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Fibrodysplasia ossificans progressiva is a rare, genetic disorder. Also known as "Stone Man Syndrome," the disorder causes hardening of connective tissues and extra bone formation throughout the body.

Fibrodysplasia ossificans progressiva (FOP) is a very rare genetic disorder of the connective tissues. FOP is also referred to as “Stone Man Syndrome,” the disorder makes muscle tissue and ligaments harden and form into bone tissue that develops outside the normal skeleton.  Fibrodysplasia ossificans progressiva is normally noticed during early childhood, it generally begins with the neck and shoulders, gradually working its way down the body and the limbs.

How rare is fibrodysplasia ossificans progressiva?

According to statistical information released by the International Fibrodysplasia Ossificans Progressiva Association, FOP is a disease which affects 1 in 2 million people. FOP has no racial, gender or ethnic patterns and there are 800 confirmed cases all around the world.  

Of the 800 confirmed cases of FOP, 285 are known to exist in the United States.

What are the causes of fibrodysplasia ossificans progressiva?

The following are causes of FOP:

  • Genetics: People with FOP are born with mutations in the activin receptor type I gene (ACVR1).  The protein helps to regulate the development and growth of bones and muscles.  When there is a mutation in the ACVR1 gene, scientists believe it results in too much bone growth, which happens in fibrodysplasia ossificans progressiva.
  • Inheritance: If fibrodysplasia ossificans progressive is inherited, it means it is passed down through an autosomal dominant trait.  In inherited FOP, one parent carries the gene and passes it to the child.  However, this disease is rarely inherited because most individuals with FOP are infertile.
  • Random occurrence: FOP can occur randomly and this is how most diagnoses are made, except those cases which are inherited.  With random FOP, the genetic mutation happens when the egg and sperm are developing.

What are the symptoms of FOP?

Fibrodysplasia ossificans progressiva is genetic in nature and the following symptoms can be indicative of the disease:

  • Children with FOP are born having large, deformed toes
  • In children born with FOP, there may be missing toe joints or a notable lump at the minor joint
  • FOP in children will usually begin with bones in the neck, and gradually it will be witnessed in the chest, shoulders and arms and finally it will reach the feet
  • The disease causes a loss of mobility in the joints
  • The inability to open the mouth fully, which can limit eating and speech
  • Extra bone formation around the rib cage which will restrict the expansion of the lungs and cause breathing issues
  • As the disease progresses its effects can be witnessed in the caudal, ventricle, distal and ventral regions of the body
Because FOP is so rare, the symptoms of the disease are often misdiagnosed as fibrosis or cancer.

FOP misdiagnosis can cause a doctor to order biopsies of the bones, which can actually result in exacerbation of lumps and cause a worsening in the disease.

What is the difference between FOP bones and normal bones?

Bone is a living tissue and made up of cartilage.  Fibrodysplasia ossificans progressiva bone appears as normal bone tissue, but it develops in the wrong places.  Osteogenesis and ossification are medical terms which refer to the formation of bone.  Most bones in the human body grow and heal up after a break through endochondral bone formation, which is how FOP bones grow.  Cartilage forms first and then the bone will eventually take the place of cartilage.

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