The role of thyroid function in borderline personality disorder and schizophrenia: a Mendelian Randomisation study

Area of Science:

• Psychiatric genetics
• Endocrinology
• Complex trait genetics

Background:

• Genome-wide association studies suggest a genetic overlap between borderline personality disorder (BPD) and schizophrenia (SCZ).
• The causal relationship between thyroid function and the risk of BPD and SCZ remains unclear.
• Investigating thyroid function's role in BPD and SCZ is crucial for understanding their etiology.

Purpose of the Study:

• To investigate the association between genetically predicted thyroid function and the risk of BPD and SCZ.
• To examine potential reverse causality from BPD and SCZ to thyroid function.

Main Methods:

• Mendelian Randomisation (MR) analyses were used to assess the effect of genetically predicted thyroid-stimulating hormone (TSH), free thyroxine (FT4), and hypothyroidism on BPD and SCZ risk.
• Bidirectional MR analyses were conducted to explore reverse causal pathways.

Main Results:

• Genetically predicted higher FT4 levels were not associated with an increased risk of BPD or SCZ.
• Genetically predicted higher TSH levels showed no association with the risk of BPD or SCZ.
• Genetically predicted hypothyroidism was not linked to BPD or SCZ risk, and no evidence of reverse causality was found.

Conclusions:

• There is a null association between genetically predicted thyroid function (FT4, TSH, hypothyroidism) and the risk of BPD or SCZ.
• The study provides no evidence to support a causal role of thyroid function in the development of BPD or SCZ.
• No reverse causal effects were detected between BPD/SCZ and thyroid function.