Table 2.

Numbers, Correlations, and Results in Quantitative Genetic Modeling for ADHD and ED (AN, OEDs, and BN)

		Number of Individuals or Pairs				Correlation			Results of Quantitative Genetic Modeling
		Within Disorder		ED and ADHD		Within Disorder	ED and ADHD		Proportion of Variance Within Disorder Explained (95% CI)		Proportion of Covariance With ADHD Explained (95% CI)		Correlations With ADHD (95% CI)
		Concordant Pairsa (Both Affected/Both Unaffected)	Discordant Pairsb	With Both Disorders	Concordant Pairsc	Within-Trait Cross-Sister Correlation (95% CI)	Phenotypic Correlation With ADHD (95% CI)	Cross-Trait Cross-Sister Correlation With ADHD (95% CI)	Additive Genetic (A)	Unique Environmental (E)	Additive Genetic (A)	Unique Environmental (E)	Additive Genetic (A)	Unique Environmental (E)
ADHD	Full-sister	787/322,529	11,117	–	–	.41 (.39, .42)	–	–	.82 (.78, .85)	.18 (.15, .22)	–	–	–	–
	Maternal half-sister	292/52,031	4713	–	–	.22 (.19, .25)	–	–
AN	Full-sister	107/328,436	5890	343	150	.21 (.18, .25)	.19 (.17, .21)	.04 (.04, .04)	.42 (.35, .49)	.58 (.52, .65)	.42 (.16, .69)	.58 (.31, .84)	.14 (.05, .22)	.33 (.18, .48)
	Maternal half-sister	5/56,103	928	99	44	.03 (−.10, .15)	.17 (.13, .21)	.004 (−.05, .06)
OEDs	Full-sister	250/324,912	9271	853	331	.23 (.20, .25)	.31 (.30, .33)	.11 (.09, .13)	.44 (.39, .49)	.56 (.51, .61)	.73 (.60, .85)	.27 (.15, .40)	.37 (.31, .42)	.26 (.14, .38)
	Maternal half-sister	19/55,133	1884	286	107	.02 (−.05, .10)	.28 (.25, .31)	.04 (.01, .08)
BN	Full-sister	34/331,325	3074	273	87	.20 (.16, .24)	.28 (.26, .30)	.07 (.07, .07)	.40 (.35, .51)	.60 (.50, .70)	.58 (.35, .81)	.42 (.19, .65)	.28 (.20, .39)	.33 (.15, .53)
	Maternal half-sister	4/56,461	571	79	37	.13 (−.02, .27)	.23 (.19, .28)	.07 (.01, .13)

Correlations were tetrachoric correlations (presented with 95% CI). Within-trait cross-sister correlations were the tetrachoric correlations of a disorder between two sisters in a pair. Phenotypic correlations with ADHD were the tetrachoric correlations between ADHD and ED within an individual. Cross-sister cross-trait correlations with ADHD were the tetrachoric correlations between ADHD in one sister and ED in the other sister in a pair. Results are from three bivariate AE models for ADHD–AN, ADHD–OEDs, and ADHD–BN. Results are presented as point estimates (95% CI). ADHD heritability was estimated in each combination of ADHD and ED, and the estimates were similar. The presented heritability and variance explained by unique environmental variance were extracted from the bivariate AE model of ADHD–OED, which was the best powered model compared with the other two models. The heritability of ADHD was estimated to be approximately 82%, and the heritabilities of the EDs were estimated to be approximately 40% to 45%. Approximately 42% of the phenotypic covariance between ADHD and AN was explained by their genetic covariance, whereas approximately 73% of the phenotypic covariance between ADHD and OEDs was explained by their genetic covariance, and the proportion for ADHD and BN was estimated to be approximately 58%. The remaining proportion of the phenotypic covariance between ADHD and each ED was explained by their unique environmental covariance. The genetic correlation between ADHD and AN was estimated to be approximately .14 (.05, .22), whereas higher genetic correlation with ADHD was found in OEDs (.37 [.31, .42]) and potentially also in BN (.28 [.20, .39]).

ADHD, attention-deficit/hyperactivity disorder; AN, anorexia nervosa; BN, bulimia nervosa; CI, confidence interval; ED, eating disorder; OEDs, other eating disorders (i.e., non-AN eating disorders).

^aThe number of pairs with both sisters affected vs. (/) the number of pairs with both sisters unaffected.

^bThe number of pairs where one sister was affected with the disorder and the other was unaffected.

^cThe number of pairs where one sister was affected with ADHD and the other affected with ED.