Table 2 Summary of studies included in the meta-analysis.

From: Effects of the δ-aminolevulinic acid dehydratase polymorphism rs1800435 on blood lead levels: a new systematic review and meta-analysis

Author and year	Age	Exposed	Sex	ALAD 1 blood lead levels (µg/dl)		ALAD 2 blood lead levels (µg/dl)		HWE	Low latitude	City or region
Author and year	Age	Exposed	Sex	Mean ± SD	N	Mean ± SD	N	HWE	Low latitude	City or region
Wetmur 1991^{13 a}	Children	Yes	Both	19.5 ± 11.6	1136	27.1 ± 15.2	142	No	No	New York
	Adult	Yes	Male	38.4 ± 16.8	160	47 ± 18	42	No	No	German
Smith 1995¹⁵	Adult	No	Both^b	7.8 ± 3.6	592	7.7 ± 3.5	96	Yes	Unknown^c
Alexander 1998¹⁶	Adult	Yes	Male	23.1 ± 12.2	114	28.4 ± 11.7	20	Yes	No	Trail British Columbia
Fleming 1998¹⁷	Adult	Yes	Both^b	22.85 ± 7.48^a	303	25.18 ± 8.38^a	65	Yes	No	New Brunswick
Sakai 2000¹⁸	Adult	Yes	Male	21.9 ± 19.7	161	22.9 ± 21.7	31	Yes	No	Japan
	Adult	No	Male	3.7 ± 1.1	54	3.6 ± 1	8	Yes	No
	Adult	No	Female	2.4 ± 0.8	50	2.6 ± 1.6	13	Yes	No
Schwartz 2000¹⁹	Adult	Yes	Both	31.7 ± 14.9	716	34.2 ± 15.9	79	Yes	No	Korea
Hsieh 2000²⁰	Adult	No	Both	6.51 ± 5.03	630	7.83 ± 5.95	30	Yes	Yes	Taiwan
Shen 2001²¹	Children	No	Both	9.7 ± 0.14	211	11.7 ± 0.12	18	Yes	Yes	Shanghai
Duydu 2003²²	Adult	No	Male	10.55 ± 1.82^a	11	10.17 ± 1.47^a	9	Yes	No	Ankara
	Adult	Yes	Male	34.42 ± 11.03^a	50	34.94 ± 6.83^a	21	Yes	No
Kamel 2003²³	Adult	No	Both	3 ± 2.18^d	31	2.8 ± 1.3^d	7	Yes	No	New England
Kim 2004²⁴	Adult	Both	Male	23.9 ± 14	1106	25.6 ± 13.7	113	Yes	No	Korea
Pérez-Bravo 2004²⁵	Children	No	Both	13.5 ± 79.74^a	84	19.2 ± 28.5^a	9	Yes	Yes	Antofagasta
Wu 2004²⁶	Adult	Yes	Both	27.7 ± 17.1	17	29.7 ± 17.6	9	Yes	Yes	Taiwan
	Adult	No	Both	10.9 ± 4.3	25	8.4 ± 3.6	6	Yes	Yes
	Adult	No	Both	4.2 ± 1.2	24	4.5 ± 1.9	6	Yes	Yes
Montenegro 2006²⁷	Adult	No	Both	7.75 ± 6.51^a	114	7.01 ± 3.92^a	28	Yes	Yes	Bauru, State of Sao Paulo
Wananukul 2006²⁸	Adult	Yes	Both	38.54 ± 11.60	237	39.78 ± 5.80	8	No	Yes	Bangkok
	Adult	Yes	Both	33.36 ± 12.85	110	30.25 ± 17.40	3	No	Yes
Weuve 2006²⁹	Adult	No	Male	5.3 ± 2.9	766	4.8 ± 2.7	149	Yes	No	Greater Boston area
Chen 2008³⁰	Children	No	Both	5.52 ± 0.22	363	5.79 ± 0.24	80	Yes	No	Urumqi
	Children	No	Both	5.34 ± 0.22	430	5.4 ± 0.25	39	Yes	No
Miyaki 2009³¹	Adult	No	Both	3.18 ± 1.8	84	4.35 ± 2.4	17	Yes	No	Kanagawa prefecture
Scinicariello 2010³²	Adult	No	Both	2.88 ± 4.04^a	2017	2.81 ± 2.69^a	370	Yes	Unknown^e
	Adult	No	Both	3.58 ± 8.05^a	1621	3.43 ± 3.22^a	49	Yes	Unknown^e
	Adult	No	Both	3.36 ± 4.81^a	1609	3.14 ± 3.51^a	137	Yes	Unknown^e
Fang 2010³³	Adult	No	Both	2.43 ± 1.31	157	2.26 ± 1.13	25	Unknown^f	Unknown^g
	Adult	No	Both	1.77 ± 0.94	156	1.88 ± 0.89	32	Unknown^f	Unknown^g
Wan 2014³⁴	Adult	No	Both	10.57 ± 2.07	63	9.12 ± 2.28	6	Yes	Yes	Southwestern China
	Adult	Yes	Both	39.58 ± 8.70	83	30.67 ± 7.04	4	Yes	Yes
Yun 2015³⁵	Adult	No	Female	6.63 ± 2.90	181	14.50 ± 6.63	17	Yes	Yes	Guangzhou
Sobin 2015³⁶	Children	No	Male	2.7 ± 1.5	111	2.6 ± 1.6	10	Yes	No	El Paso
	Children	No	Female^h	2.4 ± 1	116	1.9 ± 0.6	14	Yes	No
Mani 2018³⁷	Adult	Yes	Both	53.97 ± 28.62	415	57.69 ± 29.1	146	Yes	Yes	Karnataka
	Adult	No	Both	3.25 ± 2.26	238	3.83 ± 2.65	79	Yes	Yes
Siha 2019³⁸	Adult	Yes	Male	33.09 ± 4.29	38	27.18 ± 3.97	12	Yes	Yes	Cairo
Alvarez-Ortega 2019³⁹	Children	No	Both	4 ± 31.11^a	168	4.8 ± 15.21^a	20	Yes	Yes	Bolivar, Magdalena and Cesar
Palir 2023⁵	Adult	No	Female	12.4 ± 6.41	659	11.2 ± 5.19	164	Yes	No	Trieste, Italy
Total number					15009		2098
Subgroup number	Adult	Yes			2142		352
	Adult	No			8991		1230
	Children	Yes			1136		142
	Children	No			1634		261

