Lobstein's disease: Osteogenesis imperfecta type I. An inherited, generalized connective tissue disorder featuring bone fragility and blue sclerae (blue whites of the eyes). The classic mild form of "brittle bone disease." It is a dominant trait with males and females affected. One copy of the mutant gene is sufficient to cause the disease. Clinically it is characterized by fragile bones, the onset after birth of growth deficiency, abnormal teeth (that look as if they have been sandblasted), thin skin, blue sclerae and overly extensible joints. 10% of patients have their first fractures noted at birth, about 25% in the first year, about 50% in the preschool years, and the balance in the early school years. The chance of fractures decreases after adolescence. Common problems also include the development of bowing of the legs, curvature of the spine (scoliosis and kyphosis), umbilical and inguinal hernias and mild mitral valve prolapse (flopping down of the heart valve leaflets). Hearing impairment begins in the third decade due to otosclerosis (a disorder of the bones of the middle ear). This disease (also called osteogenesis imperfecta tarda and osteogenesis imperfecta with blue sclerae) is usually compatible with life and with ambulation. The condition results from mutations that impair the production of type I collagen, a key component of connective tissue. Mutations responsible for the disease have been identified in both the COL1A1 and COL1A2 genes. (COL1A1 is the gene for type 1 alpha-1 chain of collagen (COL1A1) and is located in chromosome17q21.31-q22.05. COL1A2 is the gene for type 2 alpha-chain of collagen (COL1A2) which is in chromosome 7q22.1). Named for Johann Lobstein (1777-1835), a surgeon in Strasbourg.