# GWAS with imputed data

Hello,

I see in the hail GWAS tutorial that n_alt_alleles is used as the independent variable, which I believe is a way of getting a sort of dosage from a hard genotype call? I was wondering how one would do a GWAS using imputed data that already has dosages (I see that there was a use_dosage option for linear regression in 0.1 but there isn’t something similar in 0.2). I have bgen files with GT, GP and dosage entry fields.

Chloe

n_alt_alleles is a method on Calls. A Call is how Hail represents a hard call, aka a GT.

You’re probably looking for gp_dosage which converts a GP array of probabilities to the expected value (which may, of course, be fractional).

>>> result_ht = hl.linear_regression_rows(
...     y=dataset.pheno.height,
...     x=hl.gp_dosage(dataset.GP),
...     covariates=[1, dataset.pheno.age, dataset.pheno.is_female])

If they already have the dosage values (and not just the genotype probability), usually the DS field (if the imputation was done with Minimac), isn’t it already equivalent to the output of n_alt_alleles without even calling this function?

Can you use mt.DS as the independent variable on your regression ?

If mt.DS is a number, then you sure can use it as an independent variable!

n_alt_alleles is strictly for hard calls. It maps from genotype calls to integers. Note that information is lost in this transition, that’s why this method exists!

hl.call("0/0").n_alt_alleles() == 0
hl.call("0/1").n_alt_alleles() == 1
hl.call("0/2").n_alt_alleles() == 1

After calling n_alt_alleles, 0/1 and 0/2 look the same!

Hi again, I had a go at using hl.gp_dosage on my GP array and got a long and horrible error. It’s too long to paste here so I’ve put it in this link:

https://pastebin.com/2NFGUrM2

I’m not sure what to make of this. I’m guessing maybe my GP field was not the shape or format that the gp_dosage method expected? I’m using bgen files in case that helps. If I try to use the direct dosage field as an independent variable I get a similarly incomprehensible error. Any thoughts?

Thanks,
Chloe

Oh dear, this is a top-5 worst error.

Any time you see a stack trace like this, you should consider it a bug to be reported (uninformative error messages / internal assertion errors are incorrect behavior).

What version are you using? I have suspicions about what’s causing this error (and we have changes going in this week that should prevent this class of error permanently) but can’t be 100% sure at the moment.

I’m using v0.2.33(-5d8cae649505) – just upgraded yesterday.

could I see your pipeline? I suspect I can provide a workaround until the next version fixes this.

Yes! It’s long and a bit convoluted, but here you go:

# set up hail with appropriate reference chromosome and sparkConf
import hail as hl
import pandas as pd
import datetime as d
hl.init(default_reference='GRCh37',spark_conf={'spark.driver.memory': '250G'})
# get useful things for later
from hail.plot import show
from pprint import pprint
hl.plot.output_notebook()

# import chr16 bgen as a MatrixTable
ef = ['GT', 'GP','dosage']
hl.index_bgen("ukb_imp_chr16_v3.bgen",contig_recoding={"01": "1"})
chr16 = hl.import_bgen("ukb_imp_chr16_v3.bgen", entry_fields=ef,sample_file="ukb52480_imp_chr16_v3_s487314.sample")
chr16.describe()
# import phenotype
# then convert to Hail table object
phenos.columns = ["eid","BMI"]
ph = hl.Table.from_pandas(phenos,key=["eid"])
# remove individuals with NaN BMI values
ph_filtered = ph.filter(hl.is_nan(ph.BMI),keep=False)
pprint(ph.count()-ph_filtered.count())
# join phenotype table onto matrixtable
chr16 = chr16.annotate_cols(phenotype = ph_filtered[chr16.s])
# get biological sex and ethnicity from uk biobank data and add it to table
usecols = ["eid","22001-0.0","22006-0.0"],
dtype={"eid":str,"22001-0.0":float,"22006-0.0":float})
# then convert to Hail table object
bios.columns = ["eid","sex","ethnic_group"]
bs = hl.Table.from_pandas(bios,key=["eid"])
# remove individuals with NaN values
bs = bs.filter(hl.is_nan(bs.sex),keep=False)
bs = bs.filter(hl.is_nan(bs.ethnic_group),keep=False)
# join to matrixtable
chr16 = chr16.annotate_cols(ukbb = bs[chr16.s])
chr16.describe()

