DrGreene.com » Medical Testing

Breakthrough Test for Down Syndrome

Dr. Alan Greene — Thu, 13 Jan 2011 23:53:27 +0000

A new technique could revolutionize the diagnosis of Down syndrome in a way that mothers will love. All it takes is 1/2 tsp of the mother’s blood for stunningly accurate results.

Then Not long ago the plan was for every pregnant woman over the age of 35 to be offered amniocentesis or chorionic villus sampling (CVS) for the diagnosis of Down syndrome. These tests are quite accurate because they directly count the chromosomes of the fetus to detect three copies of chromosome 21, the defining characteristic of trisomy 21 (Down syndrome). But there were two problems:

1. About 5% of pregnant women in the US received these invasive tests. Amnio requires a needle to be passed through a mother’s abdominal wall and through the wall of her uterus into the fetal environment to collect a sample of amniotic fluid. The miscarriage rate is somewhere between 0.03% and 0.5%. And parents often don’t get an answer until 18 weeks pregnant. With CVS the needle can be passed either through the mother’s abdominal wall or through her cervix to get a sample of the placenta. Results are available as quickly as two months earlier than with amnio, but the miscarriage risk is 1%. When you consider the millions of women who have had amnio or CVS, the miscarriages are not trivial.

2. Only about 30% of Down cases were picked up with this plan; 70% were missed! Even though older women are a higher risk group, more babies are born to younger women.

Today’s Status Quo Experts began to use clues from prenatal ultrasounds and from combinations of markers found in blood tests of mothers to more precisely target who would benefit from amnio and CVS. As the blood tests progressed from double to triple to quadruple combinations the accuracy increased — but the items tested were still circumstantial evidence that often go along with trisomy 21, not the chromosomes themselves. This led to the current status quo:

1. Amnio or CVS is still recommended for 3 to 5% of pregnant women in the US, or about 120,000 to 200,000 women per year.

2. About 90% of cases of Down syndrome are picked up by this screening program; about 10% are not picked up until birth because their mothers never received amnio or CVS.

The Breakthrough A simple, non-invasive new test reported January 2011 in the BMJ directly counts the trace levels of fetal chromsomes that make their way into the mother’s blood. The test is simple from the mother’s perspective, but uses sophisticated massively parallel gene sequencing to get the job done. More than two million tests are performed on each 1/2 tsp sample. The new test, which can be performed in the first trimester, appears remarkable:

1. In this study, the test was able to detect 100% of cases of Down syndrome. A negative test appears to virtually rule out the presence of Down syndrome.

2. Because there is a small false positive rate, confirmatory amnio or CVS would be recommended for those with a positive test. Nevertheless, this new test would eliminate the need for about 98% of all amniocentesis and CVS.

A New Era This gene-sequencing blood test is not yet routinely available. But it is a clear glimpse of the near future, when non-invasive sequencing tests will be able to precisely and directly diagnose many conditions better than ever before.

Chiu, RWK et al. “Non-invasive prenatal assessment of trisomy 21 by multiplexed maternal plasma DNA sequencing: large scale validity study.” BMJ 2011;342:c7401 doi:10.1136/bmj.c7401

Down Syndrome Testing and Vegetarians

Dr. Alan Greene — Thu, 08 Apr 2004 21:01:49 +0000

Pregnant women who are vegetarians may be unnecessarily worried by prenatal screening tests, according to a study from the Chang Gung Memorial Hospital in Taipei. The study followed the pregnancies of more than 200 women, half of them vegetarians. Results were published in the February 2004 American Journal of Obstetrics and Gynecology. Beta HCG, the same substance used to detect pregnancies in the first place, is also used to look for Down syndrome.

In vegetarian women, levels are normally higher than in non-vegetarian women (and to a lesser extent, this is also true of alpha fetoprotein – AFP — levels). This results in false positive screening tests about 3 times more often for vegetarian women. Until someone calculates normal test ranges for the two different groups, vegetarian women can breathe just a bit easier while waiting for confirming test results.

What we eat affects us in more ways than we imagine!

Can She Hear Me?

Dr. Alan Greene — Mon, 20 Oct 2003 21:36:48 +0000

Most babies with hearing loss are not diagnosed until they are 1½ to 3 years old, unless a routine screening hearing test is done. These simple tests are recommended for all babies. However, about 1 out of 3 babies in the U.S. did not receive a screening hearing test during the last full year of data, according to the October 17, 2003 issue of MMWR published by the Centers for Disease Control and Prevention.

There is a gap in screening. There is also a gap in treatment. Of those babies found to have a hearing problem during newborn screening, 1 out of 5 did not receive the treatment they needed when it would help the most.

The CDC recommends that all babies be screened using the Early Hearing Detection and Intervention 1-3-6 approach. Every baby should have a screening hearing test before 1 month of age. If the results of the screening test are suspicious, babies should have a complete hearing evaluation by age 3 months. Whenever there is proven hearing loss, treatment should be begun before the baby is 6 months old.

Has your baby or toddler had a normal hearing screening test? If you’re not certain, find out. Earlier treatment helps to maximize a child’s language skills. No matter how old a child is, it’s better to begin now than to wait.

Cheap Genetic Testing At Home?

Dr. Alan Greene — Tue, 26 Aug 2003 01:32:38 +0000

A brilliant idea may bring expensive medical tests into reach using nothing more exotic than home computer with a CD drive. Up until now, many specific protein tests have relied on $100,000 fluorescent protein readers.

