26malik
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A young man recently died during surgery under general anesthesia. Symptoms prior to his death included muscle spasms, hyperthermia, acidosis, and cardiac arrest. His family history is significant for his father dying under similar conditions and an aunt having survived the same complications during a hip replacement surgery. He is survived by his wife, a son, and a daughter. DNA has been isolated from family members and a Southern blot of restriction fragments from a specific region of chromosome 19 reveals the following pattern:
Band Size
Father
Mother
Daughter
Son
Paternal Grandfather
12 kb
___
___
___
11 kb
___
9 kb
___
___
___
___
7 kb
___
___
___
Which of the following conclusions can reasonably be drawn from these data?
A. The 11 kb band from the father carries the probable mutation and his children will not be affected
B. The 7 kb band carries the probable mutation and the son should not undergo general anesthesia with halothane
C. The 9 kb band carries the probable mutation and the daughter should not receive succinylcholine as a neuromuscular relaxant
D. The disease is X-linked recessive, so the daughter will not develop life-threatening side-effects during general anesthesia
E. The transmission of the disease is via mitochondrial inheritance, so the son will be unaffected
Edited by 26malik on 05/24/06 - 10:14 PM
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| robin082006
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This q seems to lack some info
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| doc179
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right , the Q is not complete
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| general malaise
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| 26malik
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My apologies for posting incomplete Q  .
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| mjl1717
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my pure guess is answer-c.
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| general malaise
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my guess will be B. malignant hyperthermia is associated with the use of halogenated hydrocarbons in rare individuals. likely to be inherited but it won't be either x-linked or thru mitochondrial inheritance since his father died from it. his offspring should not undergo anesthesia with halotane or its derivatives
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| 26malik
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The correct answer is B.
The history suggests an autosomal dominant disorder (the father died, the grandfather and an aunt suffered similar conditions). Limited information through 3 generations shows no skipping of generations (dominance), and a affected female confirms the autosomal transmission. The symptoms of hyperthermia, muscle spasm, autonomic and electrolyte disturbances during general anesthesia, and the pedigree argue for a diagnosis of malignant hyperthermia. In this disorder, a mutation in the ryanodine receptor-gated calcium channel of the sarcoplasmic reticulum of skeletal muscle leads to increased sensitivity to halothane and depolarizing agents. In an autosomal dominant pattern, one defective allele is sufficient to develop the trait. The father can pass on an 11 kb, a 9 kb or a 7 kb band to his children, whereas the mother can pass on a 12 kb or a 9 kb band. The DNA pattern of the father and grandfather can be compared, and the likely restriction fragment involved in the inheritance of malignant hyperthermia is the 7 kb band.
The 11 kb band from the father (choice A) does not carry the defective allele, since the grandfather did not share that same banding pattern: the only similarity between the father and his own father is the 7 kb band. However, if the statement had been true, then his children would not have a risk of malignant hyperthermia, because they do not carry the allele.
The 9 kb band does not appear to carry the defective allele (choice C), however, if it did, the daughter would have a major risk of developing malignant hyperthermia when succinylcholine was used as a neuromuscular blocking agent, because it is a depolarizing drug.
The disease is not X-linked recessive (choice D) because an aunt had a similar problem, but was resuscitated. If it were X-linked, only males would be affected, so the daughter would not be affected.
Mitochondrial inheritance (choice E) would be inconsistent with the observed transmission of the defective allele from males to their offspring.
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