# exclude non-european individuals
chr16_qc1 = chr16.filter_cols(chr16.ukbb.ethnic_group == 1)
print('Samples: %d ' % (chr16_qc1.count_cols()))

# exclude individuals not used in Biobank PCA calculation
usecols = ["eid","22020-0.0"],
dtype={"eid":str,"22020-0.0":float})
p.columns = ["eid","pca_inclusions"]
pca_inclusions = hl.Table.from_pandas(p,key=["eid"])
pca_inclusions = pca_inclusions.filter(hl.is_nan(pca_inclusions.pca_inclusions),keep=False)
to_keep = pca_inclusions.eid.collect()
set_to_keep = hl.literal(to_keep)
print('%d individuals used in PCA calc' % hl.eval(hl.len(set_to_keep)))
chr16_qc2 = chr16_qc1.filter_cols(set_to_keep.contains(chr16_qc1['s']))
print('Samples removed: %d' % hl.eval(chr16_qc1.count_cols()-chr16_qc2.count_cols()))

# exclude biological and reported sex mismatches and import age for covariates
# read in reported sex and YOB, convert YOB to age, annotate matrixTable
p = pd.read_csv("ukb40744.csv", usecols = ["eid","31-0.0","34-0.0"],
dtype={"eid":str,"31-0.0":float,"34-0.0":float})
p.columns = ["eid","reported_sex","age"]
p.age = int(d.datetime.now().year) - p.age
pt = hl.Table.from_pandas(p, key=["eid"])
chr16_qc2 = chr16_qc2.annotate_cols(ukbb2 = pt[chr16_qc2.s])
#chr16_qc2.describe()
#chr16_qc2.ukbb2.show(2)
# filter for mismatches
chr16_qc2a = chr16_qc2.filter_cols(chr16_qc2.ukbb.sex == chr16_qc2.ukbb2.reported_sex)
chr16_qc2a.describe()
print('Samples removed: %d' % hl.eval(chr16_qc2.count_cols()-chr16_qc2a.count_cols()))

# import lists of recommended exclusions and weird cases, convert to tables, filter for NaNs

# recommended heterozygosity exclusions
usecols = ["eid","22010-0.0"],
dtype={"eid":str,"22010-0.0":float})
he.columns = ["eid","het_exclusions"]
het_exclusions = hl.Table.from_pandas(he,key=["eid"])
het_exclusions = het_exclusions.filter(hl.is_nan(het_exclusions.het_exclusions),keep=False)

# recommended relatedness exclusions
usecols = ["eid","22018-0.0"],
dtype={"eid":str,"22018-0.0":float})
re.columns = ["eid","rel_exclusions"]
rel_exclusions = hl.Table.from_pandas(re,key=["eid"])
rel_exclusions = rel_exclusions.filter(hl.is_nan(rel_exclusions.rel_exclusions),keep=False)

# aneuploidy cases
usecols = ["eid","22019-0.0"],
dtype={"eid":str,"22019-0.0":float})
an.columns = ["eid","aneuploidy"]
aneuploidy = hl.Table.from_pandas(an,key=["eid"])
aneuploidy = aneuploidy.filter(hl.is_nan(aneuploidy.aneuploidy),keep=False)

# remove samples from table if they appear in recommended exclusion lists

# heterozygosity exclusions
to_remove = het_exclusions.eid.collect()
set_to_remove = hl.literal(to_remove)
print('to remove: %d' % hl.eval(hl.len(set_to_remove)))
chr16_qc3 = chr16_qc2.filter_cols(~set_to_remove.contains(chr16_qc2['s']))
print('Samples removed: %d' % hl.eval(chr16_qc2.count_cols()-chr16_qc3.count_cols()))

# relatedness exclusions
to_remove = rel_exclusions.eid.collect()
set_to_remove = hl.literal(to_remove)
print('to remove: %d' % hl.eval(hl.len(set_to_remove)))
chr16_qc4 = chr16_qc3.filter_cols(~set_to_remove.contains(chr16_qc3['s']))
print('Samples removed: %d' % hl.eval(chr16_qc3.count_cols()-chr16_qc4.count_cols()))

