From E9.5 to E12.5, Ptdsr -/-  embryos were viable and of normal size. At E13.5 and thereafter, however, most Ptdsr -/-embryos showed morphological abnormalities (Table 1). All homozygous embryos harvested were growth-retarded from E13.5 onwards, had a pale appearance, and displayed multiple developmental dysmorphologies. These included various head and craniofacial malformations, such as exencephaly, cleft palate and abnormal head shape (Figure 1f,g). Gross inspection revealed that eye development was severely affected in 14.1% of homozygous embryos. The affected animals displayed a complete unilateral or bilateral absence of the eyes (Table 1) that was never detected in Ptdsr +/+ or Ptdsr +/- littermates. Furthermore, homozygous embryos harvested between E12.5 and E15.5 had subcutaneous edema (Figure 1f,g). Because we were able to recover Ptdsr -/- embryos until E18.5, we investigated whether Ptdsr-knockout mice could be born alive. Careful observation of timed matings allowed us to recover Ptdsr -/- neonates, but homozygous pups died during delivery or within minutes after birth. Ptdsr-deficient neonates were also growth-retarded, had a pale appearance and displayed various malformations. These included cleft palate, abnormal head shape, absence of eyes and edematous skin (Figure 1h). Thus, deletion of the Ptdsr gene resulted in perinatal lethality with variable severity and penetrance of phenotypes.