Types of Ostegenesis Imperfecta
Osteogenesis Imperfecta, also known as “brittle bone disease,” is a genetic disorder characterized by bones that break easily, often from little or no apparent cause. The term “osteogenesis imperfecta” means imperfect bone formation. Sometimes the bones of the affected person break for no known reason. At times bones break often from mild trauma or with no apparent cause. Multiple fractures are common, and in severe cases, can occur even before birth. Milder cases may involve only a few fractures over a person’s lifetime.
The prevalence of OI is estimated to be 1 per 20,000 live births; however, the mild form is underdiagnosed, and the actual prevalence may be higher.
- Inheriting a faulty gene from the parent
The cause is a gene defect that affects how the body makes collagen, a protein that helps make bones strong. In some cases it is caused by a mutation, a random gene change.
- In almost all cases, mode of inheritance in osteogenesis imperfecta is dominant or involves a new dominant mutation, regardless of the clinical form of osteogenesis imperfecta observed.
- A recessive pattern of inheritance has been demonstrated in some families from South Africa. Approximately 10-15 percent of cases of OI are the result of a recessive mutation. In this situation, the parents do not have OI, but both carry the mutation in their genes. To inherit recessive OI the child must receive a copy of the mutation from both parents.
- Some have proposed possible germ-cell mosaicism as an explanation for cases occurring in families with healthy parents that have more than one child with osteogenesis imperfecta.
Types of Osteogenesis Imperfecta
TYPE I – MILD FORM
Osteogenesis Imperfecta Type I s the mildest and most common form of the disorder. In this disorder, the collagen is of normal quality but is produced in insufficient quantities. It accounts for 50 percent of the total OI population. It is characterized with mild bone fragility, relatively few fractures, and minimal limb deformities. The child might not fracture until he or she is learning to walk. General features of OI Type I are the following:
- Dominantly inherited. It can be inherited from an affected parent, or, in previously unaffected families, it results from a spontaneous mutation. Spontaneous mutations are common.
- Most fractures occur before puberty starts.
- Joints are somewhat predisposed to other connective tissue injuries, such as dislocations.
- Bone deformity is absent or minimal and occurs after fractures have occurred.Skin may bruise easily.
- Sclera usually has a blue, purple, or gray tint.
- Triangular face.
- Brittle teeth (dentinogenesis imperfecta) are possible.
- A child’s stature may be average or slightly shorter-than-average as compared with unaffected family members, but is still within the normal range for the age.
- There is a high incidence of hearing loss. Onset occurs primarily in young adulthood, but it may occur in early childhood. Hearing loss possible, often beginning in early 20s or 30s.