Deck 26: Metabolic Disorders

Question 1

What is the screening procedure for PKU?

Answer 1

Phenylketonuria (PKU) can be described as an inborn error of metabolism which involves defective metabolism of phenylalanine. This enzyme defect is caused by an impaired phenylalanine hydroxylase (PAH) enzyme.
PKU is also known as PAH deficiency. The affected individuals are unable to convert phenylalanine into tyrosine, as a result of which the levels of phenylalanine in the blood are elevated. The normal levels of phenylalanine in the blood of newborns should be 0.5 mg to 1 mg per dL.
The screening procedure for PKU involves collection of blood from the baby's heel and sending it to the laboratory. The blood needs to be collected within 48 hours after the birth of the child. The main aim of the test is to estimate the levels of phenylalanine and tyrosine in the blood. Alternatively the levels of functional PAH can also be measured. There are three main methods that can be employed for screening of PKU:
i. Guthrie test: This test was developed by Robert Guthrie, an American physician and bacteriologist.
ii. Fluorescence spectroscopy: In this screening method a fluorometer is used to analyze the fluorescence from a blood sample.
iii. Tandem mass spectrometry: In this method, the weight of molecules in the blood is measured.
After the screening procedure is completed, the baby is diagnosed as having PKU if the blood phenylalanine levels exceed 1 mg per dL.

Question 2

What is the difference between selective and non-selective screening for metabolic disorders?

Answer 2

A metabolic disorder can be described as the clinical condition when the normal metabolic processes of the body are altered by abnormal chemical reactions. These are usually caused by an inherited single gene anomaly and are mostly autosomal recessive in nature. Inherited metabolic disorders may arise as a result of a defective gene which causes a deficiency of an enzyme. Impairment of liver and the pancreas may often lead to development of metabolic disorders.
Non-selective screening can be defined as the process in which newborns are screened for a limited number of more common IEMs (Inborn Errors of Metabolism). This type of screening is low risk, cost effective and simple. This screening technique is highly effective because it provides a clear picture for most of the IEMs. As a result of this screening method, the newborn can be diagnosed early and the treatment for any detected IEM will be started immediately.
Selective screening on the other hand refers to testing for a specific genetic disorder which the infant is suspected to have. Examples of this type of screening include confirmatory testing of a disease for which an infant tested positive in the non-selective screening or testing of an infant belonging to a family with a known history of a certain genetic defect.
Thus, non-selective screening screens the infant for a wide range of metabolic disorders whereas selective screening tests for the presence of a single, specific defect.

Question 3

Why is it important to accomplish screening as soon after birth as possible?

Answer 3

Phenylketonuria (PKU) can be described as an inborn error of metabolism which involves defective metabolism of phenylalanine. This enzyme defect is caused by an impaired phenylalanine hydroxylase (PAH) enzyme. PKU is also known as PAH deficiency.
The affected individuals are unable to convert phenylalanine into tyrosine, as a result of which the levels of phenylalanine in the blood are elevated. The normal levels of phenylalanine in the blood of newborns should be 0.5 mg to 1 mg per dL.
If PKU is not treated, the levels of phenylalanine increase in the blood. The accumulation of excessive phenylalanine is thought to be the cause of mental retardation. If a baby has PKU and the treatment is started then and there, there are less chances of occurrence of problems like brain damage.
Children who are diagnosed with PKU soon after birth can start treatment right away. This helps to keep the phenylalanine levels within the suggested range and usually have normal growth and intelligence.
It is important to accomplish screening for PKU as soon as possible after birth because early diagnosis helps better and effective treatment of the disorder. Failure to diagnose the disease can lead to improper and inefficient treatment of the disease which may have serious health ramifications.

Question 4

What amino acids are restricted in maple syrup urine disease?

Question 5

What is the goal of the PKU diet?

Question 6

What amino acid becomes essential secondary to the enzymatic block in PKU?

Question 7

What is Phenex? How is it different from Similac or other standard infant formulas?

Question 8

What is periorifacial acrodermatitis, and when does it occur?

Question 9

What would be the possible long-term complications of untreated PKU?

Question 10

What is the role of carnitine supplementation?

Question 11

How long will the infant have to remain on a special diet?

Question 12

How does fasting affect disorders of fat metabolism?

Question 13

In general, how will her diet change as she grows?

Question 14

Which vitamins have been used as cofactors in mitochondrial disorders?

Question 15

Identify at least two nutrition problems based on the nutrition assessment and medical history. Determine the diagnostic term for each nutrition problem. Next, identify the etiology of each nutrition problem. Finally, identify the signs and symptoms that support the evidence for these nutrition problems.

Question 16

What are some clinical signs/symptoms that would indicate the need for a further metabolic work-up for a mitochondrial system defect?

Question 17

Compare the prescribed diet to your calculation of energy and protein requirements.

Question 18

Which vitamin deficiency can present as methylmalonic acidemia?

Question 19

Determine nutrition criteria for monitoring and evaluation for each nutrition diagnosis that you identified.

Question 20

Which vitamins are used for their antioxidant properties in the treatment of mitochondrial disorders?

Question 21

Which sugars are restricted in GSD I?

Question 22

What percentage of protein intake should come from essential amino acids in urea cycle disorders?

Question 23

Which food groups are restricted in galactosemia, and why?

Question 24

What is the mainstay of dietary management for GSD I?

Question 25

What becomes significantly elevated in the blood of a person with a urea cycle disorder prior to treatment?

Question 26

How is the diet prescription different in an individual with a more severe enzymatic defect versus a less severe defect?

Question 27

What are the initial symptoms of a child with a urea cycle disorder?

Question 28

How much protein should be given for an individual with a urea cycle disorder?

Question 29

What parameters should be monitored in an individual with a urea cycle disorder?

Question 30

In GSD, there are deficiencies of enzymes involved in synthesizing and degrading which polysaccharide?

Question 31

Describe the diet composition for an individual with GSD I.

Question 32

What typically happens when a person with hereditary fructose intolerance ingests fructose?

Question 33

What are some of the complications that an individual with hereditary fructose intolerance will encounter after ingestion of fructose?

Question 34

Describe successful dietary treatment of hereditary fructose intolerance.

Question 35

What is monitored in the red blood cells to measure dietary compliance in galactosemia?

Question 36

What are some possible theories on why some patients with galactosemia experience poor outcomes?

Question 37

What types of formula are used to treat infants with galactosemia?

Question 38

Why is MCT oil used in disorders of long-chain fat metabolism? Why can't it be used in MCADD?

Question 39

In what conditions can you breastfeed a child with an IEM? When would it be contraindicated?

Question 40

What are the three main goals for the acute treatment of an amino acid disorder?