From Genome Analysis Wiki
vt understands an augmented version introduced by [mailto:firstname.lastname@example.org Hyun] of the PED described by [http://zzz.bwh.harvard.edu/plink/data.shtml#ped plink].
The pedigree file format is as follows with the following mandatory fields:
yri NA19240 NA19239 NA19238 2
ceu NA12878,NA12878A NA12891 NA12892 female
yri NA19240 NA19239 NA19238 female