Unit 9 Project: Marcie M.
January 8, 2012
Inborn errors of metabolism are rare genetic disorders in which the body cannot metabolize certain substances in food because of a defect in specific enzymes. Treatment of IEMs is a diet change to control the substances that cannot be metabolized in order to prevent a rise in the level of the substance which can be harmful to the body. In PKU, the baby is born without the ability to properly break down an amino acid called phenylalanine which is found in foods that contain protein. Since it cannot be broken down, phenylalanine levels become dangerously high and cause severe damage to the central nervous system. PKU is passed down to an infant by both parents who are carrying the gene but may not be aware of it.
A PKU test is not done immediately after birth because the baby needs time to be able to ingest protein in order to determine if there is a problem with phenylalanine metabolism. After a few days, when the baby has eaten and has ingested protein, a PKU test can be done because there will be a more accurate outcome. Still, some tests are not 100% accurate so further blood and urine testing at 2 and 4 weeks intervals may be needed for a definite diagnosis. Just a thought - Marcie’s low birth weight puts her at risk for health problems (although she would have had PKU regardless of her birth weight since it is genetic) and makes me wonder if she may have been born before 40 weeks gestation since most babies should weigh 5.5 lbs. by week 37.
A baby who has PKU but is not diagnosed and treated within the first 2 years of life will exhibit severe developmental problems that will become irreversible. The baby will seem normal during the first few months, but as phenylalanine levels rise, the child can have seizures, will not be able to sit up, crawl, walk or talk, and will develop mental retardation. By the time the parents notice that something is wrong, the damage cannot be fixed and the child will be mentally handicapped for life. If Marcie had not been treated early, she would have developed seizures or tremors, developmental delays, behavioral or social problems, microcephaly (small head size), skin rashes, stunted growth and weight loss, vomiting, poor appetite, excessive irritability, and a musty odor on her skin, breath, and urine caused by too much phenylalanine in the body.
Although both of Marcie’s parents have brown eyes and black hair, Marcie, like other people with PKU, has blue eyes and blonde hair (and probably fair skin) because of a lack of pigmentation. When phenylalanine is broken down, it is converted into tyrosine which is then used to make melanin. Melanin is the chemical that provides pigment for hair and skin. Marcie’s body is not able to break down phenylalanine and turn it into melanin, so she has less pigmentation. Her parents look different than she does because they may be carrying the PKU gene but they do not have PKU so they are able to properly produce melanin.
A PKU diet that is absolutely free of phenylalanine is not beneficial since phenylalanine is found in protein foods, and protein is essential to the body for growth and development. The key to a PKU diet is not to cut phenylalanine out completely, but to keep it at a safe level to prevent build-up in the body. However, Marcie’s diet does not have much room for modification, since a spike in phenylalanine levels can be very dangerous for Marcie’s brain function and development. If Marcie eats the wrong foods and ingests too much phenylalanine, she could develop learning and behavioral difficulties and developmental delays. She needs to stay on a low phenylalanine diet for the rest of her life. It is very important for Marcie to follow the diet strictly and her mother has to understand that Marcie’s dietary...