WBR0953

Author	[[PageAuthor::Mugilan Poongkunran M.B.B.S [1]]]
Exam Type	ExamType::USMLE Step 3
Main Category	MainCategory::Primary Care Office
Sub Category	SubCategory::Hematology
Prompt	[[Prompt::A 26 year old female presents to the office with a 6 month history of fatigue. On further review of history, she says she has been experiencing occasional palpitations for the past 1 year for which she never consulted a doctor. Her menstrual cycles are regular and she is sexually active. Her past history is otherwise insignificant and her family history is unremarkable. She does not smoke and drink. Her vitals are temperature: 36.7 C, blood pressure: 120/80 mmHg, pulse: 102/min and respiration's: 16/min. All system examinations are normal except pallor. Her laboratory values are : Hb : 7 g/dl RBC’s : 2 million/cmm WBC’s : 6000/cmm Segmented neutrophils : 60 % Bands : 2 % Eosinophils : 2 % Lymphocytes : 32 % Monocytes : 6 % MCHC : 34 % MCV : 85 fl Her peripheral smear is shown below :]]
Answer A	AnswerA::50 percent of her offspring will be affected
Answer A Explanation	[[AnswerAExp:: Correct  : Autosomal dominant inheritance of a single parent has a 50 percent chance of transmitting the mutation to subsequent children and hereditary spherocytosis is an autosomal dominant disease.]]
Answer B	AnswerB::50 percent of her sons will be affected and 50 percent her daughters will be carriers
Answer B Explanation	AnswerBExp::''' Incorrect ''' : X-linked inheritance of a single parent will result in 50 percent of her sons to be affected and 50 percent her daughters to be carriers.
Answer C	AnswerC::25 percent of siblings will be affected and 50 percent will be carriers
Answer C Explanation	[[AnswerCExp:: Incorrect  : Autosomal recessive inheritance of each heterozygous parent has a 50 percent likelihood of transmitting the mutation, so there is a 25 percent probability that an offspring will inherit two mutations. On average, 25 percent of siblings of affected subjects will be affected, 25 percent will harbor no mutations, and 50 percent will be carriers.]]
Answer D	AnswerD::All her offspring will be affected
Answer D Explanation	AnswerDExp::''' Incorrect ''' : All offspring of affected mothers are affected (although some may be phenotypically normal) and no offspring of affected fathers are affected in mitochondrial inheritance.
Answer E	AnswerE::All her offspring will be normal
Answer E Explanation	AnswerEExp::''' Incorrect ''' : All her offspring cannot be normal because of the autosomal dominant inheritance pattern.
Right Answer	RightAnswer::A
Explanation	[[Explanation::Hereditary spherocytosis is a genetically-transmitted form of spherocytosis, an auto-hemolytic anemia characterized by the production of red blood cells that are sphere-shaped rather than donut-shaped, and therefore more prone to hemolysis. Hereditary spherocytosis is an autosomal dominant trait, caused by a variety of molecular defects in the genes that code for spectrin, ankyrin, protein 4.1, and other erythrocyte membrane proteins. The spleen's hemolysis results in observational symptoms of fatigue, pallor, and jaundice. Characteristic lab findings are reticulocytosis, decreased mean corpuscular volume, increased mean corpuscular hemoglobin concentration, increased red cell distribution width and a peripheral blood smear with the abnormally small red blood cells lacking the central pallor i.e. spherocytes are seen. Due to the law of independent assortment, the heterozygous parent of hereditary spherocytosis has a 50 percent chance of transmitting the mutation to subsequent children. Therefore, on average, 50 percent of offspring of an affected parent will be affected. These children in turn will transmit to 50 percent of their offspring (who will also be affected). Educational Objective: References: ]]
Approved	Approved::Yes
Keyword	WBRKeyword::Hereditary spherocytosis
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