Sporadic congenital malformations of newborn inbred mice

Abstract A retrospective study was made of sporadic congenital malformations in newborn mice of nine inbred strains maintained in this laboratory. Young of seven of the strains had externally observable anomalies. In four the frequency was 0.1–0.5% and the defects formed no obvious pattern. In another it was about 4% and consisted mostly of preaxial polydactyly of the forefoot. In the remaining two the frequency was greater and some of the malformations appeared to constitute particular syndromes. In the C57BL/6JKt strain the overall frequency of malformed offspring was 10.1% and the abnormalities included eye defects, polydactyly, and otocephaly. Those of the eye (microphthalmia and anophthalmia) were commonest and affected females and right eyes much more often than males and left ones. In the A/JKt strain the total frequency of malformed offspring was 10.4% and the abnormalities included cleft lip with or without cleft palate, open eyelid, and polydactyly. Cleft lip was commonest and did not show a sex or side preference. The use of inbred strains to investigate the etiology of sporadic congenital malformations of probable multifactorial origin is to be encouraged.