Familial aggregation of myasthenia gravis in affected families: a population-based study

Figures & data

Figure 1 Age-specific prevalence of myasthenia gravis in individuals with a first-degree (circle) relative affected with MG and in the general population (hollow circle) in Taiwan in 2013.

Note: This figure demonstrates a significantly higher prevalence of MG in most age bands among those with a family history than the general population.
Abbreviation: MG, myasthenia gravis.

Figure 2 Comparison of the onset age of MG in affected patients with (circle) and without (hollow circle) a family history in 2013.

Abbreviation: MG, myasthenia gravis.

Table 1 Baseline characteristics of individuals with affected first-degree relatives with myasthenia gravis and the general population

Variables	Women			Men
	With affected FDR	General population	P-value	With affected FDR	General population	P-value
N	7,405	11,903,542		7,661	11,519,413
Age, mean (SD) (years)	36.2 (18.5)	39.5 (20.9)	<0.0001	36.4 (18.6)	38.6 (21.0)	<0.0001
MG, N (%)	20 (0.28)	4,100 (0.03)		11 (0.17)	2,507 (0.02)
Place of residence, N (%)
Urban	2,678 (36.2)	3,694,254 (31.0)	<0.0001	2,582 (33.7)	3,298,256 (28.6)	<0.0001
Suburban	2,187 (29.5)	3,434,164 (28.9)		2,238 (29.2)	3,269,766 (28.4)
Rural	2,540 (34.3)	4,775,054 (40.1)		2,841 (37.1)	4,951,325 (43.0)
Income levels, N (%)
Quintile 1	1,275 (17.2)	2,526,384 (21.2)	<0.0001	1,397 (18.2)	2,426,365 (21.2)	<0.0001
Quintile 2	831 (11.2)	1,318,491 (11.1)		707 (9.2)	1,174,855 (10.2)
Quintile 3	1,789 (24.2)	3,360,952 (28.2)		2,026 (26.5)	3,303,888 (28.7)
Quintile 4	1,716 (23.2)	2,289,602 (19.2)		1,619 (21.1)	2,104,521 (21.1)
Quintile 5	1,791 (24.2)	2,398,414 (20.2)		1,910 (24.9)	2,502,208 (24.9)
Occupation, N (%)
Dependents of the insured individuals	2,714 (36.7)	4,471,275 (37.6)	<0.0001	2,343 (30.6)	3,704,412 (32.2)	<0.0001
Civil servants, teachers, military personnel, and veterans	312 (4.2)	442,845 (3.7)		333 (4.4)	570,766 (5.0)
Nonmanual workers and professionals	2,573 (34.8)	3,398,109 (28.6)		2,946 (38.5)	3,708,631 (32.2)
Manual workers	1,266 (17.1)	2,631,992 (22.1)		1,290 (16.8)	2,304,125 (20.0)
Others	540 (7.3)	959,321 (8.1)		749 (9.8)	1,231,479 (10.7)

Abbreviations: FDR, first-degree relative; MG, myasthenia gravis.

