Familial Down Syndrome Is a Result of What Type of Chromosomal Mutation?
What is Down Syndrome?
In every jail cell in the human torso there is a nucleus, where genetic fabric is stored in genes. Genes carry the codes responsible for all of our inherited traits and are grouped along rod-like structures called chromosomes. Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down's syndrome occurs when an private has a full or partial actress copy of chromosome 21.
This additional genetic cloth alters the course of development and causes the characteristics associated with Down syndrome. A few of the common concrete traits of Down syndrome are low muscle tone, small stature, an upwardly camber to the eyes, and a single deep crease across the center of the palm – although each person with Down syndrome is a unique individual and may possess these characteristics to different degrees, or not at all.
How Common is Down Syndrome?
According to the Centers for Illness Command and Prevention, approximately i in every 700 babies in the United States is born with Down syndrome, making Downward syndrome the nigh common chromosomal condition. Well-nigh six,000 babies with Down syndrome are born in the United States each year.
When Was Downward Syndrome Discovered?
For centuries, people with Down syndrome have been alluded to in art, literature and science. It wasn't until the late nineteenth century, however, that John Langdon Down, an English language physician, published an accurate clarification of a person with Down's syndrome. It was this scholarly work, published in 1866, that earned Downwards the recognition as the "father" of the syndrome. Although other people had previously recognized the characteristics of the syndrome, information technology was Downward who described the condition as a distinct and split entity.
In recent history, advances in medicine and science have enabled researchers to investigate the characteristics of people with Down syndrome. In 1959, the French physician Jérôme Lejeune identified Down's syndrome as a chromosomal status. Instead of the usual 46 chromosomes nowadays in each cell, Lejeune observed 47 in the cells of individuals with Down's syndrome. It was later determined that an extra partial or whole copy of chromosome 21 results in the characteristics associated with Down's syndrome. In the year 2000, an international team of scientists successfully identified and catalogued each of the approximately 329 genes on chromosome 21. This accomplishment opened the door to slap-up advances in Down syndrome enquiry.
Are At that place Different Types of Down Syndrome?
TRISOMY 21 (NONDISJUNCTION)
Down syndrome is usually caused by an fault in cell division chosen "nondisjunction." Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two. Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to carve up. As the embryo develops, the extra chromosome is replicated in every cell of the body. This blazon of Down syndrome, which accounts for 95% of cases, is called trisomy 21.
MOSAICISM
Mosaicism (or mosaic Down syndrome) is diagnosed when in that location is a mixture of 2 types of cells, some containing the usual 46 chromosomes and some containing 47. Those cells with 47 chromosomes comprise an extra chromosome 21.
Mosaicism is the least common form of Downwardly syndrome and accounts for only about i% of all cases of Downwards syndrome. Research has indicated that individuals with mosaic Down's syndrome may have fewer characteristics of Down's syndrome than those with other types of Down's syndrome. Still, broad generalizations are non possible due to the wide range of abilities people with Down's syndrome possess.
TRANSLOCATION
In translocation, which accounts for almost 4% of cases of Down's syndrome, the total number of chromosomes in the cells remains 46; however, an additional full or partial re-create of chromosome 21 attaches to another chromosome, ordinarily chromosome fourteen. The presence of the actress full or partial chromosome 21 causes the characteristics of Downward syndrome.
What Causes Down Syndrome?
Regardless of the type of Down syndrome a person may have, all people with Down syndrome have an extra, critical portion of chromosome 21 nowadays in all or some of their cells. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome.
The crusade of the extra full or fractional chromosome is still unknown. Maternal age is the merely factor that has been linked to an increased chance of having a babe with Down syndrome resulting from nondisjunction or mosaicism. However, due to college birth rates in younger women, 80% of children with Downward syndrome are born to women under 35 years of age.
There is no definitive scientific inquiry that indicates that Down syndrome is caused past environmental factors or the parents' activities before or during pregnancy.
The additional fractional or total copy of the 21st chromosome which causes Down syndrome can originate from either the father or the mother. Approximately 5% of the cases have been traced to the father.
Does Down Syndrome Run in Families?
All three types of Downward syndrome are genetic conditions (relating to the genes), but only ane% of all cases of Down syndrome have a hereditary component (passed from parent to child through the genes). Heredity is non a factor in trisomy 21 (nondisjunction) and mosaicism. However, in one-3rd of cases of Down syndrome resulting from translocation there is a hereditary component – accounting for near 1% of all cases of Down's syndrome.
The age of the mother does not seem to be linked to the chance of translocation. About cases are sporadic – risk – events. However, in about i-third of cases, 1 parent is a carrier of a translocated chromosome.
What Is the Likelihood of Having a 2nd Child with Down syndrome?
One time a woman has given birth to a baby with trisomy 21 (nondisjunction) or translocation, it is estimated that her chances of having another baby with trisomy 21 is ane in 100 upwards until age twoscore.
The risk of recurrence of translocation is near 3% if the father is the carrier and 10-15% if the mother is the carrier. Genetic counseling tin can make up one's mind the origin of translocation.
How Is Down Syndrome Diagnosed?
PRENATALLY
There are two categories of tests for Down's syndrome that can be performed earlier a babe is born: screening tests and diagnostic tests. Prenatal screens gauge the chance of the fetus having Down syndrome. These tests do not tell you for sure whether your fetus has Down syndrome; they only provide a probability. Diagnostic tests, on the other paw, can provide a definitive diagnosis with nearly 100% accuracy.
