History of phenylketonuria.
In 1934 a mother of two mentally retarded children aged 7 and 4 years old told Dr. Folling in Norway that her children had a peculiar odor, which prompted Dr. Folling to conduct a detailed examination of the two children, which led to the discovery of a substance called phenylketonate in their urine, and it was this discovery that led to what we now call phenylketonuria.
More than two decades later, Dr. Bickel at Birmingham Children’s Hospital in England made the first attempt to treat a 2-year-old girl with a low-phenylalanine diet, and in 1964 Dr. Guthrie in the United States established a laboratory method for blood screening for phenylketonuria. Since then, blood screening of newborns combined with low-phenylalanine dietary therapy has been fully introduced to children with phenylketonuria and their families.
In 1992, Dr. Woo in the United States found a mutated gene for phenylalanine hydroxylase in a patient with phenylketonuria, making gene therapy a possibility for the future.
What is phenylketonuria?
Phenylketonuria is a condition that is passed from one parent to the other, resulting in an impairment of the normal use of phenylalanine in the protein ingested into the body, causing changes in body chemicals that, if left unchecked, can lead to severe intellectual disability.
What is phenylalanine?
The basic components of protein are various amino acids, and phenylalanine is a type of amino acid that is not properly utilized by people with phenylketonuria.
When protein-containing foods are ingested by the body and digestion begins in the stomach, the first step in digestion is the separation of various amino acids. The separated amino acids (including phenylalanine) are absorbed into the bloodstream to perform their respective functions. During childhood, these amino acids (including phenylalanine) must be available for growth and development. However, any one diet contains too many amino acids to meet the growth and developmental needs of children. The excess amino acids are converted into other substances by special chemical enzymes in the body, and each amino acid requires its own chemical enzyme for conversion.
Usually, the excess phenylalanine is converted to tyrosine by the action of phenylalanine hydroxylase, which is necessary for the body to synthesize hormones, neurotransmitters for the brain, and melanin.
How does phenylketonuria cause mental retardation?
Phenylketonuria is caused by a lack of phenylalanine hydroxylase in the body or its inability to function, resulting in a buildup of phenylalanine in the blood, a deficiency of tyrosine, and a lack of other important chemicals synthesized from it. When phenylalanine in the blood and body tissues continues to increase, it leads to a serious intellectual disability by affecting the normal growth and development of the affected child’s brain.
How is Phenylketonuria diagnosed?
Newborns are best screened for phenylketonuria after 3 days of nursing at birth. Positive screening results require further confirmatory and typing tests to finalize the diagnosis. If a child is not screened during the newborn period, he or she should be taken to a medical professional as soon as possible when symptoms such as developmental delay, seizures, yellowing of hair, peculiar odor of urine and sweat, and eczema appear. Phenylketonuria affects about one in every 11,000 births in China, with about 1,000-1,300 children born each year.
Why do babies get phenylketonuria?
It is inherited from both parents. Perhaps your first thought is that no one in your couple’s family has phenylketonuria, so how is the disease passed on to your child?
We all know that children have traits similar to their parents, and that all genetic traits are controlled by information stored in the body’s cells called genes. The genes from the parents are copied in the fertilized egg and a new life is born, so the individual characteristics of this new life are controlled by the genes of the parents. Usually our body needs only one gene in a cell to express one characteristic. In phenylketonuria, the gene that controls the production of phenylalanine hydroxylase is wrong in both parents, and the child inherits both the wrong gene from the father and the wrong gene from the mother.
Why are the parents asymptomatic?
As a parent of a child with phenylketonuria, one of your phenylalanine hydroxylase genes is faulty and the other is normal, because a normal gene is sufficient to maintain its characteristics, so you are asymptomatic and you are a carrier of the phenylketonuria gene, and the chances of two carriers meeting are very small, about 1 in 2500.
Do all your children have phenylketonuria?
No. Each parent carries one normal gene and one faulty gene, and each child inherits one gene from each parent, so they can inherit both normal and faulty genes from their parents. Each of your newborns has a one-in-four chance of having phenylketonuria, a one-in-two chance of being a carrier of the same disease-causing gene as you, and a one-in-four chance of being perfectly healthy. These chances are the same for every pregnant woman. The fact that you already have a child with phenylketonuria does not change the chances that your newborn will have phenylketonuria in a future pregnancy.
