How to Conquer a Chromosome Abnormality— Why and how did this happen? University of Texas Health Science Center at San Antonio, School of Medicine The Chromosome 18 Clinical Research Center

Why and how did this happen? Among the top questions that parents have are: The fact is that chromosome abnor- implant in the uterus, too early to even malities occur very commonly. Chro- become a recognized pregnancy. Of How common are chromo-  mosome rearrangements, deletions those abnormal embryos that do im- some abnormalities? and/or duplications can happen during plant, 90% are miscarried, usually Incidence of Chromo‐  Why did this happen to me? cell division when chromosomes repli- during the first trimester. some Abnormalies cate and then segregate into two  When did this happen? If you do the math, 50% of concep-  50% of concepons daughter cells. Additionally, the sepa- tions have chromosome abnormalities,  90% do not implant  Did I do something that ration of chromosomes into two but 90% of those do not implant. That  90% spontaneously caused this? daughter cells can have errors in leaves 5% of conceptions with chro- aborted which one cell gets one too many mosome abnormalities surviving long  0.5% in newborns chromosomes leaving the other cell enough to become a recognized preg- with too few chromosomes. These nancy. But if 90% of those are mis- errors are believed to happen during carried, that leaves 1/2 of 1% of con- the formation of the sperm or egg ceptions having chromosome abnor- cells, before conception, or very soon malities that are survivable to birth. Inside this issue: after fertilization. This is the same as one out of every These types of errors are believed to 200 babies having a chromosome 2 Different Chromosome occur in 50% of conceptions. Howev- abnormality. Abnormality Proportions er, when these errors happen, 50% of These data are derived from what is the time the resulting embryo fails to What did I do? 2 known about in vitro fertilization.

Summary 2 Incidence of chromosome abnormality in live births

The actual incidence in live births is used today. Therefore, we predict that There will be many individuals with slightly higher—one in every 180. In a chromosome abnormalities are more chromosome abnormalities who have population of individuals with intellec- common because we can now detect no manifestation as a consequence. tual disability, 50% of them have small abnormalities that were once chromosome abnormalities. undetectable. We also predict that Frequency of Chromosome chromosome abnormalities are the Abnormalities in: The caveat is that this data was de- cause of an even higher percentage of *Live births—1 in 180 rived before the use of the high reso- the cases of intellectual and develop- *Intellectual Disability—50% lution molecular analysis techniques mental disability.

How to Conquer a Chromosome Abnormality—Why and how did this happen? Page 2

Different Chromosome Abnormality Proportions

This pie chart illustrates the propor- tions of some different chromosome

abnormalities. Down syndrome is, by Down far, the most common, with Trisomy 18 and Trisomy 13 a distant 2nd and 3rd. Trisomy 18 All other possible combinations make Trisomy 13 up 54% of all chromosome abnormali- ties. Individually, these conditions are All other rare—some being unique to a single person, but collectively this repre- sents a large number of persons.

Data from March of Dimes website 2007.

Did I do anything or was I exposed to anything that caused this to happen? By now you know that chromosome nancy can actually increase your the Hiroshima nuclear bomb and their abnormalities happen as a part of life chances of having a child with a chro- descendants might have had more and cell division—a process that does mosome abnormality. children with chromosome abnormali- not always occur perfectly. ties die due to increased radiation It is known that older mothers have an exposure—but they have not. “Probably not!” But the question remains, did you do increased risk for having a child with anything or were you exposed to an extra chromosome, such as Down This leads us to the conclusion that anything that increased your chances syndrome. It is also known that older for parents who themselves have that this would happen to you? The fathers are at risk for having a child normal chromosomes, there is no way answer is probably not. There is no with a new mutation, but not neces- to prevent having a child with a chro- data to suggest that any environmen- sarily a chromosome abnormality. mosome abnormality except to have tal exposures before or during preg- none at all. One might think that the survivors of Summary

So to summarize what we have learned so far:  The chromosome abnormality  Chromosome abnormalities occurred in the germ cells prob- occur in one of every 180 live ably before conception or very births. early after fertilization.

 They happen to everyone—but  There is currently no data that most are not compatible with suggests this could have been life. prevented in parents with nor- mal chromosomes.

UTHSCSA—Department of Pediatrics The Chromosome 18 Clinical Research Center For more information, you may contact the authors and principal investigators of the Chromosome 18 Clinical MSC 7820 Research Center at the phone numbers or email shown to the left. 7703 Floyd Curl Drive San Antonio, TX 78229-3900 Authors & Principal Investigators: Phone: 210-567-5321 Fax: 210-567-0919 Jannine D. Cody, PhD and Daniel E. Hale, MD E-mail: [email protected]

Our Motto To provide individuals and families affected by chromosome 18 abnormalities with comprehensive medical and educational information with a focus on treatment options.

We are on the web! http://pediatrics.uthscsa.edu/centers/chromosome18/

Information provided by The Chromosome 18 Clinical Research Center to:

http://www.chromosome18.org/ 210-657-4968