Trisomy 21
(Down Syndrome)Trisomy 18
(Edwards Syndrome)Trisomy 13
(Patau Syndrome)Chromosomal Abnormalities Microdeletion Syndrome Sex Chromosome Abnormalities

● Microdeletion Syndrome

Q: What causes microdeletion syndrome?

There are two main causes: ① Spontaneous changes: Most cases occur by chance during the formation of parental germ cells or during early cell divisions after fertilization. ② Inheritance from parents: In rare cases, a parent carries the same deletion and inherits it to the child. A major difference from trisomy is that it occurs independently of the mother's age.

Q: Can microdeletion syndrome be screened by NIPT?

Yes, it is possible. In recent years, the accuracy of screening tests for microdeletion syndromes has significantly improved due to NIPT using Next-Generation Sequencing (NGS). By analyzing cell-free DNA of fetal origin in maternal blood, risks can be non-invasively evaluated from early pregnancy.

Q: Is there a treatment for microdeletion syndrome?

Currently, there is no fundamental cure for microdeletion syndromes. However, symptomatic therapies such as rehabilitation, medication, and surgical treatment (e.g., for cardiac disorders) are performed depending on the symptoms. Since early diagnosis and early intervention can improve the quality of life (QOL), prenatal screening and neonatal genetic testing are crucial.

Microdeletion syndrome is a congenital disorder caused by a deletion of a part of a chromosome.
As the name suggests, microdeletion syndrome is caused by extremely small genetic changes. This change can range as small as 500,000 base pairs, and is generally said to occur when a sequence of 2 million to 3 million base pairs is missing.
The size and location of this deletion determine the type and severity of various symptoms, including developmental delay and intellectual disability. Most microdeletion syndromes occur by chance and are believed to happen regardless of the mother's age.

Diagnosis of microdeletion syndrome is made by chromosome testing.
In recent years, it has become commonly performed as a screening test for microdeletion syndrome, with its accuracy significantly improved by genetic analysis using next-generation sequencing.

＼ Understand the risk of fetal microdeletion syndrome ＼

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Causes

The cause of microdeletion syndrome lies in the deletion of a very small part of a chromosome.
This small genetic defect occurs when one or more genes present in a specific chromosomal region are lost, although the normal number of chromosomes is maintained. Such deletions can occur due to the following causes:

<Spontaneous Changes>
Most microdeletion syndromes occur by chance during the formation of parental germ cells or during early cell divisions after fertilization. It is not hereditary but occurs by chance.

<Inheritance from Parents>
In rare cases, if a parent has the same deletion, the deletion may be inherited by the child.
However, even if the parent has the same deletion, they may remain asymptomatic.
Microdeletion syndrome can cause various symptoms and developmental disorders depending on the lost region of genes.

Symptoms

Symptoms vary depending on the genes in the deleted region.
They range widely from mild to severe symptoms.

Representative Examples

1p36 Deletion Syndrome ※1

<Symptoms>
・Severe intellectual disability, developmental delay
・Characteristic facial features
・Heart diseases

<Causes>
Occurs due to deletion of the terminal portion of the short arm (p arm) of chromosome 1

4p Deletion Syndrome (Wolf-Hirschhorn Syndrome) ※2

<Symptoms>
・Characteristic facial features
・Developmental delay, intellectual disability, growth restriction
・Heart diseases

<Causes>
Occurs due to deletion of the terminal portion of the short arm (p arm) of chromosome 4

5p Deletion Syndrome (Cri du Chat Syndrome) ※3

<Symptoms>
・Low birth weight
・Developmental delay, intellectual disability
・Characteristic facial features

<Causes>
Occurs due to deletion of the terminal portion of the short arm (p arm) of chromosome 5

Prader-Willi Syndrome ※4

<Symptoms>
・Overeating, obesity
・Muscular hypotonia (low muscle tone)
・Growth restriction
・Intellectual disability

<Causes>
Occurs due to deletion or dysfunction of genes of paternal origin in a specific region of chromosome 15

Angelman Syndrome ※5

<Symptoms>
・Severe intellectual disability
・Language developmental delay
・Movement coordination disorders

<Causes>
Occurs due to deletion or dysfunction of genes of maternal origin in a specific region of chromosome 15

22q11.2 Deletion Syndrome (DiGeorge Syndrome) ※6

<Symptoms>
・Heart diseases
・Immune system disorders
・Hypocalcemia (low blood calcium)
・Characteristic facial features
・Developmental delay

<Causes>
Occurs due to deletion of the 11.2 region on the long arm (q arm) of chromosome 22

Treatment Methods

There is no cure for microdeletion syndrome, but symptomatic treatments such as rehabilitation and medication are performed according to symptoms.

References

Frequently Asked Questions

Q.What is microdeletion syndrome?

Microdeletion syndrome is a collective term for congenital disorders caused by the deletion of a part of a chromosome (approximately 500,000 to 3 million base pairs). Depending on the size and location of the deletion, the types and severity of symptoms such as developmental delay, intellectual disability, and heart disease vary. Because specific gene regions are lost while maintaining the normal number of chromosomes, detection was difficult with conventional chromosome tests (1).

Q.What causes microdeletion syndrome?

There are two main causes: ① Spontaneous changes: Most cases occur by chance during the formation of parental germ cells or during early cell divisions after fertilization. ② Inheritance from parents: In rare cases, a parent carries the same deletion and inherits it to the child. A major difference from trisomy is that it occurs independently of the mother's age (2).

Q.What types of microdeletion syndromes are there?

The six representative disorders are as follows: ① 1p36 deletion syndrome, ② 4p deletion syndrome (Wolf-Hirschhorn syndrome), ③ 5p deletion syndrome (Cri du Chat syndrome), ④ Prader-Willi syndrome, ⑤ Angelman syndrome, and ⑥ 22q11.2 deletion syndrome (DiGeorge syndrome). Each has a different deleted chromosomal region and presents diverse symptoms (3).

Q.Can microdeletion syndrome be screened by NIPT?

Yes, it is possible. In recent years, the accuracy of screening tests for microdeletion syndromes has significantly improved due to NIPT using Next-Generation Sequencing (NGS). By analyzing cell-free DNA of fetal origin in maternal blood, risks can be non-invasively evaluated from early pregnancy (1).

Q.Is there a treatment for microdeletion syndrome?

Currently, there is no fundamental cure for microdeletion syndromes. However, symptomatic therapies such as rehabilitation, medication, and surgical treatment (e.g., for cardiac disorders) are performed depending on the symptoms. Since early diagnosis and early intervention can improve the quality of life (QOL), prenatal screening and neonatal genetic testing are crucial (4).