case 4

[md90]

A 12-year-old mentally retarded boy is brought into a health clinic in Peru. His parents have noted that he seems to have difficulty with his vision. Physical examination reveals bilateral dislocated lenses and a marfanoid body habitus. Laboratory studies show increased levels fo serum methionine and serum homocysteine.

1. What is the most likely diagnosis?
2. What is the biochemical defect in this condition?
3. What vitamin supplementation would be appropriate in this condition?
4. For which conditions is this patient at greatly increased risk?
5. What enzyme deficiency is most likely to be found in a patient with increased serum homocysteine but decreased serum methionine?

[ZWobble]

1. Homocystinuria

2. Defect in enzyme cystathionine synthase which catylzes the conversion of homocystiene + serine into cystathionine, or decreased affinity of cystathione cynthase for vitamin B6.

3. Vitamin B6

4. Homocysteine damages endothelial cells leading to thrombosis

5. Not sure about the last one, does it have something to do with the methyl group that resynthesizes methionine from homocysteine?

[md90]

1. Homocystinuria

2. Defect in enzyme cystathionine synthase which catylzes the conversion of homocystiene + serine into cystathionine, or decreased affinity of cystathione cynthase for vitamin B6.

3. Vitamin B6

4. Homocysteine damages endothelial cells leading to thrombosis

5. Not sure about the last one, does it have something to do with the methyl group that resynthesizes methionine from homocysteine?

Again GOOD JOB zwobble!!!

The only thing that I would add:
4. Think CV (cardiovascular)... there's increased risk of coronary artery disease, stroke, and peripheral artery disease...; homocysteine inhibits the collagen cross-linking, and over time.. it can cause osteoporosis..
5. deficiency of methionine synthase which converts homocysteine to methionine..

Follow up question:
1. What vitamin is needed for the conversion of homocysteine to methionine, and why?
2. What amino acid becomes essential?

[IMG SURVIVOR]

B12 THATS THE ANSWER but for some reason I have B6 in my head

[md90]

B12 THATS THE ANSWER but for some reason I have B6 in my head

That's right.. B12 is needed to help in getting homocysteine to methionine; it's used in the tetrahydrofolate-methyl to the tetrahydrofolate... remember SAM...

B6 is used from homocysteine to cystathionine to cysteine along with cystathionine synthase...

the answer to what becomes essential... cysteine..

[IMG SURVIVOR]

so im not so lost

[md90]

None of us are lost... it's just that the "forest is way to thick.. and we have to thin it out a bit".... in other words, breaking down the information so that it's easier to understand........ and remember.........