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

• Chromosome 9, Partial Monosomy 9p
• Additional Chromosomal Disorders (General)

As noted above, Chromosome 9 Ring may be characterized by various craniofacial malformations; however, in some cases, such features may not be apparent. Craniofacial defects associated with Chromosome 9 Ring may include an abnormally small head (microcephaly) and/or premature fusion of the fibrous joint (suture) between bones forming the forehead (metopic suture), resulting in an unusually narrow, pointed, "triangular-" or "keel-shaped" forehead (trigonocephaly) and closely spaced eyes (ocular hypotelorism). Some affected individuals may also have abnormally slanting eyelid folds (palpebral fissures), slight protrusion of the eyes (exophthalmos), an exaggerated arch to the eyebrows, a small jaw (micrognathia) and small chin, and/or a short neck.

In some cases, Chromosome 9 Ring may also be associated with growth retardation after birth; various structural malformations of the heart (congenital heart defects), such as an abnormal opening in the partition (septum) that normally separates the lower chambers (ventricles) of the heart (ventricular septal defect); and/or variable skeletal abnormalities. Some affected males may also have genital abnormalities, including ambiguous genitalia or abnormal placement of the urinary opening (hypospadias), such as on the underside of the penis. Additional physical abnormalities have also been reported in association with Chromosome 9 Ring. These have included incomplete closure of the roof of the mouth (cleft palate); abnormal bending (clinodactyly) of certain fingers; a single crease across the palms of the hands; and/or a condition known as gastroesophageal reflux. The latter is characterized by abnormal backflow (reflux) of stomach acid into the esophagus, causing inflammation of and possible damage to the esophageal lining.

Chromosome 9 Ring is commonly characterized by moderate to severe mental retardation. However, some affected individuals may have intelligence in the low normal range. Those with the disorder may also show variable delays in the acquisition of skills requiring the coordination of mental and physical activities (psychomotor retardation) and/or behavioral abnormalities, such as agitated or withdrawn, introverted behavior.
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Chromosome 9 Ring is caused by deletion of chromosomal material from the end (distal) regions of the short arm (p) and long arm (q) of chromosome 9 and joining of the ends to form a ring. Chromosomes are found in the nucleus of all body cells. They carry the genetic characteristics of each individual. Pairs of human chromosomes are numbered from 1 through 22, with an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has a short arm designated as "p," a long arm identified by the letter "q," and a narrowed region at which the two arms are joined (centromere). Chromosomes are further subdivided into bands that are numbered outward from the centromere.

As noted above, in those with Chromosome 9 Ring, associated symptoms and findings may vary from case to case. Such clinical variability may depend upon the amount and specific location of material lost from the 9th chromosome, the stability of the ring chromosome during subsequent cellular divisions, and/or other factors. For example, in some cases, only a certain percentage of an affected individual's cells may have Chromosome 9 Ring, while other cells may have a normal chromosomal makeup (a finding known as "chromosomal mosaicism"), affecting the variability of associated symptoms and physical features.

Chromosome 9 Ring usually appears to be caused by spontaneous (de novo) errors very early during embryonic development. In such instances, the parents of the affected child usually have normal chromosomes and a relatively low risk of having another child with the chromosomal abnormality. However, it is theoretically possible that a parent of an affected individual also has Chromosome 9 Ring in all or some cells with few apparent symptoms. In such instances, it is believed that Chromosome 9 Ring may have been inherited and that the chances are greater of having another child with the chromosomal abnormality.

Chromosomal analysis and genetic counseling are typically recommended for parents of an affected child to help confirm or exclude the presence of certain chromosomal abnormalities in one of the parents, such as Chromosome 9 Ring, mosaicism, or a balanced chromosomal rearrangement involving chromosome 9.
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Chromosome 9 Ring is a rare chromosomal abnormality that is thought to affect males and females in relatively equal numbers. Since the disorder was originally described, more than 12 cases have been reported in the medical literature.
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Symptoms of the following disorders may be similar to those of Chromosome 9 Ring. Comparisons may be useful for a differential diagnosis:

Chromosome 9, Partial Monosomy 9p is a chromosomal disorder characterized by deletion (monosomy) of part of the end (distal) region of the short arm (p) of chromosome 9 (i.e., with the breakpoint usually located within band 9p22). Characteristic features include variable degrees of mental retardation; craniofacial, limb, heart (cardiac), and/or genital abnormalities; and/or other physical malformations. Common craniofacial defects include a "triangular-" or "keel-shaped" forehead (trigonocephaly); a short nose, flattened nasal bridge, and upturned nostrils (anteverted nares); prominent eyes; upwardly slanting eyelid folds (palpebral fissures); vertical skin folds that may cover the eyes' inner corners (epicanthal folds); highly arched eyebrows; a small jaw (micrognathia); a short, broad neck; and/or other features. In most cases, Partial Monosomy 9p appears to result from spontaneous (de novo) errors very early during embryonic development. (For further information, choose "Monosomy 9p" as your search term in the Rare Disease Database.)

