1800 800 340

Disability Glossary

Search for glossary terms (regular expression allowed)
Begin with Contains Exact termSounds like
Term Definition
Opitz G syndrome

Opitz G/BBB syndrome is a genetic condition that affects several structures along the midline of the body. The most common features of this condition are wide-spaced eyes (hypertelorism); defects of the larynx, trachea, and/or esophagus causing breathing problems and difficulty swallowing (dysphagia); and in males, the urethra opening on the underside of the penis (hypospadias).

Mild intellectual disability occurs in fewer than 50 percent of people with Opitz G/BBB syndrome, most likely caused by structural defects in the brain. About half of affected individuals also have cleft lip with or without a cleft palate (an opening in the roof of the mouth). Some have cleft palate alone. Heart defects, an obstruction of the anal opening (imperforate anus), and brain defects such as an absence of the tissue connecting the left and right halves of the brain (corpus callosum) occur in less than 50 percent of those affected. Facial abnormalities that may be seen in this disorder include a flat nasal bridge, thin upper lip, and low set ears. These features vary among affected individuals, even within the same family.

There are two forms of Opitz G/BBB syndrome, which are distinguished by their genetic causes and patterns of inheritance. The X-linked form of Opitz G/BBB syndrome is caused by a mutation in a specific gene, MID1, on the X chromosome. Autosomal dominant Opitz G/BBB syndrome is caused by a mutation in an as-yet unidentified gene on chromosome 22.

The signs and symptoms of the autosomal dominant form of the condition are comparable to those seen in the X-linked form. The X-linked form of Opitz G/BBB syndrome tends to include cleft lip with or without cleft palate, while cleft palate alone is more common in the autosomal dominant form. Females with X-linked Opitz G/BBB syndrome are usually mildly affected, as hypertelorism may be the only sign of the disorder.

Osteogenesis imperfecta (OI)

Osteogenesis imperfecta (OI and sometimes known as brittle bone disease, or "Lobstein syndrome") is a genetic bone disorder. People with OI are born with defective connective tissue, or without the ability to make it, usually because of a deficiency of Type-I collagen. This deficiency arises from an amino acid substitution of glycine to bulkier amino acids in the collagen triple helix structure. The larger amino acid side-chains create steric hindrance that creates a bulge in the collagen complex, which in turn influences both the molecular nanomechanics as well as the interaction between molecules, which are both compromised. As a result, the body may respond by hydrolyzing the improper collagen structure. If the body does not destroy the improper collagen, the relationship between the collagen fibrils and hydroxyapatite crystals to form bone is altered, causing brittleness. Another suggested disease mechanism is that the stress state within collagen fibrils is altered at the locations of mutations, where locally larger shear forces lead to rapid failure of fibrils even at moderate loads as the homogeneous stress state found in healthy collagen fibrils is lost. These recent works suggest that OI must be understood as a multi-scale phenomenon, which involves mechanisms at the genetic, nano-, micro- and macro-level of tissues.