Biochem Questions Thread for Step 1

[MudPhud20XX]

Hi all, again I would like to begin posting biochem questions especially for MS2 who want to review while studying MS2 subjects. Just by doing a couple questions per day I think can make a big change. These are NOT from Uworld, First aid RX, and Kaplan.
Please feel free to add yours.

A 4-year-old boy is brought to the clinic because of a 2-week history of seizures that occur about every 3 days. Medical history is relevant for developmental delay with poor sitting and limited motor movements noticed at 12 months of age. He also has delayed language skills and swallowing difficulty that developed during the past 3 months. His vision and hearing have been deteriorating. Physical examination shows muscle weakness centrally and in all extremities. Fundoscopic examination shows a red spot on the retina. Which of the following is the most likely cause of this boy’s condition?

---

Members don't see this ad.

 

[kagman]

A 5-month-old infant had his first ear infection and was feeding poorly due to the ear pain. One morning the parents found the child unresponsive and rushed him to the ER. Blood glucose level was 45 mg/dL. The child became responsive after IV dextrose. Further blood analysis showed the absence of ketone bodies, normal levels of acyl-carnitine, and the presence of dicarboxylic acids. What is the likely enzymatic defect? What is the origin of the dicarboxylic acids?

otc def ?

 

[MudPhud20XX]

otc def ?

i might be wrong, but I think it's MCAD def

Medium Chain Acyl-CoA dehydrogenase def
- profound fasting hypoglycemica
- low to absent ketones
- lethargy, coma, death if untreated
- C8 - C10 acyl carnitines in blood

 

[kagman]

A 4-month-old infant girl is brought to the pediatrician for evaluation of decreased attention to her surroundings and a noticeable twitch. Her urine has a mousy odor, and laboratory studies show a positive Guthrie test. Which metabolic intermediate is most likely to be produced in lower amounts in this patient?

tyrosine ?

My b/c sux

 

[MudPhud20XX]

tyrosine ?

My b/c sux

yup, it's PKU. btw, is mousy ordor the same as musty odor? forgive my ignorance.....

 

[MudPhud20XX]

A 35-year-old woman complains of chest pains. Physical examination reveals a midsystolic click followed by a late systolic murmur. She is diagnosed with mitral valve prolapse. Which of the following substances is associated with this valvular disease?

 

[kagman]

You have received laboratory results of a patient’s plasma electrolyte concentrations. When the patient’s blood was drawn, the phlebotomist noted it had a soapy appearance and requested analysis of lipids and proteins. These levels were found to be elevated. You intend to recalculate electrolyte concentrations based on plasma water volume, rather than total plasma volume. Compared with a blood sample with normal plasma lipid and protein levels, what differences, if any, would be noted in anion and cation concentrations?

I'd say Cation levels will be low....anion should be the same ?

 

[kagman]

A 6-year-old boy has pitting edema, abdominal pain, proteinuria, and hyperlipidemia. A kidney biopsy specimen indicates minimal change disease. The figure shows a normal electrophoretic pattern of albumin (Alb) and other plasma proteins. It also shows five abnormal patterns, each labeled with a capital letter. Which of the patterns is most likely to be seen in a patient with these symptoms?

b ?

 

[kagman]

A 35-year-old woman complains of chest pains. Physical examination reveals a midsystolic click followed by a late systolic murmur. She is diagnosed with mitral valve prolapse. Which of the following substances is associated with this valvular disease?

qn seems vague w/out options. I'd say myxoid degeneration...

 

[MudPhud20XX]

qn seems vague w/out options. I'd say myxoid degeneration...

yup good job man.
so here are the answer choices
A. chondroitin sulfate
B. dermatan sulfate
C. heparan sulfate
D. keratan sulfate I
E. keratan sulfate II

B is the answer. Mitral valve prolapse involves myxomatous degeneration involving loss of dermatan sulfate.

 

[MudPhud20XX]

I'd say Cation levels will be low....anion should be the same ?

it's actually both cation and anion increase. I thought it was tricky, but here is the solution:

Lipids and proteins typically occupy about 7% of plasma volume, with the remaining 93% being plasma water. Expressing electrolyte concentrations per volume of total plasma underestimates the real concentration in plasma water. When lipid and protein levels are elevated, this causes even lower reported electrolyte concentrations (pseudo-hyponatremia). This artefact is corrected by expressing concentrations per volume of plasma water and reveals uniformly higher electrolyte concentrations.

 

[Jabbed]

otc def ?

MCAD was right. Fasting hypoketotic hypoglycemia with the presence of dicarboxylic acids (end product of omega oxidation of fatty acids in the smooth ER) is responsive to frequent glucose administration because that precludes lipolysis.

