Cri-du-chat syndrome

Inheritance

How is Cri-du-chat syndrome inherited?

Cri-du-chat syndrome is caused by a deletion (missing genetic information) on a part of a chromosome. Genetic information is organized in the cells of the body on structures called chromosomes. Each chromosome consists of a "short arm", referred to as "p", and a "long arm", referred to as "q". Most cells in the body typically have 46 chromosomes which are organized into 23 pairs of 2. The first 22 pairs of chromosomes, which are numbered 1-22, are the same in males and females and are called autosomes. The 23rd pair of chromosomes is called the sex chromosomes and are what determine gender (XX for female and XY for male). An individual receives one chromosome from each pair from each parent at the time of conception. This means that everyone has two copies of all of the genetic information found on chromosomes 1-22, with one copy coming from each parent.

Cri-du-chat syndrome is caused by a deletion near one of the ends of one copy of chromosome 5 (called the "p" arm). The other chromosome 5 in the pair does not have the deletion. However, only having one copy of the genetic information typically found on that area of chromosome 5 in an individual's cells (because of the deletion on the other chromosome), causes the health and developmental problems people with Cri-du-chat may have.

In about 85% of individuals with Cri-du-chat syndrome the deletion on chromosome 5 is new in the child who has the syndrome, meaning that neither parent has Cri-du-chat syndrome. When a genetic change happens for the first time in a child it is called a "de novo" event. De novo events are caused by sporadic (chance) changes in either the sperm or egg that created the child. If parents have a child with Cri-du-chat syndrome resulting from a de novo change, the chance that they would have another child with the same syndrome is low (<1%).

In the remainder of cases (approximately 15%), a parent may have a translocation or other rearrangement of their genetic material. A translocation is when a portion of one chromosome attaches to another chromosome and ends up in an unexpected location. If a parent has a translocation, they have all their genetic material present, but in a rearranged form. When a parent with a translocation passes on their genetic material to their children in the egg or sperm cell, the translocation may lead to an imbalance (extra or missing genetic information) in the combination of chromosomes present in the egg or sperm. A translocation in a parent can, in some cases, lead to an increased likelihood for children of that parent to have an imbalance of genetic material in their cells, including Cri-du-chat syndrome. If a child has Cri-du-chat syndrome as a result of a parental translocation, the chance that the parent with the translocation would have another child with Cri-du-chat is increased. The specific risk depends on the translocation. However, there have been reports of risks as high as about 20% for Cri-du-chat syndrome to recur in a second child in a family as a result of a parent having a translocation.

Families who would like more information about the genetics of Cri-du-chat syndrome, their recurrence risks for Cri-du-chat syndrome in a future pregnancy, and/or a discussion about their reproductive options may benefit from genetic counseling. Genetic counselors in the United States can be found on the National Society of Genetic Counselors website. Genetic counselors in Canada can be found at the Canadian Association of Genetic Counselors website.

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How does the size of the genetic deletion affect the symptoms in Cri-du-chat syndrome?

Are there forms of Cri-du-chat syndrome that are not genetic?

How does the size of the genetic deletion affect the symptoms in Cri-du-chat syndrome?

Chromosomes are the organizational structures of genes, which contain the instructions that direct the body how to grow and develop. Chromosomes can be compared to a set of books, such as an encyclopedia, and genes are like the chapters within the books. Individuals with Cri-du-chat syndrome have a deletion of genetic information on a part of chromosome 5. This can be compared to having multiple pages/whole chapters missing from a book. The larger the deletion, the more information is missing. In general, the larger the deletion an individual has, the more symptoms of Cri-du-chat syndrome may be expected. While individuals with larger deletions might generally be predicted to have a greater "severity" in their symptoms, variability in the size of the deletion does not explain all of the variability of symptoms from one individual with Cri-du-chat syndrome to another. Even individuals with apparently identical deletions are expected to be affected somewhat differently from one another.

Are there forms of Cri-du-chat syndrome that are not genetic?

All individuals with Cri-du-chat syndrome are missing a piece of chromosome 5 (chromosome deletion). In approximately 85% of individuals with Cri-du-chat syndrome, their deletion occurred for the first time in them as a new event (de novo), as opposed to being inherited from a parent. In the additional approximately 15% of individuals with Cri-du-chat syndrome, a parent, while unaffected with Cri-du-chat syndrome, may have a chromosome rearrangement (translocation) that predisposes the chromosome deletion that causes Cri-du-chat syndrome in the child.

When an individual is affected with Cri-du-chat syndrome as a result of a de novo event, the chance that another child in the same family would also have Cri-du-chat syndrome is fairly low (<1%). When a parent carries a chromosome translocation or other rearrangement that may predispose to Cri-du-chat syndrome, the risk of recurrence in a future child may be much higher. Depending on the specific chromosome rearrangement in the parent, the risk for recurrence in a future child has been reported to be as high as 20%.

Families who would like more information about the genetics of Cri-du-chat syndrome, their recurrence risks for Cri-du-chat syndrome in a future pregnancy, and/or a discussion about their reproductive options may benefit from genetic counseling. Genetic counselors in the United States can be found on the National Society of Genetic Counselors website. Genetic counselors in Canada can be found at the Canadian Association of Genetic Counselors website.

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