Thursday, November 01, 2012

Age at Diagnosis Affects Risks

It's November again! For those new to this blog, that means it's time for me to post one diabetes fact per day, generally something I think is interesting or often ignored by the diabetes community.

Today's fact is that people diagnosed with autoimmune type 1 diabetes at different ages (and it can be diagnosed at almost any age- although autoimmune diabetes diagnoses in people under about six months should be looked at squinty) have really different overall profiles for complication rates as well as for associated conditions that aren't complications.

A person diagnosed at the age of two, compared to one diagnosed at the age of twenty, will on average have a much shorter honeymoon (if he has one at all), has about four times the risk of developing celiac, a much higher risk of leukemia, and if female, ovarian cancer. She has a dramatically lower risk of developing end stage renal failure, and a much lower risk of losing his eyesight from diabetes.

This is extremely important to know because when people talk about trends in diabetes complications, they often compare cohorts with really different ages at onset of diabetes. It's also somewhat important to know because people should always look at the ages at diagnosis in the people in any particular study before they start thinking that the study is relevant to their own risks.

While some of the difference in risk probably has to do with genetics, other parts of it clearly don't, because the difference in complication rate based on age at diagnosis is apparent within families.

Some studies that make me certain that this is factual:

The Risk of Proliferative Retinopathy in Siblings With Type 1 Diabetes, a study of sibling pairs. The younger diagnosed sibling (average age at dx: 8 years) had, after 30 years, a 37% risk of proliferative retinopathy. The older diagnosed siblings (average age at dx: 16 years) had, after 30 years, a 53% risk of proliferative retinopathy..

This study on Mortality in Finnish Type 1 Diabetics compares risks 20 years from diagnosis for people diagnosed above and below the age of 15 (all dx below age 30).  I am not entirely certain that it proves my point because it doesn't follow the younger diagnosed people longer, but it does certainly show that, in the 20 years after diagnosis, the causes of death in those diagnosed at different ages are pretty different. For one thing, at least in Finland, alcohol is a major cause of death for those diagnosed in late adolescence/ early adulthood.

Studies that compare the rate of celiac in people diagnosed with diabetes at different ages can be found by clicking the linked words in this sentence. I will admit to cherry picking: I did also find two studies that didn't find a linkage but I consider them small in comparison to the studies that do find a linkage, especially given how strong of a linkage many of these studies found.

A number of studies on kidney disease and type 1 diabetes have shown that being diagnosed young- the younger the better- with some studies not having any diabetic kidney failure in people diagnosed under age 5- is protective against kidney disease, or at least against advanced kidney disease. However, the risks don't keeping going up for older and older ages at diagnosis- those diagnosed as adults are at lower risk than those diagnosed in their teens.
When age at diagnosis is the same, type 2 diabetics are at much higher risk of kidney disease and failure than type 1 diabetics.

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