Down Syndrome; Causes, Symptoms, Diagnosis, Treatment

Down syndrome is a chromosomal disorder caused when an error in cell division results in an extra 21st chromosome. Down syndrome (DS or DNS), also known as trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21.It is typically associated with physical growth delays, characteristic facial features and mild to moderate intellectual disability.The average IQ of a young adult with Down syndrome is 50, equivalent to the mental ability of an 8- or 9-year-old child, but this can vary widely.

Types of Down Syndrome

The most common form of Down syndrome is known as trisomy 21, a condition where individuals have 47 chromosomes in each cell instead of 46.

Trisomy 21 – is caused by an error in cell division called nondisjunction. This leaves a sperm or egg cell with an extra copy of chromosome 21 before or at conception. This variant accounts for 95 percent of Down syndrome cases.The remaining 5 percent of Down syndrome cases are due to conditions called mosaicism and translocation.

Mosaic Down syndrome – results when some cells in the body are normal while others have Trisomy 21.

Robertsonian translocation – occurs when part of chromosome 21 breaks off during cell division and attaches to another chromosome, usually chromosome 14. The presence of this extra part of chromosome 21 causes some Down syndrome characteristics.

Mosaicism – Mosaicism occurs when a child is born with an extra chromosome in some but not all of their cells. People with mosaic Down syndrome tend to have fewer symptoms than those with trisomy 21.

Translocation – In this type of Down syndrome, children have only an extra part of chromosome 21. There are 46 total chromosomes. However, one of them has an extra piece of chromosome 21 attached.

Causes

Down syndrome is a common genetic syndrome caused by having all or part of an extra chromosome 21.  The most common type of Down syndrome is also known as “Trisomy 21” due to the fact that there are three copies of this chromosome instead of the usual two.

• Normally, the mother’s egg and the father’s sperm each start out with 23 chromosomes. When the egg and sperm meet at conception, a child inherits 23 chromosomes from each parent, ending up with 23 pairs of chromosomes, and a total of 46 chromosomes.
• In Down syndrome, a change occurs during cellular division such that the egg or sperm has two copies of chromosome #21 and a total of 24 chromosomes. This is called “nondisjunction.”  Researchers are still unsure of what causes the cells to divide in this manner.
• If this egg or sperm is fertilized, the baby ends up with three copies of the #21 chromosome or”Trisomy 21″ This extra genetic material causes the variety of health and developmental issues in Down syndrome.

Symptoms of Down Syndrome

They also typically have poor immune function and generally reach developmental milestones at a later age. They have an increased risk of a number of other health problems, including congenital heart defect, epilepsy, leukemia, thyroid diseases, and mental disorders.

Physical characteristics include

• Eyes that have an upward slant, oblique fissures, epicanthic skin folds on the inner corner, and white spots on the iris.
• Eyes shaped like almonds (may be shaped in a way that’s not typical for their ethnic group)
• Flatter faces, especially the nose
• Small ears, which may fold over a bit at the top
• Tiny white spots in the colored part of their eyes
• A tongue that sticks out of the mouth
• Low muscle tone
• Flat facial features
• Small head and ears
• Short neck
• Bulging tongue
• Eyes that slant upward
• Atypically shaped ears
• Poor muscle tone
• Small stature and short neck
• Flat nasal bridge
• Single, deep creases across the center of the palm
• Protruding tongue
• Large space between large and second toe
• A single flexion furrow of the fifth finger

Additional Symptoms of Down Syndrome

Down syndrome can affect a child physically, cognitively, and behaviorally. Remember that every child with the condition is unique and may possess these characteristics to different degrees or not at all.

Physical

A child with Down syndrome will have some, but perhaps not all, of the following features

• eyes that slant upward, from inner corner to outer corner
• small ears that may fold over slightly at the top
• a smaller than average mouth, and larger appearing tongue
• a smaller than average nose, with a flattened nasal bridge
• short, stocky arms and legs. Some children also have a wide space between the big toe and second toe.
• some babies with Down syndrome have short necks and small hands with short fingers
• one single crease that goes straight across the palm, and a second crease that curves down by the thumb, rather than having three creases in the palm of the hand
• shorter than average height
• low muscle tone (hypotonia) throughout the body and increased looseness or flexibility in the joints

Developmental, Cognitive, and Behavioral Symptoms

• Most children with Down syndrome have delays in meeting developmental milestones.  They typically learn to walk and talk at later times than children without Down syndrome.
• Children with Down syndrome often have mild to moderate cognitive impairment and intellectual disability
• Children with Down syndrome often have specific patterns of cognitive and behavioral features including:
  • Strengths in in social engagement and social behavior, visual learning, and word reading.
  • Challenges with attention span, verbal memory, and expressive communication.
• Tailored and specialized educational programs and support enable children with Down syndrome to learn and grow at their own pace.
• Behavioral problems such as stubborrness, impulsivity, and temper tantrums may be more common in children with Down syndrome
• A child may use “self talk” (talking out loud to himself) as a way of understanding and processing information

