Phenylketonuria is a result of a genetic disorder wherein the body cannot metabolise phenylalanine properly. This inborn metabolic perturbation results from a mutation within the PAH gene, which encodes the phenylalanine hydroxylase enzyme. In an autosomal recessive pattern, the individual has to inherit two defective copies of the PAH gene, one from either parent, to be inflicted with the disorder. A carrier-causing mutation usually does not result in symptoms and is carried only within one copy of the gene, which can be passed on to offspring.
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PKU pathophysiology is the key point in the metabolism of phenylalanine to tyrosine, catalysed by phenylalanine hydroxylase. Genetic mutations that culminate in this deficiency or dysfunction of this enzyme lead to the accumulation of the amino acid phenylalanine in both blood and the brain. Excessive levels of phenylalanine are neurotoxic, leading to impairment in normal cognitive development and intellectual disability with associated neurological defects. This accumulation will disturb normal brain development and function. Thus, early and continuing management of the disorder is important.
The symptoms of PKU usually start to appear in the first few months of life, though most conspicuously if left untreated.
Several methods do PKU diagnosis, the first one being done in most countries as the obligatory PKU newborn screening.
The hallmark treatment for PKU is dietary management. This is a very strict diet that restricts phenylalanine to very low levels except for some high-protein foods like meat, fish, eggs, dairy products, nuts, and beans. In the majority of cases, low-phenylalanine medical foods and amino-acid-based foods are required to provide phenylalanine levels that are nutritionally adequate and will help to ease metabolic control of phenylalanine to a safe level. Dietitians modify and individualise the diet according to each condition and track the nutrition of people afflicted with these conditions.
Medical therapy for PKU includes the use of sapropterin dihydrochloride (BH4)—a man-made type of cofactor, which can increase the residual activity of phenylalanine hydroxylase in some patients. It allows more liberalised dietary treatment with less pronounced blood concentrations of phenylalanine. Enzyme substitution therapy meets an option for the occurrence of an alternative route to degrade phenylalanine in the blood. Such medical manipulations, combined with the control of nutrition, provide a universal tool to control PKU and improve the quality of life among those suffering.
Adequate follow-up and monitoring constitute important aspects of the management of PKU. Periodic blood assays can monitor phenylalanine levels to educate the patient whether their dietary and medicinal treatments are working or need some adjustments. Lifelong treatments are in order as control of phenylalanine levels throughout life prevents neurologic and cognitive complications.
Conclusion
Phenylketonuria is a serious genetic disorder that can give rise to acute brain damage and neurologic impairment if untreated. The best quality of life depends upon an early diagnosis through newborn screening followed by management through dietary and medication interventions. Early recognition and diagnosis of PKU with expanded awareness and education may increase its detection in the early stage and thus provide treatment. The continued research on PKU brings new therapies that may improve outcomes. A better understanding of PKU helps not only oneself but also other people afflicted by this dreaded disease and also enhances a better understanding of metabolic and genetic disorders in general.
Typical symptoms of PKU include intellectual disability, behavioural problems, eczema, and a musty smell to the skin and urine caused by high phenylalanine in the blood.
A simple blood test is used to screen for PKU in newborns. The test is mainly done a few days after birth.
People with PKU should not consume high-protein foods in the form of meat, fish, eggs, dairy products, nuts, and some varieties of beans, as these contain high levels of phenylalanine.
There currently is no cure for PKU. It has been nevertheless successfully treated and managed through diet regulation and medical treatments controlling the levels of phenylalanine.
PKU makes daily living hard by requiring a severely limited diet, regular blood tests, and continual medical supervision to prevent neurological damage and maintain health.
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