Biochem High Yield Disorders Flashcards
What is the inheritance pattern of pyruvate dehydrogenase complex deficiency?
X-linked
What does pyruvate dehydrogenase complex deficiency cause?
Cannot convert to pyruvate to AcetylCoA. Causes a buildup of pyruvate that gets shunted to lactate (via LDH) and alanine (via ALT).
What are the sx of pyruvate dehydrogenase deficiency?
Neurologic defects, lactic acidosis, incr serum
alanine starting in infancy.
What is the treatment for pyruvate dehydrogenase deficiency?
Incr intake of ketogenic nutrients - high fat content, or high lysine/leucine.
Why is rotenone poisonous?
Inhibits Complex I of OxPhos. Decr proton gradient
Why is antimycin A poisonous?
Inhibits Complex III of OxPhos. Decr proton gradient
Why is cyanide/CO poisonous?
Inhibits Complex IV of OxPhos. Decr proton gradient
What is oligomycin poisonous?
Directly inhibits mito ATP synthase, incr proton gradient, no ATP produced bc electron transport stopped.
Why are uncoupling agents poisonous?
Incr permeability of membrane, causes drop in proton gradient and incr in O2 consumption. ATP synthesis stops but et continues. Produces heat.
What are three uncoupling agents?
2,4-Dinitrophenol, aspirin, thermogenin in brown fat.
Deficiency + inheritance pattern in G6PD deficiency?
X linked. Glucose-6-phosphate dehydrogenase. Responsible for regeneration of NADPH.
What is the secret advantage to G6PD?
Increased malarial resistance
What is the product of G6PD?
NADPH and 6-phosphogluconate –> ribulose-5-P.
What are the fates of ribulose 5-P?
Ribose-5-P (—> PRPP, nucleotide synthesis)
Glyceraldehyde-3-Phosphate (back to glycolysis)–>TGs
Fructose-6-P –> glycolysis
Enzymes in free radical defense via G6PD?
Glutathione perioxidase, glutathione reductase, G6PD.
Deficiency + inheritance pattern in essential fructosuria?
autosomal recessive defect in fructokinase.
Symptoms of essential fructosuria? Where does the fructose go?
Benign, asymptomatic. Fructose can be phosphorylated by hexokinase, or can leave the cell.
Fructose appears in blood and urine.
Deficiency + inheritance pattern in fructose intolerance?
autosomal recessive defect in aldolase B. Fructose-1-phosphate accumulates.
What happens in the cell as a result of fructose intolerance?
Fructose-1-phosphate accumulates, causing decrease in available phosphate, which results in inhibition of glycogenolysis.
What are the sx of fructose intolerance and when do patients present?
Pts present after consumption of fruit, juice, or honey.
Hypoglycemia, jaundice, cirrhosis, vomiting.
What will lab findings of fructose intolerance be?
Urine dip negative - tests glucose only. Can test for reducing sugar.
Treatment of fructose intolerance?
No intake of fructose and sucrose (glucose + fructose).
Deficiency + inheritance pattern in galactokinase deficiency?
Autosomal recessive deficiency of galactokinase, which phosphorylates Galactose.
What may accumulate if galactose is present in diet?
Galactitol (aldose reductase).
What are the sx of galactokinase deficiency?
Infantile cataracts. May present as failure to track objects of develop a social smile. Otherwise relatively mild.
What are lab findings of galactokinase deficiency?
Galactose appears in blood and urine.
Deficiency + inheritance pattern in classic galactosemia?
Autosomal recessive absence of galactose-1-phosphate-uridyltransferase. Conversion of galactose-1-P to glucose-1-P via UDP-Gal/Glu
What are symptoms of classic galactosemia?
Soon after birth, failure to thrive, jaundice, hepatomegaly, infantile cataracts, intellectual disability.
E-coli sepsis in neonates!
What is the treatment of classic galactosemia?
Exclude galactose and lactose (galactose + glucose) from diet.
What is the deficient enzyme in lactase deficiency?
Lactase
What are the types of lactase deficiency?
