.
Causes
Phenylketonuria is inherited in a recessive manner whereby the affected person inherited a trait from each parent for the disorder. An individual with one trait does not show phenylketonuria symptoms and is termed as a carrier. Phenylketonuria results from phenylalanine hydroxylase enzyme deficiency, its clinical phenotypes vary and more than 10 mutations in the enzyme gene have been seen in patients with phenylketonuria disease (Henriksen, 1991).
The phenylalanine hydroxylase gene (PAH) have the conveyed nucleotide sequence, it encodes the hepatic enzyme phenylalanine hydroxylase). This enzyme hydroxylates phenylalanine an essential amino acid leading to production of another amino acid, tyrosine and the reaction account for elimination of about 75% of phenylalanine. The autosomal disease phenylketonuria (PKU) results from absence of PheOH enzymatic activity because of PAH gene mutations. 99% of the mutant alleles that cause this disease map to the PAH gene and the other 1% maps to several genes that encode enzymes involved in the biosynthesis and regeneration of the cofactors that are involved in hydroxylation. The conversion of phenylalanine to tyrosine does not occur thus permitting the accumulation of phenylalanine in the body resulting to irreversible mental retardation (Erlandsen, 2002).
Symptoms
Phenylketonuria is characterized by mental retardation, seizures, development of supranuclear motor disturbances, epilepsy, retardation, poor development of tooth and microcephaly. These symptoms can be avoided by phenylalanine‐restricted diet consumption in advance. Neurological analysis of treated patients shows that only minor neurological symptoms like tremor or vigorous deep tendon reflexes show white matter abnormalities. However, patients show symptoms such as vomiting, irritability and a rash like eczema early in life as a result of toxic effect of phenylalanine in the brain and development of neurological symptoms (Lippincott, 1998).
The symptoms for phenylketonuria range from mild to severe and the most harsh is the classic PKU and children with classic PKU appear normal when born and these signs develop after a few months. When not treated early, these infants develop permanent brain damage affecting the child’s IQ. Many of these infants have fairer hair, skin and blue eyes compared to other family members. This is because phenylalanine has a role in melanin production. If the disease is untreated it can result to a musty odor in the urine, breath and skin of the affected person, an individual’s normal brain development is highly disrupted. These symptoms are currently avoided by early identification and newborn screening.
Phenylketonuria can be easily identified by a simple blood test of an infant and mental retardation is not noticeable for months and may develop gradually. Mild forms of this inheritable disorder, occasionally known as non-PKU and variant PKU hyperphenylalaninemia, have a less threat of brain damage. Individuals with these mild cases may not necessarily need treatment by way of a low-phenylalanine diet (Erlandsen, 2002).
Treatment
Phenylketonuria is treatable, newborn babies of about 3 days old are screened to detect the disorder as early as possible. If a child is found with PKU disorder, treatment is done to maintain the phenylalanine level of blood at 2 to 10 mg/dl. The main goal for treatment is to maintain the plasma levels of phenylalanine within normal levels through diet. A diet containing low amounts of phenylalanine than normal is prescribed as the child grows. Such a diet is strictly followed by the patient and requires monitoring and supervision by a parent. The patients who follow a given diet into adulthood develop well both physically and mentally. Screening of infants is now mandatory in some countries, such as in United States and Canada (Erlandsen, 2002).
To reintroduce the phenylketonuria diet after a ‘resting’ period to a regular diet is a challenge for many people. Periodic measurement of a patient’s phenylalanine blood level and the supervision of a nutritionist and other associates of the health care professionals, allow patients and their families to work together in steadily maintaining the phenylalanine blood level in the desirable normal range. However any illness can result to break down of normal body proteins, the release of the body’s amino acids, and then, an increase in the blood phenylalanine level (Erlandsen, 2002). The general practitioner and nutritionist can give dietary suggestions on changes to help sustain levels of phenylalanine in the desirable normal range during illness. Medical check-up frequently involves periodic progressive screening. This medical test is done for the anticipated normal progress over time, and tolerates early detection and prevention of problems.
Limitation of phenylalanine in a child’s diet is usually done with care since this is an essential amino acid as well as to prevent any brain damage. Dietary treatment of phenylketonuria is started at birth to eliminate the development of some degree of mental illness (Erlandsen, 2002).
Once a patient stops the controlled dietary treatment, one may develop behavioral and academic difficulties, lack of visual coordination and poor solving skills due to decline in IQ. Phenylalanine-free special preparations have been introduced since phenylalanine is found in approximately all natural proteins. These preparations include lofenalac and foods that have low protein content such as some cereals, fruits and vegetables are recommended (Rodney, 2000).
Expectant mothers who have phenylketonuria or who may be carriers of the gene should be introduced to a low phenylalanine diet to help protect the child before birth and to keep the blood level of phenylalanine normal during the pregnancy. This is because infants born to mothers with PKU and having phenylalanine levels not at normal levels (those who do not have a low-phenylalanine diet) have a considerable risk of mental disability whereby these infants are exposed to high levels of phenylalanine before they are born. Furthermore high levels of phenylalanine can also cause loss of pregnancy (Rodney, 2000).
Conclusion
Phenylketonuria occurrences vary with geographical location and amongst ethnic groups. If screening is done at birth, these incidences can be significantly reduced as seen in the United States. Mothers can be subjected to a low-phenylalanine diet before conception, and efforts made to keep phenylalanine blood levels as low as possible throughout pregnancy to reduce its occurrence (Rodney, 2000).
References list
Howell Rodney. (2000) Immediate Clinical Applications of the New Genetic Technology. Web.
Heidi Erlandsen. (2002) The Structural Basis of Phenylketonuria. Web.
Lippincott Williams. (1998) Neurological Aspects of Adult Phenylketonuria. Web.