What defines a genotype‑positive relative, is a karyotype required for their evaluation, and which provider orders and interprets the genetic testing?

What is a Genotype-Positive Relative?

A genotype-positive relative is a family member who has inherited the same pathogenic or likely pathogenic genetic variant identified in an affected proband (index case), but may or may not yet show clinical signs of the disease. This designation is most commonly used in the context of inherited cardiovascular diseases like hypertrophic cardiomyopathy (HCM), where genetic testing follows a cascade approach 1.

Definition and Clinical Context

A genotype-positive relative specifically refers to someone who:

• Carries the same disease-causing genetic variant (pathogenic or likely pathogenic) that was identified in an affected family member 1
• May be phenotype-negative (no clinical disease manifestations yet) or phenotype-positive (already showing signs of disease) 1
• Requires ongoing clinical surveillance if phenotype-negative, as they remain at risk for developing the disease over time 1

The term is distinct from simply having a "positive family history"—it requires actual genetic confirmation through cascade testing 1.

Does This Require a Karyotype?

No, identifying a genotype-positive relative does not require a karyotype. This is a common point of confusion:

What Testing Is Actually Used

• Targeted genetic testing (cascade testing) is performed, which looks specifically for the known pathogenic variant already identified in the proband 1
• This typically involves DNA sequencing of specific genes (such as sarcomere genes in HCM: MYH7, MYBPC3, TNNI3, TNNT2, TPM1, MYL2, MYL3, ACTC1) 1
• Gene panels may be used initially in the proband to identify the disease-causing variant 1

Why Not a Karyotype

• A karyotype analyzes chromosome number and structure (looking at all 46 chromosomes under a microscope), which is used for chromosomal abnormalities like Down syndrome or Turner syndrome 2
• Most inherited cardiovascular diseases involve single-gene mutations (point mutations, small insertions/deletions) that are not visible on a karyotype 1
• The testing required is molecular genetic testing (DNA sequencing), not cytogenetic testing (karyotype) 1, 2

Who Orders and Performs This Testing?

The Cascade Testing Process

The process begins with genetic testing of the affected proband (index case), not the at-risk relatives 1. The workflow is:

1. Initial testing in the proband is ordered by the treating cardiologist or specialist managing the affected patient 1
2. Once a pathogenic/likely pathogenic variant is identified, cascade testing can be offered to first-degree relatives 1
3. Genetic counseling is mandatory both before and after testing, performed by a cardiovascular genetics expert or trained genetic counselor 1

Who Orders the Testing

• Cardiologists or cardiovascular specialists typically initiate the process for cardiovascular conditions like HCM 1
• Genetic counselors often coordinate cascade testing for at-risk relatives 1
• Testing should ideally occur within a specialized multidisciplinary center with experience in genetic cardiovascular diseases 1

Who Interprets the Results

• Genetic testing laboratories perform the variant classification using standardized ACMG/AMP criteria (pathogenic, likely pathogenic, uncertain significance, likely benign, benign) 1
• Cardiovascular genetics experts interpret results in clinical context and guide management 1
• Genetic counselors communicate results and implications to patients and families 1

Critical Management Points

For Genotype-Positive, Phenotype-Negative Relatives

• Serial clinical surveillance is required with ECG and echocardiography every 1-2 years in children/adolescents and every 3-5 years in adults 1
• These individuals remain at risk for developing clinical disease over time 1

For Genotype-Negative Relatives

• No further clinical follow-up is required once confirmed negative for the familial variant 1
• They and their descendants can be released from lifelong surveillance 1
• Important caveat: If the variant is later downgraded to uncertain significance or benign, these relatives must be notified and clinical screening recommenced 1

When Cascade Testing Should NOT Be Done

• If no pathogenic variant was identified in the proband (only benign/likely benign variants), cascade testing of family members is not useful 1
• If only a variant of uncertain significance (VUS) was found in the proband, this is not clinically actionable and family testing is generally not recommended 1

Common Pitfalls to Avoid

• Do not test relatives before testing the proband—genetic testing in a phenotype-negative relative without a known diagnosis in the proband has very low yield 1
• Do not use broad gene panels for cascade testing—once the familial variant is known, only targeted testing for that specific variant is needed 1
• Ensure proper genetic counseling occurs—testing without counseling can lead to misunderstanding of results and psychological harm 1
• Remember that variant classifications can change over time—periodic reevaluation is necessary, and families must be recontacted if classifications are downgraded 1