Preconception Care: Genetic Screening

The goal of preconception care is to optimize our patients' health and knowledge prior to pregnancy. Preconception care includes screening and education aimed at reducing risks for both mom and baby. One of the most important parts of preconception care is screening for genetic risks.

Some diseases are caused by an interaction of biology and environment; other diseases are inherited through genetic mutation (a change in a single gene).

Many single-gene diseases are more common in certain populations. The risk of carrying/inheriting a single-gene disease depends on your ethnicity, your family history, and the way the disease is genetically transmitted (autosomal vs. sex-linked, recessive vs. dominant, complete vs. variable penetrance). Your doctor will discuss these factors when he/she recommends preconception genetic testing.

Some examples…

Cystic Fibrosis (CF)

CF is the most common life-threatening autosomal recessive condition in the non-Hispanic white population (carrier rate: 1/25). It is a progressive disease that primarily affects the lungs and gastrointestinal systems but does not affect intelligence.

CF is an autosomal recessive disease, which means that an individual must have two copies of the disease mutation in order to have the disease. Usually, this means that both parents carry and pass along the mutation to their child. A carrier (individual with only one copy of the disease mutation) is often unaware that they are a carrier and may have no family history of the disease. Screening can begin with one partner, and the other partner is only screened if the first partner screens positive (sequential screening) or both partners can be screened at the same time (parallel screening.)

Spinal Muscular Atrophy (Sma)

SMA is also an autosomal recessive disease, so an individual must carry two copies of the disease mutation in order to be affected. SMA is a progressive neurodegenerative disease that leads to atrophy of skeletal muscle and overall weakness. The incidence of SMA is approximately 1 in 10,000 live births and it is reported to be the leading genetic cause of infant death. Carrier frequencies are estimated at 1 in 40 to 1 in 60.

The symptom profile of affected children is quite variable; the most severe forms can lead to respiratory failure by 2 years of life. Other individuals with SMA can live until their 3rd decade.

Fragile X

Fragile X syndrome is the most common inherited form of mental retardation. It is an X-linked disorder that affects males more than females (1 in 3,600 males and 1 in 4,000–6,000 females). However, 1 in 250 females carries the premutation which can cause early menopause and associated fertility problems, as well as issues with balance (ataxia) later in life.

Prenatal testing for fragile X syndrome should be offered to known carriers (or family members of carriers) of the fragile X premutation or full mutation. Other women who should consider testing include women with premature ovarian aging/insufficiency or a family history of unexplained mental retardation, developmental delay, or autism.

Hemoglobinopathy

Hemoglobin is the portion of the red blood cell that carries oxygen to the body. Mutations in hemoglobin affect red blood cell structure and function and can result in anemia and multi-organ disease.

• Sickle Cell Disease: This is an autosomal recessive disorder involving hemoglobin S. Under conditions of low oxygen, these patients' red blood cells change shape (into “sickles”) and can block small blood vessels, causing damage to major organs.
• Thalassemia: These disorders (alpha and beta) result in reduced production of globin, resulting in anemia (less ability to transport oxygen). The severity of the disorder depends on the number and type of mutations.
  • Alpha thalassemia is more common in individuals of African, Southeast Asian, West Indian, and Mediterranean descent.
  • Beta thalassemia is more common in individuals of Asian, Middle Eastern, Hispanic, West Indian, and Mediterranean descent.

The HEMOGLOBINOPATHIES can often be combined (i.e. Sickle-Beta Thalassemia) to produce different, related diseases, so a full panel may be recommended, regardless of exact ethnicity.

Ashkenazi Jewish Panel

Certain autosomal recessive diseases are more common in individuals of Eastern European (Ashkenazi) Jewish descent. Because these individuals often marry other individuals of Ashkenazi descent, their children are more likely to be affected by recessive diseases (because both parents are carriers).

Currently, screening is recommended for Cystic Fibrosis, Tay Sachs Disease, Familial Dysautonomia, Canavan disease, familial hyperinsulinism, glycogen storage disease type 1, Joubert syndrome, maple syrup urine disease, and Usher syndrome types 1F and III. Additional carrier screening is available (including mucolipidosis IV, Gaucher, Bloom Syndrome, Niemann Pick, Fanconi anemia group C) and testing panels should be further tailored based on individual and family history.

Who Should Be Screened?

Ethnicity and family history provides a good framework for guiding testing. Some couples (or doctors) may decide to broaden their screening as family histories can be incomplete and complex.

Testing is ideally performed and completed before conception, to allow full counseling regarding risks and treatment.

What Can Be Done if a Couple Is at High Risk?

For many genetic disorders, preimplantation testing is available to test embryos prior to implantation/pregnancy. Testing is also available for the fetus during pregnancy.

Some couples prefer to just have their risk information in order to prepare. There are many options available.

For more information on genetic screening, or to schedule a New Patient Appointment please contact ACRM by calling 678.841.1089, or click here.