USMLE Step 1 Highlights (4)


1- A 1-year-old boy with a history of many bacterial, viral and fungal infections presents to his physician with chronic diarrhea. Laboratory tests show that both B- and T-Lymphocytes counts are very low.

What is the most likely diagnosis, etiology and treatment?

This is most likely a case of Severe Combined Immunodeficiency (SCID) caused by adenosine deaminase deficiency. Treatment is bone marrow transplantation.

2- A 50-year-old man presents with productive cough, chest pain and fever for 2 days. Last week, he returned from a trip to Phoenix, Arizona. Sputum analysis shows yeast cells. Direct Fluorescent Antibody Staining reveals broad-based budding.

What is the causative organism?

The causative organism in different cases of fungal lung infections depend on the region where infection is contracted. Blastomyces is the most common organism in Arizona. Another clue is the mnemonic: Blastomyces are Broad-Based Budding.

3- A 5-year-old boy with skin lesions everywhere present with his parents to discuss the result of biopsies taken from different skin lesions. The report shows squamous cell carcinoma on several biopsies.

What mutation is most likely found on this boy’s DNA?

Thymidine dimers due to defect in excision repair. The condition is xeroderma pigmentosum. It is autosomal recessive and results in photosensitivity and skin cancer.


By | 2016-12-10T04:10:51+00:00 September 18th, 2016|USMLE Highlights|0 Comments

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