How to Conquer a Chromosome Abnormality— What is a chromosome abnormality? University of Texas Health Science Center at San Antonio, School of Medicine The Chromosome 18 Registry and Research Society What is a chromosome 18 abnormality? Special points of interest: When confronted with a chromosome foods to how susceptible you are to Genetic material—genes, abnormality diagnosis, parents often infections. These units of instruction chromosomes, DNA have an avalanche of questions; the within your body are essentially the Chromosome anatomy first of which is “What is a chromo- cookbook of life. The individual units some abnormality?” In order to under- are called genes. Genes are organized Chromosome analysis stand what a chromosome abnormali- within cells into packages called chro- Common chromosome 18 ty is, we first need to understand what mosomes much like recipes are orga- syndromes a chromosome is and some back- nized in chapters in cookbooks. ground about genetics. You may have heard of the human You have surely noticed that children genome. Think of this as the cookbook tend to look like their parents, often of life. It contains all the recipes you having some features like their mom will ever need. And every cell in the and some like their dad. This is be- body contains the complete cookbook cause they received half of their ge- with all the recipes. As the cookbook netic material from each parent. is divided into chapters, our genome is Inside this issue: divided into chromosomes. And as Your genetic material contains the each chapter has many recipes, each instructions for every part of your Chromosome Analysis 2 chromosome contains many genes. Genome = Cookbook body. These instructions are for virtu- While the cookbook is made of paper, Chromosomes = Chapters ally everything from how your ears your genes and chromosomes are Genes = Recipes 18q- 2 are shaped to how you digest your made of DNA. 18p- 2 Chromosome anatomy—important to understand Ring 18 3 The top picture is of chromosomes The bottom picture shows the chromosomes paired up and in numerical order. This makes from a white blood cell viewed under a 3 Tetrasomy 18p light microscope. They have been analysis easier. Chromosomes are found in treated with stain that makes them pairs, one from mom and one from dad. Males have one X and one Y chromosome while Trisomy 18 3 appear to have black and white bands. However, this random assortment of females have two X chromosomes. Each chromosome has a “waistband” called a cen- 4 chromosomes is difficult to analyze Summary tromere, and two arms—the short arm is the for differences from normal. p arm and the long arm is the q arm. How to Conquer a Chromosome Abnormality—What is a chromosome abnormality? Page 2 Chromosome Analysis The analysis of chromo- changes are not compatible chromsomes. somes involves looking for with life. The majority of Because chromosomes are missing pieces, duplicated babies conceived who have made up of genetic material pieces, rearrangements chromosome changes are (genes) the results can cause or losses or gains of entire miscarried early in preg- abnormal development or func- chromosomes. Quite liter- nancy. Babies with any type tion. ally, anything you could do of chromosome changes to a piece of paper with that survive are said to have scissors, glue and a copy chromosome abnormalities. machine, could really hap- So, a chromosome abnor- pen and does really happen mality is a change in the to chromosomes. However, content or structure of the majority of these “A chromosome The Most Common Syndromes of Chromosome 18 abnormality is a 18q- change in the This picture shows 18q-, a deletion middle of the long arm and as such content or of any portion of the long arm, also would be called an interstitial dele- structure of called the q arm. Someone could tion. It is also important to appre- chromosomes.” have a deletion that is smaller or ciate that one chromosome is 18q- larger than the one pictured. The normal and only one chromosome deletion could be from the end of of the pair has the deletion the chromosome like in the picture and thus would be called a termi- nal deletion. The deletion could also be from somewhere in the 18p- Shown here is 18p-. Like 18q-, the 18p deletions can be large or small, terminal or interstitial. 18p- 18p– involves the short or p arm of one of the two copies of chromosome 18. How to Conquer a Chromosome Abnormality—What is a chromosome abnormality? Page 3 Ring 18 Shown here is Ring 18. In this chromosome can be large or condition one of the two chro- small. There could be a big q mosomes forms a ring. This arm deletion and a small p arm means that by definition, the deletion or two small deletions protective cap called the telo- or any combination. It is im- mere is missing from each end portant to note that the deletion of the chromosome. However of genes in ring chromosomes Ring 18 that does not mean that genes always involves the ends of the must be missing from both ends chromosome arms. of the chromosome—but they usually are. Again like the other two conditions, the size of the deletion from either end of the “Because Tetrasomy 18p chromosomes are Shown to the left is Tetra- chromosome 18 p arm, made up of genetic somy 18p. In this condition which is why it is called material (genes), there are two normal copies Tetrasomy 18p. the results can of chromosome 18 along with an extra chromosome com- Tetrasomy 18p cause abnormal posed of two p arms of chro- development or mosome 18. This means there function.” are a total of 4 copies of the Trisomy 18 The last major syndrome of children with Trisomy 18 usu- chromosome 18 is Trisomy 18, ally have shortened lifespans in which there are simply 3 and many die before their copies of chromosome 18. first birthday. Trisomy 18 This is, by far, the most com- mon of the chromosome 18 syndromes. However, this condition is different from the other conditions because 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/ Summary To summarize, this is what you have learned so far: Your genetic material is pack- aged in chromosomes. The chromosomes contain genes. Information provided by The Chromosome 18 Clinical Genes are the instructions for Research Center to: all body development and func- tion. There is a variety of chromo- some copy number changes that can occur. When they do occur, normal development and function is often altered. http://www.chromosome18.org/ 210-657-4968 .