Amino acid metabolic diseases
Case 1: Acute starvation:
A 23-year-old woman living alone depressed after the termination of her engagement. Two months later she was brought to the emergency room by a friend because of weakness and lethargy. She appeared thin and pale. Questioning revealed that she had not eaten for several weeks. Analysis of plasma sample indicated elevated levels of alanine, acetoacetate, beta-hydroxybutyrate, and blood urea nitrogen (BUN).
However, her plasma glucose level was within the normal range. She was hospitalized, given intravenous feeding and antidepressant medication, and subsequently switched to an 1800 cal (7500 KJ) diet. Her recovery was uneventful.
Discuss this case applying your knowledge on carbohydrate, lipid and amino acid metabolism to answer the following questions.
1. How was the patient’s body obtaining energy during the time she was not eating?
2. How was the patient able to maintain her plasma glucose level within the normal range even though she was not eating?
3. What does elevation in plasma alanine indicate? Why is the BUN elevated?
5. Why her plasma acetoacteate and beta-hydroxybutyrate levels high?
6. Would you expect to see similar conditions in a patient with uncontrolled diabetic condition? Why?
Case 2: Phenylketonuria
A 2-wk old female responded positively to a test for PKU administered on discharge from the hospital following her birth. She was called back for further testing. Serum Phe concentration was 30 mg/dl (normal: 1 mg/dl) and tyrosine was 2 mg/dl. The urine was positive for phenolic acids and FeCl3 detected ketones. A diagnosis of classic PKU was made and the child was maintained on a diet low in Phe.
1. What enzymatic reactions are defective in the patient with PKU?
2. What are the physiologic consequences of PKU?
3. Why PKU should be detected as early as possible?
4. What is the incidence of PKU among various ethnic groups?
5. What is the treatment for the patient with PKU?
Case 3: Heriditary Hyperammonemia
A 6-month-old infant began to vomit occasionally and ceased to gain weight. At age 81/2 months he was readmitted to the hospital. Routine examination and laboratory tests were normal, but after 1 wk. he became habitually drowsy, his liver was enlarged. The electroencephalogram was grossly abnormal. Since the infant could not retain milk given by gavage feeding, IV glucose was administered. He improved rapidly. Urine analysis showed abnormally high amounts of glutamine and uracil. This suggested a high blood ammonium concentration which was confirmed by the laboratory.
1. Which urea cycle enzyme (s) may be defective in this patient considering the lab data?
2. Why was the urine glutamine concentration elevated?
3. Why this disease is lethal in male patients but not in females?
4. Why the liver in this patient was enlarged?
5. How would you treat a similar patient today?
Nucleotide acid metabolism
Case 1: Gout
A 61-year-old member of a medical faculty was awarded an honorary degree 4 days before admission to the hospital. Following the ceremony he spent the evening with friends where, as he put it, the “conviviality flowed extensively.” The next morning he noticed a dull pain in the left flank, which worsened until hospitalization was
required. Physical examination revealed no overt signs of disease. A urine sample obtained on admission had a a pH of 4.5 and was +ve for protein. Microscopic examination of the centrifugal sediment from the sample revealed fine crystalline material and numerous casts. A 24-hr urine sample contained 115mg/dl of protein and 1.52 (9 mmol) of uric acid. The serum uric acid content was 11.8mg/dl (0.70mmol/L); normal is 3.5 to 7 mg/dl (0.2 to 0.4 mmol/L).
Answer the following questions:
1. Could useful information be obtained from a family history of gout? Explain.
2. Are purines and pyrimidines required in the diet? Explain.
3. What foods are high in purines and pyrimidines?
4. Would you expect a diet high in protein to be harmful to this patient? Explain.
5. What is the ionic form of uric acid in this patient’s urine? What is its solubility?
6. What is the biochemical basis for the action of drugs used in the treatment of gout?
Case 2: Acute Lymphoblastic leukemia
A 5-year-old girl was admitted to the hospital suffering from loss of appetite, weakness, pain in the joints, and fewer. The child’s spleen, liver, and lymph nodes were to be enlarged. A diagnosis of acute lymphoblastic leukemia was made. The patient was immediately given prednisone, vincristine, and L-asparginase. Allopurinol was begun as a prophylactic measure. On induction of remission, central nervous system
prophylaxis involved the injection of methotrexate and radiation treatment. Maintenance therapy involved the administration of 6-mercaptopurine and methotrexate, with occasional puleses of vincristine and prednisone for a period of 21/2 to 3 years.
Biochemical questions:
1. What is the mechanism of action of the drugs used in this case?
2. The compounds listed have some serious side effects when high dosages are administered. Why?
3. What are the side effects of cancer therapy in a 5-year-old child?
4. Why was allopurinol administered?
5. Why must the 6-mercaptopurine level be reduced if allopurinol is used in the treatment?
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