confusion on trajgwas result Interpretation

[Buckley96]

Firstly, I would like to express my appreciation for the trajgwas tool — it is an incredibly powerful and flexible resource for GWAS studies, especially in modeling longitudinal trajectories with genetic interactions. The ability to jointly analyze mean and variability effects sets it apart from traditional methods.

However, I felt a little confused regarding the interpretation of results from the following code:

trajgwas(
@formula(BP ~ 1 + age + bmi),
@formula(BP ~ 1),
@formula(BP ~ 1 + age + bmi),
:IID,
"Basic_for_trajGWAS_samplefilter.csv",
"Gencode.$(file).dn",
pvalfile = "gxe_snp_$(file).pval.txt",
analysistype = "gxe",
e = :age,
snpinds = 1:5
)

My current understanding is:
snpeffectnullbeta: The SNP×age interaction effect on the rate of BP change (e.g., risk allele carriers may show +0.2 mmHg/year faster increase than non-carriers).

snpeffectnulltau: The SNP×age interaction effect on BP variability across the age range (e.g., risk allele carriers exhibit 10% greater variance at age 60 vs. 40 compared to non-carriers).

Whether my understanding is right?If my interpretation is incorrect, could you advise on how to properly formulate the model to test these two hypotheses mentioned above?

Thank you for your guidance. Any documentation references or minimal code examples would be invaluable.

Best,
Buckley