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NONDISJUNCTION TYPE All cases of "regular" Down syndrome are inherited from one of the parents. A Trisomy in offspring results from a glitch during meiosis in the parents. Meiosis is the creation of the gametes- the egg or the sperm. If one gamete has two copies of any chromosome instead of the typical one copy, the baby will end up with a trisomy - 3 of that chromosome rather than the typical 2 (one copy of each chromosome comes from the egg, one copy from the sperm). In Down syndrome we are talking about a trisomy of the 21st chromosome.
The parent donating one extra 21st chromosome can be the mother, or more rarely, the father.
MOSAIC TYPE
In Mosaic Down syndrome (about 1 % of all cases of DS), the extra 21st chromosome was not inherited from a parent, but rather created during mitosis - cellular duplication - of the early embryo after conception. Some cells in a person with Mosaic type will be typical and some cells contain the extra 21st chromosome. A karyotype test can tell us what type Down syndrome a person has.
TRANSLOCATION TYPE:
There is also a type that accounts for a small percentage of Down syndrome occurrences which is like NDJ type, also inherited: Translocation Down Syndrome. In these translocation cases, the mother or father is a balanced carrier of the translocation, which means he or she has some rearranged genetic material, but no extra genetic material (which is where the symptoms of Down Syndrome come from, the extra proteins created from the "Critical Region" of the 21st chromosome such as DYRK, APP, SOD-1 and more). In a parent with undiscovered Translocation DS, all or part of their 21st chromosome (which is tiny, and easily dislocated) has attached itself to the end of another chromosome and expresses itself normally. But after meiosis, some egg or sperm cells now carry and extra copy of #21 chromosome. After fertilisation, there are 3 copies present.
A balanced carrier has no signs or symptoms of Down syndrome themselves, but he or she can pass the translocation on to children.
- If the father is the carrier, the risk is about 3 percent.
- If the mother is the carrier, the risk is about 12 percent.
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Is there a specific gene for down syndrome?
No.
Why does Lesch-Nyhan syndrome affect males?
The HPRT gene is located on the X chromosome. Since the HPRT gene is located on the X chromosome, Lesch-Nyhan syndrome is considered X-liked. This means that it only affects males.
What gene or chromosome is affected by down syndrome?
Chromosome 21 is tripled in Down syndrome.
What causes Lesch-Nyhan syndrome?
The syndrome is caused by a severe change (mutation) in the HPRT gene . Since the HPRT gene is located on the X chromosome, Lesch-Nyhan syndrome is considered an X-linked disorder and therefore only affects males.
How is usher syndrome inherited?
Usher syndrome is inherited as an autosomal recessive trait. The term autosomal means that the mutated gene is not located on either of the chromosomes that determine a person's sex; in other words, both males and females can have the disorder and can pass along the disorder to a child. The word recessive means that to have Usher syndrome, an individual must receive a mutated form of the Usher syndrome gene from each parent. If a child has a mutation in one Usher syndrome gene but the other gene is normal, he or she is predicted to have normal vision and hearing. Individuals with a mutation in a gene that can cause an autosomal recessive disorder are called carriers, because they "carry" the gene with a mutation but show no symptoms of the disorder. If both parents are carriers of a mutated gene for Usher syndrome, they will have a one-in-four chance of having a child with Usher syndrome with each birth.
What can down syndrome be caused by?
Down's Syndrome is caused mainly by a mutation in the gene. It is a genetic disorder, which means it was passed on from parents to offspring.
What is the possibility of someone that has siblings with down syndrome have the gene in them?
It is more than likely you do have the gene. Only if you are an identical twin.
Is down syndrome and pku caused by chromosomal abnormalities?
Down syndrome is caused by an additional chromosome while PKU is due to a mutation or defect in a gene.
What type of leukemia is associated with Down syndrome?
Acute Lymphoblastic Leukemia (ALL) and Down Syndrome both have been associated with mutations in the JAK2 gene.
What chromosome number is affected in Lowe syndrome?
Lowe syndrome is caused by a mutated gene on the X sex chromosome. Because it is X-linked, it occurs almost exclusively in males.
How many chromosome do you have when you have fragile x syndrome?
Fragile X syndrome is caused by a mutation that prevents the Fragile X mental retardation (Fmr-1) gene from being transcribed. This gene is located on the X chromosome (the sex chromosome). Since males only carry one of these chromosomes, they are twice as likely to be affected by the mutation than females.
Why are males more likely to have fragile X syndrome?
males have only one copy of the X chromosome. Males who inherit the full mutation are expected to have mental impairment. A female's normal X chromosome may compensate for her chromosome with the fragile X gene mutation
