No one would tell a diabetic teenager to get over it and start producing insulin. No loving parent would choose to ignore a child's cancer, or worry what the neighbors might think if they found out.

But mental illness is different, as Post-Dispatch reporters Tina Hesman and Matthew Frank detailed in a fascinating and troubling report on the mysteries of the teen brain.

The difference is rooted, in part, in what doctors and scientists still don't know about serious mental illness. It can be hard to diagnose when symptoms first appear, which is often during the turbulent teenage years.

Researchers recently have learned that the brains of people with serious mental illnesses such as schizophrenia, bipolar disorder and depression are different. But while those findings are true in broad categories, the technology is still too crude, and individual variations too pronounced, to use brain imaging for making diagnoses.

As a result, there remains a frustrating subjectivity in determining which disease a teenager has. Depression can look like bipolar disorder, and bipolar disorder can look like schizophrenia. Over time, the same person may be given multiple diagnoses for the same symptoms. That doesn't mean mental illness isn't real or that doctors exaggerate its incidence, only that the categories are imprecise and our understanding limited.

Often, there are treatments that can help control symptoms and allow those with mental illness to reclaim their lives. But something else stands in their way: stigma. Prejudices and misperceptions die slowly. People still label depression as self-indulgence, or blame poor parenting for mental illness. What is thought of as bad behavior can be a confused cry for help.

Young people shouldn't suffer - or die - because of stigma. But suicide remains a leading cause of death for people under the age of 21: the third leading cause in Missouri and the fourth in Illinois. Suicide rates are higher for young men, and higher in rural areas, where there is ready access to guns and fewer resources for help.

Some parents object to schools screening teens for warning signs of mental illness. Parents may think aberrant behavior and thoughts are just a passing phase, or worry - with good cause - that their child will be labeled. Others argue that they know their kids better than educators. But some of the changes that signal a serious mental illness occur so gradually that parents can miss them.

Screening is no substitute for talking - and listening - to our kids, or for knowing who they're hanging out with and what they're doing online. But it is a tool to help troubled kids get a more thorough examination - and get needed therapy sooner. After a child has taken his life, it's too late to connect the dots.