SPAG1 and primary ciliary dyskinesia: In the presented study, we examined the hypothesis that the discrepancy between the observed and expected distribution of haplotypes in SPAG1-PCD patients (the lack of homozygotes with the large deletion encompassing parts of SPAG1 and POLR2K), reflected a highly deleterious, possibly lethal effect of the loss of a functional POLR2K rather than of SPAG1 protein.