Table of ContentsView AllTable of ContentsTypesSymptomsCausesDiagnosisTreatmentPrognosisCoping
Table of ContentsView All
View All
Table of Contents
Types
Symptoms
Causes
Diagnosis
Treatment
Prognosis
Coping
Mosaic Down syndrome is a variant ofDown syndrome. Down syndrome is a congenital (present at birth) genetic condition that occurs when a person has three copies of chromosome 21 instead of two (the standard number). This is calledtrisomy21.
In mosaic Down syndrome, some of the person’s cells have three copies of chromosome 21, but some cells have two copies of this chromosome, resulting in a mixture.
This article describes the types, symptoms, causes, and management of mosaic Down syndrome.
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Types of Mosaic Down Syndrome
With mosaic Down syndrome, some cells have two copies of chromosome 21, and some cells have three. If they have no other chromosome number anomalies, some cells have 46 total chromosomes and some have 47.
Mosaic Down Syndrome Symptoms
Thesymptoms of mosaic Down syndromeare the same as symptoms of the more common type of Down syndrome, in which all of the cells have three copies of chromosome 21.
While most people with Down syndrome have similar symptoms, there is a range in severity. With mosaic Down syndrome, there is also a range in severity. There is a tendency for people with mosaic Down syndrome to have slight differences in the effects, but this is not consistent.
Changes that occur due to Down syndrome and mosaic Down syndrome include:
These changes occur because the extra genes from the extra copy of chromosome 21 cause alterations in the body’s structure, which leads to the symptoms.
A pregnancy with a fetus with Down syndrome has a higher risk of birth complications and stillbirth.
Human cells typically contain 23 pairs ofchromosomes(46 total), which carry genetic material. Each sperm or egg cell typically contains only one chromosome of each pair.
Down syndrome occurs when an embryo is conceived with a third copy of chromosome 21. Throughout pregnancy, the fetus’s cells are copied with the same set of chromosomes, so all of the growing fetus’s cells also have an extra copy of chromosome 21.
The extra chromosome can come either from the egg cell or from the sperm cell. Normally, the egg cell and eye sperm cell have only one copy of each chromosome, including chromosome 21. This results in a fetus having two copies of each chromosome in every one of its cells—for a total of 46 chromosomes.
Trisomyis the presence of a third chromosome for a chromosome pair. The extra copies of the genes contained in chromosome 21 cause several variations in fetal and child development, leading to Down syndrome’s physical characteristics.These changes begin to develop before birth.
How Does Mosaicism Happen?
In general, mosaicism is a rare genetic phenomenon. It means that the cells in the body do not have the exact same genetic pattern.
In mosaic Down syndrome, an error occurs as the embryo’s cells are making copies. This error occurs during the very early stages of pregnancy.
There are two ways that mosaic Down syndrome can occur:
In either of these situations, the embryo can eventually develop a mixture of cells with three copies of chromosome 21 and two copies of chromosome 21. It is believed that the error occurs very early during pregnancy.
It isn’t known why these errors occur, but research suggests that the chromosomes in Down syndrome are more fragile than usual and that this could predispose to the chromosomal errors that cause the mosaic pattern.
Down syndrome is diagnosed based on a child’s physical features and with achromosome test. Typically, physical features, such as facial appearance, are reliable indicators of the condition, but sometimes it isn’t completely obvious.
A definitive diagnosis is made with a chromosome test. Mosaic Down syndrome usually causes physical characteristics similar to those of Down syndrome, but the distinction between Down syndrome and mosaic Down syndrome is made based on a chromosome test.
How Down Syndrome Is Diagnosed
Chromosomal Analysis
Prenatal (before birth) testing is done withamniocentesisorchorionic villussampling. Sampling involves the placement of a needle into the uterus (with ultrasound guidance). A sample of the fluid or tissue around the fetus is collected and sent to the laboratory for analysis.They are safe tests, but there is a slight risk of complications.
Medical Tests
People with mosaic Down syndrome may have diagnostic evaluations to identify the physical effects of Down syndrome. This can include screening tests before birth, such asprenatal ultrasoundand diagnostic evaluation of symptoms.
These may include:
What to Expect During an Echocardiogram
Many of theeffects of Down syndrome can be treatedwith the same treatments used in all types of Down syndrome. No cure or treatment can correct the chromosome changes, and there is no way to prevent the physical effects of the condition from developing if a person has any form of Down syndrome.
Management of effects of Down syndrome include:
There is no cure for Down syndrome or mosaic Down syndrome. The chromosomal abnormalities cannot be fixed or treated at any age, even before birth. The effects on the body can be treated symptomatically, which can improve a person’s outcome, quality of life, and life expectancy.
The condition is not expected to worsen. But some effects might not substantially impact the quality of life when a child is young, and they may have a more significant impact as the child ages and enters adulthood.
Living with Down syndrome is challenging. Parents and caregivers for children with this condition need to seek special accommodations to effectively navigate schooling, socializing, sports, music, and other activities.
Attending a school that offers accommodations suitable for children and adolescents with Down syndrome can be helpful. Additionally, certain workplaces can also provide accommodations so that a person with Down syndrome can productively work and use their skills in a way that helps improve their quality of life.
Some families may benefit from joining a support group that includes people with Down syndrome. It can be enriching to learn from others and be a source of support for others who are dealing with the condition.
Summary
Mosaic Down syndrome is a type of Down syndrome with a slightly different chromosomal pattern than the more common type of full trisomy 21. Down syndrome occurs when a person has three copies of chromosome 21 in all their cells instead of the standard of two copies. With the mosaic pattern, some cells have two copies, andsome have three.
This often leads to the same symptoms and prognosis as the more common type of Down syndrome, but sometimes the effects may be milder. The diagnosis is made with chromosome testing, which can be done prenatally or after birth. Treatment is focused on the symptoms and effects, but there is no cure.
Down Syndrome: Facts and Statistics
5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
John ST, Gayathri K, Sahasranam KV.Cytogenetic patterns, congenital heart disease, and thyroid dysfunction in children with Down syndrome.J Pediatr.2022;245:196-200. doi:10.1016/j.jpeds.2022.01.034
Jaiswal SK, Kumar A, Rai AK.Molecular cytogenetic classification of Down syndrome and screening of somatic aneuploidy in mothers.Cytogenet Genome Res.2021;161(8-9):397-405. doi:10.1159/000519624
Plaiasu V.Down syndrome - genetics and cardiogenetics.Maedica (Bucur). 2017;12(3):208-213.
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