Chromosome 21q Deletion Syndrome

Chromosome 21q Deletion Syndrome

Article
Ear, Nose, & Throat (ENT)
Brain & Nerve
+10
Contributed byKrish Tangella MD, MBAOct 01, 2021

What are the other Names for this Condition? (Also known as/Synonyms)

  • 21q Deletion Syndrome
  • Monosomy 21q Syndrome
  • Partial Monosomy 21q Syndrome

What is Chromosome 21q Deletion Syndrome? (Definition/Background Information)

  • Chromosome 21q Deletion Syndrome is a rare chromosomal disorder that develops when there is missing genetic material on chromosome 21 (on long arm q) leading to a set of associated signs and symptoms. These may be mild or severe, depending on several factors such as the amount of genetic material lost, the number of genes affected, and the function of the affected genes
  • The condition affects newborn children (congenital manifestation). Most cases are not inherited, but individuals can pass the deletion on to their children. The common signs and symptoms that occur in individuals with Chromosome 21q Deletion Syndrome include growth and developmental delays, speech and communication challenges, poor mental health, and abnormal facial features
  • Following a diagnosis of Chromosome 21q Deletion Syndrome, the condition may be managed based on the presenting symptoms and extent of involvement of the body systems. The treatment may involve physician experts from several specialties, and can include the use of vision and hearing aids, speech and language therapy, physiotherapy, and surgery for correction of physical defects, if any
  • The prognosis is primarily dependent on the severity of the disorder, and it varies from one child to another. Many children with Chromosome 21q Deletion Syndrome are able to cope well through adequate treatment and supportive care. Some of the signs and symptoms associated with the condition are known to improve with time

Who gets Chromosome 21q Deletion Syndrome? (Age and Sex Distribution)

  • Chromosome 21q Deletion Syndrome is a rare congenital disorder. The presentation of symptoms may occur at or following the birth of the child
  • In many cases, individuals with mild signs and symptoms may be undiagnosed in their lifetime. Hence, a true incidence of the disorder may be difficult to estimate
  • Both males and females may be affected
  • Worldwide, individuals of all racial and ethnic groups may be affected

What are the Risk Factors for Chromosome 21q Deletion Syndrome? (Predisposing Factors)

In a vast majority of individuals, there are no identified risk factors for Chromosome 21q Deletion Syndrome.

  • In some individuals, a positive family history may be an important risk factor for 21q Deletion Syndrome
  • Currently, no environmental and lifestyle (including dietary) factors have been implicated
  • The syndrome is not caused by what the expectant mother does or does not do, either prior to or during pregnancy

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Chromosome 21q Deletion Syndrome? (Etiology)

  • Chromosome 21q Deletion Syndrome may be caused in the following manner:
    • A de-novo deletion of genetic material in the long arm (q) of chromosome 21, which is the most common reason for the disorder
    • Rarely, inheritance of the condition from a parent (positive family history of the condition may be noted)
  • There are two chromosomes numbered 21. Children with 21q deletions typically will have one (chromosome 21) in normal condition, while the other is abnormal. The abnormality is characterized by a loss of chromosomal material

It is important to note that a child’s development and future is not only influenced by the chromosome material duplicated/deleted and genes involved, but also by other factors such as one’s environment, involvement of other genes, and unique personality.

Additional (general) information on chromosomes, which is helpful in understanding the disorder:

Chromosomes are microscopic thread-like protein structures present in each cell nucleus that carry genetic information in the form of DNA (deoxyribonucleic acid). DNAs are nucleic acids that encodes the genetic information of any organisms; a basic unit of the DNA is termed a gene with a specific set of instructions and a defined function. Each chromosome is “X” shaped with a center, called the centromere, and two short arms (termed p arms) and two long arms (termed q arms).