# aneuploidy
to_remove = aneuploidy.eid.collect()
set_to_remove = hl.literal(to_remove)
print('to remove: %d' % hl.eval(hl.len(set_to_remove)))
chr16_qc5 = chr16_qc4.filter_cols(~set_to_remove.contains(chr16_qc4['s']))
print('Samples removed: %d' % hl.eval(chr16_qc4.count_cols()-chr16_qc5.count_cols()))

print('Total samples removed: %d' % hl.eval(chr16_qc1.count_cols()-chr16_qc5.count_cols()))

# calculate per-variant qc stats
chr16_qc5 = hl.variant_qc(chr16_qc5)
print('Total Variants: %d' % (chr16_qc5.count_rows()))

# remove non-SNPs
chr16_qc6 = hl.filter_alleles(chr16_qc5, lambda allele, i: hl.is_snp(chr16_qc5.alleles[0], allele))
chr16_qc6.describe()
print('Variants remaining: %d' % (chr16_qc6.count_rows()))

# HWE filter (Neale lab value)
chr16_qc7 = chr16_qc6.filter_rows(chr16_qc6.variant_qc.p_value_hwe > 1e-10)
print('Variants remaining: %d' % (chr16_qc7.count_rows()))

# info score filter -- using 0.4 as indicated by exploratory plot

# import and attach info score and MAF
ins = infos[[0,5,6,7]]
ins.columns = ["varid","MAF","minor_allele","info_score"]
i = hl.Table.from_pandas(ins,key=["varid"])
# join info score table onto matrixtable
chr16_qc7 = chr16_qc7.annotate_rows(SNP_info = i[chr16_qc7.varid])
chr16_qc8 = chr16_qc7.filter_rows(chr16_qc7.SNP_info.info_score > 0.4)
print('Variants remaining: %d' % (chr16_qc8.count_rows()))

# MAF filter
chr16_qc9 = chr16_qc8.filter_rows(chr16_qc8.SNP_info.MAF > 0.001)
print('Variants remaining: %d' % (chr16_qc9.count_rows()))

# import principal components calculated by uk biobank
usecols = ["eid","22009-0.1","22009-0.2","22009-0.3",
"22009-0.4","22009-0.5","22009-0.6",
"22009-0.7","22009-0.8","22009-0.9","22009-0.10"],
dtype={"eid":str,"22009-0.1":float,"22009-0.2":float,"22009-0.3":float,
"22009-0.4":float,"22009-0.5":float,"22009-0.6":float,
"22009-0.7":float,"22009-0.8":float,"22009-0.9":float,"22009-0.10":float})
p.columns = ["eid","pca1","pca2","pca3","pca4","pca5","pca6","pca7","pca8","pca9","pca10"]
pca = hl.Table.from_pandas(p,key=["eid"])

# join to matrixtable
chr16_qc9 = chr16_qc9.annotate_cols(PCA = pca[chr16_qc9.s])
chr16_qc9.describe()
# GWAS with dosages and confounders as covariates
gwas = hl.linear_regression_rows(y=chr16_qc9.phenotype.BMI,
x=hl.gp_dosage(chr16_qc9.GP),
covariates=[1.0, chr16_qc9.ukbb2.reported_sex,
chr16_qc9.ukbb2.age,
chr16_qc9.PCA.pca1, chr16_qc9.PCA.pca2,
chr16_qc9.PCA.pca3,chr16_qc9.PCA.pca4,
chr16_qc9.PCA.pca5, chr16_qc9.PCA.pca6,
chr16_qc9.PCA.pca7, chr16_qc9.PCA.pca8,
chr16_qc9.PCA.pca9,chr16_qc9.PCA.pca10])
gwas.row.describe()

Could you try doing the following right before the linear regression:

chr16_qc9 = chr16_qc9.annotate_entries(GP = chr16_qc9.GP.map(lambda x: x))

That made no difference unfortunately – still got the same long and messy error.

ack, sorry. This is probably fixed since 0.2.33’s release, but it’ll be a couple more days until we’re ready for 0.2.34. You can try this pre-release wheel: