Ring chromosome 14 syndrome
Ring chromosome 14 syndrome is a very rare human chromosome abnormality. It occurs when one or both of the telomeres that mark the ends of chromosome 14 are lost allowing the now uncapped ends to fuse together forming a ring chromosome. It causes a number of serious health issues, most notably recurrent treatment-resistant seizures and intellectual disability.
The syndrome is caused by the loss of genetic material near the end of the long arm (q) of chromosome 14 . The break that causes the telomere(s) to be lost almost never occurs exactly at the end of the chromosome. Instead, it occurs further up and several critical genes near the end of the chromosome are lost.
Ring chromosome 14 syndrome is almost never inherited. The genetic abnormality occurs randomly in sperm or egg cells or it may occur in early embryonic growth. If it occurs during embryonic growth the ring chromosome may be present in only some of a person's cells (i.e. Mosaicism).
The most common symptoms are intellectual disability and recurrent seizures developing in infancy or early childhood. Typically the seizures are resistant to treatment with anti-epileptic drugs. Many individuals exhibit slow growth, being smaller and shorter than their peers.
Other symptoms may include:
- A smaller head (Microcephaly)
- Fluid build-up in the extremities (lymphedema)
- Minor facial abnormalities
- Reduced muscle tone (Hypotonia)
- Immune deficiencies
- Abnormalities of the retina
- Digestive problems
- Behavior disorders such as Hyperactivity
Diagnosis is achieved by examining the structure of the chromosomes through karyotyping. Because of the possibility that not all cells carry the ring chromosome the karyotype analysis should examine a sufficient number of cells.
Ring chromosome 14 syndrome is extremely rare. The true rate of occurrence is unknown, but there are at least 50 documented cases in the literature.
- Zollino M., Seminara L., Orteschi D., Gobbi G., Giovannini S., Della Giustina E., Frattini D., Scarano A., Neri G. (2009). "The Ring14 Syndrome: Clinical and Molecular Definition" (PDF). American Journal of Medical Genetics 149A (6): 1116–1124. doi:10.1002/ajmg.a.32831.