grp_id: ID of phenotype group (gene_id)
grp_chr: chromosome of phenotype group (gene)
grp_start, grp_end: start and end positions of phenotype group (gene)
grp_strand: strand of phenotype group (gene)
intron: intron identifier formatted as per leafcutter (chromosome:start:end:clu_clusterid_clusterstrand_stimulants_timepoint)
n_intron_in_grp: number of phenotypes (introns) in the phenotype group (gene)
n_var_in_cis: number of variants in the cis window of the phenotype group (1mbp of gene start position)
dist_intron_var: distance between variant and phenotype (intron)
var_id: variant rsid (if available. otherwise variant_chr:position)
var_chr: variant chromosome
variant_start, variant_end: variant start and end positions
dof1: number of degrees of freedom used to compute the p-values (see https://qtltools.github.io/qtltools/)
dof2: estimated number of degrees of freedom used in beta approximation p-value calculations (see https://qtltools.github.io/qtltools/)
bml1: first shape parameter of the fitted beta distribution (alpha parameter; see https://qtltools.github.io/qtltools/)
bml2: second shape parameter of the fitted beta distribution (beta parameter). This corresponds to the effective number of independent tests in the region (see https://qtltools.github.io/qtltools/)
pvalue_nominal: nominal p-value of the association between the most significant variant and the phenotype group (gene).
r_squared: R^2 of the linear regression between phenotype (intron) and variant 
slope: beta (slope) of the linear regression between phenotype (intron) and variant
adj_emp_pval: 	adjusted empirical p-value from 1000 permutations
adj_beta_pval: adjusted empirical p-value given by the fitted beta distribution