Diagnosis of Down Syndrome

Screening tests include

• Ultrasound
• Blood tests – The results of the ultrasound are paired with blood tests.
  • First Trimester Screen – This is a two-step screening. The maternal blood is tested for two normal first-trimester proteins. Then, an ultrasound is used to look at the nuchal translucency region under the skin behind the baby’s neck. This test is done between the 11th and 14th week of pregnancy.
  • Quad Marker Screen – Maternal blood is tested for four substances that normally come from a baby’s blood, brain, spinal fluid and amniotic fluid. This test is done between the 15th and 20th weeks of pregnancy.

• Nuchal translucency testing – At 11 to 14 weeks, an ultrasound can measure the clear space in folds of tissue behind the neck of a developing baby.
• Triple screen or quadruple screen –  At 15 to 18 weeks, this measures the quantities of various substances in the mother’s blood.
• Integrated screen –  This combines the results of first-trimester blood tests and screening tests, with or without nuchal translucency, with second-trimester quadruple screening results.
• Cell-free DNA – A blood test that analyzes fetal DNA found in the maternal blood.
• Genetic ultrasound – At 18 to 20 weeks, a detailed ultrasound is combined with blood test results.

Additional prenatal tests

• Amniocentesis – Your doctor takes a sample of amniotic fluid to examine the number of chromosomes your baby has. The test is usually done after 15 weeks.
• Chorionic villus sampling (CVS) – Your doctor will take cells from your placenta to analyze fetal chromosomes. This test is done between the 9th and 14th week of pregnancy. It can increase your risk of a miscarriage, but according to the Mayo Clinic, only by less than 1 percent.
• Percutaneous umbilical blood sampling (PUBS, or cordocentesis) – Your doctor will take blood from the umbilical cord and examine it for chromosomal defects. It’s done after the 18th week of pregnancy. It has a higher risk of miscarriage, so it’s performed only if all other tests are uncertain.

Treatment of Down Syndrome

Medication can be used for

• hypothyroidism
• childhood leukemia
• seizure disorders

Surgery may be used to treat

• congenital heart problems
• upper neck abnormalities
• abnormalities of the gastrointestinal tract

Treatment for heart defects

• Almost half of children with Down syndrome are born with congenital heart defects. Babies with congenital heart conditions are treated by specialists called pediatric cardiologists. These physicians diagnose heart defects and help manage the health of children before and after treatment.
• Treatment is based on the severity of your child’s heart condition. Some mild heart defects don’t require any treatment. Others can be treated with medications, interventional procedures or surgery.

Elements of medical care include the following

• Genetic counseling
• Standard immunizations and well-child care
• Management of specific manifestations of Down syndrome and associated conditions (eg, endocrine, infectious, cardiac, respiratory, neurologic, psychiatric, dermatologic, and dental disorders)
• Early intervention programs (may improve the social quotient)

Special considerations in adolescents are as follows

• Ongoing monitoring measures, including annual audiologic evaluation and annual ophthalmologic evaluation
• Ongoing management of manifestations of the syndrome and associated conditions
• Discussion of issues related to the transition to adulthood
• Vocational training

Appropriate surgical management of associated conditions should be provided, as follows

• Timely surgical treatment of cardiac anomalies is crucial for optimal survival
• Prompt surgical repair is necessary for gastrointestinal (GI) anomalies, most commonly, duodenal atresia and Hirschsprung disease
• Surgical intervention may be necessary to stabilize the upper segment of the cervical spine if neurologic deficits are clinically significant
• Congenital cataracts must be extracted soon after birth and subsequent correction with glasses or contact lenses provided
• Careful anesthetic airway management is needed because of the associated risk of cervical spine instability
• Adenotonsillectomy may be performed to manage obstructive sleep apnea

Therapy of Down Syndrome

Generally, therapists use a combination of approaches in order to address your child’s unique social, behavioral, communication and academic needs. The goal is to develop a program that will help your child reach his or her full potential.

• Speech therapy – can help improve your child’s communication skills and help him use language to express himself.
• Occupational therapy – can improve your child’s motor skills, such as using her hands and other parts of her body,and help her deal with sensory inputs from her environment.
• Physical therapy – can increase mobility and muscle strength and help your child to work within his functional limitations.
• Behavioral therapy – is an important resource that focuses on managing emotional and behavioral problems. This therapy can also teach families how to help a child with Down syndrome cope with anger or frustration.

