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chem path > metabolic disorder > Flashcards

metabolic disorder Flashcards

1
Q

When is UK newborn screening done and how?

A

Guthrie blood spot test at 6 days of age

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2
Q

what does Guthries blood spot test for?

A

phenylketonuria
congential hypothyroidism
CF
sickle cell
MCAD (medium chain acylCoA dehydrogenase) deficiency

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3
Q

what doees conjugated hyperbilirubinaemia indicate in a newborn?

A

pathological (eg. biliary atresia, metabolic disroders etc)
-indicates issue with bilirubin processing
-unconjugated can be physiological due to immature liver or breastfeeding

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4
Q

mnemonic to remember guthrie spot test

A

Sick Children Hate Choosing Food. 6 meals include Pizza, MCDonalds and Maple Syrup

-Sickle cell
-congenital hypothyroidism
-Cystic Fibrosis
-6 days of age
-PKU
-MCADD
-MSUD

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5
Q

what is phenylketonuria?

A

-phenylanine hydroxylase deficiency (converts phenylalanine to tyrosine)
-phenylananine (found in protein containing foods) not broken down and accumulates
-it is neurotoxic

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6
Q

what is raised in phenylketonuria

A

-phenylpyruvate in blood
-pheynylacetic acid in urine

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7
Q

what screening test for PKU

A

phenylalanine serum levels

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8
Q

treatment for PKU?

A

low protein diet, amino acid supplements (must be given in first 6 wks)

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9
Q

what happens in congenital hypothyrodism

A

agenesis/dysgenesis of thyroid gland

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10
Q

what test for congential hypothyrodism

A

TSH levels (high)

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11
Q

what mutation in cystic fibrosis and outcome?

A

mutation in CFTR (F508del is most common)
-outcome: viscous secretions leads to duct blockages

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12
Q

test for CF?

A

-immune reactive trypsin
-if positive DNA mutation detection

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13
Q

what is MCADD

A

-medium chain AcylCoA dehydrogenase deficiency
-fatty acid oxidation disorder - cant convert fatty acids to ketones so cant use fats as fuel source
-blood shows hypoketotic hypoglycaemia + build up of fatty acids
-leads to hepatomegaly and cardiomyopathy
-cause of cot death

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14
Q

test for MCADD

A

acylcarnitine levels by tandem mass spectrometry

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15
Q

treatment for MCADD

A

regular carbohydrates (regular meals never fasted)

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16
Q

what urine in PKU

A

musky urine smell - due to phenylananine build up

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17
Q

what is the PKU triad

A

blonde hair, blue eyes, mental retardation

*think of nazis!

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18
Q

what is homocysteinuria & its key triad

A

accumulation of homocysteine
-key triad: lens dislocation, thromboembolism, mental retardiation
-cysteine renal stones
-kids have fair skin, brittle hair

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19
Q

what is specificity

A

the probability that someone without the disease will correctly test negative

eg. if 85 people don’t have CF but only 80 test negative = 80/85 = 94%

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20
Q

what is sensitivity

A

probability that someone with the disease will correctly test positive

eg. if 100 total CF patients and only 90 test positive = 90/100 = 90%

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21
Q

what is positive predictive value? (PPV)

A

probability that someone who tests positive actually has the disease

eg. if 95 people tested positive and only 90 of them had disease = 90/95 = 94%

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22
Q

what is negative predictive value (NPV)

A

probability that someone who tests negative doesnt have disease

eg. if 90 test negative and only 80 didn’t have disease = 80/90 = 89%

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23
Q

what does a high NPV indicate

A

low false negatives

24
Q

what does predictive value depend on

A

disease prevalence
-lower prevalence lower PPV but higher NPV

25
Q

what are group 1 metabolic conditions

A

accumulation of toxins
-organic acidaemias/acidurias
-urea cycle disorders
-aminoacidopathies

26
Q

what are some features of organic acidaemias/acidurias?

A

-high urea/ketones
-metabolic acidosis + hyperammonimea
-treat wiht low protein diet, acylcarnitine and haemofiltration
-often have funny smells (cheesy + sweaty)

27
Q

what happens in MSUD (maple syrup urine disease)?

A

-cant break down leucine & isoleucine leading to accumulation of toxic product
-encephalopathy, hypotonia, seizures
-buzzword: sweet odour (maple) + smelly feet

28
Q

features of isovalaeric acidaemia?

