iStock/ThinkstockBy DR. JENNIFER ASHTON, ABC News Senior Medical Contributor

Beloved Partridge Family star David Cassidy shocked the world when he announced that he’s battling dementia and would discontinue touring as a musician. Dementia is a brain disorder in which you see progressive worsening in memory, thinking, speech and behavior.

So here’s what you need to know about dementia and its warning signs:

The most notable and perhaps recognizable symptom is memory loss – and it’s not so much old memories… as it is learning new things. Often family picks up on this before the patient does.

There are also forms of dementia that are caused by mini strokes due to high blood pressure, as well as dementia caused by abnormal thyroid levels and even Parkinson’s disease.

While many patients exhibit a certain amount of denial of the symptoms, it’s important to see a doctor right away because there are treatments for certain forms of dementia.

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