Actor Irrfan Khan recently caused Twitter followers to panic after he posted a cryptic post about his health condition. The 51-year-old succinctly hinted that he may be suffering from a ‘rare disease’ and urged people to stop speculating. Assuring fans and followers that he’d announce it to the world when the diagnosis is made, he also requested everyone to wish the best for him. Here’s the original tweet:

🙏🏻 pic.twitter.com/JXD8NKwH3D

Our heart goes out to the actor and sincerely hope that he tides over this difficult phase of his life. But what caught most people’s attention and ultimately caused Twitter to worry about the actor’s wellbeing was the mention of the rare disease. This has led many of us to wonder what a rare disease is. Here’s a low down on what constitutes a rare disease.

A rare disease is also known as an orphan disease, which affects a very small percentage of the population. Since they are rare, there is a lack of medical means and evidence to treat these illnesses as well and patients may often have to travel long distances to find the right expert. It’s mostly genetic in nature and there are over 6000 legitimately identified rare diseases in the world.

1 Persistent Genital Arousal Disorder or PGAD

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Imagine being in a constant state of sexual arousal. Well, it’s not as great as it seems. Persistent Genital Arousal Disorder or PGAD is a condition where the person gets spontaneously and continuously sexually excited. The sufferer (for the lack of a better term) cannot be relieved even by orgasms. Not too long ago, Amanda McLaughlin a 23-year-old diagnosed with PGAD recounted how difficult it was to lead a normal life in the BBC documentary, Living Differently. “It feels like you’re about to orgasm and then it never goes away. So there’s sharp pain all the way through your legs, all the way through your pelvis. It’s just nonstop,” she says.

2 Progeria

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Readers may have heard of progeria from the 2009 Hindi movie Paa, where Amitabh Bachchan plays a 13-year-old suffering from the rare genetic disorder. Progeria or Hutchinson-Gilford Progeria Syndrome causes the sufferers to age prematurely, cutting their life short by decades. Progeria suffers don’t live past their early-twenties and most don’t reach their reproductive age.

3 Stone man syndrome

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What would happen if each one of your muscles strangely turned into bone? You’d start resembling a human statue. That’s what happens to people who suffer from fibrodysplasia ossificans progressiva or stone man syndrome. The soft tissues of the body, including muscle tissue and connective tissues become ossified or replaced by bone. Over time, the disease impairs the sufferer’s ability to move around and perform basic bodily functions like breathing.

4 Treeman syndrome

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Epidermodysplasia verruciformis or treeman syndrome causes the sufferer to develop tree bark-like projections, growing out of their hands, fingers, palms and feet and eventually spreading out to the rest of their body. There’s no way to predict the course of the disease. A 25-year-old Bangladeshi man Abul Bajandar who was suffering from the disease underwent 16 operations to get the lesions removed from his hands two years ago. And as of January 2018, it was reported that the bark-like lesions were re-growing on his hands.

5 Neurofibromatosis type 1

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It’s a rare disease where the human body sprouts bulbous tumours that grow along the nerves in the skin, the brain and other parts of the body. It’s considered to a genetic disorder that one can inherit from the parents and can happen because of a mutation of the genes.

6 Elephant man disease or Proteus syndrome

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Joseph Carey Merrick, on whom the movie The Elephant Man is based, is the most noted examples of this disease. Due to his extreme deformities, Merrick was constantly exhibited in freak shows. Proteus syndrome, the disease he was suffering from, caused his bones, skin and other tissues to overgrow, giving him an asymmetrical, otherworldly appearance.

(The above story first appeared on LatestLY on Mar 06, 2018 06:06 PM IST. For more news and updates on politics, world, sports, entertainment and lifestyle, log on to our website latestly.com).