Phenylketonuria
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What is phenylketonuria?
Phenylketonuria (commonly known as PKU) is an inherited disorder that increases the blood levels of a substance called phenylalanine. Phenylalanine is an amino acid (a building block of proteins) that is obtained through the diet. It is found in all proteins and in some artificial sweeteners. If PKU is not treated, excess phenylalanine can build up to harmful levels in the body, causing mental retardation and other serious health problems.
The signs and symptoms of PKU vary from mild to severe. The most severe form of this disorder is known as classic PKU. Infants with classic PKU appear normal until they are a few months old. Without treatment with a special low-phenylalanine diet, these children develop permanent mental retardation and behavioral problems. Seizures, delayed development, and movement disorders are also common. Affected individuals may have a musty or mouse-like odor as a side effect of excess phenylalanine in the body. Children with classic PKU tend to have lighter skin and hair than unaffected family members and are also likely to have skin disorders such as eczema.
Less severe forms of PKU (sometimes called moderate or mild PKU) have a smaller risk of brain damage. People with very mild cases may not require a special treatment diet.
Babies born to mothers with high levels of phenylalanine have a significant risk of mental retardation because they are exposed to very high levels of phenylalanine before birth. These infants may also grow more slowly than other children. Other characteristic medical problems include heart defects or other heart problems, small head size (microcephaly), and behavioral problems. Women with PKU and uncontrolled phenylalanine levels also have an increased risk of pregnancy loss.
How common is phenylketonuria?
Most cases of PKU are detected by newborn screening and treatment is started promptly. As a result, the severe signs and symptoms of classic PKU are rarely seen.
The occurrence of PKU varies among ethnic groups and geographic regions worldwide. In the United States, PKU is detected in 1 in 10,000 to 15,000 newborns.
What genes are related to phenylketonuria?
Mutations in the PAH gene cause phenylketonuria.
The PAH gene produces an enzyme called phenylalanine hydroxylase, which converts the amino acid phenylalanine to other essential compounds in the body. Normal levels of this amino acid are important for brain function. If gene mutations reduce the activity of phenylalanine hydroxylase, phenylalanine from the diet can build up to toxic levels in the bloodstream and other tissues. Excess phenylalanine damages nerve cells, resulting in brain damage.
Classic PKU, the most severe form of the disorder, occurs when phenylalanine hydroxylase activity is severely reduced or absent. As a result, people with untreated classic PKU have very high levels of phenylalanine that cause brain damage. Mutations in the PAH gene that allow some enzyme activity cause mild or moderate forms of PKU.
How do people inherit phenylketonuria?
This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder each carry one copy of the altered gene but do not show signs and symptoms of the disorder.
Source: National Institutes of Health
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Recent findings from P.J. Lee and co-authors highlight research in life sciences
2009 JUN 1 - (NewsRx.com) -- A report, 'Adults with late diagnosed PKU and severe challenging behaviour: a randomised placebo-controlled trial of a phenylalanine-restricted diet,' is newly published data in Journal of Neurology, Neurosurgery, and Psychiatry. "Although early diagnosis and treatment in phenylketonuria (PKU) leads to excellent outcomes, a population of adults born before the introduction of newborn screening exists. They can have severe intellectual disabilities and behavioural problems, and are often dependent on full-time carers," scientists in London, the United Kingdom report. "Anecdotal evidence suggests that a diet that lowers blood phenylalanine concentration can have significant benefits upon behaviour. A prospective double-blind randomised placebo-controlled crossover trial of phenylalanine-restricted diet was performed in a group of 34 adults (aged 21-61 years, median 49) with late diagnosed PKU with severe challenging behaviour. Only 17 completed the 60 week study: seven withdrew before the end of the baseline period; five withdrew during the first diet period; five withdrew during the second diet period (after moving into placebo phase). The mean (SD) blood phenylalanine was 1570 (222) micromol/l during baseline, 553(158) mumol/l during the active phase and 1444 (255) micromol/l during the placebo phase. In the 22 participants exposed to both active and placebo phases, no differences were demonstrated in behaviour assessed by the Aberrant Behavior Checklist and Vineland Adaptive Behavior Scales, behaviour diaries or on video analysis of direct observations. However, 76% of carers' comments were scored as positive during the active phase, compared with 54% during the placebo phase (chi(2)=38.06, p<0.001). There are significant challenges in studying people with intellectual disabilities and considerable difficulties in instituting phenylalanine-restricted diet in this population," wrote P.J. Lee and colleagues, . The researchers concluded: "However, if attempted, there are potential benefits to quality of life for the individuals with PKU and their carers." Lee and colleagues published their study in the Journal of Neurology, Neurosurgery, and Psychiatry (Adults with late diagnosed PKU and severe challenging behaviour: a randomised placebo-controlled trial of a phenylalanine-restricted diet. Journal of Neurology, Neurosurgery, and Psychiatry, 2009;80(6):631-5). For additional information, contact P.J. Lee, National Hospital for Neurology & Neurosurgery, Charles Dental Metabolic Unit, London, UK. The publisher's contact information for the Journal of Neurology, Neurosurgery, and Psychiatry is: Springer, 233 Spring Street, New York, NY 10013, USA. Keywords: United Kingdom, London, Life Sciences, Metabolic Disease, Genetics, Phenylketonuria, Clinical Trial Research, Neurosurgery, Psychiatry, Neurology, Surgery, Urology. This article was prepared by Biotech Business Week editors from staff and other reports. Copyright 2009, Biotech Business Week via NewsRx.com.
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