Aims of the study

The primary goal was to identify genes that might increase the risk of developing anorexia nervosa using the candidate gene approach. The researchers focused on the EPHX2 gene, which is involved in cholesterol function. Individuals with anorexia nervosa often show high cholesterol levels that return to normal once they start putting weight back on.

Procedures of the study

To investigate genetic associations, the researchers collected and analysed DNA samples from a large group of participants. They compared genetic sequences between people diagnosed with anorexia (cases) and those without (controls) to spot differences that might indicate risk factors.

Participant selection and initial sample

• Cases - The study included 1,205 individuals diagnosed with anorexia nervosa. The initial group consisted of 262 white European women with early-onset severe anorexia of the restricting type, with or without purging behaviours.
• Controls - There were 1,948 individuals without anorexia or related eating disorders. Controls were not underweight.
• Exclusion criteria - Women who regularly binge ate were excluded to keep the sample homogeneous, reducing the chance that genetic findings could be confused with those of other eating disorders.
• Key participant details - Cases had an average symptom onset age of 14 years, a lifetime lowest body mass index (BMI) of 15 or less, and were assessed at age 19 or older.

Genetic analysis process

The team sequenced DNA to examine variations in the 152 candidate genes:

1. Initial screening in the core sample of 262 cases and 80 matched controls.
2. Replication phase to verify findings, using an additional 500 cases and 500 controls, plus data from 444 cases of anorexia or eating disturbances and 1,146 controls from prior studies.

This replication sample method tests associations in one group and confirms them in another, strengthening evidence that identified genes are genuinely linked to the disorder.

Results of the study

The analysis revealed several genetic associations with anorexia nervosa, highlighting specific gene variants that appeared more frequently in affected individuals. These findings connected genetics to physical and psychological aspects of the disorder.

Key genetic associations

• Individual variant analysis - The strongest links were with two variants in the ESR2 gene (oestrogen receptor beta). Prior research had suggested oestrogen's role in anorexia.
• Group variant analysis - When examining clusters of variants together, the strongest associations emerged in the ITPR3 gene and the EPHX2 gene.

Replication and further insights

• In the replication samples, variants in EPHX2 and ESR2 continued to show associations with anorexia, confirming their potential relevance.
• One EPHX2 variant was linked to changes in BMI and cholesterol levels over time.
• EPHX2 variants also showed connections to depressive and anxiety symptoms in women with anorexia, and influenced how BMI related to these symptoms.
• The EPHX2 gene was active in brain regions associated with feeding behaviours, anxiety, and depression.

These results indicate that genetic variations, particularly in EPHX2, may contribute to both the physical symptoms (like low BMI and high cholesterol) and mental health aspects of anorexia.

Conclusions of the study

Based on the findings, the researchers concluded that variations in the EPHX2 gene represent a novel genetic factor increasing susceptibility to anorexia nervosa. This discovery provides a starting point for deeper investigations into the disorder's causes, which remain poorly understood despite its severity.