new_n_lost
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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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| me007
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c
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| paganini
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C. looks like a klinefelter
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| new_n_lost
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| new_n_lost
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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.
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FORUM RULES-- Those who believe in telekinesis, raise my hand. I get enough exercise just by pushing my luck --P4U World.." The pure and simple truth is rarely pure and never simple."
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