updated eye section

A fellow WS mom pointed out that elastin may not cause the star burst pattern in the eye, so I dug a little deeper on the subject. Although I couldn't find information on genetically why our little ones have the star burst pattern in their eyes, I did find great information about how the iris is structured differently to cause the pattern... if you've already read the eyes section, check it out one more time.

I also fixed the links to blogs and websites on the right. It seems I had some broken links... enjoy!

Interpreting microarray results

So, if you are one of the chosen few to get a microarray genetics test to diagnose Williams syndrome, you will receive a result that will look something like this:

"A 1.55 Mb deletion was observed at 7q11.23 from linear location 72,337,897 - 73,837,643"

Size of the deletion

So what does this mean? Let's start with the 1.55 Mb. Mb stands for million basepairs. DNA is made up of a string of base pairs (adenine or A, thymine or T, guanine or G and cytosine or C). A stretch of base pairs or gene is basically the blueprint for one functional protein. So, if you get results that there is a 1.55 Mb deletion then your child is missing 1, 550,000 total base pairs from their DNA. The classic or average deletion in a person with WS is 1.5-1.8 Mb.

Chromosome maps

Chromosome labels give specific information about the location of the gene so that scientists can communicate information easily. The WS deletion is at 7q11.23. The first number on the location marker represents the chromosome the gene is found on. There are 23 total chromosomes in the human genome and Williams syndrome is a deletion on the 7th chromosome.

The next letter tells the scientists which half of the chromosome to find the gene. Chromosomes look like two threads tied together near the center by something called the centromere. Think of the centromere like a belt. The belt usually fits off-center so one side of the chromosome will have longer sections (called arms) than the opposite side of the centromere. This is where the q comes in. The q (short for queue) means that the deletion sits on the long arm of the chromosome. If the deletion was on the short arm it would say p (short for petite).

When scientists study a chromosome, they stain it and take a photograph called a karyotype. The stain will create a banding pattern on the chromosome. This band is how genes are grouped and labeled. The numbers at the end of the chromosome map indicate how far that band sits from the centromere. The 11 indicates that the WS region is the 11th band away from the centromere and sits at a sub-band 23.

So what genes are missing?

The final section of the microarray results will tell you what gene locations are missing. The base pairs are numbered throughout the chromosome. So, this hypothetical person is missing base pairs #72,337,897-73,837,643. At the end of this blog post, I've listed the genes in the WS region with their base pair ranges. You can see what region of the chromosome your child is missing and then look up the functions of the genes, some of which I've described on the genetics page of this blog. You'll find that there are some numbers missing from the list. These areas are considered "genetic junk" Most genes have long strands of base pairs that do not code for any useful protein and are largely ignored by the body.

Mitral valve prolapse

Valve prolapse is not as common among individuals with WS but it does occur in some. In the world of congenital heart defects (CHD) which are heart defects present at birth, it actually affects about 2-3% of the CHD population.

What is a valve?

In order to understand how prolapse occurs, you should first be familiar with the function and anatomy of a valve. Valves are used throughout the cardiovascular system to direct blood flow. They act like one-way doorways that swing open, allowing blood to move through, and close behind, preventing it from flowing backwards. This essentially seals off each chamber in the heart so that when the muscles squeeze and push blood into a vessel, blood isn't pushed backwards. This is important for many reasons. Without valves, blood pressure would be more difficult to achieve. You wouldn't have the pressure of the blood pushing on the vessels if it had another outlet to flow into. Second, if there were multiple outlets, some blood could get caught in limbo between the two chambers, just swishing back and forth and not really moving anywhere. This is dangerous because it could cause it to clot. Clots can lead to several issues including heart attack. So, you can see, valves are important structures to keep everything flowing properly.

Valves are structured much like a balloon or parachute, attached to cords called chordae tendonae and anchored to the muscle wall of the ventricle (lower heart chamber). The valve itself is made up of cusps or flaps that fit together tightly to create a seal. On the left side of the heart you find the mitral valve between the two chambers (left atrium and left ventricle). The mitral valve also has two other names- the bicuspid valve, because it has 2 cusps or flaps, and the left a-v valve, because it separates the left atrium (a) from the ventricle (v). There is an analogous valve on the right side of the heart called the tricuspid or right a-v valve that functions in the same way and can also undergo prolapse for all the same reasons.

What does it mean to have valve prolapse?

When a person is born with valve prolapse, the layers of tissue that form the flaps or cusps of the valve are thicker than normal. The valve cusps are made up of three layers of tissue. One of those layers is connective tissue. When prolapse is present, the connective tissue builds up into a thicker layer than normal. This causes the cusp to fit improperly with the others and makes a leaky seal.

Most people with mitral valve prolapse show no signs of heart distress. If the seal does not allow too much blood to flow backwards, the overall function of the heart is maintained. Doctors will hear a murmur or click when they listen to the person's heart. A murmur is a swishing sound created when the blood squeezes through that opening. The smaller the opening, the louder the murmur will actually be.

Some people have a larger opening in the valve or it can progressively become worse over time. If the opening becomes large and a significant amount of blood flows backwards you can have issues with clotting and blood pressure. When blood flows backwards into the atrium it is called mitral regurgitation. If this occurs, a cardiologist will most likely prescribe medication called beta blockers or blood thinners to prevent clotting.

As the opening becomes larger, a lot of pulling can take place on the cords that anchor the valve. They can become stretched out, causing the opening to become larger still and eventually can rupture or break. You can imagine what would happen to a parachute if you cut one of the cords that attaches it. The parachute would become loose and wouldn't catch the air properly. The same thing can happen to the valve. If this happens, the heart simply wouldn't function properly and a valve repair or replacement surgery may be necessary.

If my child has valve prolapse, what can I do to prevent this from progressing?

Although the progressive nature of this condition can be scary, most people go their entire life without any issues. Whenever a child has a CHD, it's important to maintain optimal cardiovascular health by monitoring their diet, getting proper cardiovascular exercise and seeing a cardiologist regularly to monitor the defect. Diet, especially watching sodium intake and avoiding caffeine and energy drinks, will keep their heart functioning properly.

Sources:
Mitral valve diseases in Williams syndrome by Collins

Mitral valve prolapse by Medline

New genetics page

Check out the genetics page, which is now complete!

Welcome!

Welcome to my new blog! I'm only beginning to set up all the pages, so I'll update this as I go and let you know when each section is ready. The conditions that I'm including on each page are considered likely issues in WS according to guidelines given to pediatricians and family practitioners. I'm willing to add others, by request, so if you wonder about a condition or how something works, just let me know and I'll try to include it.

For now, the cardiovascular page is finished. I hope you find it useful!