Paediatrics: Osteogenesis imperfecta

Osteogenesis imperfecta

An inherited condition affecting collagen matura-tion and organization. The incidence is around 1/20 000. Osteogenesis im-perfecta (OI) is due to a mutation in type I collagen gene that predisposes to fracture formation. Following a fracture, initial bone healing is normal, but there is no subsequent remodelling and the bone heals with deformity. 10% are clinically asymptomatic.

Clinical features

•   Bones:

•   low birth weight/length for gestational age;

•   short stature;

•   50% scoliosis.

•   Joints: ligamentous laxity resulting in hyperextensible joints.

•   Specific signs and X-ray features (see Table 20.2).

Investigations and diagnosis

•   Prenatal US scan may detect severe forms in foetus.

•   Molecular genetic testing (pre- or postnatal).

•   Biochemistry: normal/increased alkaline phosphatase (ALP).

•   Skin biopsy: assess collagen in cultured fibroblasts.

•   Bone biopsy: histology—increased Haversian canal + osteocyte lacunae diameters, increased cell numbers.

Treatment 

No curative treatment. Aim to prevent and manage frac-tures with long-term rehabilitation.

Prevention 

Strategies to decrease fracture frequency include:

•   oral calcium supplements;

•   bisphosphonates;

•   synthetic calcitonin.

Surgical interventions

Intramedullary rods (fixed length/telescoping) to prevent bowing of long bones, especially for fractures in children >2yrs old. Corrective surgery for scoliosis deformities >50°.

Prognosis

In severe OI a good predictor of future walking is being able to sit by 10mths. May develop cardiopulmonary or neurological complications. Usually develop progressive shortening and deformity caused by multiple fractures, e.g. ‘sabre’ tibia, ‘accordion’ femora.