Billy Joel's daughter Alexa Ray Joel reacted to his normal pressure hydrocephalus (NPH) diagnosis in an Instagram post shared on May 24, a day after the musician revealed he is dealing with the condition.

When fluid builds up around or inside your brain and inhibits typical functioning, it results in normal pressure hydrocephalus, or NPH, according to the Cleveland Clinic. This may lead to difficulties thinking and concentrating, as well as impair movement and memory. The condition may be reversible, and its symptoms could look a lot like dementia.

Alexa Ray Joel posted a message on Instagram this weekend to support her father, rock 'n' roll legend Billy Joel, who announced he is battling a brain disorder called normal pressure hydrocephalus.