amino acid disorders

Question 1

AR
deficient homogentisic acid oxidase (unable to degrade tyrosine, homogentisic acid → maleylacetoacetic acid)
↑ homogentisic acid in urine (turns black when exposed to air) + CT (dark color)
brown pigmented sclera
arthralgia: deposited in cartilage of joints

Answer 1

alkaptonuria

Question 2

treatment of alkaptonuria

Answer 2

add vit C

avoid phenylalanine + tyrosine foods

Question 3

tyrosinase deficiency (dopa → melanin) or defective tyrosine transport (can't get tyrosine into cell to be metabolized into melanin) or absence of melanocytes (from neural crest cells)
↑ risk of thymidine dimers from UV radiation →↑ risk skin cancer

Answer 3

albinism

Question 4

cystathionine synthase deficiency (homocysteine → cystathionine) or ↓ affinity of CS for B6 (pyridoxyl phosphate) or homocysteine methyltransferase (homocysteine → methionine)
↑ homocysteine in urine (diagnostic)

Answer 4

homocystinuria

Question 5

symptoms of homocystinuria

Answer 5

ID
tall stature
osteoporosis
kyphosis
atherosclerosis
subluxation of lens

Question 6

treatment of homocystinuria

Answer 6

if cystathionine synthase: ↓ methionine in diet, ↑ cysteine in diet, ↑ B6/B12

Question 7

defect of renal tubular amino acid transporter in proximal convoluted tubule for COLA:
cystine
ornithine
lysine
arginine

Answer 7

cystinuria

Question 8

complications of cystinuria

Answer 8

cystine kidney stones: prevent with acetazolamide (carbonic anhydrase inhibitor → HCO3 can’t be reabsorbed → alkalinize urine)

Question 9

urine smells like maple syrup
I Love Vermont maple syrup = branched chain amino acids:
Isoleucine, Leucine, Valine

Answer 9

maple syrup urine disease

Question 10

deficiency of branched chain α ketoacid dehydrogenase complex → no degradation of branched amino acids (Isoleucine, Leucine, Valine) →↑ αketoacids in blood/urine+ branched amino acids

Answer 10

maple syrup urine disease

Question 11

complications of maple syrup urine disease

Answer 11

ID
severe CNS defects
death

Question 12

AR
defect of a transporter in intestine + kidneys transporting neutral amino acids (no reabsorption): tryptophan → tryptophan excreted in urine and gut
no tryptophan → no niacin (pellagra = vitamin B3 deficiency) → 3D’s: dermatitis, diarrhea, dementia

Answer 12

hartnup disease