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MEDI 202 - Genes To Community > Inborn Errors of Metabolism > Flashcards

Inborn Errors of Metabolism Flashcards

1
Q

What are the different forms of IEM?

A

Carbohydrate disorders, Fatty acid oxidation defects, Aminoacidopathies

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2
Q

What are examples of carbohydrate disorders?

A

Galactosemia, fructosemia

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3
Q

What are some examples of fatty acid oxidation defects?

A

Medium chain acyl-CoA, dehydrogenase deficiency.

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4
Q

What are some examples of aminoacidopathies?

A

Phenylketonuria, Alkaptonuria

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5
Q

What are oligosaccharides?

A

Two or more monosaccharides linked by O-glycosidic bonds

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6
Q

What is lactose synthase?

A

Heterodimer compromising the α-lactalbumin and β4galactosyltransferase -1

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7
Q

What is the function of prolactin?

A

Stimulates the expression of α-lactalbumin in the lactating mammary gland

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8
Q

What is α-lactalbumin?

A

The enzyme that produces the breast milk

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9
Q

What is the reversible equation between glucose, galactose and lactose?

A

Lactose and water —-(lactase)—-> Galactose + Glucose

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10
Q

Where is lactase located?

A

The brush border (microvilli) of the small intestine

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11
Q

What is lactase and what is its function?

A

β-D-galactosidase that catalyses the breakdown of lactose to galactose and glucose

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12
Q

What other deficiencies affect the carbohydrate absorption?

A

Surcease, isomaltase and trehalase deficiencies

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13
Q

What is lactase deficiency?

A

The failure to express the enzyme (lactase) that hydrolyses lactose into galactose and glucose in the small intestine

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14
Q

What are some symptoms that occur as milk is ingested for people with IEM??

A

Stools have a low pH
Stools contain glucose produced by bacteria action on undigested lactose

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15
Q

What happens to lactose in lactase-deficient individuals?

A

Gut bacteria ferment lactose to lactic acid, methane, and acetate

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16
Q

What does bacterial fermentation cause?

A

Abdominal cramps, bloating and nausea

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17
Q

What is lactose malabsorption?

A

Failure to digest or absorb lactose in the small intestine

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18
Q

Why does the lactase enzyme decrease in numbers after weaning?

A

The quantity of lactose taken in is less, if any dairy products are consumed the enzyme cannot break it down so gut bacteria have to do so.

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19
Q

What are symptoms of lactose intolerance?

A

Flatulence
Abdominal discomfort
Bloating
Diarrhea

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20
Q

What are the common symptoms of galactosemia?

A

Failure to thrive
Predisposition to sometimes life-threatening infections
Jaundice
Liver failure

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21
Q

What causes jaundice in galactosemia?

A

The liver is unable to break down bilirubin

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22
Q

How does galactose enter the liver?

A

Freely from the blood to the hepatocytes

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23
Q

Where is galactose metabolised?

A

In the liver

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24
Q

Explain the pathway galactose into glucose.

A

Enters liver through GLUT 2
GALK transforms galactose into galactose-1-phosphate
Galactose-1-phosphate turns into glucose-1-phosphate through GALT
PGM1 converts glucose-1-phosphate into glucose-6-phosphate
Glycolysis

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25
Q

Why are cells not equipped or adapted to utilise galactose for metabolism?

A

Most galactose is removed and metabolised through the liver, excreted through urine

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26
Q

How does galactose become galactose-1-phosphate?

A

Through galactokinase (phosphorylation, so ATP is used up)

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27
Q

What is the role of galactose in the body?

A

Required for glycosylation of glycoproteins and glycolipids in non-liver tissues

  • Enhances immune system
28
Q

What is the role of galactose in the respiratory system?

A

Salfated galactose residues

29
Q

What does galactose in the respiratory system prevent?

A

Pneumonia, Influenza

30
Q

What is the role of galactose in metabolism?

A

Biosynthesis of many complex carbohydrates

31
Q

What are the complex carbohydrates that galactose biosynthesises?

A

Glycoproteins, glycolipids

32
Q

What is the role of galactose in the gastrointestinal system?

A

To maintain bacteria flora

33
Q

Why is the conversion of galactose into glucose thermodynamically not a favorable reaction?

A

it uses too much ATP (3 molecules)

34
Q

What is the galactose pathway in the liver?

A

Lactose to Galactose + Glucose (lactase)
Galactose to Galactose-1-phosphate + UDP glucose (Galactokinase)
Galactose-1-phosphate to Glucose-1-phosphate + UDP galactose (Galactose-1-phosphate uridyl transferase)

UDP galactose and UDP glucose are reversible with each other (UDP Galactose-4-epimerase GALE)

35
Q

Why does UDP galactose change to UDP glucose?

