Chromosome 18 ring syndrome. 18 ring syndrome.
Incidence
Very rare syndrome. Sporadic.
Clinical Characteristics
Chromosome 18 Ring is a rare disorder in which there is loss (deletion) of genetic material from one or both ends of the 18th chromosome and joining of the chromosomal ends to form a ring. Associated symptoms and findings may vary greatly in range and severity from case to case, depending upon the amount and location of lost genetic material and other factors. A ring may also be formed without the loss of any genetic material. However, many individuals with the disorder are affected by mental retardation; low muscle tone (hypotonia); growth retardation; repeated infections during the first years of life; and/or malformations of the skull and facial (craniofacial) region. Such craniofacial features often include an unusually small head (microcephaly), widely spaced eyes (ocular hypertelorism), and/or vertical skin folds that cover the eyes' inner corners (epicanthal folds). Chromosome 18 Ring is usually caused by spontaneous (de novo) errors very early in the development of the embryo that appear to occur randomly for unknown reasons (sporadically). In summary, it is an abnormality of chromosome 18 in which both ends have been lost (deletion) and the broken ends have reunited to form a ring-shaped figure, usually associated with mental retardation, craniofacial dysmorphism, and limb deformities, and other defects.
Precipitants
None
Provocation Tests
None
Diagnostic Procedures
Karyotype. Chromosome 18 Ring.