Repeated USMLE Questions Step 1- 2

Q- An 18-year-old man presents to the office for evaluation of multiple swellings in his neck. On examination, he has multiple large lymph nodes in his neck. Neurological examination reveals poor coordination on walking. Biopsy of lymph node is positive for lymphoma. He is diagnosed with ataxia-telangiectasia.

What is the etiology of this disorder?

A- Defective DNA repair mechanisms

B- Deletion of VHL gene on chromosome 3

C- Mutation in the NF1 gene on chromosome 17

D- Mutation in PKD1 on chromosome 16

E- Mutation in APC gene on chromosome 5

A- Defective DNA repair mechanisms- Ataxia-telangiectasia is a recessive autosomal disorder caused by defective DNA repair mechanisms. It results in weakness of immune systems which leads to multiple infections and increasing risk of cancer. enzymes are all normal.

Q- Which one of the following conditions is most likely occurs in a patient with thrombocytopenia?

A- Cerebral hemorrhage

B- Hemarthrosis

C- Petechiae

D- Subungual hemorrhage

C- Petechiae- It is the most common condition in a patient with thrombocytopenia. Other types of hemorrhages on the list most likely occur with hemophilia.

Q- Serum sickness is involving which one of the following types of hypersensitivity?

A- Type 1 (IgE mediated reaction)

B- Type 11 (Antibody-mediated reaction)

C- Type 111 (Immune complex reaction)

D- Type 1V (T-cell-mediated reaction)

C- Type 111 (Immune complex reaction)- Serum sickness is involving an immune complex reaction and so, it is considered type 111 hypersensitivity. Other diseases involving type 111 of hypersensitivity are post-streptococcal glomerulonephritis, rheumatoid arthritis and systemic lupus erythematosus.

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