WBR0119

Author	[[PageAuthor::William J Gibson (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Genetics
Sub Category	SubCategory::Reproductive
Prompt	[[Prompt::A young couple presents to the physician's office for infertility after 18 months of failed attempts at conception despite appropriate measures. Upon further questioning, the woman had previously conceived and given birth to a healthy child in a separate relationship. The man is currently being evaluated for infertility. On physical examination, the patient is found to have low muscle mass, gynecomastia, and small testes. Laboratory studies reveal markedly elevated LH and FSH. The physician orders chromosomal karyotyping to confirm the diagnosis. Which of the following is the most likely karyotype of this patient?]]
Answer A	AnswerA::46,XXY
Answer A Explanation	AnswerAExp::Patients with Klinefelter's syndrome have an additionally X chromosome. The total number of chromosomes is thus 47, not 46.
Answer B	AnswerB::44,XXY
Answer B Explanation	[[AnswerBExp::Patients with Klinefelter's syndrome have an additional X chromosome. The total number of chromosomes is thus 47, not 44. Denoting a karyotype includes the total number of chromosomes, including autosomes and sex chromosomes, followed by the identity of sex chromosomes.]]
Answer C	AnswerC::45,XO
Answer C Explanation	[[AnswerCExp::45,XO is the karyotype of patients with Turner syndrome.]]
Answer D	AnswerD::46,XX/XY
Answer D Explanation	AnswerDExp::This karyotype refers to a rare mosaic chromosomal abnormality which causes some cells in the body to have XX chromosomes and some to have XY chromosomes. This karyotype causes intersex conditions.
Answer E	AnswerE::47,XXY
Answer E Explanation	[[AnswerEExp::This karyotype is the typical karyotype of patients with Klinefelter’s syndrome.]]
Right Answer	RightAnswer::E
Explanation	[[Explanation::The normal human karyotype contains a total of 22 pairs of autosomes (22 x 2 = 44), and one pair of sex chromosomes (1 x 2 = 2). Thus, the total number of chromosomes in a normal human is 46. The standard method to denote a karyotype portrays the total number of autosomes and sex chromosomes followed by the identity of sex chromosomes to show the gender. For example, 46,XX is the karyotype of a normal human female and 46,XY is the karyotype for a normal human male. Klinefelter’s syndrome (KS) is the most frequent chromosomal aberration in males. It is caused by the presence of two X chromosomes along with a single Y chromosome, resulting in a karyotype of 47,XXY. Individuals with KS are phenotypically males, but often have stigmata of their chromosomal aberration. Signs and symptoms include small testes, increased height, gynecomastia, osteopenia, learning disabilities, abdominal adiposity, and infertility with azoospermia. Lab results showing hypergonadotropic hypogonadism (low testosterone, elevated LH and FSH) are consistent with the diagnosis. Patients with Klinefelter’s syndrome are often diagnosed during work-up for infertility because many patients appear phenotypically normal. Educational Objective: The standard method to denote a karyotype among normal humans portrays the total number of autosomes and sex chromosomes followed by the identity of sex chromosomes to show the gender. Klinefelter’s sydrome is caused by an extra X chromosome in an otherwise normal male. Patients with karyotype usually have a karyotype of 47,XXY. References: Groth KA, Skakkebaek A, Host C, Gravholt CH, Bojesen A. Klinefelter syndrome - a clinical update. J Clin Endocrinol Metab. 2013;98(1):20-30 First Aid 2014 page 574]]
Approved	Approved::Yes
Keyword	WBRKeyword::Klinefelter syndrome, WBRKeyword::Sex, WBRKeyword::Chromosome, WBRKeyword::Karyotype, WBRKeyword::Karyotyping, WBRKeyword::Genetics, WBRKeyword::Reproductive, WBRKeyword::Gender, WBRKeyword::Infertility, WBRKeyword::Klinefelter's syndrome, WBRKeyword::Syndrome, WBRKeyword::XXY, WBRKeyword::Hypergonadotropic, WBRKeyword::Hypogonadism, WBRKeyword::Hypergonadotropic hypogonadism, WBRKeyword::Testosterone, WBRKeyword::Gynecomastia, WBRKeyword::Testes
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