Additional chromosomal disorders may have symptoms and findings similar to those potentially associated with Chromosome 9 Ring. Chromosomal testing is necessary to confirm the specific chromosomal abnormality present. (For further information on such disorders, choose the name of the specific chromosomal disorder in question or use "chromosome" as your search term in the Rare Disease Database.)
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Diagnosis
In some instances, Chromosome 9 Ring may be suggested before birth (prenatally) by specialized tests such as ultrasound, amniocentesis, and/or chorionic villus sampling (CVS). During fetal ultrasonography, reflected sound waves create an image of the developing fetus, potentially revealing certain findings that suggest a chromosomal disorder or other developmental abnormalities. With amniocentesis, a sample of fluid that surrounds the developing fetus is removed and analyzed, while CVS involves the removal of tissue samples from a portion of the placenta. Chromosomal analysis performed on such fluid or tissue samples may reveal the presence of Chromosome 9 Ring.

In most cases, Chromosome 9 Ring is diagnosed or confirmed after birth (postnatally) based upon a thorough clinical evaluation, characteristic physical findings, and chromosomal analysis. Various specialized tests may also be performed to help detect and/or characterize certain abnormalities that may be associated with the disorder. For example, a thorough cardiac evaluation may be advised to detect any heart abnormalities that may be present. Such evaluations may include a thorough clinical examination, evaluation of heart and lung sounds through use of a stethoscope, and specialized tests that enable physicians to evaluate the structure and function of the heart (e.g., x-ray studies, electrocardiography [EKG]), echocardiography).

Treatment
The treatment of Chromosome 9 Ring is directed toward the specific symptoms that are apparent in each individual. Such disease management may require the coordinated efforts of a team of medical professionals, such as pediatricians; physicians who diagnose and treat disorders of the skeleton, muscles, joints, and related tissues (orthopedists); heart specialists (cardiologists); and/or other health care professionals.

For some affected individuals, physicians may recommend surgical repair or correction of certain craniofacial, genital, and/or other malformations associated with the disorder. In addition, for those with congenital heart defects, treatment with certain medications, surgical intervention, and/or other measures may be required. The specific surgical procedures performed will depend upon the severity and location of the anatomical abnormalities, their associated symptoms, and other factors.

Early intervention may also be important in ensuring that affected children reach their potential. Special services that may be beneficial include special education, speech therapy, physical therapy, and/or other medical, social, and/or vocational services. Genetic counseling will also be of benefit for affected individuals and their families. Other treatment for this disorder is symptomatic and supportive.
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Research on birth defects and their causes is ongoing. The National Institutes of Health (NIH) is sponsoring the Human Genome Project which is aimed at mapping every gene in the human body and learning why they sometimes malfunction. It is hoped that this new knowledge will lead to prevention and treatment of birth defects in the future.

TEXTBOOKS
Jones KL. Smith’s Recognizable Patterns of Human Malformation. 5th ed. Philadelphia, PA: W.B. Saunders Company; 1997:46-47.

Thoene JG, ed. Physicians' Guide to Rare Diseases. Montvale, NJ: Dowden Publishing Company Inc; 1995:33.

Buyse ML, ed. Birth Defects Encyclopedia. Dover, MA: Blackwell Scientific Publications; For: The Center for Birth Defects Information Services Inc; 1990:354.

JOURNAL ARTICLES
Seghezzi L, et al. Ring chromosome 9 with a 9p22.3-p24.3 duplication. Eur J Pediatr. 1999;158:791-93.

Cavaliere ML, et al. Phenotypic variability in the chromosome 9 ring. Acta Biomed Ateneo Parmense. 1997;68(suppl 1):85-89.

Lanzi G, et al. Ring chromosome 9: an atypical case. Brain Dev. 1996;18:216-19.

Kontiokari T, et al. Ring chromosome 9. Duodecim. 1995;111:439-41.

Blennow E, et al. Characterization of supernumerary ring marker chromosomes by fluorescence in situ hybridization (FISH). Am J Hum Genet. 1993;53:433-42.

Manouvrier-Hanu S, et al. Another case of ring chromosome 9 associated with gastroesophageal reflux [letter]. Am J Med Genet. 1989;32:558.

Manouvrier-Hanu S, et al. Ring chromosome 9. Case report and review of the literature. Ann Genet. 1988;31:250-53.

Leung AK, et al. A case of ring (9)/del(9p) mosaicism associated with gastroesophageal reflux. Am J Med Genet. 1988;29:43-48.

Fryns JP, et al. Moderate mental retardation and nonspecific dysmorphic syndrome associated with ring chromosome 9. Hum Genet. 1979;50:29-32.