Will you know if your next child has phenylketonuria?
It is possible to find out if a baby has phenylketonuria early in pregnancy, but first both parents and the child with the disease need to be genetically diagnosed first, and then conceive based on definitive results, and then wait until a certain gestation period to take amniotic fluid and chorion for prenatal diagnosis.
Is it possible to have a child with phenylketonuria?
Yes. Both men and women can have children just like anyone else, and if the spouse is not a carrier, their child will not be a carrier. The chance of a future spouse of a child with phenylketonuria being a carrier of the phenylketonuria gene is 1 in 50, so the chance of their child inheriting phenylketonuria is 1 in 100. If the spouse is also from a family with phenylketonuria, the chance of their child having the disease is much higher. If the spouse is also a Phenylketonuric patient, then it is certain that all their children will have Phenylketonuria.
What should a woman with phenylketonuria do when she gets pregnant?
Women with phenylketonuria want to have and raise children. During pregnancy, the baby’s intelligence and body are damaged by high levels of phenylalanine in the mother’s womb. This damage is permanent and begins to occur early in the pregnancy. This damage can be avoided if a low phenylalanine diet is started before pregnancy and maintained until the baby is born. Low phenylalanine concentrations at the time of conception and throughout the pregnancy must be ensured to ensure normal growth and development of the child.
The female patient must always be in contact with a medical professional and good dietary formulas must be established prior to the planned pregnancy. There must be strict dietary control and regular monitoring throughout the pregnancy.
How should parents be treated?
In addition to special dietary care, children with phenylketonuria should be treated like healthy children, without being overly sympathetic or protective.
Special dietary formulas may seem complicated, trust your doctor to provide the support and help you need.
What should I do if Phenylketonuria is diagnosed?
Once the condition is diagnosed, you should feed your child with a low-phenylalanine formula diet until the blood concentration of phenylalanine drops to normal levels. Since phenylalanine is an essential amino acid for human growth and development, even a person with phenylketonuria must consume the minimum amount of phenylalanine needed to ensure growth and development every day. Therefore, the small amount of phenylalanine required by infants can be obtained through calculated amounts of breast milk or regular infant formula.
How to prepare a diet for phenylketonuria?
Regular dietary formulas contain much more phenylalanine than children with phenylketonuria can tolerate. In contrast, the principle of dietary formula for Phenylketonurics is to provide only the minimum amount of phenylalanine necessary to ensure the growth and development of the child.
A. Fish, meat, eggs and milk are all rich in protein, which means they contain large amounts of phenylalanine, so these foods are prohibited.
B. Other foods contain small amounts of protein, which can be consumed by calculating the amount. However, the blood phenylalanine concentration must be checked regularly to keep it within a certain safe range.
C. Most fruits, vegetables, oils, candies and jams can be consumed.
D. The daily protein needs of patients with phenylketonuria are mainly supplied by protein substitutes that do not contain phenylalanine. These protein substitutes need to be obtained by prescription from a medical professional and can provide a minimum amount of safe protein for the growth and development of the affected child.
Usually a professional pediatrician will choose a product that is most suitable for your child and family and will advise you on the total amount of daily intake and how to consume it. Protein substitutes are a vital part of the diet for people with phenylketonuria and must be consumed in a daily ration at each meal to ensure stable phenylalanine concentrations throughout the day. Adequate vitamins and minerals must also be included in the daily diet. These must be supplied by prescription.
How do I monitor my blood phenylalanine levels?
If your child’s phenylalanine level is too high or too low, you should contact your doctor as soon as possible so that the diet can be adjusted.
Can special dietary formulas be interrupted?
There is no doubt that children with phenylketonuria must consume a strict low-phenylalanine diet throughout their growth and development. For adolescents and adults, a lifelong restriction of phenylalanine intake is recommended under the supervision of a physician. Dietary control is particularly important for female patients of childbearing age.