Biochemistry and Embryology

Question 0

What is vitamin B2? What does deficiency result in?

Answer 0

riboflavin (component of of FAD and FMN – cofactor in succinate dehydrogenase rxn in TCA cycle)

2C’s of B2:
Cheilosis (inflammation of lips, scaling and fissures at corners of mouth)
Corneal vascularization

Question 1

What are the signs of vitamin A overuse?

Answer 1

skin changes, hepatosplenomegaly, intracranial hypertension (papilledema)

Question 2

What is vitamin B3? What does deficiency result in?

Answer 2

niacin
deficiency leads to glossitis and pellagra

3D’s of B3:
Dementia
Dermatitis
Diarrhea

Question 3

How does vitamin C excess present?

Answer 3

nausea, vomiting, diarrhea, calcium oxalate nephrolithiasis

can increase risk of iron toxicity in predisposed pts

Question 4

Infant with vomiting, lethargy, hypertonicity, rigidity – mother notices burnt sugar odor in diaper? Defect?

Answer 4

Maple Syrup Urine Disease

defect in alpha-ketoacid dehydrogenase (B1 cofactor)
inability to degrade branched-chain AAs (leucine, isoleucine, valine)

Question 5

Name two markers that indicate a neural tube defect.

Answer 5

• increased level of acetylcholinesterase (AChE) in amniotic fluid
• increased level of AFP in amniotic fluid and maternal serum

indicate failure of neural tube fusion

Question 6

Megaloblastic anemia with high urinary excretion of orotic acid? Treatment?

Answer 6

Orotic aciduria
autosomal recessive
disorder of pyrimidine synthesis (cannot convert orotic acid to UMP)

Treatment: supplement with uridine

Question 7

Defect in Lesch-Nyhan syndrome? Symptoms?

Answer 7

defect in HGPRT (hypoxanthine-guanine phosphoribosyltransferase)
leads to defective purine salvage

HGPRT:
Hyperuricemia
Gout
Pissed off (aggression, self-mutilation)
Retardation
dysTonia

• increased uric acid; excess uric acid production
• decreased HGPRT levels
• increased levels of downstream enzymes (PRPP)

Question 8

Describe the mechanism of valproate teratogenicity.

Answer 8

increases risk of neural tube defects

inhibits maternal folate absorption in the gut

Question 9

Fair skinned infant with blue eyes and mousy body odor? What becomes essential?

Answer 9

Phenylketonuria (PKU)

Tyrosine becomes essential

Question 10

What vitamin is deficient in Wernicke syndrome? What enzymes use this vitamin as a cofactor?

Answer 10

Thiamine

ATP

• Alpha ketoglutarate dehydrogenase (TCA cycle)
• Transketolase
• Pyruvate dehydrogenase

also branched-chain ketoacid hydrogenase (defective in maple syrup urine disease)

Question 11

Niemann-Pick: enzyme deficiency? accumulated substrate? findings?

Answer 11

Sphingomyelinase deficiency
Sphingomyelin accumulation

Findings:

• progressive neurodegeneration
• hepatosplenomegaly
• cherry-red spot on macula
• foam cells (lipid-laden macrophages)

Question 12

Tay-Sachs: enzyme deficiency? accumulated substrate? findings?

Answer 12

Hexosamidase A deficiency
GM2 ganglioside accumulation

Findings:

• progressive neurodegeneration
• cherry-red spot on macula
• NO hepatosplenomegaly (vs. Niemann-Pick)

Question 13

Child with bilateral lens subluxation, dies of stroke with MCA thrombosis – what should have been supplemented?

Answer 13

Homocysteinuria
defect in methionine metabolism, resulting in excess homocysteine

supplement with vitamin B6

Question 14

What enzymes does lead poisoning act on in heme synthesis?

Answer 14

ALA dehydratase (step after rate-limiting ALA synthase) and ferrochetalase (last step)

Question 15

What substrates inhibit ALA synthase?

Answer 15

glucose and heme

ALA synthase – rate-limiting step of heme synthesis

Question 16

High blood ammonium levels and increased urine orotic acid secretion?

Answer 16

Ornithine transcarbamylase deficiency

Question 17

What reactions use tetrahydrobiopterin as a cofactor?

Answer 17

Used by hydroxylase enzymes in the synthesis of:

• tyrosine
• dopa
• serotonin
• nitric oxide

Question 18

Child with intellectual disability, seizures, and pallor of both skin and catecholeminergic brain structures? Defect?

Answer 18

Phenylketonuria
due to defect in phenylalanine hydroxylase or to tetrahydropterin cofactor deficiency

Treatment: phenylalanine restriction, tyrosine supplementation