In that location is an extensive menu of prenatal screening tests at present available for pregnant women. Most screening tests involve a claret test and an ultrasound (sonogram). The blood tests (or serum screening tests) measure quantities of diverse substances in the blood of the mother. Together with a woman's age, these are used to judge her chance of having a child with Downwards syndrome. These blood tests are often performed in conjunction with a detailed sonogram to check for "markers" (characteristics that some researchers experience may have a significant association with Down syndrome). New advanced prenatal screens are at present able to observe chromosomal material from the fetus that is circulating in the maternal blood. These tests are not invasive (like the diagnostic tests below), but they provide a high accuracy rate. Still, all of these screens will non definitively diagnose Down's syndrome. Prenatal screening and diagnostic tests are now routinely offered to women of all ages.
The diagnostic procedures bachelor for prenatal diagnosis of Down syndrome are chorionic villus sampling (CVS) and amniocentesis. These procedures, which carry up to a i% risk of causing a spontaneous termination (miscarriage), are near 100% accurate in diagnosing Down syndrome. Amniocentesis is ordinarily performed in the second trimester betwixt xv and xx weeks of gestation, CVS in the commencement trimester betwixt nine and 14 weeks.
AT BIRTH
Down's syndrome is usually identified at birth by the presence of sure concrete traits: depression musculus tone, a single deep crease beyond the palm of the mitt, a slightly flattened facial profile and an upward camber to the eyes. Because these features may be present in babies without Down's syndrome, a chromosomal assay called a karyotype is washed to confirm the diagnosis. To obtain a karyotype, doctors draw a blood sample to examine the baby's cells. They photograph the chromosomes and and then group them by size, number, and shape. By examining the karyotype, doctors tin can diagnose Down syndrome. Another genetic test chosen FISH can apply similar principles and confirm a diagnosis in a shorter amount of time.
Preferred Language Guide
Use this language when referring to Down syndrome and people who accept Down syndrome:
- People with Down syndrome should always be referred to as people outset.
- Instead of "a Down syndrome child," it should exist "a child with Downward syndrome." Too avoid "Down'south child" and describing the status every bit "Downward's," equally in, "He has Down's."
- Downwardly syndrome is a condition or a syndrome, not a illness.
- People "have" Down syndrome, they practice not "endure from" it and are not "afflicted by" it.
- "Typically developing" or "typical" is preferred over "normal."
- "Intellectual disability" or "cognitive inability" has replaced "mental retardation" as the appropriate term.
- NDSS strongly condemns the utilise of the give-and-take "retarded" in any derogatory context. Using this word is hurtful and suggests that people with disabilities are non competent.
Downwards vs. Down's
- NDSS uses the preferred spelling, Down syndrome, rather than Down syndrome.
- Down syndrome is named for the English language medico John Langdon Down, who characterized the condition, but did non have it. An "apostrophe due south" connotes ownership or possession.
- While Down syndrome is listed in many dictionaries with both popular spellings (with or without an apostrophe southward), the preferred usage in the United States is Down syndrome. The AP Stylebook recommends using "Down's syndrome," also.
These downloadable versions of the Preferred Language Guide are available to impress and distribute:
- NDSS Preferred Language Guide
- NDSS Fact Canvas and Language Guide
Resources
EXTERNAL Resources
- Brighter Tomorrows
www.brightertomorrows.org
Brighter Tomorrows is a spider web-based resource for parents who accept received a diagnosis of Down syndrome either prenatally or at nascence. The site provides answers to common questions, educates about Down's syndrome and shares the stories of other parents with similar situations. - Downwards Syndrome Pregnancy
www.downsyndromepregnancy.org
This site provides information and support to expectant parents preparing for the birth of a babe with Down Syndrome.
- International Mosaic Down Syndrome Clan
www.imdsa.org
Offers support and resources to families of and individuals with mosaic Down syndrome through the lifespan
- Medline Plus: Wellness Topics – Down syndrome
www.nlm.nih.gov/medlineplus/downsyndrome.html
An overview and list of resources on Down syndrome and prenatal testing from Medline Plus, a service of the Us National Library of Medicine and the National Institutes of Health
- National Guild of Genetic Counselors
world wide web.nsgc.org
Observe members of NSGC through the Find A Genetic Advisor search function
- Understanding a Down syndrome Diagnosis
www.lettercase.org
Understanding a Down's syndrome Diagnosis is an accurate, counterbalanced and upwardly-to-date booklet for use when delivering a diagnosis of Down's syndrome. It is available as a free e-volume from Lettercase.
DVDS
- Down syndrome: The First xviii Months. Huckleberry Shoes Productions.
BOOKS
- A Parent's Guide to Down Syndrome: Toward A Brighter Future. Pueschel, S. (2000). Baltimore, MD: Brookes Publishing.
- Babies with Down's syndrome: A New Parents' Guide (Third Edition). Skallerup, Due south. (Ed.) Bethesda, MD: Woodbine House. (2008)
- Downs: The History of a Disability. Wright, D. New York, NY: Oxford University Printing. (2011)
- Tales of Normansfield: The Langdon Down Legacy. Merriman, A. Beccles, UK: The Down's syndrome Clan. (2007)
- The Guide to Good Wellness for Teens and Adults with Down's syndrome. McGuire, D. and Chicoine, B. Bethesda, Doc: Woodbine House. (2010)
Source: https://www.ndss.org/about-down-syndrome/down-syndrome/
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