Table 2 Relative risks for myasthenia gravis in first-degree relatives

Type of affected relative	Sex of affected relative	Sex of individual	Number of cases	Prevalence (%)	Relative risks (95% confidence intervals)a
Any	Male	Male	6	0.20	9.46 (3.37–26.55)
		Female	6	0.21	6.23 (2.81–13.81)
		All	12	0.20	7.50 (3.93–14.33)
	Female	Male	5	0.11	5.21 (2.19–12.39)
		Female	14	0.31	9.84 (4.70–20.57)
		All	19	0.21	8.01 (4.46–14.41)
	All	Male	11	0.14	6.88 (3.46–13.68)
		Female	20	0.27	8.39 (4.75–14.80)
		All	31	0.21	7.78 (4.80–12.60)
Parent	Male (father)	Male	2	0.11	7.26 (1.82–28.90)
		Female	2	0.12	4.68 (1.17–18.68)
		All	4	0.11	5.62 (2.11–14.96)
	Female (mother)	Male	1	0.04	2.42 (0.34–17.17)
		Female	4	0.17	6.98 (2.62–18.56)
		All	5	0.10	5.07 (2.12–12.13)
	All	Male	3	0.07	4.35 (1.41–13.48)
		Female	6	0.15	6.00 (2.70–13.32)
		All	9	0.10	5.33 (2.79–10.18)
Offspring	Male (son)	Male	2	0.35	8.12 (2.04–32.36)
		Female	1	0.14	2.73 (0.39–19.32)
		All	3	0.24	4.89 (1.59–15.05)
	Female (daughter)	Male	2	0.22	5.20 (1.33–20.38)
		Female	4	0.36	7.17 (2.69–19.11)
		All	6	0.30	6.40 (2.88–14.24)
	All	Male	4	0.27	6.30 (2.36–16.78)
		Female	5	0.28	5.42 (2.25–13.03)
		All	9	0.27	5.82 (3.03–11.16)
Sibling	Male (brother)	Male	2	0.35	18.15 (4.54–72.54)
		Female	3	0.55	17.92 (5.85–54.87)
		All	5	0.45	18.06 (7.57–43.11)
	Female (sister)	Male	2	0.19	12.40 (3.15–48.85)
		Female	6	0.60	20.78 (6.75–63.95)
		All	8	0.39	17.84 (7.22–44.11)
	All	Male	4	0.25	14.67 (5.53–38.93)
		Female	9	0.58	19.74 (8.56–45.52)
		All	13	0.41	17.85 (8.71–36.56)
Twin	Male (brother)	Male	N/A	N/A	N/A
		Female	N/A	N/A	N/A
		All	N/A	N/A	N/A
	Female (sister)	Male	N/A	N/A	N/A
		Female	N/A	N/A	N/A
		All	N/A	N/A	N/A
	All	Male	N/A	N/A	N/A
		Female	N/A	N/A	N/A
		All	N/A	N/A	N/A
Spouse	Female	Male	1	0.06	1.47 (0.21–10.41)
	Male	Female	1	0.07	1.36 (0.19–9.62)
	All	All	2	0.06	1.42 (0.20–10.10)

Notes:

a Adjusted for age, sex, place of residence, quintiles of income levels, occupation, and family size. N/A because of no MG cases with affected twin.

Abbreviations: MG, myasthenia gravis; N/A, not applicable.

Table 3 Relative risks of other autoimmune diseases in individuals with affected first-degree relatives affected with myasthenia gravis

Autoimmune rheumatic diseases	Sex	With affected relatives		General population		Relative risk (95% confidence interval)a
		Number of cases	Prevalence (%)	Number of cases	Prevalence (%)
With affected first-degree relatives with myasthenia gravis
Rheumatoid arthritis	All	38	0.25	44,449	0.19	1.68 (1.22–2.30)
Sjögren’s syndrome	All	18	0.12	20,477	0.09	1.73 (1.09–2.74)
Systemic lupus erythematosus	All	30	0.20	21,579	0.09	2.18 (1.53–3.12)
Autoimmune thyroid disease	All	233	1.64	219,205	0.90	1.90 (1.66–2.18)

Note:

a Adjusted for age, sex, place of residence, quintiles of income levels, occupation, and family size.

Table 4 Epidemiological studies of MG in different countries

Region	Year	Cases	Population	Incidence per million/year	Prevalence per million	First author
Hong Kong	1987	262	5,610,000	4	53.5	Yu^Citation37
Western Denmark	1990	290	2,800,000	5	78	Christensen^Citation32
Italy	1994	86	2,925,000	14.7	NA	Tola^Citation33
United Kingdom	1997	100	685,000	11	150	Robertson^Citation34
Greece	1992–1997	843	10,475,878	7.4	70.63	Poulas^Citation35
Sweden	1932–2002	2,045	11,634,543	NA	248	Fang^Citation36
Italy	2008	119	493,753	NA	240	Montomoli^Citation40
Denmark	1996–2009	693	5,511,000	9.2	NA	Pedersen^Citation38
Norway	2008–2009	534	4,858,199	NA	138	Boldingh^Citation31
Netherlands	2011–2012	671	4,929,344	NA	167	Boldingh^Citation31
Korea	2010–2014	10,138	47,990,000	6.9	129.9	Lee^Citation39
Taiwan	1995–2013	6,638	23,422,955	NA	280	Liu (present study)

Abbreviations: MG, myasthenia gravis; NA, not available.

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