- Primary (age-dependent decline due to absence of lactase-persistent allele; seen in asian/african/native americans).
- Secondary: loss of brush border due to gastroenteritis, autoimmune dz, etc.
- Congenital lactase deficiency: rare.
What are the sx of lactase deficiency?
Bloating, cramps, flatulence, osmotic diarrhea.
What are the lab findings of lactase deficiency?
Stool w/ low pH. Breath has high hydrogen content w/ lactose tolerance test. Intestinal bx shows normal mucosa in hereditary types.
Treatment of lactase deficiency?
No dairy, or add lactase pills to diet.
What does aldose reductase do?
Converts glucose to sorbitol (and galactose to galactitol).
How is sorbitol handled by tissues?
Converted to fructose by sorbitol dehydrogenase
Which tissues don’t have sorbitol dehydrogenase?
schwann cells, retina, kidney. Lens mostly. Diabetes causes havoc 2/2 sorbitol accumulation bc of chronic hyperglycemia.
Purpose of urea cycle?
Eliminate nitrogen generated by breakdown of amino acids.
Order of Urea cycle?
Ordinarily, Careless Crappers Are Also Frivolous About Urination.
Ornithine, Carbamoyl Phosphate, Citrulline, Aspartate, Arginosuccinate, Fumarate, Arginine.
What can cause hyperammonemia?
Liver Disease
Hereditary defects in urea cycle
What does hyperammonemia deplete and lead to?
Leads to depletion of alpha-ketoglutarate due to excess NH4+, leading to inhibition of TCA.
What is alpha-ketoglutarate used in?
1) TCA
2) Picks up ammonia from aspartate to become glutamate, asparate becomes oxaloacetate –> Malate. SHUTTLE! AST is enzyme.
Sx of hyperammonemia?
tremor (asterixis), slurring of speech, somnolence, vomiting, cerebral edema, blurring of vision
Treatment of hyperammonemia?
1) limit protein in diet
2) lactulose acidifies the GI tract and traps NH4+ for excretion
3) Rifaximin decreases colonic ammoniagenic bacteria
4) Benzoate/phenylbutyrate bing amino acid and lead to excretion, can decrease ammonia levels.
What cause of hyperammonemia has an identical presentation to deficiency of carbamoyl phosphate synthetase I?
N-acetylglutamate is a required cofactor for CAP synthetase I, which brings ammonia into the urea cycle. Absence –> hyperammonemia.
What is the presentation of N-acetylglutamate deficiency?
In infants as poorly regulated respiration and body temperature, poor feeding, developmental delay, intellectual disability.
What is the most common urea cycle disorder and its inheritance pattern?
Ornithine transcarbamylase deficiency, X-linked recessive.
What does OTC do?
Ornithine + CAP –> citruline via OTC. Cannot eliminate ammonia, CAP excess converted to orotic acid (pyrimidine synthesis pathway).
What is the presentation of OTC deficiency?
Usually presents in first few days of life, may present later. sx of hyperammonemia.
Lab findings w/ OTC deficiency?
Increased orotic acid in blood and urine, decreased BUN,. Diff from orotic aciduria bc no megaloblastic anemia (caused by insufficient pyrimidine).
What is the deficiency and inheritance pattern in PKU?
Phenylalanine hydroxylase. Autosomal recessive.
What is the deficiency in malignant PKU?
Tetrahydrobiopterin cofactor.
What are the lab findings with PKU?
Incr phenylalanine, and excess phenylketones in urine. Phenylacetate, phenylactate, and phenylpyruvate.
What is the presentation of PKU?
Sx: Intellectual disability, growth retardation, seizures, fair skin, eczema, musty body odor. Newborn screening 2-3 days after birth (normal at birth bc of maternal enzyme).
Treatment of PKU?
decr phenylalanine, incr tyrosine, BH4 supplementation. No aspartame!
What are the findings of maternal PKU with improper dietary therapy?
Infant with microcephaly, intellectual disability, growth retardation, congenital heart defects.