What are the signs and symptoms of Fibrodysplasia ossificans progressiva? Fibrodysplasia ossificans progressiva (FOP) is characterized by the gradual replacement of muscle tissue and connective tissue (such as tendons and ligaments) by bone, restricting movement. This process generally becomes noticeable in early childhood, starting with the neck and shoulders and proceeding down the body and into the limbs. The formation of extra-skeletal bone causes progressive loss of mobility as the joints become affected. Speaking and eating may also become difficult as the mouth becomes affected. Over time, people with FOP may become malnourished because of the inability to eat. They may also develop breathing difficulties as a result of extra bone formation around the rib cage that restricts expansion of the lungs. Any trauma to the muscles of an individual with FOP (a fall or an invasive medical procedure) may trigger episodes of muscle swelling and inflammation followed by more rapid ossification in the injured area. Flare-ups may also be caused by viral illnesses such as the flu. People with FOP are generally born with malformed big toes. This abnormality of the big toes is a characteristic feature that helps to distinguish this disorder from other bone and muscle problems. Affected individuals may also have short thumbs and other skeletal abnormalities. The Human Phenotype Ontology provides the following list of signs and symptoms for Fibrodysplasia ossificans progressiva. If the information is available, the table below includes how often the symptom is seen in people with this condition. You can use the MedlinePlus Medical Dictionary to look up the definitions for these medical terms. Signs and Symptoms Approximate number of patients (when available) Abnormality of the skin 90% Ectopic calcification 90% Limitation of joint mobility 90% Short hallux 90% Spinal rigidity 90% Clinodactyly of the 5th finger 50% Respiratory insufficiency 50% Anemia 7.5% Cognitive impairment 7.5% Glaucoma 7.5% Hallux valgus 7.5% Seizures 7.5% Intellectual disability 6% Abnormality of the first metatarsal bone - Alopecia - Autosomal dominant inheritance - Broad femoral neck - Conductive hearing impairment - Ectopic ossification in ligament tissue - Ectopic ossification in muscle tissue - Ectopic ossification in tendon tissue - Metaphyseal widening - Progressive cervical vertebral spine fusion - Respiratory failure - Scoliosis - Sensorineural hearing impairment - Short 1st metacarpal - Small cervical vertebral bodies - Widely spaced teeth - The Human Phenotype Ontology (HPO) has collected information on how often a sign or symptom occurs in a condition. Much of this information comes from Orphanet, a European rare disease database. The frequency of a sign or symptom is usually listed as a rough estimate of the percentage of patients who have that feature. The frequency may also be listed as a fraction. The first number of the fraction is how many people had the symptom, and the second number is the total number of people who were examined in one study. For example, a frequency of 25/25 means that in a study of 25 people all patients were found to have that symptom. Because these frequencies are based on a specific study, the fractions may be different if another group of patients are examined. Sometimes, no information on frequency is available. In these cases, the sign or symptom may be rare or common.