 

[Sailey]

Answer to your MCD question I think the answer is B.
In minimal change leakage has to do with + or - charge. B is the option where there is decrease in + charged proteins and increase in negatively charged proteins.

 

[MudPhud20XX]

While examining a surgical biopsy specimen by electron microscopy, a pathology resident notices that many of the cells contain large numbers of a particular cytoplasmic organelle (see figure). He is fairly sure that he has correctly identified these structures; however, to confirm their identity, he performs enzyme histochemistry. Which of the following is a marker enzyme that is characteristic of this organelle?

 

[Sailey]

Q. MCAD deficiency causes elevated LFTs, muscle enzyme elevation, Rhabdomyolysis, CHF, neurologic impairment and cerebral edema. Which of the following resembles these features?
a) Mcardle disease
b) Lesch-nyhan syndrome
c) Hurler syndrome
d) Reyes syndrome
e) Pompe disease

 

[MudPhud20XX]

Q. MCAD deficiency causes elevated LFTs, muscle enzyme elevation, Rhabdomyolysis, CHF, neurologic impairment and cerebral edema. Which of the following resembles these features?
a) Mcardle disease
b) Lesch-nyhan syndrome
c) Hurler syndrome
d) Reyes syndrome
e) Pompe disease

I am going with Pompe which has heart, liver, and muscle problem. hopefully i got it right... good question man.

 

[MudPhud20XX]

An afebrile 50-year-old man with a 30-year history of smoking two packs of cigarettes a day complains of flushing in his face, watery diarrhea, and a 14-kg (30-pound) weight loss over the past 6 months. Physical examination shows an enlarged, nodular liver and a grade 3 pansystolic murmur heard best along the left parasternal border. The murmur increases in intensity on inspiration. Which laboratory study would be most useful in confirming the diagnosis?

 

[Jabbed]

Q. MCAD deficiency causes elevated LFTs, muscle enzyme elevation, Rhabdomyolysis, CHF, neurologic impairment and cerebral edema. Which of the following resembles these features?
a) Mcardle disease
b) Lesch-nyhan syndrome
c) Hurler syndrome
d) Reyes syndrome
e) Pompe disease

D. Reyes

 

[Jabbed]

An afebrile 50-year-old man with a 30-year history of smoking two packs of cigarettes a day complains of flushing in his face, watery diarrhea, and a 14-kg (30-pound) weight loss over the past 6 months. Physical examination shows an enlarged, nodular liver and a grade 3 pansystolic murmur heard best along the left parasternal border. The murmur increases in intensity on inspiration. Which laboratory study would be most useful in confirming the diagnosis?

Serotonin levels? Assuming carcinoid syndrome.

 

[Sailey]

Answer D. is right. page 349 USMLE secrets

 

[Jabbed]

A patient has developed acute pancreatitis with associated steatorrhea. The patient also reports new-onset impairment of night vision, although visual acuity is normal. Another expected finding in this patient would be which of the following?
(A) Nystagmus
(B) Easy bruising
(C) Dermatitis
(D) Loss of teeth
(E) Orange tonsils

 

[seminoma]

A patient has developed acute pancreatitis with associated steatorrhea. The patient also reports new-onset impairment of night vision, although visual acuity is normal. Another expected finding in this patient would be which of the following?
(A) Nystagmus
(B) Easy bruising
(C) Dermatitis
(D) Loss of teeth
(E) Orange tonsils

B. Fat malabsorption so Vit A,D,E,K deficiency (Vit K for easy bruising). Alcoholic? Or maybe valproic acid toxicity?

 

[Jabbed]

B. Fat malabsorption so Vit A,D,E,K deficiency (Vit K for easy bruising). Alcoholic? Or maybe valproic acid toxicity?

Correct! Fat-soluble hypovitaminosis (A, D, E, K) indicated by steatorrhea.

A) Nystagmus --> Thiamine (B1) deficiency causing Wernicke encephalopathy
B) Easy bruising --> Vitamin C or Vitamin K deficiency
C) Dermatitis --> Vitamin B deficiencies
D) Loss of teeth --> Vitamin C deficiency
E) Orange tonsils --> Tangier's disease?

 

[Jabbed]

B. Fat malabsorption so Vit A,D,E,K deficiency (Vit K for easy bruising). Alcoholic? Or maybe valproic acid toxicity?

I don't think the etiology of pancreatitis is important in this case. Considering alcoholic pancreatitis would make A also viable. Depakote toxicity is unlikely to present with just acute pancreatitis (AFAIK).