Researchers at the University of California San Diego have used a conventional inkjet printer, CD drive, and Linux software to achieve the same results. They burned the CD with some music (Beethoven’s Fifth) to provide a background digital pattern. Their printer has an attachment for printing labels on the backs of CDs. Reversing the CDs in the printer, and putting reactive molecules in the printer cartridges instead of ink, the creators of this new technology spray the mirror face of a recordable CD with invisible molecules that will react with a specific protein, thus making a CD for a specific lab test.

These CDs could be produced and sold widely, a different CD for each test or group of tests. Then the surface is wiped with a sample from a patient and cleaned (spit and wipe, for instance). If the protein you are testing for is present, it will stick to the molecules “printed” on the CD. Pop the CD into a conventional computer drive, and a program can read the difference between the original CD recording and the results after wiping with the sample. This could lead to easy, inexpensive home testing, not just for AIDS, pregnancy, step throat, etc. but also for a long list of genetic conditions that now require major laboratories to do sophisticated tests.

The team plans to distribute their idea through open-source licencing. The Royal Society of Chemistry will publish their paper in their September 21, 2003 Journal of Organic and Biomolecular Chemistry. This work could lead to a new era in medical testing and information, much like the Model T car did to transportation. This could change everything.

X-Ray or a CT Scan?

Dr. Alan Greene — Wed, 12 Mar 2003 04:18:26 +0000

Dr. Greene’s Answer:

I was taught as a pediatric resident that skull x-rays were obsolete, that if you were wondering about a fracture you should just get the CT to avoid exposing the child to radiation twice. I now disagree. While a CT scan can indeed answer the skull fracture question (and more), it takes hundreds of times more radiation to do this. If a skull fracture would be the only reason for getting a CT, you can settle that question with a regular skull x-ray first, saving many children from unnecessary CT scans.

Reviewed By:

Khanh-Van Le-Bucklin M.D. & Liat Simkhay Snyder M.D.

February 14, 2008

Who Should Receive a CT Scan?

Dr. Alan Greene — Wed, 12 Mar 2003 04:10:20 +0000

Dr. Greene’s Answer:

We want to CT children when the expected health benefit is clearly greater than the tiny increased risk of eventual cancer. To do this, we want to use other signs and symptoms to help decide which children are the most likely to have an important injury inside the skull.

The CT scan is intended to help solve the mystery of what is going on inside the body: When used properly, I would still expect that many children who receive CTs will turn out to be well. Nevertheless, it is wonderful whenever we can use other clues to remove children from the ‘mystery’ group without the amount of radiation exposure needed for a CT scan.

After suffering severe traumatic injury to the head, we would likely all agree that a child would benefit from detailed imaging of the extent of injury to the skull and brain. The controversy arises when deciding how to treat children who have sustained a minor trauma, or “mild traumatic brain injury.”

Research so far suggests that after a relatively minor head trauma the most important kids to scan include those who are dizzy or who have changes in vision or behavior (including everything from excessive sleepiness to vomiting, to seizures). Children under 2 are also good candidates. They are at high risk and often can’t tell us if they are experiencing vision changes or dizziness. Those whose injuries were obtained at great force – such as those in bicycle accidents – are also in the high risk group of internal head injuries, as are those in whom a skull fracture has been found.

Reviewed By:

Khanh-Van Le-Bucklin M.D. & Liat Simkhay Snyder M.D.

February 14, 2008

Who are Radiologists?

Dr. Alan Greene — Wed, 12 Mar 2003 04:01:28 +0000

Dr. Greene’s Answer:

A radiologist is a physician who specialized in imaging techniques after completing medical school. If one is involved in doing or interpreting the CT scan, there is a higher chance that it will be set for a child. X-ray techs may also be knowledgeable, but they have completed technical school — not medical school.

Reviewed By:

Khanh-Van Le-Bucklin M.D. & Liat Simkhay Snyder M.D.

February 14, 2008

When should a CT Scan be Performed?

Dr. Alan Greene — Wed, 12 Mar 2003 03:40:02 +0000

Dr. Greene’s Answer:

CT scans are usually the best imaging studies for looking inside the skull following head trauma. They are also the best imaging studies for other specific situations, including looking inside the lungs for cancer.

After a head trauma, the advantages of CT scans are most clear for those children under 2, those experiencing dizziness, vision, or behavior changes, those with skull fractures, and those with a mechanism of injury likely to cause a serious problem (this is one reason I’m such a big fan of bicycle, skateboard, scooter, and motorcycle helmets). If the doctor has a high degree of suspicion that there is a problem, a CT scan can be the wisest thing to do.

Reviewed By:

Khanh-Van Le-Bucklin M.D. & Liat Simkhay Snyder M.D.

February 14, 2008

When are MRIs not practical?

Dr. Alan Greene — Wed, 12 Mar 2003 02:10:32 +0000

Dr. Greene’s Answer:

The MRI is a very strong magnet — you would not want it to move around metal clips in the head, or anywhere else in the body!

Reviewed By:

Khanh-Van Le-Bucklin M.D. & Liat Simkhay Snyder M.D.

February 14, 2008

Other Radiation Exposures

Dr. Alan Greene — Wed, 12 Mar 2003 00:39:09 +0000

Dr. Greene’s Answer:

Plain chest x-rays use a very low level of radiation (you get about the same level of background radiation every 3 days or so just from living on planet earth). Some types of x-rays though, such as barium enemas, give as much radiation as CT scans.