A Peripheral Feature of FOP Enters Center Stage

As the saying goes: If you want to hide something, put it
where everyone can see it. And, the most obvious things are often
the last to be discovered. So it is for the little (and sometimes
not so little) bumps that are found on the inside of the leg bones,
just below the knees, in more than 90 per cent of FOP patients
worldwide.

Even more astonishing, these bumps are found not
just below the knees, but can occur on any bone of the skeleton
- dwarfed by the heterotopic bone that has masked their presence
for more than 300 years. These bumps called osteochondromas, or
exostoses, are the most frequent benign tumors of bone, and can
be felt easily on physical examination.

Osteochondromas initially were con- sidered an unusual feature
of FOP, but were under-diagnosed due to their often asymptomatic
nature. In fact, they are the most common clinical feature
of FOP after the malformations of the great toes.

Our findings on FOP osteo-chondromas will be published soon
in The Journal of Bone and Joint Surgery, and demonstrate
a previously unrecognized and robust occurrence of proximal
tibial osteochondromas in patients with FOP. The results have
important clinical implications. Because of the rarity of
FOP, physicians often fail to recognize the disorder in
patients who have congenital malformations of the great toes
or soft tissue masses during childhood.
The remarkable association of osteochondromas bone formation,
but also benign osteochondral lesions of skeletal formation.

This finding provides insight into the genetic cause of
osteochondromas and is therefore of great interest not only
to physicians who treat patients with FOP, but to all orthopaedic
physicians, pediatricians, geneticists, and surgeons worldwide
who will encounter more common conditions in which these le-
sions occur. Finally, the discovery illustrates that the molecular
basis of a disease can be revealed not only by discovering the
genetic cause of the disease, but by discovering unanticipated
clinical features of a condition whose genetic cause is already
known.

As the editors of the Journal of Bone & Joint Surgery
said in their review of the article, "Thank you for submitting your
manuscript entitled: Proximal Tibial Osteochondromas in Patients
with FOP. Your observations of this rare group of patients continue
to enhance our understanding of orthopaedic basic science, and we
are sure that many readers of the Journal will be interested in this
manuscript.

The FOP Lab crew poses for a moment in the hallway

The study is well-defined for an unusual entity. The in-depth
discussion of genetic factors and their role in normal and
abnormal bone formation is clear. The manuscript thoughtfully
extends the description of a rare but important condition (FOP),
by adding observations from a significant subpopulation about
the association with proximal tibial osteochondromas.

Since the genetic defect for FOP has been tenaciously pursued,

and masterfully defined, it is logical to propose that this same defect
plays a role in the development of osteochondromas, a far more
frequent clinical entity (throughout the world). Despite the rarity
of patients with FOP, it is of enormous value and relevance to our
understanding of bone biology. The manuscript is written with
balance and clarity, as it describes this additional feature of the
disease. The impact of FOP and the biology of BMPs and their
receptors may well provide insight into other skeletal disorders
including the pathophysiology of osteochondromas."