Genetic testing for Ebstein anomaly

In humans, mutations in the NKX2-5 gene provided the first evidence that genetic factors are etiologically crucial in non-syndromic congenital heart diseases (14). The most common phenotypes are secundum atrial septal defect and atrioventricular conduction disturbance, but cases of EA are also reported (15, 16).

MYH7 mutations are predominantly found in EA associated with left ventricular non-compaction cardiomyopathy (LVNC) (17); a convincing hypothesis regarding this association is that LVNC is the result of altered cell regulation during wall formation (18) and EA may be caused by an arrest in directional growth during this process (19, 20).

TPM1 encodes α-tropomyosin, which is involved in myocardial contraction, as well as in stabilization of non-muscle cytoskeletal actin filaments. Nijak et al. reported an LVNC-EA family with a TPM1 mutation, and established an association between EA and TPM1-related LVNC (21).

Pathogenic variants may include missense and nonsense mutations and small deletions.

The test is listed in the Orphanet database and is offered by 2 accredited medical genetic laboratories in the EU, and in the GTR database, offered by 11 accredited medical genetic laboratories in the US.

Guidelines for clinical use of the test are described in Genetics Home Reference (ghr.nlm.nih.gov)

A multi-gene next generation sequencing panel is used for the detection of nucleotide variations in coding exons and flanking introns of the above genes.

Potentially causative variants and regions with low coverage are Sanger-sequenced. Sanger sequencing is also used for family segregation studies.

To perform molecular diagnosis, a single sample of biological material is normally sufficient. This may be 1 ml peripheral blood in a sterile tube with 0.5 ml K₃EDTA or 1 ml saliva in a sterile tube with 0.5 ml ethanol 95%. Sampling rarely has to be repeated.

Gene-disease associations and the interpretation of genetic variants are rapidly developing fields. It is therefore possible that the genes mentioned in this note may change as new scientific data is acquired. It is also possible that genetic variants today defined as of “unknown or uncertain significance” may acquire clinical importance.

Identification of pathogenic variants in the above genes confirms the clinical diagnosis and is an indication for family studies.

A pathogenic variant is known to be causative for a given genetic disorder based on previous reports, or predicted to be causative based on loss of protein function or expected significant damage to proteins or protein/protein interactions. In this way it is possible to obtain a molecular diagnosis in new/other subjects, establish the risk of recurrence in family members and plan preventive and/or therapeutic measures.

Detection of a variant of unknown or uncertain significance (VUS): a new variation without any evident pathogenic significance or a known variation with insufficient evidence (or with conflicting evidence) to indicate it is likely benign or likely pathogenic for a given genetic disorder. In these cases, it is advisable to extend testing to the patient’s relatives to assess variant segregation and clarify its contribution. In some cases, it could be necessary to perform further examinations/tests or to do a clinical reassessment of pathological signs.

The absence of variations in the genomic regions investigated does not exclude a clinical diagnosis but suggests the possibility of:

Unexpected results may emerge from the test, for example information regarding consanguinity, absence of family correlation or other genetically-based diseases.