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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{Rim}} {{Alison}}
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
Line 20: Line 20:
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Hematology
|SubCategory=Hematology
|Prompt=A 2 year old boy is brought by his mother to the physician's office for delayed speech. The mother informs the physician that unlike his older siblings his age, the patient is very irritable and is unusually hyperactive. Further questioning reveals that the patient/s family lives in an old house that has chipped paint. Physical examination is remarkable for pallor. Complete blood count (CBC) shows hemoglobin: 9.8 g/dL and MCV: 68 fl. Peripheral smear of the patient's blood shows basophilic stippling. Based on the simplified diagram of heme synthesis shown below, which of the following steps is most likely inhibited in this patient?
|Prompt=A 2-year-old male is brought by his mother to the physician's office for delayed speech. The mother informs you that, unlike his older siblings at his age, the patient is irritable and hyperactive. Further questioning reveals that the patient's family lives in an old house with chipped paint. Physical examination is remarkable for pallor. Complete blood count (CBC) demonstrates hemoglobin levels of 9.8 g/dL and MCV: 68 fl. A peripheral smear of the patient's blood displays basophilic stippling. Based on the simplified diagram of heme synthesis shown below, which of the following steps is most likely inhibited in this patient?


[[Image:WBR0344.png|500px]]
[[Image:WBR0344.png|500px]]
|Explanation=The patient is most likely diagnosed with lead toxicity. Lead toxicity is not uncommon in developing countries in very young children. Patients typically present with failure to meet developmental milestones, speech delay, hyper or hypoactivity, and irritability. The patient's exposure to chipped paints in old houses (pre-1960s) puts the patient at hight risk for lead toxicity. Physical examination showing pallor is also consistent with the diagnosis. In patients with lead toxicity, work-up shows microcytic hypochromic anemia with low MCV, as shown in this patient. Additionally, peripheral smear shows basophilic stippling.
|Explanation=The patient in this scenario is most likely experiencing [[lead toxicity]]. [[Lead toxicity]] in young children is common in developing countries. Patients typically present with failure to meet developmental milestones, speech delay, hyper- or hypoactivity, and irritability. The patient's exposure to chipped paint in his old house (pre-1960s) increases his risk for lead toxicity. In patients with lead toxicity, work-up typically demonstrates microcytic hypochromic anemia with low MCV levels and a peripheral smear displays basophilic stippling.


Lead inhibits 2 enzymes of heme synthesis: ALA-dehydratase (the second step of heme synthesis) and ALA-ferrochelatase (the last step of heme synthesis).
Lead inhibits two enzymes of heme synthesis: [[ALA-dehydratase]] (the second step of heme synthesis) and [[ALA-ferrochelatase]] (the last step of heme synthesis).


(To note, the image above is simplified. Some intermediate products and enzymes are not listed in this illustration of heme synthesis).
(To note, the image above is simplified. Some intermediate products and enzymes are not listed in this illustration of heme synthesis).


Educational Objective: Lead inhibits ALA-dehydratase and ferrochelatase.
|EducationalObjectives= Lead inhibits ALA-dehydratase and ferrochelatase.
|References= First Aid 2014 page 380
 
