Homocystinuria Flashcards

1
Q

inheritance pattern

A

autosomal ressevive disorder

1 in 344000

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2
Q

problem metabolising

A

methionine causing excess homocystine to be excreted in the urine

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3
Q

homocystine

A

oxidised form of homocysteine

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4
Q

homocystinurias affects

A

connective tissue

muscles

CNS

CVS

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5
Q

outline the homocystinuria pathway

A
  1. dietary and endogenous protein are sources of methionine
  2. methionine is converted to homocysteine
  3. however defect in cystathione B-synthase (most common) means homocysteine is not converted to cystathionine
  4. cystathione B-synthase requires active form of Vit B6 to act as a co-factor
  5. cystathionine is converted to cystein
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6
Q

therefore a defect in cystathione B synthase causes an accumulation of

A

homocysteine

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7
Q

why is homocystine in excess and not homocysteine?

A

is two homocysteines joined together by a disulphide bond (i.e. the oxidized form of homocysteine). The form of homocysteine that appears in the urine of homocystinuria patients is mostly (~98%) homocystine (hence the name homocystinuria).

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8
Q

elevated plasma homocystein shown to be associated with

A

CVD

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9
Q

cystine

A

s two cysteine amino acids bound together by a disulphide bond

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10
Q

homocystinuira vs marfan syndrome

A
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11
Q

Homocystinuria vs Marfan syndrome

A
  • Marfan syndrome is a genetic disorder of connective tissue.
  • Some of the clinical features of homocystinuria, such as lens dislocation and skeletal deformities, are similar in Marfan syndrome
  • High levels of homocysteine affect connective tissue and bone (mechanism by which this occurs is not known).
  • Excess homocysteine causes damage to collagen and elastic fibres in connective tissue by binding to lysine residues in proteins.
  • Metabolites of methionine are toxic to neurones and cause neurological dysfunction
  • Symptoms in homocystinuria which are not seen in Marfan syndrome
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