Physiological and Behavioural Characterisation of a Novel Steroid Sulfatase-Deficient Mouse

Steroid sulfatase (STS) cleaves sulphate groups from steroid hormones. In humans, STS deficiency is associated with X-linked ichthyosis, an increased predisposition to neurodevelopmental and mood conditions (including Attention Deficit Hyperactivity Disorder, autism, depression and anxiety), and cardiac arrhythmia risk. Until recently, no single-gene 'knockout' mammalian model existed; previous work in such a model is limited to skin phenotypes. We generated a novel C57BL/6J mouse model with a deletion in exon 2 of Sts. We examined gene expression and enzyme activity in liver and brain samples of homozygous mice, and assessed the breeding performance and health of male and female deletion-carriers. Subsequently, we compared performance across a range of behavioural paradigms in wildtype and homozygous male and female mice: elevated plus maze, open field, rotarod, spontaneous alternation, and acoustic startle/prepulse inhibition. We also investigated serum steroid hormone levels by liquid chromatography-mass spectrometry and measured heart weights and two morphological indices (bodyweight/tibia length) post mortem. Homozygous mice almost completely lacked STS expression/activity. Genetically-altered mice exhibited grossly-normal breeding performance, health, and endocrinology. Homozygous mice were more active and had higher normalised heart weights than wildtype mice. We also found significant genotype × sex interactions on bodyweight and on two behavioural measures (potentially reflecting lower anxiety in homozygous males and heightened anxiety in homozygous females). The 'Sts-deletion' mouse represents an experimentally-tractable model in which to identify and characterise phenotypes associated with STS deficiency. The mechanistic basis of the associations described here requires further investigation, and whether these translate to humans remains to be tested.