Family History and Genetics

I thought it would be helpful to add some information about family history and genetics.  This is all from the CDC website http://www.cdc.gov/ncbddd/genetics/index.html

Understanding genetic factors and genetic disorders is important in learning more about preventing birth defects, developmental disabilities, and other unique conditions among children.

Family History
Collecting your family's health history can be important for your child's health. You might not realize that your mother’s diabetes or your cousin’s sickle cell disease could affect your child, but this family history information can be important for keeping your child healthy.

Family history can help your child’s doctor make a diagnosis if your child shows signs of a disorder. It can reveal whether your child has an increased risk for a disease. If so, the doctor might suggest screening tests. Many genetic disorders first become obvious in childhood, and knowing about a history of a genetic condition can help find and treat the condition early.

Genetics Basics
Genetics research studies how individual genes or groups of genes are involved in health and disease. Understanding genetic factors and genetic disorders is important in learning more about preventing birth defects, developmental disabilities, and other unique conditions among children.

Some genetic changes have been associated with an increased risk of having a child with a birth defect or developmental disability. Genetics also can help us understand how birth defects and developmental disabilities happen.

Genetic Disorders:
Genetic disorders can happen for many reasons. Genetic disorders often are described in terms of the chromosome that contains the gene. If the gene is on one of the first 22 pairs of chromosomes, called the autosomes, the genetic disorder is called an autosomal condition. If the gene is on the X chromosome, the disorder is called X-linked.

Genetic disorders also are grouped by how they run in families. Disorders can be dominant or recessive, depending on how they cause conditions and how they run in families.
Dominant
Dominant diseases can be caused by only one copy of a gene with a DNA mutation. If one parent has the disease, each child has a 50% chance of inheriting the mutated gene.
Recessive
For recessive diseases, both copies of a gene must have a DNA mutation in order to get one of these diseases. If both parents have one copy of the mutated gene, each child has a 25% chance of having the disease, even though neither parent has it. In such cases, each parent is called a carrier of the disease. They can pass the disease on to their children, but do not have the disease themselves.

Single Gene Disorders:
Some genetic diseases are caused by a DNA mutation in one of a person’s genes. For example, suppose part of a gene usually has the sequence TAC. A mutation can change the sequence to TTC in some people. This change in sequence can change the way that the gene works, for example by changing the protein that is made. Mutations can be passed down to a child from his or her parents. Or, they can happen for the first time in the sperm or egg, so that the child will have the mutation but the parents will not. Single gene disorders can be autosomal or X-linked.

For example, sickle cell disease is an autosomal single gene disorder. It is caused by a mutation in a gene found on chromosome 11. Sickle cell disease causes anemia and other complications. Fragile X syndrome, on the other hand, is an X-linked single gene disorder. It is caused by a change in a gene on the X chromosome. It is the most common known cause of intellectual disability and developmental disability that can be inherited (passed from one generation to the next).

Chromosomal Abnormalities:
Different Number of Chromosomes
People usually have 23 pairs of chromosomes. But, sometimes a person is born with a different number. If a person has an extra chromosome it is called trisomy. If a person has a missing chromosome it is called monosomy.
For example, people with Down syndrome have an extra copy of chromosome 21. This extra copy changes the body’s and brain’s normal development and causes intellectual and physical problems for the person. Some disorders are caused by having a different number of sex chromosomes. For example, people with Turner syndrome usually have only one sex chromosome, an X. Women with Turner syndrome can have problems with growth and heart defects.
Changes in Chromosomes
Sometimes chromosomes are incomplete or shaped differently than usual. When a small part of a chromosome is missing, it is called a deletion. If it has moved to another chromosome, it is called a translocation. If it has been flipped over, it is called an inversion.
For example, people with Williams syndrome are missing a small part of chromosome 7. This deletion can result in intellectual disability and a distinctive facial appearance and personality.

Complex Conditions:
A complex disease is caused by both genes and environmental factors. Complex diseases also are called multifactorial. Many birth defects and developmental disabilities are complex conditions. For example, while some orofacial clefts are associated with single gene disorders, the majority most likely are caused by changes in several genes acting together with environmental exposures.

Genetic Counseling 
In genetic counseling, specially-trained professionals help people learn about genetic conditions, find out their chances of being affected by or having a child or other family member with a genetic condition, and make informed decisions about testing and treatment.

Reasons for Genetic Counseling:
There are many reasons that people go for genetic counseling, such as:
  • A family history of a genetic condition
  • To learn about genetic screening for diseases that are more common in certain ethnic groups (e.g., sickle cell disease in African Americans and Tay-Sachs disease in Ashkenazi Jews)
  • To discuss abnormal results from tests during pregnancy (such as a blood test, ultrasound, chorionic villus sampling (CVS), or amniocentesis)
  • To learn about the higher chance for certain types of genetic conditions (such as Down syndrome) in the baby if mother-to-be is 35 years of age or more, or is concerned at any age about her chances of having a child with a genetic condition
  • To learn about the effects of being exposed to x-rays, chemicals, illness, or prescribed or illicit drugs while pregnant
  • A woman has had several miscarriages or infant deaths
  • Trouble getting pregnant (infertility)
  • A genetic condition or birth defect occurred in a previous pregnancy
  • A child has birth defects, disabilities, or conditions found by newborn screening
  • To find out if there is a genetic cause for developmental delays or health problems
  • Steps to get ready for a healthy pregnancy and baby (such as screening for genetic conditions)
About Genetics Professionals:
Clinical geneticists and genetic counselors often work together as part of a health care team. They diagnose and care for people with genetic conditions and give information and support to people with genetic conditions and their families.
Clinical Geneticists
Clinical geneticists are medical doctors with special training in genetics. In addition to educating families about genetic conditions, they perform clinical exams and order lab tests to diagnose the causes of birth defects and other genetic conditions. They can explain how a genetic condition may affect a person and give advice about treatment options and recurrence risks for future pregnancies.

Genetic Counselors
Genetic counselors are professionals who have special training to help people and families cope with and understand genetic conditions. They are also trained to provide counseling and support for people and families with genetic conditions.

What Genetics Professionals Do:
Some of the things a genetic counselor or clinical geneticist might do during a clinical visit include:
  • Ask questions about medical, family, and pregnancy history
  • Talk about birth defects and genetic conditions
  • Explain chances of a genetic condition occurring or recurring within the family
  • Discuss how genetic conditions are passed down in the family
  • Talk about illnesses and chemicals that can cause birth defects
  • Recommend and order tests that can help diagnose a condition, and explain test results
  • Discuss treatment options for a genetic condition
  • Help people deal with feelings about how genetic conditions affect their families
  • Answer medical questions and address emotional concerns
  • Explore reproductive options
  • Refer people to other resources for help

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