Recommendations for investigation of the family: cause not identified—clinical and genetic investigations
COR	LOE	Recommendations	References
1	B‐NR	1. Family screening should be advised in first‐degree relatives of SUD subjects with a negative autopsy (or with no autopsy) when the decedent's age is <45 years (and in all patients with a clear phenotype regardless of age).	80, 81, 143, 144, 334
1	B‐NR	2. Family screening should include genetic testing and clinical evaluation when genetic testing of a proband with SUD detects a pathogenic or likely pathogenic variant.	70, 80, 81, 84, 143, 144, 189, 334
2a	B‐NR	3. It is reasonable to take a medical history and perform physical examination, standard and high precordial lead ECG, echocardiography, and exercise testing in first‐degree relatives of SUD subjects.	80, 81, 143, 144, 334
2b	C‐LD	4. Depending on the results of other investigations (ECGs, echocardiography, and exercise testing), it may be reasonable to perform ambulatory cardiac rhythm monitoring and CMR in first‐degree relatives of SUD subjects.	70, 81, 143, 189, 360
2a	B‐NR	5. It is reasonable to screen select postpubertal family members of SUD subjects with pharmacological testing including sodium channel blocker when baseline testing or proband findings increase suspicion of the target diagnosis.	143, 189, 205, 275, 288, 334
2b	B‐NR	6. It may be reasonable to screen first‐degree relatives of SUD subjects with pharmacological testing including epinephrine challenge (if exercise testing is impractical) and sodium channel blockade.	189, 205, 275, 288, 334