According to the authors of “Protective effect of CRHR1 gene variants on the development of adult depression following childhood maltreatment: replication and extension“ [PMID: 19736354], theirs is “the first instance of Genes x Environment research that stress has been ascertained by more than 1 study using the same instrument“. The gene they speak of is the Corticotropin-releasing hormone receptor 1 (CRHR1) gene (SNPs rs7209436, rs110402, rs242924 which can form a so-called T-A-T haplotype which has been associated with protection from early life stress (as ascertained using the Childhood Trauma Questionnaire CTQ)).
The research team examined several populations of adults and, like many other studies, found that early life stress was associated with symptoms of depressive illness but, like only 1 previous study, found that the more T-A-T haplotypes a person has (0,1,or 2) the less likely they were to suffer these symptoms.
Indeed, the CRHR1 gene is an important player in a complex network of hormonal signals that regulate the way the body (specifically the hypothalamic pituitary adrenal axis) transduces the effects of stress. So it seems quite reasonable to see that individual differences in ones ability to cope with stress might correlate with genotype here. The replication seems like a major step forward in the ongoing paradigm shift from “genes as independent risk factors” to “genetic risk factors being dependent on certain environmental forces”. The authors suggest that a the protective T-A-T haplotype might play a role in the consolidation of emotional memories and that CRHR1 T-A-T carriers might have a somewhat less-efficient emotional memory consolidation (sort of preventing disturbing memories from making it into long-term storage in the first place?) – which is a very intriguing and testable hypothesis.
On a more speculative note … consider the way in which the stress responsivity of a developing child is tied to its mother’s own stress responsivity. Mom’s own secretion of CRH from the placenta is known to regulate gestational duration and thus the size, heartiness and stress responsiveness of her newborn. The genetic variations are just passed along from generation to generation and provide some protection here and there in an intertwined cycle of life.
The flowers think they gave birth to seeds,
The shoots, they gave birth to the flowers,
And the plants, they gave birth to the shoots,
So do the seeds they gave birth to plants.
You think you gave birth to the child.
None thinks they are only entrances
For the life force that passes through.
A life is not born, it passes through.