Table 1 Descriptive overview of human studies, in which KLK8 was associated to mental health phenotypes

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]