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Chromosome 6 is an extremely rare chromosomal disorde r in which a portion of the 6th chromosome (6q) is present three times (trisomy) rather than twice in cells of the body. Synonyms of Chromosome 6, Partial Trisomy 6q include 6q+ syndrome, distal duplication 6q, and distal trisomy 6q.

This chromosomal disorder results from the partial duplication of the long arm of chromosome 6. Chromosome 6 presents with a highly variable phenotype with some common characteristics of growth and developmental delay, intellectual disability, craniofacial dysmorphism (such as microcephaly, flat facial profile, frontal bossing, hypertelorism, downward-slanting palpebral fissures, flat nasal bridge, anteverted nares, bow shaped mouth, and micrognathia), shower webbed neck and joint contractures.

Signs and Symptoms
Associated symptoms and findings may vary in range and severity from case to case.


 * 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)
 * Physical abnormalities

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)
 * downwardly slanting eyelid folds (palpebral fissures)
 * small, "bow-shaped" mouths with thin lips
 * a small jaw (micrognathia)
 * incomplete closure of the roof of the mouth (cleft palate)
 * a large, flat nose
 * malformed ears

Chromosome 6 is also often associated with abnormal bending (flexion), extension, and fixation of certain joints (contractures), such as fingers, wrists, and/or other regions, causing limitation of movement and abnormal postures. Affected individuals may also have webbing or fusion of certain fingers and/or toes (syndactyly), and other deformities in the hand and feet.

In rare cases, individuals affected may also have internal organ malformations including heart (cardiac), intestinal, kidney (renal), and/or brain (cerebral) abnormalities. Individuals may also suffer from major congenital heart defects including atrial septal defect, ventricular septal defect and patent arterial duct as well as other renal abnormalities like hydronephrosis and a hypoplastic kidney.

Cause
Individuals with Chromosome 6, the end portion of the distal region of the arm of the sixth chromosome is present three times, hence trisomy. This duplication may occur completely or partially. Chromosomes are threadlike structures of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. Coiled in proteins called histones, DNA carries the genetic characteristics of each individual. In humans with Chromosome 6, there are 46 chromosomes that are arranged in 22 pairs called autosomes, numbered from 1 through 22, and an unequal 23rd pair of X and Y chromosomes for males and two X chromosomes for females. Each chromosome has two arms; a short arm designated as "p" and a long arm identified by the letter "q". Furthermore, chromosomes are further divided into regions and numbered bands.

In general, trisomy is caused by spontaneous genetic mutations that occur at the time of fertilization. The cause of this is generally unknown and is so far unpreventable. The most important risk of trisomy is maternal age as women in their late 30s and 40s have a higher chance of trisomy conditions occurring.

Pathophysiology/Mechanism
For many of the Trisomy 6 cases seen, this disorder has resulted from a parental chromosomal rearrangement, usually from the maternal origin. Paternal chromosomal rearrangements have been reported in rare instances. This said parental rearrangement usually occurs as a balanced translocation which occur when portions of certain chromosomes break off and are rearranged. This results in the shifting of genetic material and an altered set of chromosomes. It is balanced because while it consists of an altered set of chromosomes, the number is still balanced, which usually means it is harmless to the carrier. However, with regards to the carrier's offspring, this chromosomal rearrangement may be associated with an increased risk of abnormal chromosomal development.

Chromosomal analysis and genetic counseling are typically recommended for parents of an affected child to help confirm or exclude the presences of a balanced translocation or other chromosomal rearrangement in one of the parents.

Diagnosis
In some cases, this Chromosome 6, Trisomy 6 may be theorized before birth by specialized tests including ultrasound, amniocentesis, and/or chorionic villus sampling (CVS). Using these sonographies to create an image of the developing fetus, it may reveal findings that suggest a chromosomal disorder or other abnormalities.

However, Chromosome 6 may be diagnosed after birth by clinical evaluation, physical findings, and chromosomal analysis. The first steps in diagnosis are a medical history and physical examination.

Additional specialized tests may also be performed to help detect and/or characterize certain abnormalities that may be associated with the disorder.

These additional clinical tests include:


 * Karyotyping
 * FISH-metaphase
 * Uniparental disomy study (UPD)
 * Deletion/duplication analysis
 * Detection of homozygosity

Treatment/Management
Treatment for Chromosome 6, Trisomy 6 is mostly toward the specific symptoms apparent in each individual. Usually with combined efforts from a team of medical professionals, including pediatricians, surgeons, and other physicians who specialize in disorders of the skeleton, muscles, joints, and related tissues, physical therapists, and/or other health care professionals.

Most commonly, therapy involves treating the symptoms such as the certain craniofacial, limb, genital, and/or internal organ malformations associated with the disorder. This treatment usually occurs from surgical correction recommended by physicians. Otherwise, early intervention and special services may be beneficial to ensure that children affected reach their potential. This may include special education, and other medical, social, and/or vocational services.

Prognosis
Like above, early intervention may be important in ensuring that affected children reach their potential. However, prognosis is highly variable as a number of patients have died in infancy due to respiratory or severe feeding problems. Otherwise, the prognostic significance of trisomy 6 is not well established.

Epidemiology (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.

Research Directions
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.