Osteogenesis Imperfecta

OSTEOGENESIS IMPERFECTA AKA: • • • • • •

Brittle bone disease Ekman-Lobstein disease Fragilitas ossium OI Osteopsathyrosis Vrolik disease

DEFINITION Osteogenesis imperfecta (OI) is a connective tissue disorder characterized by fragile bones, weak muscles, and loose ligaments. Bone problems can include bowing of the long bones, scoliosis (curvature of the spine), a barrel chest, and joint problems. Varying degrees of short stature and decreased muscle mass and strength may also be present. RISKFACTORS •

•

•

S/SX • • • • • • • • •

The defect may be inherited in an autosomal dominant pattern from an affected parent. This means that an affected parent, who carries a single gene for the disorder, has a 50% chance of having children with the disorder. Any child who inherits this gene will be affected. The defect may be acquired by a spontaneous mutation occurring in the individual egg or sperm that formed the child. In this case, neither parent carries a gene for the disorder or is affected by it. The parents, in this case, are no more at risk than the general population for having another child with the disorder. The defect may be acquired through a pattern of inheritance called mosaicism. This occurs when neither parent is affected, but one carries a percentage of sperm or eggs which contain the genetic defect. Therefore, though the parents are unaffected, some of their children may have the disorder and others will not. It is estimated that about 2% to 7% of unaffected parents who have had a child with OI will have another child with OI due to the phenomenon of mosaicism. Bones that fracture easily Short stature Hearing loss Discolored, brittle teeth Blue sclera (blue color in the whites of the eyes) Skeletal deformities of limbs, chest, and skull Scoliosis (curvature of the spine) Respiratory difficulties Weak muscles

• • • • •

Excessive sweating Constipation Tendency to bruise easily Loose joints and ligaments High-pitched voice

History: •

Patients most commonly present with bone fragility.

•

Prenatal screening ultrasound during second trimester shows bowing of long bones, fractures, limb shortening, and decreased skull echogenicity.

•

Easy bruising

•

Repeated fracture after mild trauma. However, these fractures heal readily.

•

Deafness (50% by age 40 years in type I)

Physical: Physical examination can vary depending on the type. It forms the basis for Sillence classification. •

•

Type I o o

A: Dentinogenesis imperfecta is absent. B: Dentinogenesis imperfecta is present.

o

Symptoms of both subtypes include the following:  Blue sclera present (However, blue sclera also may occur in other disorders, such as Turner syndrome, Paget disease, or osteopetrosis.)  In utero fractures - 10% (Fractures are more common during infancy.)  Mild-to-moderate bone fragility (Frequency of fractures decreases after puberty.)  Kyphoscoliosis  Hearing loss  Premature arcus senilis  Easy bruising  Mild short stature

Type II o

Dentinogenesis imperfecta

o o o o o o o •

Type III o o o o o o o

•

Blue sclera may be present. Hearing loss is not applicable to type II OI. Perinatal lethality Small nose, micrognathia Connective tissue fragility In utero fractures are present in 100% cases Short trunk

Dentinogenesis imperfecta Sclera of variable hue No hearing loss In-utero fractures in 50% of cases (The remaining half of cases have fractures in neonatal period.) Limb shortening and progressive deformities Triangular facies with frontal bossing Pulmonary hypertension

Type IV o

Subtype A: Dentinogenesis imperfecta is absent.

o

Subtype B: Dentinogenesis imperfecta is present.

o

Symptoms of both subtypes include the following:  Normal sclera  Normal hearing  Fractures that begin in infancy (In utero fractures are rare.)  Mild angulation and shortening of long bones  No bleeding diathesis

Causes: Osteogenesis is an inherited disorder. •

Type I is autosomal dominant.

•

Type II is autosomal dominant with new mutation.

•

Type III is autosomal dominant with new mutation. Rarely, recessive forms also are observed.

•

Type IV is autosomal dominant.

TREATMENT Medical Care: •

No medical therapy is involved, other than the treatment of infections when they occur.

•

For severe cases presenting with severe osteopenia and repeated fractures, cyclic administration of intravenous aminohydroxypropylidene (ie, pamidronate) may reduce the incidence of fracture and increase bone mineral density.

Surgical Care: Surgical interventions include intramedullary rodding, surgery for basilar impression, and correction of scoliosis. •

Intramedullary rodding o

In patients with type III OI, intramedullary rodding may improve weight bearing on legs, thus, enabling the child to walk at an earlier age.

o

Intramedullary rodding may decrease range of joint motion.

•

Surgery for basilar impression is reserved for cases with neurological deficiencies, especially those caused by compression of brain stem and high cervical cord.

•

Correction of scoliosis o

Correction of scoliosis may be very difficult because of bone fragility.

o

Spinal fusion may be helpful.

Consultations: •

Genetic counseling o

Offer genetic counseling to the parents of a child with OI who plan to have subsequent children.

o

During genetic counseling, the possibility that the parents may harbor new mutations, such as asymptomatic somatic and germline mosaicism, needs to be discussed.

COMPLICATIONS •

Hyperplastic callus formation

•

Repeated respiratory infections

•

Basilar impression with brainstem compression

•

Cerebral hemorrhage caused by birth trauma

•

Cord compression

NI Management focuses on supportive therapy to minimize fractures and maximize function, minimize disability, foster independence, and maintain overall health. Ideally, OI is managed by a multidisciplinary team including specialists in medical therapy of OI, orthopedics, and rehabilitation medicine. Supportive therapy is individualized depending upon the severity, the degree of impairment, and the age of the affected individual. Considerable support is generally required by medical personnel to help parents feel comfortable caring for infants with OI type II. Activity: • • • • • • • • • • •

Parents need special instructions in handling the children. Parents need to know how to position the child in the crib and hold the child with the least possibility of causing fractures. Parents should discourage upright sitting in infants younger than 1 year to decrease development of basilar impression later in life. Hip-knee-ankle-foot orthosis helps early achievement of upright activity. Encourage shock-absorbing footwear with arch support. Bracing of limbs Mobility devices such as scooters and chairs for children and modified automobiles for adults Analgesics for pain Endurance training Promotion of appropriate physical activity Physical and occupational therapy for increased stability of bone, improved mobility, prevention of contractures, prevention of head and spinal deformity, aerobic fitness, and muscle strengthening

Children with OI should be seen by the dentist twice yearly, beginning in early childhood or even infancy.

Hearing evaluation should be performed at 3-5 year intervals after adolescence until hearing loss is identified. DX Diagnosis/testing. The clinical diagnosis of OI is based on family history, a history of fractures, characteristic physical findings including scleral hue, and radiographic findings. Radiographic findings include fractures of varying ages and stages of healing, wormian bones, "codfish" vertebrae, and osteopenia. Analysis of bone biopsies is an adjunct to the diagnosis of OI type V and OI type VI. Biochemical testing (i.e., analysis of the structure and quantity of type I collagen synthesized in vitro by cultured dermal fibroblasts) detects abnormalities in 98% of individuals with OI type II, about 90% with OI type I, about 84% with OI type IV, and about 84% with OI type III. About 90% of individuals with OI types I, II, III, and IV (but none with OI types V, VI and VII) have an identifiable mutation in either COL1A1 or COL1A2. Such testing is clinically available.

* Carrier Detection Carrier testing using molecular genetic techniques is not offered because it is not clinically available.