A

-cheesy/sweaty smell (baby smells like sweaty feet)
-leucine build up causes smell

29
Q

how many urea cycle disorders are there + example?

A

9
ornithine trancabamylase deficiency (x-linked)

30
Q

what happens in urea cycle disorders

A

high serum ammonia (as urea not formed) leading to encephalopathy & developmental delay, respiratory alkalosis, vomiting, neuro symptoms worse with high protein

31
Q

how to treat urea cycle disorders

A

low protein diet (stops ammonia formation)

32
Q

what is urea cycle

A

protein metabolism produces ammonia (toxic). urea cycle converts it to less toxic substance (urea) to be easily excreted

33
Q

male infant presents with failure to thrive, neuro signs (eg. tremor) and tachypnoea. what defect?

A

urea cycle disorder

(neuro signs + tachypnoea = encephalopathy + metabolic alkalosis = increased ammonia)

34
Q

what are some aminoacidopathies

A

PKU
maple syrup urine disease

35
Q

what are group 2 metabolic disorders

A

-glycogen storage disorders
-galactosaemia
-fatty acid oxidation disorders

36
Q

how many glycogen storage disorders + 1 example?

A

9
-Von Gierke’s

37
Q

what happens in glycogen storage disorders

A

-deficiency of glucose - 6 phosphate.
-cant produce glucose and release it from liver
-glucose-6 phosphate rises and glycogen accumulates in liver & kidneys
-hepatomegaly, hypoglycaemia, neutropaenia
-hepatoblastoma risk high

38
Q

how to treat glycogen storage disorders

A

regular carbohydrates

39
Q

what happens in galactossaemia?

A

-deficiency in GALT in galactose metabolism so galactose-1 phosphate accumulates in organs/tissues like liver
-causes infant cataracts (no social smile cos they cant see)
-high conjugated bilirubin (jaundice) because liver dysfunction
-recurrent infections (eg. E.coli UTI) - at risk of sepsis becas=yse lower immune system

40
Q

how to treat galactossaemia

A

low lactose/galactose diet

41
Q

infant with jaundice + sepsis who became unwell after starting breastfeeding?

A

galactossaemia

42
Q

what happens in fatty acid oxidation disorders?

A

cant convert fatty acids to ketones to use fats as fuel source
-hypoglycaemia, cardiomyopathy, rhabdomylosis, low ketones
-non-ketotic hypoglycaemia

43
Q

how do you screen for fatty acid oxidation disorders

A

blood acylcarnitine

44
Q

how do you manange fatty acid oxidation disorders

A

no fasting - regular carbs

45
Q

what are group 3 metabolic disorders

A

-defects in large molecule synthesis
-peroxisomal disorders
-glycosylation disorders

46
Q

what happens in peroxisomal disorders

A

-malfunctioning peroxisomes that are needed for lipid metabolism
-cannot catabolise very long fatty acids or make bile salts
-poor feeds, seizures, retinopathy, hepatomegaly, hypotonia
(needed for neurological function)

47
Q

what happens in glycosylation disorders

A

-glycosylation is addition of sugars to proteins and lipids to help with stability and function - this is dysfunctional
-retardation & nipple inversion

48
Q

how to identify glycosylation disorders

A

measure serum transferrins

49
Q

what are group 4 metabolic disorders

A

lysosomal disorders eg. Tay Sachs or Fabrys

50
Q

what happens in Tay sachs (lysosomal disorders)

A

-deficiency in HEX-A enzyme so GM@ ganglioside accumulates in nerve cells
-neuroregression, hepatomegaly, cardiomyopathy
-cherry red spot on macula (also seen In Fabrys)
-predominant in Ashkenazi jews

51
Q

what is red flag for tay sachs

A

dysmorphic + regression

52
Q

what ethnicity has tay sachs

A

ashkenazi jews

53
Q

what are group 5 metabolic disorders

A

mitochondrial eg. MELAS, POEMS, Kearns Sayre

54
Q

what inheritance for mitchondrial disorders

A

maternal inheritance

55
Q

what happens in mitochondrial disordes

A

-involve CNS, muscle, heart (energy tissues)
-high lactate & CK leads to myopathy (lactic acidosis)

56
Q

how to diagnose mitochondrial conditions

A

muscle biopsy

57
Q

what is reye syndrome

A

-rapidly worsening brain disease
-vomiting, seizures, loss of consciousness, liver toxicity (but no jaundice), respiratory arrest
-common after viral illness or kids taking aspirin

chem path (20 decks)

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