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Yr 2 - EMS > Inborn Errors of Metabolism > Flashcards

Inborn Errors of Metabolism Flashcards

1
Q

What are inborn errors of metabolism?

A

Rare genetic (inherited)disordersin which the body cannot properly turn food into energy. Thedisordersare usually caused by defects in specific proteins (enzymes) that help metabolise parts of food.

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2
Q

When does ammonia accummulate?

A

In patients with urea cycle defects

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3
Q

What are the clinical effects of hyperammonaemia?

A
  • lethargy- poor feeding- vomiting- tachypnoea- convulsions- coma - death

This is a medical emergency

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4
Q

What is the urea cycle?

A

A cycle of biochemical reactions that produces urea from ammonia.

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5
Q

What is the purpose of the urea cycle?

A

Amino acid catabolism results in waste ammonia which is toxic

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6
Q

What are porphyrins? Whar are they essential for?

A

Porphyrins are important in the synthesis of haem, so are essential for the function of haemoglobin.

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7
Q

What is porphyria?

A

Porphyrias are disorders caused by defects in the biosynthetic pathway of haem leading to buiildup of porphyrins.

The type of porphyria depends on where in the haem synthesis pathway is defected.

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8
Q

What are the possible signs of acute porphyria?

A
  • Severe abdominal pain
  • Pain in your chest, legs or back
  • Constipation or diarrhoea
  • Vomiting
  • Insomnia
  • Heartbeat you can feel (palpitations)
  • High blood pressure
  • Anxiety or restlessness
  • Seizures
  • Mental changes
  • Breathing problems
  • Muscle pain/tingling/weakness/paralysis
  • Red or brown urine
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9
Q

What porphyrins accumulate in acute porphyria?

A

ALA and PBG (blockage early on in pathway)

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10
Q

Describe the pathway from ALA –> Haem

A

ALA –> PBG –> Uroporphrin –> Coproporphrin –> Protoporphrin –> Haem

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11
Q

What porphyrins accumulate in photosensitive porphyria?

A
  • Uroporphrin
  • Coproporphrin
  • Protoporphrin
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12
Q

What occurs in photosensitive porphyria?

A

When light shines on them, they generate heat –> painful skin lesions

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13
Q

What are the signs of photosensitive porphyria?

A
  • Sensitivity to the sun/artificial light
  • Sudden painful erythema and oedema
  • Blisters that take weeks to heal
  • Itching
  • Fragile skin
  • Increased hair growth
  • Red or brown urine
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14
Q

Describe the pathway that converts triglycerides into energy

A
  1. Triglycerides are broken down into fatty acids and glycerol
  2. Fatty acids are oxidised into acetyl CoA
  3. Acetyl CoA enters TCA cycle which produces energy

OR

  1. Acetyl CoA is converted into ketone bodies by ketogenesis
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15
Q

Where does ketogenesis primarily occur?

A

Mitochondria of liver cells

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16
Q

What is androgen insensitivity syndrome?

A

Androgen insensitivity syndrome (AIS) is when a person who is genetically male (who has one X and one Y chromosome) is resistant to male hormones (called androgens). As a result, the person has some or all of the physical traits of a woman, but the genetic makeup of a man.

17
Q

What causes AIS?

A

Defective androgen receptor

18
Q

Describe the phenotype in AIS

A

Wide range - patients with AIS can have different presentations within the same family (with same mutations)

Can range from a healthy female phenotype to having partial defects resulting in ambiguous genitalia

19
Q

What are typical presentations of AIS?

A

Primary amenorrhoea, infertility, usually need surgical resection of residual gonads

20
Q

How are inborn errors of metabolism diagnosed?

A
  • Pre-symptomatic screen

- Investigation of symptomatic individuals

21
Q

How are symptomatic individuals investigated for inborn errors of metabolism?

A
  • test body fluids for abnormal metabolites
  • measure enzyme activities
  • histochemical / immunochemical staining
  • DNA analysis
22
Q

What route tends to be followed in the investigation of IEM?

A
  1. Metabolite testing (most IEM labs)
  2. More complicated metabolite testing (some IEM labs)
  3. Enzyme analysis/functional studies (only a few IEM labs)
  4. Mutation/gene analysis (genetics labs)

Tests generally become more specific, complex and costly

23
Q

If IEM disorders are genetic, why does gene analysis not occur first?

A
  • Cost/time (but both rapidly reducing with NGS)
  • Completely exclude disorders, not all mutations maybe covered (+large deletions etc)
  • Significance of mutation not always known, often poor genotype phenotype relationship
24
Q

What is metabolomics?

A

Metabolomics is the large-scale study of small molecules, commonly known as metabolites

25
Q

What does a basic urine metabolic screen involve?

A
  • Spot tests
  • Organic acids
  • Amino acids
  • Sugar Chromatography
  • Oligosaccharides/Sialic Acids
  • Mucopolysaccharides
26
Q

What are organic acidaemias?

A

A term used to classify a group of metabolic disorders which disrupt normal amino acid metabolism, particularly branched-chain amino acids, causing a buildup of acids which are usually not present

27
Q

What 3 branched amino acids are involved in organic acidaemias?

A
  1. Leucine
  2. Valine
  3. Isoleucine
28
Q

What are the 4 main types of organic acidemiaes?

A
  1. Methylmalonic acidemia
  2. Propionic acidemia
  3. Isovaleric acidemia
  4. Maple syrup urine disease (MSUD)
29
Q

What is the cause of organic acidemias?

A

Most result from defective autosomal genes for various enzymes important to amino acid metabolism.

Neurological and physiological harm is caused by this impaired ability to synthesise a key enzyme required to break down a specific amino acid, resulting in acidemia and toxicity to specific organs systems.

30
Q

How are organic acidemiaes inherited?

A

Most are inherited as autosomal recessive diseases.

31
Q

What is acideima?

A

A condition of raised blood acidity (where pH has fallen below normal)

32
Q

What is MSUD?

A

Maple syrup urine disease (MSUD) is an autosomal recessive metabolic disorder affecting branched-chain amino acids. It is one type of organic acidaemia.

MSUD is a metabolic disorder caused by a deficiency of an enzyme, leading to a buildup of the branched-chain amino acids (leucine, isoleucine, and valine) and their toxic by-products (ketoacids) in the blood and urine.

Leads to distinctive sweet odour of urine.

Yr 2 - EMS (60 decks)

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