Information on the following diseases can be found in the Related Disorders section of this report:

• Trigonocephaly (autosomal dominant type)
• Trigonocephaly (autosomal recessive)
• Trigonocephaly with Short Stature and Developmental Delay

One of the distinguishing features of C syndrome is a condition in which the skull is a triangular shape primarily due to premature closure of the bones (trigonocephaly). Patients with this disorder also have a distinct face in which the nasal bridge is broad with a short nose, and there are vertical folds over the inner corners of the eyes (epicanthus). A deeply furrowed palate in the mouth, abnormalities of the outer ear, crossed eyes (strabismus), joints that may be bent in a fixed position or dislocated, and loose skin are all features typically found in patients with C syndrome.

Epicanthus, retardation, loss of muscle tone, abnormalities of the sternum, facial palsy, webbed fingers and/or toes, short limbs, heart defects, failure of one or both testicles to move down into the scrotum (cryptorchidism), abnormalities of the kidneys and lungs, deformity of the lower jaw and/or seizures may also be found in individuals with C syndrome.

Until recently C syndrome was thought to be transmitted as an autosomal recessive trait. However, it is now believed that the disorder occurs as a result of gonadal mosaicism. It is not known at the current time what chromosome the gene defect is on. Research is in progress to identify the gene.

Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated "p" and a long arm designated "q". Chromosomes are further sub-divided into many bands that are numbered. For example, "chromosome 11p13" refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.

Genetic diseases are determined by the combination of genes for a particular trait that are on the chromosomes received from the father and the mother.

Recessive genetic disorders occur when an individual inherits the same abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The risk for two carrier parents to both pass the defective gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier like the parents is 50% with each pregnancy. The chance for a child to receive normal genes from both parents and be genetically normal for that particular trait is 25%. The risk is the same for males and females.

All individuals carry a few abnormal genes. Parents who are close relatives (consanguineous) have a higher chance than unrelated parents to both carry the same abnormal gene, which increases the risk to have children with a recessive genetic disorder.

Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50% for each pregnancy regardless of the sex of the resulting child.

Only about 70 cases have been reported in the world's medical literature. C syndrome is a very rare disorder that seems to affect males and females in equal numbers.

Symptoms of the following disorders can be similar to those of C Syndrome. Comparisons may be useful for a differential diagnosis:

Trigononcephaly (autosomal dominant type) is a rare disorder inherited as an autosomal dominant trait. Patients with this disorder are born with a triangular shaped skull partially caused by premature closure of the bones which can cause compression of the brain. A small head and skin tags on the ears have been found in several cases. Mental development is normal in all cases. This disorder affects males five times more often than females. There have been six patients from one family reported in the medical literature.

Trigonocephaly (autosomal recessive) is a rare disorder that is inherited as an autosomal recessive trait. Patients with this disorder are born without the nerve fibers that are related to the sense of smell, as well as a malformation in which the skull is a triangular shape partially caused by premature closure of the bones (trigonocephaly). There have been multiple affected siblings reported in the medical literature.

Trigonocephaly with Short Stature and Developmental Delay is a rare disorder inherited as an X-Linked trait. This disorder has been characterized by a malformation in which the skull is a triangular shape partially caused by premature closure of the bones of the skull (trigonocephaly), short stature and moderate mental retardation in three males recorded in the medical literature. The other two related patients had a closed space between the bones at the back of the skull, a narrow forehead, widely spaced eyes, a small head circumference, low weight, and slow mental and physical development.

Typically the borders or joints of the skull close between the ages of 28 and 32 years. Patients with Trigonocephaly with Short Stature and Developmental Delay have closure between the ages of 2 and 3 years. There have been five related patients described in the medical literature and all were males.

When Trigonocephaly is severe surgery may be performed to relieve the pressure on the brain and cosmetically improve facial appearance. Other treatment is symptomatic and supportive.

Genetic counseling may be of benefit for patients and their families.

Information on current clinical trials is posted on the Internet at www.clinicaltrials.gov. All studies receiving U.S. government funding, and some supported by private industry, are posted on this government website.

For information about clinical trials being conducted at the National Institutes of Health (NIH) Clinical Center in Bethesda, MD, contact the NIH Patient Recruitment Office:

Tollfree: (800) 411-1222
TTY: (866) 411-1010
Email: prpl@cc.nih.gov

For information about clinical trials sponsored by private sources, contact:
www.centerwatch.com

McKusick VA, ed. Online Mendelian Inheritance In Man (OMIM). The Johns Hopkins University. C Syndrome. Entry Number; 211750: Last Edit Date; 3/17/2004.

TEXTBOOKS
Bohring A. C Syndrome. In: NORD Guide to Rare Disorders. Lippincott Williams & Wilkins. Philadelphia, PA. 2003:162-63.

Gorlin RJ, Cohen MMJr, Levin LS., eds. Syndromes of the Head and Neck. 3rd ed. Oxford University Press, London, UK; 1990:889-90

JOURNAL ARTICLES
Yatsenko SA, Cheung SW, Scott DA, et al. Deletion of 9q34.3 syndrome: genotype-phenotype correlations and an extended deletion in a patient with feature of Opitz C trigonocephaly. J Med Genet. 2005;42:328-35.

Czako M, Riegel M, Morava E, et al. Opitz "C" trigonocephaly-like syndrome in a patient with terminal deletion of 2p and partial duplication of 17q. Am J Med Genet A. 2004;131:310-12.

Phadke SR, Patil SJ. Partial trisomy 13 with features similar to C syndrome. Indian Pediatr. 2004;41:614-17.

Azimi C, Kennedy SJ, Chitayat D, et al. Clinical and genetic aspects of trigonocephaly: a study of 25 cases. Am J Med Genet A. 2003;117:127-35.

Miller C, Losken HW, Towbin R, et al. Ultrasound diagnosis of craniosynostosis. Cleft Palate Craniofac J. 2002;39:73-80

Bohring A, Silengo M, Lerone M, et al. Severe end of Opitz trigonocephaly © syndrome or new syndrome. Am J Med Genet. 1999;85:438-46.

FROM THE INTERNET
Opitz Trigonocephaly Syndrome Family Network (OTSFN). nd. 4pp.
www.geocities.com/HotSprings/Villa/1407/?20055

Opitz trigonocephaly syndrome. Multiple Congenital Anomaly/Mental Retardation (MCA/MR) Syndromes. nd. 3pp.
www.nlm.nih.gov/cgi/jablonski/syndrome_cgi?term=C+syndrome&field=name

Bohring A. Letter to Opitz C Families. August 12, 1998. 3pp.
www.geocities.com/HotSprings/Villa/1407/bohring2.html?200511