|AnswerA=A
|AnswerA=A
|AnswerAExp="A" corresponds to ALA-synthase, inhibited by B6 deficiency and in hereditary conditions, such as X-linked ALA-synthase deficiency.
|AnswerAExp= "A" corresponds to ALA-synthase, inhibited by B6 deficiency and in hereditary conditions, such as X-linked ALA-synthase deficiency.
|AnswerB=B
|AnswerB=B
|AnswerBExp="B" corresponds to ALA dehydratase, inhibited by lead.
|AnswerBExp= See explanation.
|AnswerC=C
|AnswerC=C
|AnswerCExp="C" corresponds to porphobilinogen deaminase. Deficiency of this enzyme causes acute intermittent porphyria.
|AnswerCExp= "C" corresponds to porphobilinogen deaminase. Deficiency of this enzyme typically causes acute intermittent porphyria.
|AnswerD=D
|AnswerD=D
|AnswerDExp="D" corresponds to uroporphyrinogen III synthase. It is not a clinically important enzyme.
|AnswerDExp= "D" corresponds to uroporphyrinogen III synthase. [[Uroporphyrinogen III synthase]] deficiency is associated with [[Gunther's disease]].
|AnswerE=E
|AnswerEExp= "E" corresponds to uroporphyrinogen decarboxylase, which is typically deficient in porphyria cutanea tarda.
|AnswerEExp="E" corresponds to uroporphyrinogen decarboxylase. It is deficient in porphyria cutanea tarda.
|RightAnswer=B
|RightAnswer=B
|WBRKeyword=lead, poisoning, toxicity, ALA, dehydratase, ferrochelatase, anemia, microcytic, hypochromic, basophilic, stippling, peripheral, smear, old, house, chipped, paint, irritability, speech, delay
|WBRKeyword=lead poisoning, lead toxicity, ALA, dehydratase, ferrochelatase, anemia, microcytic, hypochromic, basophilicstippling, peripheral smear, old, irritability, speech delay
|Approved=No
|Approved=Yes
}}
}}

Revision as of 15:40, 15 July 2014
Author [[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Alison Leibowitz)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pathophysiology
Sub Category SubCategory::Hematology
Prompt [[Prompt::A 2-year-old male is brought by his mother to the physician's office for delayed speech. The mother informs you that, unlike his older siblings at his age, the patient is irritable and hyperactive. Further questioning reveals that the patient's family lives in an old house with chipped paint. Physical examination is remarkable for pallor. Complete blood count (CBC) demonstrates hemoglobin levels of 9.8 g/dL and MCV: 68 fl. A peripheral smear of the patient's blood displays basophilic stippling. Based on the simplified diagram of heme synthesis shown below, which of the following steps is most likely inhibited in this patient?

]]

Answer A AnswerA::A
Answer A Explanation AnswerAExp::"A" corresponds to ALA-synthase, inhibited by B6 deficiency and in hereditary conditions, such as X-linked ALA-synthase deficiency.
Answer B AnswerB::B
Answer B Explanation AnswerBExp::See explanation.
Answer C AnswerC::C
Answer C Explanation AnswerCExp::"C" corresponds to porphobilinogen deaminase. Deficiency of this enzyme typically causes acute intermittent porphyria.
Answer D AnswerD::D
Answer D Explanation [[AnswerDExp::"D" corresponds to uroporphyrinogen III synthase. Uroporphyrinogen III synthase deficiency is associated with Gunther's disease.]]
Answer E AnswerE::
Answer E Explanation AnswerEExp::"E" corresponds to uroporphyrinogen decarboxylase, which is typically deficient in porphyria cutanea tarda.
Right Answer RightAnswer::B
Explanation [[Explanation::The patient in this scenario is most likely experiencing lead toxicity. Lead toxicity in young children is common in developing countries. Patients typically present with failure to meet developmental milestones, speech delay, hyper- or hypoactivity, and irritability. The patient's exposure to chipped paint in his old house (pre-1960s) increases his risk for lead toxicity. In patients with lead toxicity, work-up typically demonstrates microcytic hypochromic anemia with low MCV levels and a peripheral smear displays basophilic stippling.

Lead inhibits two enzymes of heme synthesis: ALA-dehydratase (the second step of heme synthesis) and ALA-ferrochelatase (the last step of heme synthesis).

(To note, the image above is simplified. Some intermediate products and enzymes are not listed in this illustration of heme synthesis).
Educational Objective: Lead inhibits ALA-dehydratase and ferrochelatase.
References: First Aid 2014 page 380]]

Approved Approved::Yes
Keyword WBRKeyword::lead poisoning, WBRKeyword::lead toxicity, WBRKeyword::ALA, WBRKeyword::dehydratase, WBRKeyword::ferrochelatase, WBRKeyword::anemia, WBRKeyword::microcytic, WBRKeyword::hypochromic, WBRKeyword::basophilicstippling, WBRKeyword::peripheral smear, WBRKeyword::old, WBRKeyword::irritability, WBRKeyword::speech delay
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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