Fibrodysplasia ossificans progressiva (FOP)

The majority of individuals with FOP have a mutation in the ACVR1 gene, which is located on chromosome 2 (2q24.1). A small number of individuals with the disorder have other mutations in the same gene. The inheritance pattern of FOP is autosomal dominant and in the majority of cases the change takes the form of a new mutation.

FOP is a progressive disorder where muscles, tendons, ligaments, and other connective tissue are transformed into bone (ossification), resulting in increasing stiffness and immobility. The first signs and symptoms usually appear during early childhood at 2-5 years of age. The ossification can be painful. It usually takes place spontaneously, but it could also be induced by injury, infection, muscle soreness following exercise, and surgical procedures. The new bone that forms is permanent. The degree to which mobility is affected following the formation of new bone varies considerably. Malpositioning could cause aching and neuralgia. Ossification between the vertebrae could result in deformation of the spine and loss of mobility in the chest, which could affect breathing. Ossification of the tympanic membrane (ear drum) and between the small auditory bones implies that many people suffering from FOP also report hearing loss.

There is no treatment for FOP. Pain relief and anti-inflammatory drugs are used to alleviate the pain and prevent the transformation into bone. Cortisone is often used if there is a flare-up. Low-intensity physiotherapy and habilitation are a key part of the treatment. It is important that individuals with FOP avoid falls, pressure, and deep wounds as far as possible as this could stimulate bone formation.

FOP, Myositis ossificans progressive (MOP), Stone man syndrome

FOP can cause ossification in the mouth and face. Temporomandibular ankylosis, which leads to inability or reduced ability to open the mouth, can occur in adolescence resulting in difficulty eating, speaking, and tooth brushing.

• Individuals with FOP should early be identified in dental care and receive preventive and monitoring of occlusal development. Preventive dental care is an important means of avoiding extensive dental treatment. When providing dental care, the risk of injury induced by light pressure must be taken into account.
• Treatment sessions ought to be kept short to minimise impact on the temporomandibular joint.
• Surgery ought to be avoided as far as possible as all muscle procedures could result in new bone formation.
• In the case of severe injury – to the jaw for example – it is important to contact an FOP specialist (the names of reference persons and FOP specialists can be found in the National Board of Health and Welfare Rare Disease Database, reference below). A decision regarding cortisone treatment must be taken as soon as possible and within 24 hours if it is to be effective against bone formation.
• Mouth-widening surgery is contraindicated.
• A mandibular injection should not be given as it could lead to bone formation in the m. pterygoideus and rapid temporomandibular ankylosis. If possible, infiltration anaesthesia ought to be used instead. Interligamentary infiltration could also be effective if performed with extreme caution.
• Plaque removal can take place.
• Individually adapted aids are required to provide the best possible oral care at home.
• Feeding and swallowing difficulties are investigated and treated by a specialist team at the hospital or multidisciplinary treatment centre.
• If an individual is having difficulty communicating, it is important to contact a speech pathologist at an early stage for advice and, if necessary, alternative and augmentative communication techniques.