Is Williams Syndrome the Same as Down Syndrome?

Reviewed on 2/19/2021

What Is Williams syndrome vs. Down syndrome?

Williams syndrome and Down syndrome are both chromosomal disorders affecting people from birth. However, Williams syndrome is caused by a missing chromosome, while Down syndrome is caused by an extra chromosome.
Williams syndrome and Down syndrome are both chromosomal disorders affecting people from birth. However, Williams syndrome is caused by a missing chromosome, while Down syndrome is caused by an extra chromosome.

What is Williams syndrome?

Williams syndrome is a genetic disorder that affects approximately one in 25,000 births. The syndrome is named for Dr. J.C.P. Williams, who first diagnosed the condition. He saw a pattern in children at his hospital receiving treatment for cardiovascular problems. These children shared traits like similar facial features and an unusually friendly and outgoing demeanor.

Williams syndrome is also called:

What is down syndrome?

Of all chromosomal conditions, Down syndrome is the most common with one in 700 babies diagnosed with Down syndrome. Most people are born with 46 chromosomes, but those with Down syndrome have an extra copy of chromosome 2.

While the physical features and behaviors are very similar, there are three different types of Down syndrome:

  • Trisomy 21: Around 95% of those diagnosed with Down syndrome have Trisomy 21. In this type, each cell in your body has three copies of chromosome 21 instead of the usual two copies.
  • Translocation Down syndrome: Approximately 3% of people diagnosed with Down syndrome have an extra part or whole chromosome 21, but it is attached to a different chromosome rather than being a completely separate chromosome 21.
  • Mosaic Down syndrome: Around 2% of the people with Down syndrome have some cells with an extra chromosome 21, but other cells have the standard two copies of the chromosome. 

What are signs of Williams syndrome vs. Down syndrome?

Signs of Williams syndrome

Typical markers of Williams syndrome include:

  • Facial features: Those diagnosed with Williams syndrome often have a broad forehead, short and broad nose, full cheeks, and a wide mouth with full lips. These features are sometimes considered elfin-looking.
  • Personality: People with Williams syndrome are outgoing and tend to be very interested in other people. They are very empathetic toward others, but also have high anxiety, often accompanied by phobias. Attention deficit disorder (ADD) is also common in those with Williams syndrome.
  • Cardiovascular disease: The genetic code missing from chromosomes can cause large blood vessels to be too narrow. This form of cardiovascular disease is called supravalvular aortic stenosis (SVAS), and it occurs frequently in people with Williams syndrome. If left untreated, it can cause shortness of breath, high blood pressure, chest pain, and heart failure
  • Developmental concerns: Children with Williams disease often have issues with developing motor skills and gross fine motor skills.

Signs of Down syndrome

People who have Down syndrome may look similar and have similar qualities, but the conditions manifest differently for each person. 

  • Intellectual development: Generally speaking, kids with Down syndrome have lower IQs and speak slower than other children.
  • Facial features: Those diagnosed with Down syndrome often have a flattened face, especially through the nose, and almond-shaped eyes that slant upward. They also have smaller ears and a short neck
  • Health concerns: Half of all babies born with Down syndrome have heart defects that may be life threatening. In addition, Down syndrome increases your risks for developing Alzheimer’s disease earlier in life.

What are causes of Williams syndrome vs. Down syndrome?

Causes of Williams syndrome

Williams syndrome occurs when genetic code is missing from chromosome 7, which contains approximately 25 genes. Because of this genetic deficiency, people with Williams syndrome don’t produce enough proteins like elastin. This is the reason for several of the cardiovascular and physical characteristics that are most associated with Williams syndrome.

Causes of Down syndrome

Similar to Williams syndrome, Down syndrome occurs because of a chromosome disorder resulting from an extra copy of chromosome 21. While Down syndrome doesn’t tend to run in families, one in three children with Down syndrome have a parent who carries a translocated chromosome 21. 

The mother’s age at conception is linked to an increased chance of your baby developing the condition. For pregnancies when the mom is 20 years old, the chance of having a baby born with Down syndrome is one in 2,000. By age 40, the chance increases to one in 100.

How to diagnose Williams syndrome vs. Down syndrome

Diagnosing Williams syndrome

Your doctor will ask questions about the signs and symptoms you or your child exhibits that are similar to Williams syndrome. Diagnosis will also include:

There are two tests used to provide a confirmed diagnosis of Williams syndrome. The first is a FISH test, which is used to look for the chromosomes that are missing in those with Williams syndrome.

A chromosomal microarray uses millions of markers to determine what pieces of DNA are missing or where there are extra pieces of DNA. This provides a better idea of how severely a person will be physically and mentally impacted by the condition.

Diagnosing Down syndrome

Since it is a common chromosomal condition, two tests are used to diagnose Down syndrome during pregnancy. This helps doctors prepare to identify and treat any heart defects present at birth. 

A screening test indicates your chances of having a baby with Down syndrome based on your age, health, and genetics. Diagnostic tests are done first using the mother’s blood and then amniotic fluid around the baby in the womb

If your screening test during pregnancy shows a high likelihood for Down syndrome, your doctor may run diagnostic tests to confirm. These can include:

Treatments of Williams syndrome vs. Down syndrome

Treating Williams syndrome

While some symptoms of Williams syndrome can shorten the expected lifespan, infants and children who receive a diagnosis can live a long life with proper treatment.

Your treatment plan will be individualized based on the symptoms and severity of your case. Interventions may include:

  • Feeding therapy for infants with feeding problems
  • Physical therapy for weak muscles or developmental delays
  • Special education programs for children with developmental delays
  • Behavioral counseling
  • Medication for attention deficit disorder or anxiety
  • Surgery to address life-threatening heart deformities 
  • Medications or diet modifications for excessive calcium in the blood

Treating Down syndrome

There is no cure for Down syndrome. Early detection is the key to increasing the life expectancy of a child born with Down syndrome. Surgery may be necessary to address health concerns like heart defects. Other treatments include services like:

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References
Centers for Disease Control and Prevention: "Facts about Down Syndrome."

Global Down Syndrome Foundation: "Congenital Heart Defects and Down Syndrome: "What Parents Should Know."

Kennedy Krieger Institute: "Genetic, Metabolic & Chromosomal Disorders."

National Down Syndrome Society: "What is Down Syndrome?"

National Institute on Aging: "Alzheimer's Disease in People with Down Syndrome."

National Organization for Rare Disorders: "Williams Syndrome."

Stanford Medicine: "Williams Syndrome."

St. Louis Children's Hospital: "Williams Syndrome."

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