When should couples consider genetic carrier screening if they are from the same family?

When two people who are related by blood (called consanguineous couples) plan to have children together, they face a higher chance of both carrying the same altered gene. If both partners carry a change in the same gene, each pregnancy has a chance of the child inheriting both copies and developing an autosomal recessive condition. Genetic carrier screening can help identify these shared risks before pregnancy, allowing couples to make informed decisions about their reproductive options.

Why consanguinity increases genetic risk

Everyone carries a small number of gene changes that could cause disease if paired with the same change from the other parent. Most of the time, these changes cause no problems because the person has one working copy of the gene from their other parent.

When two people are related, they share more of their DNA than unrelated couples. This means they are more likely to carry the same gene changes inherited from a common ancestor. If both partners carry a change in the same gene, each pregnancy has a 1 in 4 (25%) chance of the child inheriting both altered copies and developing the condition.

The closer the family relationship, the higher the shared DNA:

• First cousins share about 12.5% of their DNA
• Second cousins share about 3% of their DNA
• More distant relatives share progressively less

Even relatively distant family relationships can increase the chance of sharing rare gene changes, particularly for conditions that are more common in specific populations or ethnic groups.

What conditions can carrier screening detect?

Carrier screening typically looks for autosomal recessive conditions – diseases that only develop when someone inherits two copies of an altered gene (one from each parent). These panels can screen for hundreds of genes at once.

Examples of autosomal recessive conditions that carrier screening can detect include:

• Cystic fibrosis – affects the lungs and digestive system
• Sickle cell disease – affects red blood cells and oxygen delivery
• Thalassaemia – affects the production of haemoglobin in red blood cells; alpha-thalassemia can range from mild anaemia to severe forms requiring intensive treatment
• Spinal muscular atrophy – affects muscle strength and movement
• Smith-Lemli-Opitz syndrome – affects cholesterol metabolism and can cause developmental delays, distinctive facial features, and multiple organ abnormalities

Modern expanded carrier screening panels can test for many hundreds of conditions simultaneously. One study examining expanded carrier screening across over 3,000 patients found that the technology can identify carrier status for a wide range of genetic conditions, though the clinical implications vary.

When to consider carrier screening

Carrier screening is worth considering for consanguineous couples before or early in pregnancy. Testing before conception gives you the most time to understand your results and explore your options.

You might particularly want to discuss screening with your GP or a genetic counsellor if:

• You and your partner are related by blood, even if the relationship is distant (second cousins or closer is generally considered higher risk, but more distant relationships can still increase risk for some conditions)
• There is a known genetic condition in your shared family – screening can confirm whether either or both of you carry the relevant gene change
• You come from a population where certain conditions are more common – some genetic conditions are found more frequently in specific ethnic or geographic groups
• You are planning a pregnancy or are in early pregnancy – earlier testing gives you more time to consider your options

You do not need to have a family history of genetic disease to benefit from screening. Many people carry gene changes without knowing it, because no one in recent generations has been affected.

What the screening involves

Carrier screening is typically done using a blood sample or a cheek swab (buccal swab). The sample is sent to a laboratory that analyses your DNA for changes in multiple genes at once.

The process generally includes:

1. Pre-test genetic counselling – a specialist explains what the test covers, what the results might mean, and helps you decide whether testing is right for you
2. Sample collection – blood draw or cheek swab (the method depends on the specific test)
3. Laboratory analysis – the lab examines your DNA for known gene changes
4. Results and post-test counselling – a genetic counsellor explains your results and what they mean for your family

Results usually take a few weeks from when the laboratory receives your sample. Turnaround times vary depending on the type of test and the laboratory.

Understanding your results

Carrier screening results fall into a few categories:

• Negative (not a carrier) – you do not carry a detectable change in the genes tested. This reduces but does not eliminate the risk, as no test detects every possible gene change.
• Carrier (positive) – you carry one copy of a gene change. Carriers are typically healthy but can pass the change to their children.
• Uncertain – a variant of uncertain significance (VUS) means a gene change was found but it is not yet known whether it causes disease. Most VUS are eventually reclassified as benign (harmless).

If both partners are found to be carriers for the same condition, a genetic counsellor will explain:

• The 25% (1 in 4) chance with each pregnancy that the child will inherit both copies and be affected
• What the condition involves and how it affects quality of life
• Your reproductive options, which might include IVF with preimplantation genetic testing, prenatal diagnosis, egg or sperm donation, or accepting the risk

Genetic counselling is an essential part of the screening process. The counsellor helps you interpret your results in the context of your family history and supports you in making decisions that are right for your family.

Limits of carrier screening

Carrier screening is a powerful tool, but it has limitations:

• Not every gene change is detectable – the test looks for known changes in specific genes. New or very rare changes may not be identified.
• Not every condition is included – even large panels do not screen for every genetic condition. The conditions included are chosen based on severity, treatability, and how well they can be detected.
• Results can be uncertain – variants of uncertain significance can leave you without a clear answer, and interpretation of genetic changes continues to evolve as scientists learn more.
• Does not detect all types of genetic risk – carrier screening focuses on autosomal recessive conditions. It does not typically detect chromosomal abnormalities, dominant conditions (which only need one altered copy to cause disease), or complex multifactorial conditions.

No screening test can guarantee a healthy baby, but carrier screening can give you important information about specific genetic risks.

What you can do at Jeen

At Jeen, we offer comprehensive carrier screening options for couples planning a pregnancy, including those who are related by blood.

Our Carrier Screening service screens 1,008 genes for inherited recessive disease. The test includes 30-minute genetic counselling with a specialist to help you understand your results and their implications. Sample collection uses an at-home buccal swab (cheek swab), which is included in the price, or you can arrange an in-clinic blood draw for an additional £40. Results are available within 17-21 working days of the laboratory receiving your sample, and variant interpretation is aligned with NHS Genomic Medicine Service standards.

For couples who want the most comprehensive pre-conception genetic assessment, our Carrier Screening + Karyotype bundle combines our 1,008-gene carrier panel with chromosome-level karyotype analysis in a single integrated report. This option includes one genetic counselling session covering both tests and requires one blood draw. The bundle saves £80 for individuals or £130 for couples compared with ordering the tests separately.

If you prefer whole-exome sequencing for the most extensive carrier screening available, our CGT - Igenomix Carrier Genetic Test analyses 1,993 genes (male) or 2,057 genes (female), covering over 2,200 inherited recessive conditions. The test includes 30-minute pre-test genetic counselling, with results reviewed by your genetic counsellor. Blood collection is not included: you can arrange a blood draw at any of our 200+ partner collection points for an additional £40, or book a home-nurse visit for £65. Results are available within 25 working days of the laboratory receiving your sample.

All our carrier screening services include specialist genetic counselling to help you understand what the test covers, interpret your results, and discuss your options. The NHS offers carrier screening for specific conditions in certain circumstances, but typically screens for a smaller set of conditions compared with expanded carrier screening panels.