osteogenesis imperfecta type i

description

osteogenesis imperfecta (oi) is a clinically and genetically heterogeneous group of inherited disorders of connective tissue, frequently of collagen type i, characterized by bone fragility. associated features in some individuals include blue sclerae, dentinogenesis imperfecta, hearing loss, deformity of the spine and long bones and joint hyperextensibility. the disorder is currently categorized into 4 major types, according to the phenotypic classification of sillence. there are several sub-types as well as marked heterogeneity at the clinical, radiological and molecular level within these groups. there is marked inter- and intra-familial variability making prenatal diagnosis difficult even in families with an established diagnosis. clinically oi type l is characterized by blue sclerae and mild to moderately severe bony fragility. about 10% of patients may never have fractures. osteopenia may not be detectable on skeletal x-rays. oi type l can be subdivided into those with normal teeth (la) and those with dentinogenesis imperfecta (lb). hearing loss increases with age and results from both conductive and sensori-neural deficits. birth weight and length are usually normal. short stature is generally mild although by adulthood half the affected patients are below the 3rd percentile for height. about 20% of adults have kyphosis or scoliosis. head size is usually large for height. osteogenesis imperfecta type l is inherited in an autosomal dominant fashion. germ cell mosaicism is a well-recognized phenomenon in oi type l, accounting for sibling recurrences to seemingly normal parents. although less marked than in achondroplasia, increased paternal age has been noted in new cases.