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Y elective pathobiochemistry > Disorders of amino acid metabolism > Flashcards

Disorders of amino acid metabolism Flashcards

1
Q

Newborn screens for inborn errors of

Amino acid metabolism (6)

A

Tyrosinemia

Arginosuccinic Aciduria

Citrullinemia

Phenylketonuria

Maple Syrup Urine disease

Homocystinuria

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2
Q

Newborn screens for inborn errors of

Organic Acid metabolism

A 
Propionic acidemia
Glutaric acidemia type 1
Isovaleric acidemia
Methylmalonic aciduria
Mathylmalonyl-coA mutase deficiency
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3
Q

Newborn screens for inborn errors of

fatty acid metabolism

A

Long chain hydroxyacyl-CoA dehydrogenase deficiency

Medium chain acyl-CoA dehydrogenase deficiency

Very long chain acyl coa dehydrogenase deficiency

Trifunctional protein deficiency

Carnitine uptake defect

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4
Q

Newborn screens for inborn errors of

other miscelaneous systems

A

Cystic fibrosis

Congenital hypothyroidism

Biotinidase deficiency

Congenital adrenal hyperplasia

Galactosemia

SCID

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5
Q

What enzyme defect causes alkaptonuria?

A

HGD, homogentisate dioxygenase.

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6
Q

What amino acid degradation pathways are impaired in alkaptonuria?

A

Homogentisate is downstream of both Tyrosine and Phenylalanine metablism, when it accumulates it is excreted in urine in its oxidized form, Alcaptone.

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7
Q

Symptoms of alkaptonuria?

A

Ochronosis. Black pigment deposition of homogentisate in the connective tissue.

Dense black pigment in the intervertebral discs, synovial cartilage, tendons and ligaments, ear and nose cartilage, skin.

Dark/black urine especially after protein rich meal.

Joint and bone pain develops after age 30 and can be debilitating.

Bone density can be low, fractures.

Tendons and ligament tears also increase.

Galstones,
Kidney stones increased rate.

Valvular heart disease at increased rates.

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8
Q

What is the most frequent inborn metabolic disease?

A

Phenylketonuria

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9
Q

What is the Guthrie assay?

A

A drop of blood is obtained from an infant and collected on a piece of filter paper. A disk is punched out and placed on an agar gel plate containing Bacillus subtilis and B-2-thienylalanine. The agar gel is able to support bacterial growth but the B-2-thienylalanine inhibits bacterial growth. However, in the presence of extra phenylalanine leached from the impregnated filter paper disk, the inhibition is overcome and the bacteria grow.

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10
Q

What are the two types of Phenylketonuria?

A

Classical PKU - Phenylalanine hydroxylase defect

Cofactor deficient PKU - Dihydrobiopterin reductase defect.

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11
Q

Symptoms of PKU

A

Mental retardation, correlates strongly with the load of phenylalanine in blood during infancy

Seizures

Hypertonic muscles

Musty urine and sweat

Fair hair and skin

High plasma phenylalanine

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12
Q

How is phenylalanine metabolized in PKU

A

aminotransferase generates
phenylpyruvate and alanine

Phenylpyruvate converted to
Phenylacetate and Phenyllactate which makes urine smell.

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13
Q

What transports phenylalanine into neurons?

A

LAT1 the neutral amino acid transporter

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14
Q

How does extremely high phenylalaline levels affect neurons?

A

Causes abnormal myelination

Abnormal protein synthesis and neurotransmitter production.

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15
Q

Phenylketnouria treatment

A

Very strict control of phenylalanine intake

Tyrosine and Tryptophan supplementation (Phenylalanine is a precursor)

Phenylalanine ammonia lyase enzyme substitution therapy.

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16
Q

Essential amino acids

A

PVT TIM HALL

17
Q

What is missing in cofactor deficient PKU?

A

Dihydropteridin Reductase (DHPR) usually,

Therefore Tetrahydrobiopterin cannot be regenrated from Dihydrobiopterin.

or

A defect in de novo synthesis of biopterin (synthesized from from GTP)

18
Q

How is cofactor deficient PKU diagnosed?

A

Administering THB, tetrahydrobiopterin decreases plasma Phenylalanine levels and increases Tyrosine levels

19
Q

How is cofactor deficient PKU treated?

A

strict control of phenylalanine in diet.

L-DOPA 5-OH-tryptophan, and tetrahydrobiopeterin supplementation.

20
Q

What enzyme is defective in Albinism?

A

Tyrosinase. preventing Melanin synthesis from tyrosine.

21
Q

What are the symptoms of albinism

A

Light sensitivity
Vision defects
Skin cancer

22
Q

What causes Maple Syrup Urine Disease?

A

Branched Chain Ketoacid Dehydrogenase defect. BCKD

23
Q

What amino acids are involved in maple syrup urine disease?

A

Leucine Isoleucine Valine

24
Q

What subunits are involved in oxidative decarboxylation by BCKD,

what are the cofactors for each

A

E1 Ketoacyl dehydrogenase TPP, thiamine pyrophosphate
E2 Dihydrolipoyl transacetylase FAD
E3 Dihydrolipoyl dehydrogenase NAD

25
Q

What subunit of the BCKD enzyme is common to other enzymes and what are they?

A

E3
BCKD
Pyruvate dehydrogenase
alpha ketoglutarate dehydrogenase.

26
Q

Symptoms of BCKD deficiency

A 
Growth retardation
Ketoacidosis
Brain edema
Seizures
Maple Syrup urine

Increased Branched chain amino acids and keto acids in plasma
Leucine and ketoisocaproic acid especially.

27
Q

How does leucine cause brain toxicity?

A

Edema
Impaired myelination
Impaired protein and neurotransmitter synthesis

28
Q

What transporter brings leucine into neurons

A

LAT1 .

Neutral amino acid transporter

29
Q

How is ketoisocaproic acid toxic to the brain?

A

ketoisocaproic acid + glutamate
makes
leucine + alpha-ketoglutarate

It reduces glutamate and GABA availability.

Causes a defect in transport of reducing equivalents

30
Q

What transporter brings ketoisocaproic acid into neurons?

A

MCT1 monocarboxilate transporter.

31
Q

What is the GABA shunt?

A

a-KG from the TCA cycle shunted to produce succinate and NADH via a GABA intermediate.
a-Ketoglutarate –> glutamate –> GABA –> GABAT –> Succinic semialdehyde –> succinate.

32
Q

What reducing equivalents are transported in/out of the mictochondrial membrane?

A

Malate/aKG
Aspartate/Glutamate.

Malate aspartate shuttle

33
Q

Where is the defect in thiamine responsive MSUD

A

In the E 1 subunit of the BCKD, which uses TPP as a cofactor.

34
Q

Therapy for BCKD defeciency?

A

Diet control of Leu Ile Val.

Hemodialysis during crises

Liver transplant.

35
Q

What happens if there is a defect in the E3 subunit

A

Pyruvate dehydrogenase
aKG dehydrogenase
BCKD
are all deficient

Lactic acidosis and severe ketoacidosis.

Y elective pathobiochemistry (11 decks)

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