Myositis Ossificans Progressiva (MOP), also known as Fibrodysplasia Ossificans Progressiva, is a condition caused by formation of bone within muscles. When muscle is damaged, instead of the muscle repairing itself, the tissue turns into bone. The bone formation is usually first noticed in early childhood as a series of hard lumps in the neck or along the spine. The lumps, which may be tender, gradually shrink in size as the affected muscles are replaced by bone.

MOP is progressive - a person with the condition will find that more muscles become affected as they get older. The rate of progression does vary from one person to another though, and the condition can actually be inactive for up to several years.

Not every muscle is vulnerable to the condition, MOP does not generally affect the following:

  • Eye muscles
  • Face muscles
  • Tongue muscles
  • The gullet
  • The intestines
  • Continence (bladder and bowel) muscles
  • The heart
  • The diaphragm

MOP doesn't affect intelligence. Nor does it shorten a person's lifespan - several people in Britain with MOP are over 60. Worldwide, about one person in a million has the condition, which seems to affect men and woman equally.

It's thought that the condition is caused by a basic genetic error that occurs at conception. The chance of it happening is very small (less than one in a million if both parents are unaffected). A person with MOP does though have a one in two chance of passing the condition on if they have children.

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