Educational assistance

• Children under age 3 who have Down syndrome or other developmental challenges are eligible to receive developmental services through state-run, federally mandated programs. These programs have different names in each state.
• From age 3 until the 22nd birthday, children can access supports through the public school system.

 Support of Down Syndrome

• The Program Coordinator – at the Down Syndrome Program facilitates our Allen C. Crocker lecture series approximately one evening each month at Children’s. Meetings feature different topics and speakers. Parents who attend are a diverse group with children of all different ages.
• Understanding a Down Syndrome Diagnosis – is a booklet that our Down Syndrome Program shares with expectant parents that visit us for a prenatal visit. It is also sold by Lettercase and was created with input from both the medical and Down syndrome communities, including representatives of ACOG, NSGC, ACMG, NDSC, and NDSS, to provide accurate, up-to-date, and balanced prenatal information about Down syndrome.
• Diagnosis to Delivery – A Pregnant Mother’s Guide to Down Syndrome is a free online book that offers information and suggestions to expectant mothers expecting a baby with Down syndrome. The book includes information on how to inform relatives, how to prepare for your baby’s birth, and what to consider on birth announcements. It is also available in Spanish.

Complication of Down Syndrome

Medical complications often accompany Down syndrome. These may include:

• Heart defects – About half the children with Down syndrome are born with some type of congenital heart defect. These heart problems can be life-threatening and may require surgery in early infancy.
• Gastrointestinal (GI) defects – GI abnormalities occur in some children with Down syndrome and may include abnormalities of the intestines, esophagus, trachea and anus. The risk of developing digestive problems, such as GI blockage, heartburn (gastroesophageal reflux) or celiac disease, may be increased.
• Immune disorders –  Because of abnormalities in their immune systems, people with Down syndrome are at increased risk of developing autoimmune disorders, some forms of cancer, and infectious diseases, such as pneumonia.
• Sleep apnea – Because of soft tissue and skeletal changes that lead to the obstruction of their airways, children and adults with Down syndrome are at greater risk of obstructive sleep apnea.
• Obesity – People with Down syndrome have a greater tendency to be obese compared with the general population.
• Spinal problems  Some people with Down syndrome may have a misalignment of the top two vertebrae in the neck (atlantoaxial instability). This condition puts them at risk of serious injury to the spinal cord from overextension of the neck.
• Leukemia – Young children with Down syndrome have an increased risk of leukemia.
• Dementia – People with Down syndrome have a greatly increased risk of dementia — signs and symptoms may begin around age 50. Having Down syndrome also increases the risk of developing Alzheimer’s disease.
• Other problems – Down syndrome may also be associated with other health conditions, including endocrine problems, dental problems, seizures, ear infections, and hearing and vision problems.
• Congenital heart defects
• Hearing loss
• Poor vision
• cataracts (clouded eyes)
• Hip problems, such as dislocations
• Leukemia
• Chronic constipation
• Sleep apnea (interrupted breathing during sleep
• Dementia (thought and memory problems)
• Hypothyroidism (low thyroid function)
• Obesity
• Late tooth growth, causing problems with chewing
• Alzheimer’s disease later in life

People with Down syndrome are also more prone to infection. They may struggle with respiratory infections, urinary tract infections, and skin infections.

Associate health problem

• children with Down syndrome typically have intellectual disability, hypotonia (low muscle tone) and characteristic facial features, such as upward slanted eyes and a flattened nasal bridge.  Some medical conditions are more common in individuals with Down syndrome, therefore special tests and extra medical care are needed.
• children with Down syndrome have an increased risk for certain medical conditions.  Health care guidelines exist to help clinicians screen and manage these conditions.  Some of these conditions include
• Congenital heart defects, which occur in almost half of children born with Down syndrome. Some children require surgery to correct their heart.
• pulmonary hypertension, a condition that affects arteries in the heart and lungs, and which often resolves in the newborn period.
• gastrointestinal malformations such as Hirschsprung’s disease and Duodenal Atresia. These are usually treated, often with surgery, in the newborn period.
• seizures, especially a type called “infantile spasms” in babies or other types of seizures in older children.  These are often well-managed with medication.
• ear infections and hearing impairment. Some children may require ear tubes.
• visual or hearing impairment.  Some children may use glasses.
• atlantoaxial instability (cervical spine vertebrae may be more flexible causing a small but increased risk for spinal cord injury or compression).
• obesity/Overweight
• childhood leukemia
• thyroid conditions, such as hypothyroidism
• colds and respiratory infections, like bronchitis, and pneumonia
• sleep dysfunction and obstructive sleep apnea

References

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