A

UDP galactose is toxic in high quantities so it transforms into UDP glucose which is useful

36
Q

What is classic galactosemia caused by?

A

A mutation in the galactose-1-phosphate transferase (GALT)

37
Q

What is type II galactosemia caused by?

A

A mutation in the galactokinase (GALK)

38
Q

What is type III galactosemia caused by?

A

A mutation in UDP - GAlactose-4-epimerase (GALE)

39
Q

What happens if GALT is not working properly?

A

Galactose is not converted into glucose so there is a build-up of galactose

40
Q

What is galactose also converted into?

A

Galactitol and galactonate

41
Q

Which enzyme converts galactose into galactilol?

A

Aldose reductase

42
Q

Which disease occurs when galactose is converted to excessive galactitol?

A

Cataracts

43
Q

What is the diagnostic test for PKU?

A

FeCl3 which detects phenylalanine in urine

44
Q

What happens if phenylalanine is present in the urine?

A

FeCl3 changes colour to green, blue or black from orange/yellow

45
Q

What enzyme converts phenylalanine into tyrosine?

A

PAH

46
Q

Where does PAH-mediated hydroxylation occur?

A

Liver and renal tubules of kidney

47
Q

What is BH4?

A

A cofactor required for PAH activity

48
Q

What is DHPR? What is its function?

A

Cofactor required for the hydroxylation of Phenylalanine, Tyrosine, and Tryptophan.

Catalyses age recycling of tetrahydrobiopterin

49
Q

What is PAH-mediated hydroxylation the rate-limiting step of?

A

Intermediary metabolism of L-Phe

50
Q

What is PKU?

A

PAH deficiency, autosomal recessive.
Defects in the production of BH4 which may result in hyperphenylalanine

51
Q

What are the symptoms of PKU?

A

Increased phenylalanine
Increased phenyl-ketones
Increased phenylamine
Deficiency of tyrosine
Fair skin, blue eyes, light blonde hair
Mousy or musty door of urine

52
Q

What is the function of phenylalanine?

A

It is involved in the body’s production of melanin, decreased production of phenylalanine so decreased melanin

53
Q

What happens if PKU goes untreated?

A

Microcephaly
Eczematous skin rash
Mousy or musty odor in urine
Severe mental retardation

54
Q

Why can PKU cause sever mental retardation?

A

Greatly increased concentration of phenylalanine impairs brain development and function

55
Q

What is the metabolic catabolism of phenylalanine?

A

Phenylalanine to Tyrosine (Phenylalanine hydroxylate)

Tyrosine to p-OH-phenylpyruvate (tyrosine aminotransferase)

p-OH-phenylpyruvate to homogenistic acid (4-OH-phenylpyruvate deoxygenase)

Homogenistic acid to maleylacetoacetate (homogenistic acid oxidase)

Maleylacetoacetate to Fumarylacetoacetate (maleylacetoacetate isomerase)

Fumarylacetoacetate to Fumarate + Acetoacetate (fumarylacetoacetate hydrolase)

56
Q

In the phenylalanine metabolic cycle what causes PKU?

A

Inability to transform phenylalanine to tyrosine

57
Q

In the phenylalanine metabolic cycle what causes Alkaptonuria?

A

Inability to convert homogenistic acid to maleylacetoacetate

58
Q

What causes alkaptonuria?

A

Deficiency of the enzyme homogenistic deoxygenate

59
Q

What are the signs of alkaptonuria?

A

Homogenistic acid and alkapton in urine
Blue-black pigmentation in connective tissues
Arthritis
Urine turns dark with standing or alkalisation

60
Q

What happens in β-oxidation?

A

Carbon number is reduced by two each time

61
Q

Where does β-oxidation take place?

A

Mitochondrial matrix

62
Q

What are the carbon units lost during β-oxidation become?

A

CO2 in the muscle or generate ketone bodies in the liver

63
Q

What are the symptoms of fatty acid oxidation diseases?

A

Asymptomatic
Hypoglycaemia
Lethargy
Coma
Sudden death

64
Q

What causes hypoglycemia in patients with fatty acid oxidation diseases?

A

There is reduced levels of hepatic glucose, that is why β-oxidation needs to happen.

65
Q

What might cause sudden death in patients with fatty acid oxidation disorders?

A

Prolonged fasting, acute illness

MEDI 202 - Genes To Community (23 decks)

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