Genetics - Disorders Of Metabolism

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Inheritance and mutation (loss, gain) for most genetic disorders of metabolism 

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AR, loss of function

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Hereditary fructose intolerance pts are asx unless they ingest 

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Fructose or sucrose

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MC single-gene disorder of carb metabolism

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Classic galactosemia

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Pathophys, S/S, long-term effects, tx of galactosemia

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- Galactose isn't metabolized to glucose

- Instead metabolized to galactonate and         galactitol

- Dz not well understood

- S/S in newborn: FTT, poor suckling, jaundice

- Unless treated, results in hyperammonemia, sepsis, and death

- Tx: restrict intake of galactose

- Long term effects: poor growth, dev delay, MR

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Mutation that causes galactosemia

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Loss of fxn mutation in GAL-1-uridyl transferase (converts galactose 1-phosphate to glucose 1-phosphate)

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Hyperphenylalaninemia - disorder of ....

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AA metabolism

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Tyrosinemia - disorder of ...

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AA metabolism

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Maple Syrup Urine Dz - disorder of 

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AA metabolism

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Tyrosinemia pathophys

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Inability to metabolize tyrosine to fumarate and acetoacetate - leads to liver tox

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MSUD pathophys

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Inability to use branched-chain AAs for energy, leads to progressive neurodegeneration and death

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PKU is caused by ...

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A loss of fxn mutation in phenylalanine

hydroxylase gene

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Hyperphenylalaninemia causes

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Disruption of myelin on neurons and protein synthesis; causes severe MR if untreated

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Tx for PKU

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Restrict phenylalanine, but not completely eliminate as it is essential

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MCAD deficiency - disorder caused by ....

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Defect in lipid metabolism

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LCHAD deficiency- disorder caused by...

pathophys

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Inability to use long-chain FAs for energy; causes liver failure, CM, and death

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MC single-gene disorder of lipid metabolism

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MCAD deficiency

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MCAD pathohys, S/S, tx

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Deficiency of medium-chain acyl-coenzyme A dehydrogenase that breaks down medium-chain FAs for energy

 

Causes accumulation of FA intermediates, failure to produce ketones, and

exhaustion of glucose

 

S/S: episodic hypoglycemia

 

Tx: avoid fasting

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Mucopolysaccharidoses (MPS disorders) - what type of disorder

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Lysosomal storage dz

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Sphingolipidoses - what type of disorder

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Lysosomal storage dz

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TS dz pathophys, S/S

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Loss of fxn mutation in a chain of hexosaminidase gene that normally catalyzes the breakdown of sphingolipid, GM2 ganglioside

 

GM2 ganglioside accumulates in lysosomes and has detrimental effects esp on the brain

 

Infants normal until 3-6m, then progressive neurodegeneration until death 2-4y, cherry red spot on retina

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Lysosomal storage dsz are caused by

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Lack of degredative fxn in lysosomes or transport of degredative enzymes into lysosomes; causes accumulation of enzyme substrates in lysosomes that cause dz

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Urea cycle disorders cause...

pathophys, s/s, tx

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accumulation of nitrogenous wastes and

hyperammonemia that leads to lethargy, coma, and maybe death.

 

Presents in neonatal period or later

 

Tx: restrict protein to a level that is enough for dev and growth 

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Cystinuria is a defect of ....

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transport of dibasic AAs (cystine, lysine, arginine, and ornithine

 

 

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Cystinuria pathophys, s/s, tx

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Excess excretion of dibasic AAs - cystinuria causes nephrolithiasis that leads to infection, HTN, and renal failure

 

Tx: drinking water and alkalinizing urine

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3 dzs of heavy metal transport

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Hereditary Hemochromatosis

Menkes Dz

Acrodermatitis enteropathica

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Menkes dz

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gut epithelium cannot export copper to liver

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Acrodermatitis enteropathica

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gut epithelium is unable to absorb zinc 

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Reye syndrome is a phenocopy of ...

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Urea cycle defect

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MCAD deficiency is a phenocopy for....

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Reye syndrome

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Inheritance pattern of common form of hereditary hemochromatosis

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AR

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Ethnic group mostaffected by hereditary hemochromotosis

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Northern Europeans

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Homozygous advantage of hereditary hemochromatosis

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Protects against Fe deficicency and anemia

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MC mutation that causes common form of hereditary hemochromatosis 

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Missense mutation in B-2 microglobin domain of HFE gene that acts as an iron sensor

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Pathphys of hereditary hemochromatosis

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Involves a cell's ability to sense iron levels; excessive amouts of iron are absorbed from the small intestine causing fatigue, joint pain, decreased libido, increased skin pigmentation, CM, liver enlargement, and cirrhosis

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Most men who are homozygous for HH mutation...

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Don't develop clinical sx and those who do are seldom symptomatic before 40s