Osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a genetic disorder characterized by bones that break very easily. Its symptoms and signs range from mild to severe, therefore we divide OI into VIII types and they are used to describe how severely a person is affected. People suffering from OI have not only frequent fractures, but also muscle weakness, loose joint laxity, scoliosis[1], brittle teeth and hearing loss. Interesting fact is that type I is the mildest and most common form of OI - it is believed that 50 to 60 percent of people with OI have Type I.[2]

Type I

Almost all cases of OI are caused by a dominant genetic mutation that affects the body’s production of type 1 collagen. Our body produces more types of collagen; however, only one is associated with OI. This type I collagen is the main protein building block in bone and moreover it is also important in other connective tissues such as tendons or ligaments. It means that when there is a problem with the body’s production of type 1 collagen, the bones are brittle and break more easily.

However, OI type I is different from the other types in an important way. Whereas people with types II, III etc. have low levels of abnormal type 1 collagen, people with type I have normal type 1 collagen but approximately only half the typical amount.

People are affected of OI type I in different ways, which may vary from person to person. This type of OI has several main characteristics. For instance, the bones are predisposed to fracture and most of the fractures may occur before puberty and again in later years. Generally, people may break same bones for many times. Joints are somewhat predisposed to other connective tissue injuries, such as dislocations and they are very loose, with some muscle weakness and lax ligaments. The height of such a person in much below average and scoliosis can be also seen.  Lastly, brittle teeth and blue sclera[3] are possible with type I.

Type II

The most severe form of OI is type II. Children born with this time usually have very short limbs and small chests. Their skulls are soft and their legs are often in a frog-leg position. The skeleton is characterized by absence or limitation of calvarial mineralization, therefore the babies have for instance flat vertebral bodies – they are very short and they have broad femurs or ribs. Intrauterine fractures are common in the skull, long bones, or vertebrae[4]. Moreover, lungs are underdeveloped and respiratory and swallowing problems are common. Scalars may be grey dark blue.

Type III

            This type is most severe for those children, who survive neonatal period. At birth, newborns generally have mildly shortened and bowed limbs, small chests and a soft calvarium[5]. This type is characterized by structurally defective type I collagen, which is present in a very poor quality within matrix. Multiple long-bone fractures and rib fractures may occur at birth. The most frequent are fractures of the long bones, the tension of muscle on soft bone, and the disruption of the growth plates and much more. The head is often large relative to body size. Children usually have short stature and adults are often shorter than 105 cm[6].

Type IV

This type does not affect people a lot. It cause a few fractures just like type I or more severe form like Type III. Type IV does not have to be diagnosed at birth, because the fractures can occur later (mainly when the kid starts to walk). The kids are lighter and shorter for their age, but not so drastically. Bones humerus and femur[7] are short. The most frequent are long bone fractures, vertebral compression[8], scoliosis, and ligament laxity may also be present.

Type V          

This type is moderate in severity. The frequency of fractures is similar to type IV as well as the deformation of skeleton. People mostly suffer from large, hypertrophic calluses in the largest bones at fracture or surgical procedure sites. Hypertrophic calluses[9] can spontaneously occur.

Type VI

This one is very rare. It is moderate in severity and its symptoms are similar to type IV. This type is characterized by a mineralization defect seen in biopsied bone.

Type VII

This type is in some ways very similar to type IV. The other cases are similar to type II (except the fact newborns have white sclera, small heads and round faces.) At this type it is common for leg bones, humerus and femur to be short. The stature is short as well.

Type VIII

Except for white sclera, this type resembles types II or III. People suffer mostly from severe growth deficiency and extreme under-mineralization of the skeleton.

            Type IX

            This type is also known as a silent type of OI II and III without the abnormality of type I collagen. It is characterized by shorter, undertubulated, bowed, fractured bones, but without rhizomelia.

            These are nine known types of Osteogenesis imperfecta. Sometimes, up to 13 types can be identified; however, these are the most common and inspected ones. As you can see, some of them differ in many ways, but some types are quite similar. Even though some types might look the same, there is nothing that every type has. The only similarity is that all of these are types of bone disease, where bones are being broken because there is a problem with the body’s production of type 1 collagen.

Articles used

http://www.oif.org/site/PageServer?pagename=AOI_Types

http://www.niams.nih.gov/Health_Info/Bone/Osteogenesis_Imperfecta/type_1.asp

http://ghr.nlm.nih.gov/condition/osteogenesis-imperfecta