CI: confidence interval; HWE: Hardy–Weinberg equilibrium; SD: standard deviation.
^aSD was obtained from the SE of a mean by multiplying by the square root of the sample size: .
^bThe volunteers were predominantly male.
^cVolunteers were recruited at the 1991 International Brotherhood of Carpenters and Joiners convention in Atlantic City, New Jersey.
^dSDs were obtained from the 95% CIs. . The t statistic for a 95% confidence interval from a sample size of “n” was obtained by typing = tinv (1-0.95, n-1) into a cell in a Microsoft Excel spreadsheet.
^eThe participants in this study were from a representative sample across the U.S., which was conducted by the Third National Health and Nutrition Examination Survey (NHANES III), 1988–1994.
^fALAD2-2 homozygosity is rare. Although it was mentioned in the article that the ALAD genotype distribution was in accordance with the previously mentioned gene distribution patterns, no accurate data for ALAD2-2 homozygotes were provided; therefore, in the present study, we did not calculate whether this distribution was in accordance with HWE.
^gThe participants in this study were derived from the National Registry of U.S. Veterans. In the published version, geographical location information was not found. If the specific value was not provided, the sample size data were obtained by multiplying the total number of people by the percentage and then rounding the resulting product to the nearest integer.
^hOne sample of ALAD2-2 patients was not included in the study because of limited data.

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Table 2 Summary of studies included in the meta-analysis.

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