 

[Jabbed]

You see a 56-year-old female patient in follow-up after discharge from the hospital. She was treated for ketoacidosis and hyperglycemia and now is on basal and rapid acting insulins. You wonder if she really has type 1 diabetes mellitus and was in ketoacidosis or has type 2 diabetes mellitus and had a hyperosmolar state with lactic acidosis. What lab test would help you decide between the two scenarios?

 

[seminoma]

Could rifampin, pza, or inh cause orange tonsils?

 

[worldbeater]

Rifampin causes orange secretions of any fluid as a side effect, so I would say it could cause "orange tonsils"

 

[Sailey]

Answer to #74
Anti glutamic acid decarboxylase antibodies
Good Q Jabbed.

 

[DermViser]

A 6-year-old boy has pitting edema, abdominal pain, proteinuria, and hyperlipidemia. A kidney biopsy specimen indicates minimal change disease. The figure shows a normal electrophoretic pattern of albumin (Alb) and other plasma proteins. It also shows five abnormal patterns, each labeled with a capital letter. Which of the patterns is most likely to be seen in a patient with these symptoms?

Oh, I know where this is from.

 

[Jabbed]

You see a 56-year-old female patient in follow-up after discharge from the hospital. She was treated for ketoacidosis and hyperglycemia and now is on basal and rapid acting insulins. You wonder if she really has type 1 diabetes mellitus and was in ketoacidosis or has type 2 diabetes mellitus and had a hyperosmolar state with lactic acidosis. What lab test would help you decide between the two scenarios?

(A) Insulin levels
(B) C-peptide levels
(C) Fasting blood glucose levels
(D) Random blood glucose levels
(E) Hemoglobin A1C levels

 

[Sailey]

(A) Insulin levels
(B) C-peptide levels
(C) Fasting blood glucose levels
(D) Random blood glucose levels
(E) Hemoglobin A1C levels

a. insulin levels

 

[Sailey]

A 31 y/o female gives birth to a child with irreversible brain damage and elevated levels of phenylalanine in blood. Which of the following is responsible?
a. Fathers genes
b. Grand mother's genes
c. mother's genes
d. mutation
e. mother's diet

 

[pathologyDO]

A 31 y/o female gives birth to a child with irreversible brain damage and elevated levels of phenylalanine in blood. Which of the following is responsible?
a. Fathers genes
b. Grand mother's genes
c. mother's genes
d. mutation
e. mother's diet

My best answer is E. The mothers diet included lots of phenylalanine and the baby had PKU, which is autosomal recessive and requires copies from both parents.

 

[MudPhud20XX]

A 31 y/o female gives birth to a child with irreversible brain damage and elevated levels of phenylalanine in blood. Which of the following is responsible?
a. Fathers genes
b. Grand mother's genes
c. mother's genes
d. mutation
e. mother's diet

I know it's PKU, but not sure about the answer. D? I guess? mutation in phenylalanine hydroxylase I guess?

 

[MudPhud20XX]

A 49 yr old man with rare recessive condition is at high risk for deep vein thrombosis and stroke and has had replacement of ectopic lenses. He has a normal hematocrit and no evidence of megaloblastic anemia.
A mutation in the gene encoding which of the following is most likely to cause this dz?
A. cystathionine synthase
B. homocysteine methyltransferase
C. fibrillin
D. lysyl oxidase
E. branched chain alpha ketoacid dehydrogenase

 

[Jabbed]

A 31 y/o female gives birth to a child with irreversible brain damage and elevated levels of phenylalanine in blood. Which of the following is responsible?
a. Fathers genes
b. Grand mother's genes
c. mother's genes
d. mutation
e. mother's diet

My best answer is E. The mothers diet included lots of phenylalanine and the baby had PKU, which is autosomal recessive and requires copies from both parents.

It is the mother's diet, but I think it's maternal PKU in this case. i.e. the mother has PKU and doesn't control her diet, leading to phenylalanine excess and teratogenic effects.

 

[Jabbed]

A 49 yr old man with rare recessive condition is at high risk for deep vein thrombosis and stroke and has had replacement of ectopic lenses. He has a normal hematocrit and no evidence of megaloblastic anemia.
A mutation in the gene encoding which of the following is most likely to cause this dz?
A. cystathionine synthase
B. homocysteine methyltransferase
C. fibrillin
D. lysyl oxidase
E. branched chain alpha ketoacid dehydrogenase

Disease is homocystinuria, which could be caused by deficiencies in A or B. Going with A, which is absent in classical homocystinuria.

