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Mosaic Down Syndrome

Have you ever seen any of your students or children with down syndrome other than the symptoms expected in down syndrome? For example, no speech or posture problems, no internal organ problems such as the heart, or giving test results equal or above with their peers. Or your child with mental retardation or your child’s stubborn-like behavior in individuals with down syndrome.

What is Down Syndrome?

Down syndrome is a genetic disorder.

In the cells of individuals with normal development, there are 46 chromosomes consisting of 2 helixes of 23 chromosomes each. There are 23 chromosomes in the ovaries and sperms out of 2 in this dna helix. When the ovarium and sperm are fertilized, these two 23 chromosome sequences combine to form a 2-helix with 46 chromosomes. In Down syndrome, the number of chromosomes from the egg or sperm is 24, not 23. While there must be 23 chromosomes coming from eggs or sperm, the 21st chromosome is double. When merged, an individual with Down syndrome has 3 chromosomes, not 2 in the 21st chromosome.

What is Mosaic Down Syndrome?

In mosaic down syndrome, there are 46 chromosomes during the first fertilization, but during the proliferation of cells, one cell has 47 chromosomes instead of 46. In other words, some cells in the body of individuals with mosaic down syndrome have 46 chromosomes and some cells have 47 chromosomes.

The cells reproduce by dividing up to a certain number after fertilization. The number of cells of 47 chromosomes that occur during proliferation affects the anatomic system in which it is located in terms of down syndrome symptoms.

For example, if the group of 47 chromosomes is dense in the muscular system, postural disorders and speech are dense because the tongue is also a muscle. But if the cells with more than 46 chromosomes are in the nervous system, they can get similar results with their peers in IQ tests. If 47 chromosome cells are few in the circulatory system, the likelihood of heart problems may decrease.

Similarly, if cells with 47 chromosomes are more in the nervous system; Symptoms such as intelligence, behavior, learning are compatible with individuals with down syndrome. But if there are more than 46 chromosome cells in the muscular system, they may not have problems with the muscular system issues such as speech and posture. Again, if there are more than 46 chromosome cells in the skeletal and muscular system, the down syndrome may not be understood from the external appearance.

How is Mosaic Down Syndrome Diagnosed?

While Down syndrome can be understood through a single cell, in the world, genetic testing is performed on 20 different cells for mosaic down syndrome. The percentage of mosaic down syndrome is determined by determining how many of these 20 cells have down syndrome. For example, if 4 of these 20 cells have 47 chromosomes, the diagnosis is made as “20% mosaic down syndrome”. This test should be applied separately for each system.

Is it understandable during pregnancy?

It is being studied in the world that mosaic down syndrome can be understood during pregnancy. Researches are also conducted on whether it can be determined whether or not symptoms such as low IQ and heart problems can be detected before birth. It has not been finalized yet.

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