Humans have 46 chromosomes in the cell nucleus, in 23 pairs, of which one pair is named the sex chromosome. In males, it is designated XY, for chromosome X and chromosome Y; while, in females, it is designated XX, for a pair of chromosome X. The other 22 pairs of chromosomes are numbered chromosome 1 through 22, approximately according to size (with chromosome 1 being the largest; chromosome 21 being the smallest) and are referred to as autosomes or somatic chromosomes. During conception, the embryo inherits one copy of each chromosome from each parent (i.e., mother and father). Any alteration in the chromosome numbers or structure, such as via addition or deletion of chromosomal material, can result in mild to severe genetic abnormalities that may manifest as birth defects, growth delays, and intellectual disabilities.

A chromosome deletion disorder indicates that a certain portion of the chromosomal material is missing, which may be detected through molecular genetic testing. Depending on the nature and amount of material deleted, the manifestation of a set of signs and symptoms are noted.

What are the Signs and Symptoms of Chromosome 21q Deletion Syndrome?

The signs and symptoms of Chromosome 21q Deletion Syndrome may be significantly different from one individual to another. The degree of signs and symptoms are often related to the amount of chromosome material deleted and the number of genes affected. As a general rule, a small loss of chromosome material generally results in milder signs and symptoms. Conversely, larger deletion of the chromosome material generally results in severe signs and symptoms. It is important to note that exceptions may also occur, where individuals with small amount of chromosomal loss, may have disproportionately severe presentations.

The commonly noted signs and symptoms of 21q Deletion Syndrome include:

  • Developmental delay
  • Some feeding difficulties due to swallowing difficulties
  • Poor gross motor skills; fine motor skills
  • Presence of abnormal hands and feet
  • Distinctive facial features
    • Small-sized head
    • Long and narrow face
    • Eyes that slant somewhat downwards
    • Prominent nose bridge; long nose with a broad tip
    • Short philtrum
  • Epileptic seizures are noted in children
  • Hearing and vision impairment
  • Speech and learning disabilities
  • Constipation may be noted in some cases
  • Minor genital abnormalities may be noted in some boys
  • Intellectual disability 
  • Behavioral issues may be also noted

How is Chromosome 21q Deletion Syndrome Diagnosed?

Children can have varying signs and symptoms. Some children with mild signs and symptoms may go undiagnosed in their lifetimes. Given the rarity of the condition, the healthcare provider should have a high index of suspicion to consider Chromosome 21q Deletion Syndrome in the differential diagnosis. Often, specialized tests are necessary to confirm the disorder.

Chromosome 21q Deletion Syndrome is diagnosed on the basis of the following information:

  • Complete physical examination and thorough medical history evaluation, including family medical history
  • Assessment of the presenting signs and symptoms, including evaluation of body systems such as vision, hearing, muscles, heart, kidneys, central nervous system, genitalia, and immune system
  • Hearing and vision assessment through various tests
  • Laboratory tests, as needed, such as electrolyte levels, serum calcium levels, thyroid function test, kidney function test, urine tests, sex hormone studies, etc.
  • Radiological studies of the affected regions, as needed
  • Kidney and urinary tract scans
  • Brain scans (to determine corpus callosum): These may include prenatal ultrasounds and MRI scans, and CT/MRI scans after development of the child
  • Neurological examination that involves the central nervous system (brain and spinal cord)
  • Behavioral studies
  • Prenatal studies including abdominal ultrasonography
  • Specialized genetic testing techniques are often required to confirm the diagnosis. This may include:
    • Fluorescence in situ hybridization (FISH) testing
    • Array comparative genomic hybridization (array-CGH)
    • DNA sequencing

Often, karyotyping of the chromosome is not adequate to diagnose the condition, since individuals with this condition can have normal karyotype chromosomal studies.

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complications of Chromosome 21q Deletion Syndrome?

The complications of Chromosome 21q Deletion Syndrome may include:

  • Severe emotional stress for parents and caregivers
  • Pregnancy complications
  • Intrauterine growth retardation (IUGR)
  • Failure to thrive
  • Delayed milestone achievement
  • Risk of falls and injury due to seizures
  • Severe intellectual deficiency
  • Inappropriate or violent behavior
  • Physical abnormalities that can cause difficulties in day-to-day living
  • Reduced quality of life

Complications may occur with or without treatment, and in some cases, due to treatment also.

