amino acid metabolism

Question 1

Phenylketonuria: what is missing? labs?

Answer 1

decr. pheynlalanine hydroxylase or decr. tetrahydrobiopterin cofactor (malignant PKU). tyrosine becomes essential. incr. Phe causes excess phenylketones in the urine.

Question 2

findings of PKU; tx

Answer 2

intellecutal disability, growth retardation, seizures, fair skin eczema, musty odor (this is a disorder of aromatic aa metab). treat wti h decr. phe and incr. tyr in diet. avoid aspartame

Question 3

what is maternal PKU

Answer 3

lack of proper dietary therapy during pregnancy. findings in infant: microcephaly, intellectual disability, growth retardation, congenital heart defects

Question 4

PKU screening

Answer 4

2-3 days after birth. levels normal at birth b/c of maternal enzyme during fetal life

Question 5

alkaptonuira

Answer 5

congenital deficiency of homogentisate oxidase in the degradative pathway of tyrosine to fumate. autosomal recessive. benign. find a build up of homogentisic acid. see dark CT, brwon pigmented sclera, urine turns black on prolonged exposure to air, and may have bad arthralgias (homogentisic acid toxic to cartilage)

Question 6

What enzymes may be deficient in homocystinuria?

Answer 6

cystathione synthase deficiency, decr. affinity of cystathione synthase for pyridoxal phosphate (B6), or homocystein methyltransferase deficiency. all cause excess homocystein.
(recall that homocystein can go to methionine via homocystein methytransferase, or to cystathione via cystathione synthase. that rxn requires B6)

Question 7

findings for homocystinuria

Answer 7

incr. homocysteine in urine, intellectual diability, osteoporosis, tall stature, kyphosis, lens subluxation, thrombosis, and atherosclerosis (stroke and MI)

Question 8

cystinuria: what is the defect? manifestation?

Answer 8

defect of renal PCT and intestinal amino acid transporter for cystein, ornithine, lysine, and argining. can lead to precipitation of cystine stones (hexogonal). autosomal recessive.

Question 9

cystinuria: dx and tx

Answer 9

urinary cyanide nitroprusside test. give urinary alkalinization (potssium citrate, acetazolamide) and chelating agents to incr. the solubility of cystine stones. good hydration

Question 10

maple syrup urine disease

Answer 10

blocks degradation of branched amino acids (isoleucine, leucine, valine) d/t decr. alpha hetoacid dehydrogenase (B1). causes incr. alpha-ketoacids in the blood, esp. those of leucine.

Question 11

manifestations of maple syrup urine disease. tx

Answer 11

CNS defects, intellectual disability, death. tx: limit isoleucine, leucine, and valine, and supplement thiamine.