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Chromosome 6, Partial Trisomy 6q

NORD is very grateful to Shashikant Kulkarni, PhD, Director of CytoGenomics and Molecular Pathology, Director of Clinical & Molecular Cytogenetics, Department of Pathology, Washington University School of Medicine, for assistance in the preparation of this report.

Synonyms of Chromosome 6, Partial Trisomy 6q

  • 6q+ Syndrome, Partial
  • Chromosome 6, Trisomy 6q2
  • Distal Duplication 6q
  • Distal Trisomy 6q
  • Duplication 6q, Partial
  • Trisomy 6q, Partial
  • Trisomy 6q Syndrome, Partial

Disorder Subdivisions

  • No subdivisions found.

General Discussion

Chromosome 6, Partial Trisomy 6q is an extremely rare chromosomal disorder in which a portion of the 6th chromosome (6q) is present three times (trisomy) rather than twice in cells of the body. Associated symptoms and findings may vary in range and severity from case to case. However, many affected infants and children have slow physical development (growth retardation); mental retardation; malformations of the skull and facial (craniofacial) region; an unusually short, webbed neck; abnormal bending (flexion) or extension of certain joints in fixed postures (joint contractures); and/or other physical abnormalities. In most cases, Chromosome 6, Partial Trisomy 6q has been the result of a balanced translocation in one of the parents.

Symptoms

As noted above, the symptoms and physical findings associated with Chromosome 6, Trisomy 6q may be variable. However, in many cases, the disorder is characterized by growth delays before and after birth, severe to profound mental retardation, a delay in the acquisition of skills requiring coordination of muscular and mental activity (psychomotor retardation), distinctive malformations of the skull and facial (craniofacial) region, musculoskeletal abnormalities, and/or additional physical features.

Characteristic craniofacial abnormalities may include a small head (microcephaly); an abnormally flat face and back region of the head (occiput); "almond-shaped," protruding, widely spaced eyes (ocular hypertelorism); and/or downwardly slanting eyelid folds (palpebral fissures). Affected individuals may also have a small, "bow-shaped" mouth with thin lips, a small jaw (micrognathia), incomplete closure of the roof of the mouth (cleft palate), a large, flat nose; malformed ears, and/or thin, arched eyebrows. In some cases, the fibrous joints (i.e., coronal and sagittal sutures) between certain bones in the front and the sides of the skull (frontal and parietal bones) may close prematurely (craniosynostosis), causing the head to grow upward (turricephaly). As a result, the head may appear unusually long, narrow, and pointed at the top, and the forehead may be abnormally prominent.

Many individuals with Chromosome 6, Partial Trisomy 6q also have distinctive abnormalities of the neck. The neck may be unusually short and wide, with abnormal webbing across the front (anterior) and/or side (lateral), potentially restricting movement of the jaw and neck. In addition, the hairline may be abnormally low on the back of the neck (nape).

Chromosome 6, Partial Trisomy 6q is also often associated with abnormal bending (flexion), extension, and fixation of certain joints (contractures), such as the fingers, wrists, and/or other regions (e.g., elbows, knees, hips), causing limitation of movement and abnormal postures. Affected individuals may also have webbing or fusion of certain fingers and/or toes (syndactyly), deformities in which the hands and/or feet are twisted out of shape or position (clubhands and/or clubfeet), abnormal curvature of the spine (scoliosis), reduced diameter of the chest; and/or widely spaced nipples.

Genital abnormalities may also be present. In affected females, there may be underdevelopment of the skin folds surrounding the vaginal opening (hypoplastic labia). In affected males, genital abnormalities may include an abnormally small penis (micropenis), underdevelopment of the scrotum; abnormal placement of the urinary opening (hypospadias), such as on the underside of the penis; and/or undescended testes (cryptorchidism).

In rare cases, individuals with Chromosome 6, Partial Trisomy 6q may also have various internal organ malformations. These may include heart (cardiac), intestinal, kidney (renal), and/or brain (cerebral) abnormalities.

Causes

In individuals with Chromosome 6, Partial Trisomy 6q, all or a portion of the end (distal) region of the long arm (q) of chromosome 6 is present three times (trisomy) rather than twice in cells of the body. 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" and a long arm identified by the letter "q." Chromosomes are further subdivided into regions and bands that are numbered. For example, the distal region of the long arm of chromosome 6, which is referred to as "6q2," includes bands 6q21 to 6q27.

Reports indicate that, in those with the disorder, the duplicated portion of 6q2 has begun at various points (i.e., breakpoints) between bands 6q21 to 6q26 and may extend to the end (or "terminal") of chromosome 6q (qter). It is possible that the range and severity of associated symptoms may depend on the specific length and location of the duplicated portion of 6q.

In most reported cases, Chromosome 6, Partial Trisomy 6q has resulted from a balanced chromosomal rearrangement in one of the parents, usually of maternal origin. However, paternal chromosomal rearrangements have been reported in rare instances. The parental chromosomal rearrangement has usually been a "balanced translocation". Translocations occur when portions of certain chromosomes break off and are rearranged, resulting in shifting of genetic material and an altered set of chromosomes. If a chromosomal rearrangement is balanced, meaning that it consists of an altered but balanced set of chromosomes, it is usually harmless to the carrier. However, such a chromosomal rearrangement may be associated with an increased risk of abnormal chromosomal development in the carrier's offspring.

