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Screening for Canavan Disease Recommended for Ashkenazi Jews

Miryam Z. Wahrman, Ph.D.

"They are not able to do anything physically for themselves," explained Orren Alperstein Gelblum, describing some of the effects of Canavan Disease on children. Gelblum, who lost a child to Canavan Disease, is President and a founder of the Canavan Foundation in New York City. "Some children seem to develop a little bit in that direction, and then lose whatever they may have developed," Gelblum continued. "[They have ] very little motor coordination.... Our experience is that they are severely retarded children. Some people claim that their [affected] children do understand some language. Our experience is that it's minimal.... and speech is nonexistent."

Canavan Disease is a genetic disorder which is prevalent in the Ashkenazi Jewish population. It is estimated that one in forty Ashkenazi Jews is a carrier for the disease. That means that statistically 1 in 6,400 children of Ashkenazi couples could inherit the disease.

The prevalence and seriousness of the disease has led to the development of a reliable DNA test for Canavan Disease and to a recent recommendation by the American College of Obstetricians and Gynecologists (ACOG) that "molecular carrier screening for Canavan disease should be offered... if both members of the couple are of Ashkenazi Jewish genetic background. This screening could be combined with screening for Tay-Sachs disease because both disorders are more common in this group."

"The test sensitivity is extremely high for persons of Ashkenazi Jewish descent, and virtually 100% in families in which the disease causing mutations have previously been identified." explained Dr. Darryl DeVivo, Professor and Director of Pediatric Neurology at Columbia University College of Physicians and Surgeons.

Canavan Disease arises from inheritance of two copies of the defective gene, one from each parent. Parents who are carriers of Canavan show no symptoms, however, since they have one normal copy of the gene which can compensate for the defective version they carry. Each time two carriers conceive a child, there is a 25 percent chance that child will inherit the defective gene from both parents and develop Canavan Disease.

In 1993 scientists discovered that Canavan Disease is caused by a defect in the ASPA gene - which produces the enzyme aspartoacylase. In normal brain cells aspartoacylase breaks down a chemical called N-acetylaspartic acid, or NAA; so when aspartoacylase is missing, NAA accumulates and causes brain damage. Excess NAA causes destruction of myelin, an insulating material in parts of the brain and in nerves. When myelin is damaged, nerve cells, or neurons, become impaired in their ability to integrate messages within the brain and in transmission of messages between the brain and the body. For instance, visual signals from the eye are not transmitted properly to the brain, so children with Canavan Disease progressively lose their sight. On the other hand, the nerve which transmits signals from the ear to the brain is much shorter, and does not depend as much on myelin, so most Canavan children retain acute hearing.

The test relies on detection of a specific mutation, or error, in the DNA. For Ashkenazi Jews, more than 97% of Canavan cases are due to one of two possible mutations. Therefore, screening for those two mutations can identify most carriers in the Ashkenazi Jewish population. [In the general population Canavan can be caused by any one of more than 70 different mutations, thus it is much harder to screen for. It is also much less prevalent in the general population, although the precise percentage of carriers has not been calculated.]

"The fact that ACOG has now established a standard of care for Canavan Disease to recommend screening for Ashkenazi Jews is a terrific thing," remarked Gelblum. "Because in the past Tay Sachs wasn't really recognized as a disease that required screening until ACOG established a standard of care for it...." Gelblum explained that in the past many physicians were not aware of the importance of screening for Canavan. She continued, "Sometimes the ob-gyns would know about it and would support the screening, but more often than not they wouldn't. So now that ACOG has established this standard of care, ob-gyns will know about Canavan's Disease and screening for it."

"I think the reason why...I was so moved to work on the issue was because I have an 18 month old, and I'm Ashkenazi and my husband is Ashkenazi," related Jennifer Hahn, consultant to the Canavan Foundation. "[When I was pregnant] I went to a Park Avenue doctor, a Jewish doctor, who was trained in Israel and is very in touch with the Jewish community, and it was never mentioned to me that I needed to be screened for this. And I just feel remarkably lucky that I have a healthy child, and also a little frightened that I didn't know that I might have been at risk for this... I was screened for Tay Sachs at the recommendation of my doctor, and if he had said, you know you need to be screened for Tay Sachs and Canavan' I would have automatically."

"Our first child was perfectly healthy, and then 4 years later our second child was born..." related Gelblum. "It was clear to us early on that something was wrong, but it took us over a year to find out exactly what it was. And at that time we really were not comfortable trying to have additional children because we didn't know if the prenatal testing would be accurate."

"Now that it is," she continued, "people who have the misfortune to have had a Canavan child, can go ahead and be assured that their next child or children will be free of Canavan Disease. So that's a wonderful thing. Also the fact that carrier screening is now accurate and available will make it possible for families to have healthy children."

"Children with Canavan Disease seem to die in their first or second decade of life. Occasionally they may last a couple of more years," explained Gelblum. "They don't all die within the first five years, as do children with Tay Sachs."

"The course of the disease really varies and because it's so variable, some of the children are in and out of the hospital..." she continued. "They tend to have urinary tract infections, pneumonia... some children who live a little bit longer develop scoliosis which puts pressure on the heart... they have feeding problems, and seizures are fairly common in this disease.... Some children are institutionalized, and some are not. Our daughter lived at home. She died when she was 7 . Some people's children have lived at home for a while, and as the children got older and more difficult - physically - to handle, to lift, they were placed in institutions close by."

"Care of a Canavan child can be completely time consuming - all consuming." reported Gelblum. "While they can be very happy, cheerful children, they can also be very fussy and difficult and so it can be a very difficult experience."

Reports of experimental gene therapy for Canavan Disease, being performed at Yale University, present hope that one day a cure may be found for this genetic disease. A recent New York Times Magazine article described the saga of 2 year old Jacob Sontag, who is one of the first Canavan children to receive gene therapy - via injections of DNA containing the healthy ASPA gene directly into his brain.

"There's little evidence currently that gene therapy is a cure for kids," explained Hahn. "While I think the story is a very moving portrait of [the Sontag] family... it's unfortunate that the facts about screening and testing were not properly relayed... It brought the tribulations of families going through it to the public eye, but in terms of reporting the news about prevention, it lacked some very important elements."

In fact, the preeminent journal, Nature, reported last year that, although more than 200 gene therapy clinical trials had been attempted addressing a variety of genetic disorders, "there is still no single outcome that we can point to as a success."

"Everyone hopes that there will be a cure or treatment at some point down the road," Hahn asserted. "But right now, without that, prevention is the most important goal for my organization."

"No family has to go through what [the Sontag] family is going through," she emphasized. "No Jewish family has to go through that. Because there is screening, there's testing for parents and there's a test for a pregnancy already underway."

Orrin Gelblum has experienced the trials and tribulations of living with, loving and losing a Canavan child. "If I were in the position of being pregnant and I knew I was carrying another Canavan child, I would not choose to have another Canavan child," confessed Gelblum. "But that doesn't diminish the experience that I had with my child who passed away."

"I do believe that people should have the information and should know realistically what it is they're facing," concluded Gelblum. "It's a very private decision that people make who discover that they're carriers. I can tell them the very complex, difficult experience it could be to have a Canavan child, but the decision of what to do is a very private one."

The Gelblums now have a third child - a son - who is free of the disease.

Information on the Canavan Foundation can be accessed on the internet at www.canavanfoundation.org. The foundation can also be reached at (212) 316-6488

Dr. Miryam Z. Wahrman is Professor of Biology and Director of General Education at William Paterson University of New Jersey.

 

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