Eggs laid by KCNQ^18B homozygous mothers fail to hatch into larvae. This embryonic lethality is only associated with homozygous KCNQ^18B mothers. Homozygous KCNQ^18B males have normal fertility, as they produce adult progeny when mated to wild-type females. Heterozygous embryos from homozygous KCNQ^18B females and wild-type males still fail to hatch, even with a copy of the wild-type gene from the male. The lack of paternal rescue indicates that the time window when KCNQ is critical lies before the zygotic expression of the gene.

The nuclei of 1-2 hour old embryos laid by KCNQ^18B mutant females are disorganised in comparison to wild-type. Some nuclei appear to be broken down into smaller fragments, whereas others have clustered abnormally, indicating that development of the mutant embryo is arrested before the cellularisation stage.

Homozygous KCNQ^18B mutants develop into adulthood and display an approximately 50:50 male to female ratio. They do not exhibit any gross anatomical abnormalities; they also exhibit no obvious defects in such basic motor skills as walking and flying.