What is the genetic basis and phenotype for Down syndrome?

The genetic basis for DS is trisomy 21: the presence in the genome of three chromosomes 21 instead of two, how it is normal. Chromosome 21 is the smallest human chromosome and contains 200 to 300 genes. Analysis of the chromosome revealed 127 known genes, 98 predicted genes and 59 pseudogenes (5).

What is the phenotype for Down syndrome?

Down syndrome (Down, 1866), a particular combination of phenotypic features that includes mental retardation and characteristic facies, is caused by trisomy 21 (Lejeune et al., 1959), one of the most common chromosomal abnormalities in liveborn children.

What is the genetic inheritance pattern of Down syndrome?

Most cases of Down syndrome are not inherited. When the condition is caused by trisomy 21, the chromosomal abnormality occurs as a random event during the formation of reproductive cells in a parent. The abnormality usually occurs in egg cells, but it occasionally occurs in sperm cells.

How genotype contributes to disease phenotype Down syndrome?

Down syndrome (DS) is one of the most frequent congenital birth defects, and the most common genetic cause of mental retardation. In most cases, DS results from the presence of an extra copy of chromosome 21. DS has a complex phenotype, and a major goal of DS research is to identify genotype–phenotype correlations.

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Can a Down syndrome child look normal?

Some of the children with Mosaic Down syndrome that we know do not actually look as if they have Down syndrome – the usual physical features are not obvious. This raises some important and difficult social issues and identity issues for both parents and children, which parents have discussed with us.

What are the 3 types of Down syndrome?

There are three types of Down syndrome:

  • Trisomy 21. This is by far the most common type, where every cell in the body has three copies of chromosome 21 instead of two.
  • Translocation Down syndrome. In this type, each cell has part of an extra chromosome 21, or an entirely extra one. …
  • Mosaic Down syndrome.

Does Down syndrome affect the phenotype?

Down syndrome (DS) is one of the most frequent congenital birth defects, and the most common genetic cause of mental retardation. In most cases, DS results from the presence of an extra copy of chromosome 21. DS has a complex phenotype, and a major goal of DS research is to identify genotype–phenotype correlations.

Does Klinefelter syndrome affect intelligence?

Most males with the 47,XXY karyotype have normal intelligence. Intellectual disability occurs in males with Klinefelter syndrome variants, who have a higher number of X chromosomes. About 70% of patients have minor developmental and learning disabilities.

What are the signs of Down syndrome during pregnancy?

Some common physical signs of Down syndrome include:

  • Flat face with an upward slant to the eyes.
  • Short neck.
  • Abnormally shaped or small ears.
  • Protruding tongue.
  • Small head.
  • Deep crease in the palm of the hand with relatively short fingers.
  • White spots in the iris of the eye.
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Can Down syndrome be prevented?

Down syndrome can’t be prevented, but parents can take steps that may reduce the risk. The older the mother, the higher the risk of having a baby with Down syndrome. Women can reduce the risk of Down syndrome by giving birth before age 35.

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