A change in the number of chromosomes leads to a chromosomal disorder. These changes can occur during the formation of reproductive cells (eggs and sperm) or in early fetal development. In humans the most common form of aneuploidy is trisomy, or the presence of an extra chromosome in each cell. Monosomy, or the loss of one chromosome from each cell, is another kind of aneuploidy.

Aneuploidy is common in cancerous cells. Molecular biologist Peter Duesberg has proposed that it may even be the cause of, and not a symptom of, most cancers (PMID 15085930). This view is still hypothetical, but is increasingly respected by mainstream cancer researchers.

Disomy

A disomy is the presence of a pair of chromosomes, or the normal amount for some organisms including humans. It is not a disorder, or aneuploid, but is the absence of aneuploidism.

Trisomy

A trisomy is the presence of three, instead of the normal two, chromosomes of a particular numbered type in an organism. Thus the presence of an extra chromosome 21 is called trisomy 21. Most trisomies, like most other abnormalities in chromosome number, result in distinctive birth defects. Many trisomies result in miscarriage or death at an early age.

A partial trisomy occurs when part of an extra chromosome is attached to one of the other chromosomes. A mosaic trisomy is a condition where extra chromosomal material exists in only some of the organism's cells.

While a trisomy can occur with any chromosome, few babies survive to birth with most trisomies. The most common types that survive without spontaneous abortion in humans are:

Trisomy 21 (Down syndrome)
Trisomy 18 (Edward's syndrome)
Trisomy 13 (Patau syndrome)
Trisomy 9
Trisomy 8 (Warkany syndrome 2)

Trisomy involving sex chromosomes includes:

XXX (Triple X syndrome)
XXY (Klinefelter's syndrome)
XYY (XYY syndrome)

Monosomy

Monosomy is the presence of only one chromosome from a pair in a cell's nucleus. Monosomy is a type of aneuploidy. Partial monosomy occurs when the long or short arm of a chromosome is missing.

Human genetic disorders arising from monosomy are:

X0 (Turner syndrome)
cri du chat syndrome -- a partial monosomy caused by a deletion of the end of the short (p) arm of chromosome 5

Sources

This article incorporates public domain text from The U.S. National Library of Medicine.

Read more at Wikipedia.org

• [List your site here Free!]

Aberrant Nuclear Projections of Neutrophils in Trisomy 13
From Archives of Pathology & Laboratory Medicine, 2/1/04 by Salama, Mohamed E

A 26-year-old gravida 2, para 1 woman was referred to the Medical Genetics Clinic for consultation at 25 weeks of gestation for a questionable "double bubble" (gastric and duodenal distension proximal to a presumed atretic site) that was observed on ultrasound examination. A repeat ultrasound examination revealed a fetus growing appropriately for gestational age but with an echogenic bowel. The double bubble was not seen, but a fluid-filled structure was identified, probably representing a distended gallbladder. The family history revealed no birth defects or mental retardation. This woman's first child was alive with no abnormalities. The mother declined amniocentesis. Because of the echogenic fetal bowel, maternal blood was drawn to evaluate titers for toxoplasmosis, other infections, rubella, cytomegalovirus infection, and herpes simplex infection and to search for cystic fibrosis mutations. Because of partial French-Canadian ancestry, she was also tested for Tay-Sachs carrier status. Results of all those tests were normal or negative.

A 2750-g girl was born at 35 weeks' gestation by normal vaginal route. Apgar scores were 4 at 1 minute, 6 at 5 minutes (after intubation), and 8 at 10 minutes. Postaxial polydactyly of all 4 extremities was noted, and echocardiography for respiratory distress and hypotension revealed tetralogy of Fallot. At this point, it was thought that the child might have either Edwards syndrome or Patau syndrome. The cardiac malformation greatly compromised her condition, resulting in refractory hypotension and hypoxemia, and the family decided to withdraw ventilator support. A few hours after her death, the Genetics Laboratory reported preliminary fluorescent in situ hybridization findings consistent with trisomy 13 (Patau syndrome) (Figure, A: fluorescent in situ hybiridization image of a cell showing +13; the green signal is the 13 probe and the orange signal is the 21 probe). The final karyotype report confirmed the trisomy 13 (Figure, B). Review of a peripheral smear revealed 2 or more small threadlike projections from the nuclei in more than 80% of the neutrophils (Figure, C).

Trisomy 13 usually occurs by nondisjunction during gametogenesis. The prognosis is poor. Fetal death is frequent, and 90% of these babies that are born alive die within 1 year. Most have severe brain anomalies (especially holoprosencephaly). Heart defects, polydactyly and other limb anomalies, facial clefting, abdominal wall defects, and kidney malformations are also common. Any affected child may have some but not all of these problems. If the child survives the early weeks, growth is slow, and healing of wounds and recovery from illness are compromised. The few who live longer do not usually walk or speak meaningfully. Thus, they are significantly more severely handicapped than most children with Down syndrome.1

Huehns et al2 reported numerous pedunculated nuclear projections attached to the surface of nuclei in neutrophils of persons with trisomy 13. Electron microscopic examination revealed the presence of chromatin in these projections. Huehns et al2 concluded that this feature is specific to trisomy 13. Walzer et aP proposed that a finding of 2 or more projections in 15% of the leukocytes is highly suggestive of D^sub 1^ trisomy. In normal females, 2% to 10% of mature neutrophils exhibit a single drumstick (nuclear projection) (Figure, D), representing the inactivated X chromosome.

A pathologist's identification of structural anomalies of the neutrophils on a blood smear can provide rapid (less than 1 hour) support to the clinical suspicion of trisomy 13. This information may assist clinicians and families facing complex decisions about life support or transport after the delivery of an infant with multiple anomalies. Even in the most advanced centers, a fluorescent in-situ hybridization report usually requires 24 hours to obtain.

References

1. Baty BJ, Brent BL, Carey JC. Natural history of trisomy 18 and trisomy 13: I. Growth, physical assessment, medical histories, survival, and recurrence risk. Am J Med Genet. 1994;49:175-188.

2. Huehns ER, Lutzner M, Hecht F. Nuclear abnormalities of the neutrophils in D^sub 1^ (13-15) trisomy syndrome. Lancet 1964;13:589-590.

3. Walzer S, Gerald PS, Breau G, O'Neill D, Diamond LK. Hematologic changes in the trisomy syndrome. Pediatrics. 1966;38:419-429.

Mohamed E. Salama, MD; Veena Shah, MD; Robert Roger Lebel, MD, FACMG; Daniel L. VanDyke, PhD, FACMG

Accepted for publication October 1, 2003.

From the Departments of Pathology and Medical Genetics, Henry Ford Hospital, Detroit, Mich.

Reprints: Mohamed E. Salama, MD, Department of Pathology K-6, Henry Ford Hospital, 2799 West Grand Blvd, Detroit, MI 48202 (e-mail: msalama1@hfhs.org).

Return to Trisomy

Home

Contact

Resources

Exchange Links

ebay