Chromosomal defects

Chromosome defects arise at the level of the individual chromosome or at the level of the chromosomal set, so affecting chromosomal number in subsequent cell replications. 

Some animal studies with ozone or thetic photochemical smog have shown chromosomal defects in circulating lymphocytes, a more rapid appearance of benign pulmonary tumors, and an increase in neonatal mortality consistent with a mutagenic effect. 

Sperm evaluation11 Sperm number (count, concentration), quality (morphology, motility), chromosomal defects... 

In some sufferers of Down syndrome, the somatic cell nuclei do not contain three chromosomes 21. However, there is a chromosomal defect relating to chromosome 21 what might it be ... 

This boy has a sex-linked chromosomal defect, known as fragile-X, that can cause mental retardation and other symptoms. Doctors are treating fragile-X syndrome children successfully with experimental drugs. 

Wilson s disease is a genetically determined, autosomal recessive copper storage disease with a reduced discharge of copper into the bile. Due to pathological copper deposits in the liver and brain as well as various other organs, sequelae develop above all in the liver and CNS. The other affected organs are generally involved in the disease as late manifestation. The chromosomal defect is still not fully clarified. 

Trisomy 18 (Edwards syndrome) is caused by a nondisjunction event during meiosis that results in a fetus having an extra copy of chromosome 18. Although it occurs in only 1 in 8000 births, it is probably the most common chromosome defect at the time of conception. The dramatic change in prevalence is due to the very high fetal loss rate both before 8 weeks ( 80%) and during the second and third trimesters (-70%). Approximately 25% of affected fetuses have... 

Nicolaides KH, Azar G, Byrne D, Mansur C, Marks K. Fetal nuchal translucency ultrasound screening for chromosomal defects in first trimester of pregnancy. BMJ 1992 304 867-9. 

Increased nuchal translucency as a marker for fetal chromosomal defects. N Engl J Med 1997 337 ... 

Developmental Effects. Slight increases in child mortality from chromosomal defects and from congenital anomalies of the nervous system, circulatory system, and other unspecified anomalies were reported in the progeny of the radiation-exposed population of the Techa River region. However, the contribution of radioactive strontium to this effect is uncertain. No studies were located regarding... 

Down s syndrome A congenital form of mental retardation due to a chromosome defect in which there are three copies of chromosome no. 21 instead of the usual two (seeTRisoMY). The affected individual has a short broad face and slanted eyes (as in the Mongolian races), short fingers, and weak muscles. Down s syndrome can be detected before birth by amniocentesis, it is named after the British physician John Down (1828-96), who first studied the incidence of the disorder. 

Various types of chromosomal defects have been associated with hereditary disease. Trisomies are among the most spectacular. In cases of trisomies, instead of having 22 pairs of identical chromosomes, the cells contain 22 pairs and three identical chromosomes. As a result, the total number of chromosomes in the cell is increased by one [176-180]. Autosomal trisomies are usually associated with severe damage to the fetus and are therefore often incompatible with life. Thus,... 

A legitimate question is whether all chromosomal defects develop during meiosis when sperm cells and ova are produced. Chromosomal aberrations may appear at any time during embryonic development,... 

Redding, A., Hirschhorn, K. Guide to human chromosome defects. Birth Defects 4, 1-16 (1968)... 

The Philadelphia translocation t(9 22) (q34 qll) or Philadelphia chromosome is a chromosomal defect resulting in gene fusion of the BCR and ABL genes. The resultant fusion gene is the BCR-ABL oncogene. The Philadelphia chromosome is a cytogenetic abnormality seen in 95 % of chronic myeloid leukemia patients and 15-30 % of adults with acute lymphoblastic leukemia. 

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