Your guide to health and prenatal genetics
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Assess your personalised prenatal risks, choose screening tests, and find nearby maternity clinics

What is microdeletion?

Microdeletion is a relatively small loss of the portion of the chromosome which includes several genes. Microdeletions are too small to be detected by conventional microscopic methods and usually detected by higher resolution molecular techniques.

Microdeletion syndromes are defined as a group of clinically recognisable disorders characterised by a small deletion of a chromosomal segment. The size and position of the microdeletion determine which clinical features are manifested and how severe they are.  

Unlike most of the trisomies, which are more likely to occur in elderly mothers, microdeletions occur randomly and are independent of maternal age or other traditional risk factors. They equally affect any baby regardless of race or mother’s age.

Therefore, it may be important to screen all pregnancies, because:

  • microdeletions are common and can be severe;
  • the risk of microdeletion is the same across all maternal ages;
  • microdeletions often go undiagnosed early;
  • microdeletion disorders can be treated with early childhood intervention.

In fact, microdeletions are more common than Down syndrome (Trisomy 21) in younger women. The most common microdeletion syndrome 22q11 is more common than Trisomy 18 and 13 combined as well as cystic fibrosis, a common disease which can be screened.

Clinically important microdeletions can occur in up to 1 in 60 pregnancies. Microdeletions can result in child’s physical and intellectual impairments that often can be more severe than the whole chromosomes abnormalities.

Today, modern DNA sequencing technologies allow to detect microdeletions from a direct measure of fetal cell-free DNA (cfDNA) floating in the mother’s blood by a non-invasive prenatal test (NIPT), whereas previously only invasive techniques (chorionic villus sampling (CVS) or amniocentesis) could detect microdeletions. Invasive techniques are still required to finally confirm or exclude positive NIPT results for microdeletions, since NIPT are classified as screening tests and invasive tests are diagnostic.  However, after negative result for microdeletions test you can be very confidently reassured (with confidence of above 99%), that the baby is indeed not affected. NIPT focuses on finding microdeletions that can adversely affect child’s physical and mental development.

The table below provides a general overview of common microdeletions which typically can be screened for by some NIPTs:


Frequency in live births


22q11 deletion (DiGeorge syndrome)

1 in 2,000-4,000

The most common microdeletion syndrome. Patients show characteristic head and face anomalies, cleft palate, mental retardation, immunodeficiency due to absent thymic gland, low calcium in blood and certain heart defects.


1p36 deletion syndrome

1 in 5,000-10,000

The disorder is characterised by developmental delay, brain abnormalities, heart defects, hearing loss, severe intellectual disorder and behavioural problems.

15q11 deletion

(Angelman/Prader-Willi syndromes)

1 in 10,000-20,000


Microdeletion of a long arm of the chromosome 15 which is inherited from a mother, results in Angelman syndrome (AS, or “happy-puppet syndrome”), and microdeletion of the paternally inherited chromosome causes Prader-Willi syndrome (PWS). These disorders result in typical distinctive features, severe intellectual disability, difficult behavioural problems.

5p deletion

(Cri-du-chat syndrome)

1 in 20,000-50,000

Patients have intellectual disability, developmental delay, small head size (microcephaly), hypotonia, distinctive faces, heart defects and a characteristic cat-like cry.

4p deletion

(Wolf-Hirschhorn syndrome)

1 in 50,000

It is characterized by a distinctive facial appearance (Greek warrior helmet), developmental delay, intellectual disability, and seizures.

11q deletion (Jacobsen syndrome)

1 in 100,000

It is characterized by developmental delay, cognitive impairment, distinctive faces, bleeding disorders and some behaviour disorders.

8q deletion (Langer-Giedion syndrome)


It is characterized by benign bone tumours (exostoses), short stature,  intellectual disability and distinctive facial features. Also called trichorhinophalangeal syndrome type II.

If further diagnostic testing confirms the baby has a microdeletion, knowing this information in advance can help you take some measures to improve the health and quality of life by early prevention of symptoms and treatment from the moment the child is born. Genetic counselling is essential in such situations.