can be treated with routine surgery. Another characteristic of this syndrome is a mild spondyloepiphyseal dysplasia which can cause reduced height. Another sign of Stickler syndrome is mild to severe hearing loss that, for some people, may be progressive (see hearing loss with craniofacial syndromes). The joints of affected children and young adults may be very flexible (hypermobile). Arthritis often appears at an early age and worsens as a person gets older. Learning difficulties not due to a deficit in intelligence can also occur because of hearing and sight impairments if the school is not informed and the student is not assisted within the learning environment. Stickler syndrome is thought to be associated with an increased incidence of mitral valve prolapse of the heart, although no definitive research supports this. Causes The syndrome is thought to arise from a mutation of several collagen genes during fetal development. It is a sex independent autosomal dominant trait meaning a person with the syndrome has a 50% chance of passing it on to each child. There are three variants of Stickler syndrome identified, each associated with a collagen biosynthesis gene. A metabolic defect concerning the hyaluronic acid and the collagen of the 2-d type is assumed to be the cause of this syndrome. Genetics Mutations in the COL11A1, COL11A2 and COL2A1 genes cause Stickler syndrome. These genes are involved in the production of type II and type XI collagen. Collagens are complex molecules that provide structure and strength to connective tissue (the tissue that supports the body's joints and organs). Mutations in any of these genes disrupt the production, processing, or assembly of type II or type XI collagen. Defective collagen molecules or reduced amounts of collagen affect the development of bones and other connective tissues, leading to the characteristic features of Stickler syndrome. Other, as yet unknown, genes may also cause Stickler syndrome because not all individuals with the condition have mutations in one of the three identified genes. Diagnosis Types Genetic changes are related to the following types of Stickler syndrome: Stickler syndrome, COL2A1 (75% of Stickler cases) Stickler syndrome, COL11A1 Stickler syndrome, COL11A2(non-ocular) Stickler syndrome, COL9A1 (recessive variant) Stickler syndrome, COL9A2 (recessive variant) Stickler syndrome, COL9A3 (recessive variant) Stickler Syndrome, LOX3 (Recessive, 7 cases reported) Whether there are two or three types of Stickler syndrome is controversial. Each type is presented here according to the gene involved. The classification of