Table 1.

Descriptive overview of human studies, in which KLK8 was associated to mental health phenotypes

Phenotype	Tissue	Parameters assessed	Main finding	Reference
Schizophrenia	Peripheral blood	Singe nucleotide polymorphisms (genotyping assay)	Rare Val286Ile missense mutation in exon 6 detected in a patient with schizophrenia	[56]
Bipolar disorder	Peripheral blood	Singe nucleotide polymorphisms (genotyping assay)	Significant allelic association between several SNPs and bipolar disorder: rs1722550 (P = 0.019), rs1701946 (P = 0.018), rs1612902 (P = 0.002), rs1701946 plus rs1612902 (P = 0.0068)	[56]
Depression	Peripheral blood	Expression levels (mRNA) of KLK8 (RT-PCR), patients diagnosed with major recurrent depression and first episode depression	Higher KLK8 expression in patients with recurrent depression compared to first episode patients	[64]
	Peripheral blood	Expression levels (mRNA) of KLK8 (RT-PCR), patients diagnosed with major recurrent depression and healthy subjects	Higher KLK8 expression in patients with depression compared to controls	[63]
	Peripheral blood	Methylation levels of KLK8 (450 K methylation array), depression symptomatology score in monozygotic twins	Methylation levels in the promotor region of KLK8 is associated with depression symptomatology in general population	[65]
Alzheimer’s disease	Hippocampal and parietal cortex	Expression (RT-PCR), of KLK8 in Alzheimer’s disease (AD) and control tissue	11.5-fold increase in KLK8 mRNA levels in AD hippocampus compared to controls	[66]