USMLE Forum Archives - USMLE Step 1 - Pathology 24
Pathology 24
TheOne - 11-02-06 21:24
A 15-year-old boy is evaluated by a clinician for failure to develop normal male secondary sexual characteristics. Physical examination reveals small testes, a small penis, and gynecomastia. The boy has had some difficulties in school, and the parents say that the school psychometrist said he had an IQ of 90. This patient's condition is most likely to be related to which of the following?
A. Deletion
B. Nondisjunction of an autosomal chromosome
C. Nondisjunction of a sex chromosome
D. Non-Robertsonian translocation
E. Robertsonian translocation
TheOne - 11-02-06 21:24
A 15-year-old boy is evaluated by a clinician for failure to develop normal male secondary sexual characteristics. Physical examination reveals small testes, a small penis, and gynecomastia. The boy has had some difficulties in school, and the parents say that the school psychometrist said he had an IQ of 90. This patient's condition is most likely to be related to which of the following?
A. Deletion
B. Nondisjunction of an autosomal chromosome
C. Nondisjunction of a sex chromosome
D. Non-Robertsonian translocation
E. Robertsonian translocation
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#2
Re: Pathology 24 Youngdoctor - 11-03-06 20:02 A 15-year-old boy is evaluated by a clinician for failure to develop normal male secondary sexual characteristics. Physical examination reveals small testes, a small penis, and gynecomastia. The boy has had some difficulties in school, and the parents say that the school psychometrist said he had an IQ of 90. This patient's condition is most likely to be related to which of the following?
A. Deletion
B. Nondisjunction of an autosomal chromosome
C. Nondisjunction of a sex chromosome
D. Non-Robertsonian translocation
E. Robertsonian translocation
Where can i find the explanation?.
#3
Re: Pathology 24
TheOne - 11-04-06 18:03 Explanation: The correct answer is C. The boy probably has Klinefelter's syndrome (47, XXY), which has the typical presentation described in the question. The condition arises as a result of failure of separation (nondisjunction) of the sex chromosomes, and can be related to either paternal nondisjunction (slightly more common) or maternal nondisjunction. Deletions (choice A) are a common form of genetic disease and contribute to many genetic recessive diseases. Examples of nondisjunction of autosomes (choice B) include trisomies such as most cases of Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18), and Patau syndrome (trisomy 13). There are two types of translocations: non-Robertsonian (choice D) and Robertsonian (choice E). Non-Robertsonian (reciprocal) translocations result when two non-homologous chromosomes exchange genetic material. Robertsonian translocations are a special type of translocation that involve exchange of genetic material from the long arms of one acrocentric chromosome to the long arms of another acrocentric chromosome, with fusion of the centromeres. Four percent of cases of Down's syndrome are caused by this mechanism.
#4
Re: Pathology 24 galaxy - 05-27-10 19:49 the boy probably looks like being a klinefelter, i.e., 47XXY due to non disjunction of the maternal or paternal sex chromosomes..........
#5
Re: Pathology 24 babbu5508 - 06-21-10 15:11 C. Nondisjunction of a sex chromosome leading to the genotype 47XXY causing klinefelter's syndrome..with eunuchoid proportions and decreased IQ nad failure of development of secondary sexual characters
#6
Re: Pathology 24 bingousmle - 06-30-10 22:16 Failure of separation (nondisjunction) of the sex chromosomes, and can be related to either paternal nondisjunction or maternal nondisjunction.
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