Table 2.

Quality assessment of each article included in the systematic review.

References	Study design	Selection				Comparability	Outcome			Total stars
		Representati-veness of the sample	Sample size justification	Exclusion of other relevant diseases	Ascertainment of exposure (C9orf72)	Control for confounding factors	Assessment of outcome (HLD diagnosis)	Statistical test
Hensman Moss et al. (2014a)	Cross-sectional	+			++		++	+		6/10
Kostic et al. (2014)	Cross-sectional	+		+	++		++	+		7/10
Koutsis et al. (2015)	Cross-sectional	+		+	++		++	+		7/10
Mariani et al. (2016)	Cross-sectional	+		+	++		++	+		7/10
Martins et al. (2018a)	Cross-sectional	+		+	++		++	+		7/10
Baine et al. (2018)	Cross-sectional	+		+	++		++	+		7/10
Ida et al. (2018)	Cross-sectional	+		+	++		++	+		7/10
Kaur et al. (2020)	Cross-sectional	+			++			+		4/10
References	Study design	Selection				Comparability	Exposure			Total stars
		Case definition (HLD diagnosis)	Representativeness of the cases to target population	Selection of community-based controls	Definition of controls	Control for confounding factors	Ascertainment of exposure (C9orf72)	Same method used for cases and controls	All cases and controls were assessed for exposure
Rikos et al. (2020)	Case-control	+	+	+	+		+	+	+	7/9
Fedotova et al. (2016)	Case-control		+	+	+		+	+	+	6/9

HLD, Huntington-Like Disorder.