It is a common autosomal trisomy among live –born children ,it has frequency of about 1 in 800 of live birth . It doesnt usually run in families and it increases with the mother age.
Children with this syndrome are invariably mentally retarded. There is similarity between people with Alzheimer disease and adults ”over 30” with down syndrome . They share memory loss, confusion, anxiety ,and lost of ability to perform simple tasks like dressing or feeding .
The physiological symptoms There are of small statures due to delayed maturation of the skeletal system and their muscle tone is poor. They have a characteristic face appearance. It is broad and flat with a small nose ,irregular teeth, abnormally shaped ears and thick lips . Many of them have peculiar small fold of skin across this inner part of the eye this gives the eyes a slightly oriental look. The name “mongolism” is derived from this characteristic
They have large furrowed tongue. 40%of children with the syndrome have major heart defects. Defects of kidneys ,thyroid gland and Adrenal glands are so common with this syndrome. Some highly usual dermatoglyphic (glyphic=craving) patterns of hand creases ,fingerprints and foot prints are also associated with this syndrome.
Hipbones are abnormally shaped and the feets little fingers often short and curved inward. Males have poorly developed genitals and Are invariably sterile,in females ovarian defects and irregular menstruation but fertility is possible. Many children learn to talk but speech is usually thick and harsh sounding ,perhaps in part because of hearing defects.
This syndrome affects about one in 4,500 Live-born children. Approximately 65 % of those individuals are females ,males with the syndrome are more likely to undergo spontaneous abortion. Karyotype:(47,XX or XY+18) means having extra 18 chromosome.
They have multiple abnormalities including severe mental and physical retardation.Such as :1-elongated skull with low set malformed ,sometimes pointed ears ,their jaw and oral cavity is small .2-They carry their fingers in an abnormal position with the second finger overlapping the third. Life expectancy of males is about 3 months ,in affected females it is about nine months.
Virtually no live –born babies having trisomy 16 are seen, cause this trisomy is often encountered in early abortuses Karyotype:47 chromosome including an extra chromosome which is chromosome number 16
It occurs in about one in 5,000 live births. Affected children rarely survive more than3-4 moths after birth .Karyotype: (47, XX or XY +13) Having extra 13 chromosome is the reason for that abnormality. Affected children are severely retarded both mentally and physically.
Small skull and eyes. The ears are often malformed and deafness in common. Many have malformed thumbs and extra digits. 70%have heart defects.
A chromosome abnormality that causes individuals to have an abnormal number ofchromosomes is called aneuploidy. If the zygote has an additional chromosome(three instead of two) it is trisomic for that chromosome. If the zygote is missing achromosome it is monosomic. Aneuploid cells occur as a result of chromosomebreakage or nondisjunction errors that happen during meiosis. Two types of errorsoccur during nondisjunction: homologous chromosomes dont separateduring anaphase I of meiosis I or sister chromatids dont separate during anaphaseII of meiosis II.In sex chromosomes, nondisjunction results in a number of abnormalities. Klinefeltersyndrome is a disorder in which males have an extra X chromosome. The genotypefor males with this disorder is XXY. People with Klinefelter syndrome may also havemore than one extra chromosome resulting in genotypes which include XXYY,XXXY, and XXXXY. Other mutations result in males that have an extra Ychromosome and a genotype of XYY. These males were once thought to be tallerthan average males and overly aggressive based on prison studies. Additionalstudies however have found XYY males to be normal. Tuner syndrome is a conditionthat affects females. Individuals with this syndrome, also called monosomy X, havea genotype of only one X chromosome (XO). Trisomy X females have an additionalX chromosome and are also referred to as metafemales (XXX).Nondisjunction can occur in autosomal cells as well. Down syndrome is mostcommonly the result of nondisjunction affecting autosomal chromosome 21. Downsyndrome is also referred to as trisomy 21 because of the extra chromosome.
45 XO, encompasses severalconditions in human females, ofwhich monosomy X (absence of anentire sex chromosome, the Barrbody) is most common. It isa chromosomal abnormality inwhich all or part of one of the sexchromosomes is absent(unaffected humans have 46chromosomes, of which two aresex chromosomes). Normal femaleshave two X chromosomes, but inTurner syndrome, one of those sexchromosomes is missing or hasother abnormalities.
47, XXY, or XXY syndrome is acondition in which human males havean extra X chromosome. While femaleshave an XX chromosomal makeup,and males an XY, affected individualshave at least two X chromosomes andat least one Y chromosome. Becauseof the extra chromosome, individualswith the condition are usually referredto as "XXY Males", or "47, XXY Males"
XYY syndrome is an aneuploidy (abnormal number) ofthe sex chromosomes in which a human male receives anextra Y-chromosome, giving a total of 47 chromosomesinstead of the more usual 46. This producesa 47,XYY karyotype which occurs in 1 in 1000 male births.Some medical geneticists question whether the term"syndrome" is appropriate for this condition[ because itsclinical phenotype is norma and the vast majority (anestimated 97% in Britain) of 47,XYY males do not knowtheir karyotype.
Triple X syndrome is a form of chromosomal variation characterized by the presence of an extra X chromosome in each cell of a human female. The condition always produces females, with an XX pair of chromosomes, as well as an additional chromosome, resulting in the formation of XXX.