A 54-year-old man comes to the emergency department with a 3-month history of fatigue and exertional dyspnea. He has early satiety and frequent upper abdominal discomfort. On physical examination, the patient has palpable splenomegaly but no lymphadenopathy. Laboratory tests are as follows: Reverse transcription polymerase chain reaction is used to diagnose chronic myelogenous leukemia in this patient. Which of the following is most likely to be detected by this test?

Question

A 54-year-old man comes to the emergency department with a 3-month history of fatigue and exertional dyspnea.  He has early satiety and frequent upper abdominal discomfort.  On physical examination, the patient has palpable splenomegaly but no lymphadenopathy.  Laboratory tests are as follows:  Reverse transcription polymerase chain reaction is used to diagnose chronic myelogenous leukemia in this patient.  Which of the following is most likely to be detected by this test?

Quizplus · Accepted Answer

Reverse transcription polymerase chain reaction (RT-PCR) is used to detect and quantify levels of messenger RNA (mRNA) in a sample. It is similar to regular PCR in that it uses sequence-specific primers, thermostable DNA polymerase, and a pool of deoxyribonucleoside triphosphates to amplify a DNA template. In RT-PCR, this template is generated by the action of reverse transcriptase on the mRNA sample, producing a complementary DNA (cDNA) strand that can then be amplified by PCR. Because cDNA is complementary to the mRNA sequence, it contains the exons of a gene along with the 5′ and 3′ untranslated regions. Chronic myelogenous leukemia (CML) is characterized by uncontrolled proliferation of the myeloid stem cell line due to a chromosomal translocation. This translocation causes the BCR gene on chromosome 22 to fuse with the ABL gene on chromosome 9, forming the BCR-ABL fusion gene. The BCR-ABL fusion protein product is a constitutively active tyrosine kinase that accelerates cell division and increases genetic instability. RT-PCR can be used to identify mRNA transcribed from the BCR-ABL fusion gene and therefore diagnose CML. (Choice A) Fluorescence in situ hybridization (FISH) techniques allow direct localization of genes to their respective chromosomes by using a labeled DNA probe complementary to the sequence of interest. (Choices B and E) RT-PCR amplification uses an mRNA template, so it cannot detect changes in the parts of the gene that are not transcribed (eg, promoter and enhancer regions). Other PCR techniques that use chromosomal DNA can detect changes in these nontranscribed regions. (Choice C) RT-PCR is used to detect levels of mRNA expression; it does not identify proteins. A Western blot study can detect the BCR-ABL protein by using monoclonal antibodies directed against BCR or ABL. Educational objective: Reverse transcription polymerase chain reaction (RT-PCR) is used to detect and quantify levels of mRNA in a sample. It uses reverse transcription to create a complementary DNA template that is then amplified using the standard PCR procedure. RT-PCR can be used to diagnose chronic myelogenous leukemia by identifying an mRNA transcript containing both BCR and ABL exons in affected cells. __________ References: Real time polymerase chain reaction in diagnosis of chronic myeloid leukemia. (http://www.ncbi.nlm.nih.gov/pubmed/24613116)

A 54-Year-Old Man Comes to the Emergency Department with a 3-Month