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  #1  
Old 12-15-2011
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Kids Black Discoloration of Morning diapers!

A 6-month-old infant is brought to a pediatrician by his parents for a routine check-up. The child has been doing well and has met all developmental milestones appropriately. However, the parents report that they occasionally notice wet diapers that appear dark or even black. This discoloration is seen most frequently in the morning, during the first diaper change of the day. The urine stream has never been observed to demonstrate dark coloration. No other family membersare known to have had this problem. No abnormalities are found on physical exam. Routine lab results and urine dipstick are within normal limits.
What is the genetic basis for this disease?

A. Autosomal recessive caused by phenylalanine hydroxylase mutation
B. Autosomal recessive caused by homogentisate dioxygenase mutation
C. Autosomal recessive caused by an amino-acid transporter mutation
D. Autosomal dominant caused by a phenylalanine hydroxylase mutation
E. Autosomal dominant caused by a homogentisate dioxygenase mutation

Last edited by sam88; 12-15-2011 at 11:52 PM.
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  #2  
Old 12-16-2011
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Default B

I feel B. Alkaptonuria
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Matched!!!
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Old 12-16-2011
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@daulth
i go with you.
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Old 12-16-2011
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the ans is B
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Ill go with B
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Old 12-16-2011
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Its B ......
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Old 12-17-2011
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The correct answer is B. Autosomal recessive caused by homogentisate dioxygenase mutation.
This patient has alkaptonuria. Alkaptonuria is an autosomal recessive condition caused by mutations in homogentisate 1, 2-dioxygenase, a hepatic enzyme normally involved in tyrosine catabolism. This enzyme deficiency results in the buildup of large amounts of homogentisic acid, which is subsequently cleared by the kidney. However, despite rapid renal clearance, slow deposition of homogentisic acid and its oxidized polymers occurs in cartilage and collagenous tissues over the course of several years. Therefore, alkaptonuria does not generally result in problems during infancy. However, as homogentisic acid is deposited in body tissues, gray-brown discoloration of the sclerae and dark pigmentation of cartilaginous sites such as the ears may eventually develop. Deposition of homogentisic acid in joints results in ochronotic arthritis. One of the most distinct features of alkaptonuria is the blackening of standing urine. This darkening results from the oxidation of homogentisic acid when exposed to air. The oxidized polymeric product gives the urine its characteristic dark appearance in this disease. Urine can be analyzed by gas chromatography/mass spectrometry to demonstrate greatly elevated levels of homo-gentisic acid. Treatment is largely symptomatic. Vitamin C and dietary restriction of tyrosine and phenylalanine intake may be helpful. Life expectancy is normal in alkaptonuria. None of the other disease choices listed in Question 1 would classically result in black urine.
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