Keratinous biomarker of mercury exposure associated with amyotrophic lateral sclerosis risk in a nationwide U.S. study

Figures & data

Table 1 Population characteristics.

	Controls	ALS patients	univariate
	n = 210	n = 70	p Value
Age (mean (range))	54.0 (35–66)	55.5 (30–66)	0.08
Smoking	n (%)	n (%)
Never	129 (61.4)	34 (48.6)	0.13
Current	13 (6.2)	4 (5.7)
Past	68 (32.4)	32 (45.7)
Smoked <5 years	147 (70.0)	42 (60.0)	0.16
5+ years	63 (30.0)	28 (40.0)
Education			0.085
High school or less	32 (15.2)	12 (17.1)
Technical or some college	72 (34.3)	13 (18.6)
College degree	51 (24.3)	24 (34.3)
Graduate school	55 (26.2)	21 (30.0)
Race/ethnicity			1
White, non-Hispanic	203 (96.7)	68 (97.1)
Other	7 (3.3)	2 (2.9)

Figure 1 Spline plot showing the non-linear relationship between nail mercury levels and ALS risk. (A) Log odds of ALS plotted by nail mercury (log10(µg/g) adjusted for age and smoking. (B) Odds ratios for ALS risk associated by nail mercury (log10(µg/g).

Table 2 Logistic regression odds ratios for ALS risk by nail Hg level calculated from spline model.

		Multivariable^a
Percentile	Hg (µg/g)	Odds Ratio	(95%CI)
25th vs. 5th	0.041 vs. 0.016	0.53	(0.37–0.76)
75th vs. 25th	0.21 vs. 0.041	0.8	(0.55–1.15)
90th vs. 75th	0.38 vs. 0.21	1.54	(1.07–2.22)

^a Adjusted for age, smoking status.

Table 3 ALS risk associated with categorized nail Hg levels.

		Controls	ALS patients	Univariate		Multivariable^a
Nail mercury level	µg/g	n = 210 (%)	n = 70 (%)	Odds ratio	(95%CI)	Odds ratio	(95%CI)	p Value
<25th percentile	<0.042	41 (19.5)	30 (42.9)	1.0 (ref)		1.0 (ref)
25th–90th percentile	0.042–0.38	154 (73.3)	27 (38.6)	0.24	(0.13–0.45)	0.21	(0.11–0.41)	4.18E–06
<90th percentile	<0.38	195 (92.9)	57 (81.4)	1.0 (ref)		1.0 (ref)
≥90th percentile	≥0.38	15 (7.1)	13 (18.6)	2.96	(1.32–6.61)	2.64	(1.12–6.18)	0.024

^a Adjusted for age, smoking status.

Table 4 Factors associated with high nail Hg levels in controls.

	Toenail Hg by 90th percentile			Multivariable^a
	<90th	≥90th	Univariate
Analysis restricted to controls	n = 1094	n = 122	p Value	OR	(95%CI)
Age (mean (SD))	46.81 (6.20)	46.79 (6.26)	0.96	0.99	(0.96–1.02)
Smoking (%)	n (%)	n (%)	0.014
Never	737 (67.4)	68 (55.7)		1.0 (ref
Current	87 (8.0)	9 (7.4)		1.27	(0.54–2.63)
Past	270 (24.7)	45 (36.9)		1.97	(1.29–3.00)
Ever smoker	357 (32.6)	54 (44.3)	0.013
Race, ethnicity (%)			0.91
Non-Hispanic White	980 (89.7)	109 (89.3)
Other	113 (10.3)	13 (10.7)
Education level of participant (%)			0.048
High school or less	122 (11.2)	11 (9.0)
Some college or technical degree	359 (32.8)	27 (22.1)
Bachelor's degree	353 (32.3)	51 (41.8)
Master or Doctoral degree	260 (23.8)	33 (27.0)
Household income per-person (mean (SD))	$38,263 (23,921)	$56,393 (35,211)	3.37E–07
Income bracket (%)			1.80E–06
Less than $100,000	614 (58)	45 (39)		1.0 ref
$100,000 to $200,000	363 (34)	45 (39)		1.75	(1.13–2.71)
$200,000+	89 (8)	25 (22)		4.05	(2.32–6.96)

^a Model includes age, smoking status, and income bracket. Missing race n = 1, income n = 35.