 

[Jabbed]

(A) Insulin levels
(B) C-peptide levels
(C) Fasting blood glucose levels
(D) Random blood glucose levels
(E) Hemoglobin A1C levels

You see a 56-year-old female patient in follow-up after discharge from the hospital. She was treated for ketoacidosis and hyperglycemia and now is on basal and rapid acting insulins. You wonder if she really has type 1 diabetes mellitus and was in ketoacidosis or has type 2 diabetes mellitus and had a hyperosmolar state with lactic acidosis. What lab test would help you decide between the two scenarios?

Answer: B

She's receiving exogenous insulin, so her insulin levels will be relatively normal. If she has type I diabetes and is taking insulin, she would have 0 levels of C-peptide (marker of endogenous insulin production). If she has type II diabetes and is taking insulin, she would still have some basal level of endogenous insulin production. Thus C-peptide would be normal/low-normal.

 

[Jabbed]

23 year old female with severe generalized abdominal pain and an acute psychotic episode after ingesting barbiturates. CT brain and CT abdomen are normal, still waiting on labs and a urine sample, but the nurse tells you that the specimen was so dark that she must have a bad UTI. What is the most likely enzymatic deficiency?

 

[Chipster.]

23 year old female with severe generalized abdominal pain and an acute psychotic episode after ingesting barbiturates. CT brain and CT abdomen are normal, still waiting on labs and a urine sample, but the nurse tells you that the specimen was so dark that she must have a bad UTI. What is the most likely enzymatic deficiency?

Sounds like AIP so I think the answer is PBG deaminase.

 

[Jabbed]

Sounds like AIP so I think the answer is PBG deaminase.

Correct. Expect to see a microcytic anemia when the cbc comes back.

 

[pathologyDO]

Ectopic lenses could be Marfans or Homocysteinuria. Since this is associated with an autosomal recessive inheritance I will go with Homocysteinuria, a cystathionine synthase deficiency

 

[Jabbed]

A mother brings her 6-year-old son to the pediatrician as she is concerned about “mental ******ation.” Blood work demonstrated a microcytic anemia and basophilic stippling. During the history, it became apparent that the boy often spends time with his grandparents, who owned a 100-year-old house. The boy admits to eating paint chips from the radiators in the apartment. The boy’s anemia is most likely the result of what?

 

[worldbeater]

Lead poisoning, he will have an inhibition with delta ALA dehydratase and ferrochetolase. Check for eleveated FEP.

 

[kagman]

While examining a surgical biopsy specimen by electron microscopy, a pathology resident notices that many of the cells contain large numbers of a particular cytoplasmic organelle (see figure). He is fairly sure that he has correctly identified these structures; however, to confirm their identity, he performs enzyme histochemistry. Which of the following is a marker enzyme that is characteristic of this organelle?

Wild guess s100+ ? Are those melanosomes ?

 

[Jabbed]

Lead poisoning, he will have an inhibition with delta ALA dehydratase and ferrochetolase. Check for eleveated FEP.

Correct. Bonus points: how will the RBCs appear on microscopy?

 

[Transposony]

What is the origin of the dicarboxylic acids?

Omega oxidation of very-long-chain fatty acids (VLCFA, >22 carbons) in peroxisomes (ER).

 

[Transposony]

You have received laboratory results of a patient’s plasma electrolyte concentrations. When the patient’s blood was drawn, the phlebotomist noted it had a soapy appearance and requested analysis of lipids and proteins. These levels were found to be elevated. You intend to recalculate electrolyte concentrations based on plasma water volume, rather than total plasma volume. Compared with a blood sample with normal plasma lipid and protein levels, what differences, if any, would be noted in anion and cation concentrations?

The electrolyte concentration will be increased in plasma water volume compared to normal since proteins and lipids in normal plasma "dilutes" them.

 

[Transposony]

Correct. Bonus points: how will the RBCs appear on microscopy?

Microcytic, hypochromic anemia.

 

[Transposony]

While examining a surgical biopsy specimen by electron microscopy, a pathology resident notices that many of the cells contain large numbers of a particular cytoplasmic organelle (see figure). He is fairly sure that he has correctly identified these structures; however, to confirm their identity, he performs enzyme histochemistry. Which of the following is a marker enzyme that is characteristic of this organelle?

Gaucher’s disease---> Lysosome inclusions- Tartrate-resistant acid phosphatase.

 

[Transposony]

Ectopic lenses could be Marfans or Homocysteinuria. Since this is associated with an autosomal recessive inheritance I will go with Homocysteinuria, a cystathionine synthase deficiency

"high risk for deep vein thrombosis and stroke" points towards Homocysteinuria.
Another point to differentiate (if they give you the direction of the lens dislocation) is:
In Marfans, lens dislocates upwards since they are looking up @ Mars being Mar's fan and,
In Homocysteinuria, lens dislocates downwards since they are looking down peeing out homocysteine.