How is Chromosome 21q Deletion Syndrome Treated?

There is no cure for Chromosome 21q Deletion Syndrome since it is a genetic condition. The treatment is usually given to manage the signs and symptoms and any complication that develops. It also depends on the severity of the signs and symptoms and the body systems affected. Individuals with mild signs and symptoms may require periodic monitoring without significant medical intervention. Often, a multidisciplinary team of specialists including pediatricians, ophthalmologists, otolaryngologists, neurologists, internists, cardiologists, endocrinologists, surgeons, and other healthcare professionals are involved in managing the condition.

The treatment measures for 21q Deletion Syndrome may involve:

  • Seizure control using anticonvulsant medication, vitamin supplements, and ketogenic diet
  • Employing suitable learning strategies via music therapy, visual and tactile books, learning through fun and play, and lots of repetition. Writing by holding a pencil may be very difficult; but touchscreen computers and keyboards are known to be easier to use and learn
  • Speech and language therapy; the use of sign language may be beneficial; rectification of hearing impairment may improve speech and language development
  • Physiotherapy for weakened muscles, including incorporating daily exercise regimen
  • Development of motor skills via daily exercises, swimming, hydrotherapy, and other adapted activities; use of specially-designed toys and daily-used items (such as spoons and cups)
  • Use of walking aids including foot orthotics and special footwear and shoe inserts; wheelchair assistance may be necessary
  • For feeding difficulties, use of feeding tubes (temporary nasogastric or gastrostomy tubes), medications, feed thickeners, bottle-feeding expressed milk, including special diets and nutritional supplements
  • Severe constipation may require dietary changes, including increased intake of fiber and wholegrains, along-with the administration of laxatives
  • Surgical correction of physical defects, as assessed by a healthcare expert
  • Psychotherapy, behavior modification, and establishing discipline techniques, as necessary
  • Social skills training support groups and exercises
  • Occupational therapy

Regular medical screening at periodic intervals with tests and physical examinations are necessary and highly recommended.

How can Chromosome 21q Deletion Syndrome be Prevented?

Chromosome 21q Deletion Syndrome may not be preventable since many of these genetic disorders are diagnosed at or following the birth of the child. A majority of cases are sporadic occurrences, which means there is no family history of the condition.

In some rare cases, the condition may be familial, meaning they occur within families. In expecting parents with a familial history:

  • Genetic testing of the expecting parents (and related family members) and prenatal diagnosis (molecular testing of the fetus during pregnancy) may help in understanding the risks better during pregnancy
  • If there is a family history of the condition, then genetic counseling will help assess risks, before planning for a child
  • Active research is currently being performed to explore the possibilities for treatment and prevention of inherited and acquired genetic disorders

It is important to note that the chances of both the parents with normal chromosomes having another child with 21q Deletion Syndrome is highly unlikely. This may be confirmed via specialized prenatal testing and preimplantation genetic diagnosis (PGD), if needed. Prenatal tests may include chorionic villus sampling (CVS) and amniocentesis.

What is the Prognosis of Chromosome 21q Deletion Syndrome? (Outcomes/Resolutions)

The prognosis of Chromosome 21q Deletion Syndrome is dependent upon the severity of the signs and symptoms and associated complications, if any.

  • It may be assessed on a case-by-case basis, but it is generally difficult to predict the long-term outlook
  • Children with mild conditions are generally able to cope well via appropriate treatment and adaptive behaviors as they get older
  • Some children may require lifelong medical support and care

Additional and Relevant Useful Information for Chromosome 21q Deletion Syndrome:

The following DoveMed website link is a useful resource for additional information:

http://www.dovemed.com/diseases-conditions/rare-disorders/

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Krish Tangella MD, MBA

Pathology, Medical Editorial Board, DoveMed Team

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