What is POH?

Progressive Osseous Heteroplasia or POH is often considered a ‘sister’ condition of FOP, due to some similarities the conditions share.

Whilst FOP Friends exists to support people and families living with FOP in the UK, it also supports those who are living with POH.  Families of those affected by POH have found friendship, comfort and support from those families living with FOP.  We believe that we are all stronger together.

Many of the medical practitioners both in the UK and the US, who are experts in the field of FOP, are also knowledgeable about POH.  FOP Friends can signpost people to POH medical experts.  People and families affected by POH are warmly invited to join our community, and attend any events that we hold.

We have produced a short reel of facts and information about POH.  You can view it here: What is POH?

The information provided here is a brief overview of POH, taken from the guidebook “What is POH? A Guidebook for Families” (Second Edition 2002) by Prof. Fred Kaplan, Prof. Eileen Shore et al.

This is an invaluable guide for anyone looking for an introduction to the condition.

Credit: The POH Association

Download the full guide here…

Progressive Osseous Heteroplasia (POH) is a rare genetic condition in which the body makes extra bone in locations where bone should not form.  It is an exceedingly rare condition, with approximately fewer than 60 patients identified in the world.  However, it is likely there are others living with the condition who have been misdiagnosed or undiagnosed.

POH is caused by a mutation in the GNAS gene.  In most cases, the mutation occurs randomly in a person with no family history of POH. In some cases, the mutation is inherited from a parent.

POH causes extra bone to develop below the skin in subcutaneous tissue (fat tissue beneath the skin), muscles, tendons, and ligaments.  This “out-of-place extra bone formation” is commonly referred to as heterotopic ossification.  Sometimes the bone can appear almost like grains of rice under the skin, other times there may be larger lumps.

For extra reading, visit the Genetic and Rare Diseases Information Center. 

The condition is often first noted in infancy with the appearance of small “rice-grain” particles of bone in the skin.  A parent may describe this as a roughness in the skin.  Due to its rarity, many medical professionals may not have heard of the disease so misdiagnosis for a different condition is possible.

In people with POH, nodules and lace-like webs of extra bone extend from the skin into the subcutaneous fat and deep connective tissues, and may cross joints.  Extra bone formation near the joints leads to stiffness, locking, and permanent immobility.  During childhood, bone formation may progress from the skin into subcutaneous tissue and extend into deeper structures including muscle, tendon and ligament.  Affected areas may be small or large and involve scattered and variable regions of the body surface.

The condition does not involve any other organ system and does not affect the formation of any portions of the normal skeleton at birth.  POH is often congenital, meaning that it may be present at birth.

In most children, symptoms of POH usually begin during the first few months of life.  The majority of affected children are diagnosed with POH before the age of ten. Bone formation begins typically in small patches of skin, and can occur in any region of the body.

People who have POH experience different rates of new bone formation.  In some people, the progress is rapid while in most it is more gradual.  In each child, the exact rate of progression is unpredictable.  In any affected area, there appears to be a progression from superficial to deeper tissues.

For example, extra bone formation shows its effects first in the skin, then progresses through subcutaneous tissue, and then to deeper tissues like muscle.  In some individuals, the bone formation may involve a small area of the body, and in others, relatively large or multiple areas of the body.

Very often, the extra bone formation may predominate more on one side of the body.  Although the limbs are most commonly affected, bone formation may also involve the head, chest, abdomen, pelvis and back.

Unfortunately, POH does not improve over time.  The “P” in POH stands for “progressive”, that means that POH will likely progress, or get worse, as a person gets older.  As POH is part of a person’s genetic make-up, people with POH are born with the condition, even though the extra bone may not be present at birth.  People with POH will not outgrow the condition.

The extra bone that has been produced by POH does not spontaneously disappear.  The body of a person with POH does not make extra bone all of the time; a person with POH may go for months or years without apparent progression of the condition.  Nevertheless, there is always a chance that extra bone can form.