Rare cases have also been reported in which the parental chromosomal rearrangement has been an inversion. An inversion is characterized by breakage of a chromosome in two places and reunion of the segment in the reverse order.

There have also been rare cases in which Chromosome 6, Partial Trisomy 6q has appeared to result from spontaneous (de novo) errors very early in embryonic development. In such de novo cases, the parents of the affected child usually have normal chromosomes and a relatively low risk 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 a balanced translocation or other chromosomal rearrangement in one of the parents.

Affected Populations

Chromosome 6, Partial Trisomy 6q is an extremely rare chromosomal disorder that appears to affect males and females equally. Approximately 30 cases have been reported in the medical literature.

Related Disorders

Additional chromosomal disorders may have features similar to those potentially associated with Chromosome 6, Partial Trisomy 6q. 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.)

Standard Therapies

Diagnosis
In some cases, Chromosome 6, Partial Trisomy 6q 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 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 studies performed on such fluid or tissue samples may reveal the presence of Partial Trisomy 6q.

Chromosome 6, Partial Trisomy 6q may also be diagnosed and/or confirmed after birth (postnatally) by a thorough clinical evaluation, characteristic physical findings, and chromosomal analysis. Additional specialized tests may also be performed to help detect and/or characterize certain abnormalities that may be associated with the disorder.

Treatment
The treatment of Chromosome 6, Partial Trisomy 6q is directed toward the specific symptoms that are apparent in each individual. Such treatment may require the coordinated efforts of a team of medical professionals, such as pediatricians, surgeons; physicians who specialize in disorders of the skeleton, muscles, joints, and related tissues (orthopedists), physical therapists, and/or other health care professionals.

For some affected individuals, physicians may recommend surgical correction of certain craniofacial, limb, genital, and/or internal organ malformations associated with the disorder. In addition, physical therapy, the use of certain orthopedic appliances, and/or additional orthopedic techniques, including surgery, may be advised to help manage musculoskeletal abnormalities, such as joint contractures and scoliosis. The surgical procedures performed will depend upon the severity of the anatomical abnormalities, their associated symptoms, and other factors.

Early intervention may be important in ensuring that affected children reach their potential. Special services that may be beneficial include special education and/or other medical, social, and/or vocational services. Genetic counseling will also be of benefit for the families of affected individuals. Other treatment for this disorder is symptomatic and supportive.

Investigational Therapies

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 web site.

For information about clinical trials being conducted at the 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

Organizations related to Chromosome 6, Partial Trisomy 6q

(Please note that some of these organizations may provide information concerning certain conditions potentially associated with this disorder [e.g., mental retardation, craniofacial abnormalities, etc.].)

References

TEXTBOOKS
Gorlin RJ, et al., eds. Syndromes of the Head and Neck. 3rd ed. New York, NY: Oxford University Press; 1990:78.

Buyse ML. Birth Defects Encyclopedia. Dover, Mass: Blackwell Scientific Publications, Inc; 1990:344-45.

JOURNAL ARTICLES
Conrad BA, et al. Duplication 6q22-->qter: definition of the phenotype. Am J Med Genet. 1998;78:123-26.

Dellacasa P, et al. Partial trisomy of the long arm of chromosome 6. A clinical case. Minerva Pediatr. 1993;45:517-21.

Brondum-Nielsen K, et al. Chromosome painting using FISH (fluorescence in situ hybridization) with chromosome-6-specific library demonstrates the origin of a de novo 6q+ marker chromosome. Clin Genet. 1993;43:235-39.

Uhrich S, et al. Duplication (6q) syndrome diagnosed in utero. Am J Med Genet. 1991;41:282-83.

Bartalena L, et al. A case of partial 6q trisomy diagnosed at birth. Pathologica. 1990; 82:549-52.

Franchino CJ, et al. Partial trisomy 6q: case report with necropsy findings. J Med Genet. 1987;24:300-03.

Chase TR, et al. Duplication 6q24 leads to 6qter in an infant from a balanced paternal translocation. Am J Med Genet. 1983;14:347-51.

Taysi K, et al. Trisomy 6q22 leads to 6qter due to maternal 6;21 translocation. case report review of the literature. Ann Genet. 1983;26:243-46.

Neu RL, et al. An infant with trisomy 6q21 leads to 6qter. Ann Genet. 1981;24:167-69.

Turleau C, et al. Trisomy 6qter. Clin Genet. 1981;19:202-206.

Stamberg J, et al. Partial trisomy 6q, due to balanced maternal translocation (6;22) (q21; p13) or (q21; pter). Clin Genet. 1981;19:122-25.

Duca D, et al. Familial partial trisomy: 6q25 leads to 6qter. J Genet Hum. 1980;28:31-37.

Schmid W, et al. Trisomy 6q25 to 6qter in a severely retarded 7-year-old boy with turricephaly, bow-shaped mouth, hypogenitalism and club feet. Hum Genet. 1979;46:279-84.

Tipton RE, et al. Duplication 6q syndrome. Am J Med Genet. 1979;3:325-30.

The information in NORD’s Rare Disease Database is for educational purposes only. It should never be used for diagnostic or treatment purposes. If you have questions regarding a medical condition, always seek the advice of your physician or other qualified health professional. NORD’s reports provide a brief overview of rare diseases. For more specific information, we encourage you to contact your personal physician or the agencies listed as “Resources” on this report.

Report last updated: 2009/04/10 00:00:00 GMT+0

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