0.1.2 Amino Acid Metabolism

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Back 1

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Front 2

What four disorders are related to Phenylalanine and Tyrosine metabolism?

Back 2

Phenylketonuria
Albinism
Alkaptonuria
Tyrosinosis

Front 3

Describe Phenylketonuria

Back 3

Phenylketonuria - PKU 1
Deficiency: phenylalanine hydroxylase (PAH)
Consequence: ↓ melanin, tyr becomes essential
Symptoms: "mousy" urine, all neonates tested in 1st week
Treatment: Low protein diet, sapropterin (BH4)

Phenylketonuria - PKU 2
Deficiency: dihydrobiopterin reductase (BH2 back to BH4)
Consequence: Same, severe CNS functions (↓ catecholamines, serotonin)
Symptoms: same
Treatment: low protein diet, dietary bioptin and NT precursors. Poor prognosis due to inability to get meds across blood-brain barrier

Front 4

Describe Alkaptonuria

Back 4

Deficiency: homogentisic acid oxidase
Consequence: homogentisic acid deposits in CT and is excreted rather than going to maleylacetoacetate and later, fumarate, acetoacetate and the TCA cycle
Symptoms: relatively benign - dark standing urine, CT discoloration, severe arthritis later in life
Treatment: low Phe & Tyr diet

Front 5

Describe Tyrosinemia

Back 5

Deficiency: fumaryl acetoacetate hydrolase
Consequence: build up of fumaryl acetoacetate causes liver and renal failure
Symptoms: "cabbage" smell to urine
Treatment: Ineffective (usually fatal) restrict Phe & Tyr (2 essential AAs)

Front 6

Describe Albinism

Back 6

Deficiency:
Consequence:
Symptoms:
Treatment:

Front 7

Define maple syrup urine disease

Back 7

Deficiency: branched chain a-keto acid dehydrogenase
Consequence: excess branched chain keto acids made
Symptoms: in infant - ↓ feeding, vomiting, ↓ weight gain, lethargy, neurological (muscle hypo & hypertonia, seizures, encephalopathy), smell of maple syrup in urine
Treatment: Ineffective - dietary restrictions (3 essential AAs & tissue damage can release them), thiamine-PP (vit B1).
Living to adulthood is possible.

Front 8

Define Methylmalonic Aciduria

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Deficiency: Methylmalonyl CoA mutase
Consequence: metabolic acidosis secondary to ↑ methylmalonic acid in blood.
Symptoms: neurological - seizures, encephalopathy
Treatment: dietary avoidance of valine, isoleucine (branched AAs degraded in redundant pathways), Vit B12 (cobalamin) supplements

Front 9

What two disorders are associated with branched chain amino acid metabolism?

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Maple syrup urine disease (MSUD)
Methylmalonic aciduria

Front 10

What disorder is associated with sulfar containing amino acid metabolism?
Which AAs are affected?

Back 10

Homocystinuria
Methionine & Cysteine

Front 11

Describe Homocystinuria

Back 11

Deficiency: crystathionine beta-synthase (VIT B6 DEPENDENT) (transulfuration pathway)
Consequence: homocystine builds up in CT, plasma and urine rather than conversion to cystathionine and then cysteine
Symptoms: ↑ homocysteine urine level, dislocation of lens, skeletal abnormalities, mental retardation, premature arterial disease
Treatment: Effective - Oral B6, dietary restriction