Amino Acid Errors

Question 1

Phenylketonuria

PKU

Answer 1

Deficiency of hepatic phenylalanine
hydroxylase (PAH, which converts Phe Tyrosine with help of BH4
PK >1200 - 600 uM
Musty odor to urine
 Skin conditions (eczema)
 Decreased hair/skin pigmentation (from
tyrosinase inhibition)
Phe intake must be 240-350 mg/day

Question 2

Maple Syrup Urine Disease

Answer 2

Branched chain ketoacid dehydrogenase (BCKAD) deficiency

Question 3

MSUD Sx

Answer 3

Maple syrup odor in cerumen at 12- 24 hrs
Ketonuria, irritability, poor feeding Encephalopathy
stereotyped mvmts i.e. “fencing” or “bicycling”)

Question 4

MSUD Tx

Answer 4

Eliminate dietary protein intake with judicious isoleucine and valine supplement (400-600 mg/d)

Question 5

Tyrosemia Type 1

Answer 5

Autosomal Recessive; fumarylacetoacetate  hydrolase (FAH) deficiency
• Type 1: hepatorenal nitisinone
• Type 2: oculocutaneous; tyrosine crystals in eyes, hyperkeratosis of
palms and soles 
• Type 3: may be asymptomatic, some
developmental delay

Question 6

Tyrosemia Diagnostics

Answer 6

Serum: high succinylacetone, Tyr, Met, and Phe

 Urine: high succinylacetone, Tyr metabolites, ALA

Question 7

Tyrosemia Tx

Answer 7

Nitisinone (Orfadin)
 NTBC (decreases succinylacetone)
 Phe and Tyr dietary restriction

Question 8

Homocysteinuria

Answer 8

Defect in CBS enzyme (which normally

converts homocysteine cystathionine)

Question 9

Homocysteinuria Sx

Answer 9

Skeletal defects (Marfanoid habitus, osetoporosis, scoliosis
ctopio lentis and/or myopia
Recurrent thromboembolism
Elevated methionine and homocysteine
 Low CBS activity

Question 10

Homocysteinuria Tx

Answer 10

B6 (pyroxidine) for 50% that are B6 responsive  Betaine treatment (adolescents/adults) and/or
folate/B12 supplement
 Protein-restricted diet