TABLE 1

Summary of previous studies on familial aggregation and heritability of sarcoidosis. Only familial aggregation studies with a control group were considered for this table

First author, year of publication [ref.]	Country	Probands n		Relatives n	Mean age at inclusion years		Sarcoidosis ascertainment		Estimates of familial aggregation/heritability
First author, year of publication [ref.]	Country	Cases	Controls	Relatives n	Cases	Relatives	Probands	Relatives	Estimates of familial aggregation/heritability
Headings, 1976 [11]	USA	80	Prevalence estimate	523 parents and full siblings	34	Not reported	Biopsy proven	Reported by probands	7.2% of proband cases with ≥1 FDR with sarcoidosis Heritability: 60–70%
McGrath, 2000 [17]	UK	406	Prevalence estimate	Not reported	40	Not reported	Biopsy and non-biopsy proven	Reported by proband, confirmed by family doctor	5.9% of proband cases with ≥1 family member with sarcoidosis Relative risk in siblings: 36–73
Rybicki, 2001 [15]	USA	706	706	10 862 FDRs 17 047 SDRs	42 (median)	Not reported	Biopsy proven	Reported by proband	Odds ratio in FDRs: 3.8 (1.9–7.6) Odds ratio in SDRs: 5.2 (1.5–18.2)
Rybicki, 2001 [16]	USA	179	Prevalence estimate and simulation	488 parents and full siblings	43	66 in parents, 45 in siblings	Biopsy and non-biopsy proven	Reported by relative	Relative risk in FDRs: 2.5 (1.6–3.7)
Sverrild, 2008 [21]	Denmark and Finland	210	NA	210 twin pairs (50 MZ, 160 DZ)	Not reported	NA	Register-based	NA	Concordance rates: 0.148 in MZ twins, 0.012 in DZ twins Heritability: 66% (45–80%)

FDR: first-degree relative; SDR: second-degree relative; MZ: monozygotic; DZ: dizygotic; NA: not applicable.