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A Tale of Two Marys

By Dr. A. Paul Chous

Last month, I saw two patients with type 2 diabetes named Mary. Each has had diabetes about 12 years, is of Northern European ancestry and in her mid-fifties, takes essentially the same diabetes medications (Glucophage, Lipitor, lisinopril and a baby aspirin) and a multivitamin daily, and has average blood pressure around 125/80, but that’s where the similarity ends.

The first Mary has severe diabetic retinopathy in each eye and has undergone three sessions of macular laser treatment for diabetic macular edema; the second Mary has no diabetic retinopathy whatsoever.

The first Mary has a moderately severe cataract in one eye that will need to be surgically removed, and a milder one in the other; the second Mary has clear lenses with no cataract at all.

The first Mary has a recent glycosylated hemoglobin (HbA1c) reading of 6% and her medical record shows A-1-c readings between 5.8% and 6.5% over the last ten years; the second Mary’s most recent HbA1c is 7.8% while her medical record shows A-1-c readings ranging from 7.5% to 10% over the last ten years.

Please re-read that last sentence – there is no typo. With all things appearing relatively equal, the Mary with decidedly worse blood sugar control has no eye complications from diabetes while the Mary with historically excellent blood sugar control has experienced two significant eye complications, retinopathy and cataract, caused by diabetes. How is this possible?

Let me first reveal my cards by saying that I don’t have the answer. In fact, I spoke with a retina specialist and two prominent endocrinologists about my patients and none of us has a definite answer. We do have some ideas, however. The first is that there is some undetected hormonal or metabolic abnormality in the case of the Mary with eye complications, or some protective hormonal or metabolic influence in the case of the Mary with healthy eyes. I reviewed all of their laboratory findings with one of the endocrinologists but we detected nothing unusual or even remotely suspicious.

Because there is good evidence that blood sugar fluctuation leads to blood vessel damage and eye disease independently of average blood sugar levels as reflected by the A1C test (see my previous article titled “An ‘Excursion’ to Miss”), we scrutinized the blood glucose log book of each Mary but, again, found little substantial difference in overall glucose variability (the first Mary consistently had lower readings, as you would expect). It is worth noting that we didn’t have readings every minute, as we would get from a continuous glucose monitor, relying instead on two to four home readings a day for each patient for our analysis, so there is a possibility we simply didn’t have enough data points to examine.

The other possibility is that my two patients have different genes that make them more (in the case of the first Mary) or less (in the case of the second Mary) susceptible to the damaging effects of elevated blood sugar levels. For example, Investigators in Israel have discovered that different genes responsible for metabolizing iron in our bodies have a dramatic effect on the likelihood of developing severe retinopathy in patients with type 1 diabetes, irrespective of blood sugar control. Interestingly, another study of type 2 patients in Brazil found no such increase in risk, so the jury is still out on the influence of these particular genes. It does suggest, however, that any number of different genes may affect our risk for eye and other complications of diabetes.

So what is the moral of this ‘Tale of Two Marys’? Should we still encourage both women to strive for good blood glucose control? Absolutely. Because large clinical studies prove that patients as a whole do better with tighter blood sugar control, following the results of such studies is smart and maximizes our chances of avoiding complications. It does teach us, however, that there are probably a number of factors determining complications, genetic and otherwise, that we don’t yet fully understand or even appreciate. We also need to be very careful about blaming the actions of those who suffer complications and, conversely, praising the actions of those who haven’t.

For more information on diabetic eye disease, consult Dr. Chous’ book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.

Read more about Dr. Chous here.

Visit Dr. Chous' website here.