Narrow axis: an inherited anomaly of the second cervical vertebra in the rabbit.

Narrow axis, an inherited anomaly resulting in a marked narrowing of the second cervical vertebra, has been observed in strain X/J rabbits. This condition is first recognizable on X rays at 32-33 days gestation. For size comparisons 21 measurements of the first five cervical vertebrae were taken on the skeletons of each of 14 strain X/J animals (7 normal and 7 with narrow axis) and 14 IIIC/J animals for control at two months of age and 27 strain X/J (11 normal and 16 narrow axis) and 14 strain IIIC/J at seven months of age. The primary effect appeared to be a premature fusion of the centrum with its neural arches. Expression is variable. The effect on the posterior articulation of the atlas appeared to be secondary and adaptive. The other cervical vertebrae and the foramen magnum were relatively unaffected. In the 20-year period encompassed in this report, X rays of 3244 rabbits were used for genetic analysis. Inheritance appears to be due to a single autosomal recessive gene with incomplete penetrance. The condition is neither sex-linked nor sex-limited. We propose the symbol nx for the gene responsible for narrow axis in the rabbit.

Vitamin A, beta carotene, and hereditary buphthalmus in the rabbit.

Rabbits with hereditary buphthalmus, AXBU/J strain, were fed various levels of supplementary vitamin A or its precursor beta carotene, in addition to a vitamin A deficient diet, to test the hypothesis that the bu gene acts by reducing either the conversion of beta carotene to vitamin A or the utilization of vitamin A. Measurements were taken on an age series of skulls of manifest and of prodromal buphthalmics to see if there were any observable differences in optic foramen size associated with the clinical manifestations of buphthalmus. Constriction of the optic nerve by bone alteration has been reported to be associated with vitamin A deficiency. The original hypothesis was not a tenable one as the rabbit with hereditary buphthalmus readily converted beta carotene to vitamin A, no bony changes in the optic foramen were observed with manifest buphthalmus, high levels of beta carotene or vitamin A were unable to block the clinical development of buphthalmia, and no correlation was observed between intraocular pressure and serum vitamin A levels in rabbits fed either beta carotene or pure vitamin A.

Frequency of congenital abnormalities and of anatomical variations among JAX rabbits.

The frequency of congenital abnormalities and anatomical variations as observed among JAX rabbits is reported. Data were drawn from 32,082 inbred and partially inbred rabbits and 3,208 hybrids from the colony of the Jackson Laboratory over an eight-year period. Data reported here include stillbirths, rabbits dying from natural causes, and those killed for specific experimental regimens. Frequency data are based on the number of abnormalities observed in each category as a function of the total number of animals necropsied. This is approximately 95% of the animals born during the eight-year period and gives the frequency of abnormalities within each category rather than the number of individuals with one or more abnormalities. Anatomical variations have been found in almost all organ systems of JAX rabbits. Their presence adds to our knowledge of the characteristics of these strains, a knowledge that is critical to the understanding of the results of experimental manipulation or for determination of the presence of new mutations. There is considerable between-strain variation. Where frequencies are relatively high, the conditions are either known or suspected to be of genetic origin. Most of the anomalies are not deleterious, or their frequency is so low as to cause no problems within the colony. Hybrid populations have substantially fewer anomalies than do the parental strains. Where frequency is relatively high, it tends to be intermediate between the parental strains.

Hereditary macrostomus in the rabbit: a model for Treacher Collins syndrome, one form of mandibulofacial dysostosis.

Macrostomus in the rabbit was diagnosed externally by the presence of papillae at the corners of the mouth. Internally the effect is on the zygomatic complex and is extremely variable. Inheritance appears to be due to a single autosomal recessive gene with incomplete penetrance. We propose the symbol mst for the gene responsible for this condition. Evidence is presented to suggest that this gene is very likely in linkage group IV. Macrostomus in the rabbit is a model for the Treacher Collins syndrome, one form of mandibulofacial dysostosis in humans.

Genetics and pathology of hereditary adrenal hyperplasia in the rabbit: a model for congenital lipoid adrenal hyperplasia.

One-hundred-twenty-nine cases of adrenal hyperplasia in the rabbit were shown to be associated with a fully penetrant autosomal recessive gene, symbolized ah. The mutant is viable prenatally, may be recognized by gross examination of the adrenal at least as early as 19 days of gestation, but dies soon after birth. There is an external feminizing effect of the gene and the model is similar to the feminizing congenital lipoid adrenal hyperplasia reported in man. This mutant is being maintained in strain IIIVO/ahJ.

Hereditary chondrodystrophy in the rabbit. Genetics and pathology of a new mutant, a model for metatropic dwarfism.

Thirty-one cases of a new hereditary chondrodystrophy in the rabbit have been shown to be associated with a fully penetrant autosomal recessive gene symbolized cd. The mutant is viable prenatally but does not survive after birth. It differs from the two other inherited chondrodystrophies, dachs and achondroplasia, but is very similar to the metatropic dwarf reported in man.

Hereditary vestigial pulmonary arterial trunk and related defects in rabbits.

In a population of IIIVO/J rabbits at the Jackson Laboratory a vestigial pulmonary arterial trunk is the commonest expression of a malformation involving the heart and great vessels. There appears to be a series of effects from a completely absent pulmonary trunk through a vestigial but patent pulmonary trunk and/or pulmonary valve stenosis on the one hand to a vestigial or absent ascending aorta on the other. In a few cases the pulmonary trunk is bulbous and the ductus arteriosus is vestigial or absent. In almost all cases of this syndrome, there is also a high ventricular septal defect. The animals appear perfectly normal in every other respect. In its extreme forms this mutation is lethal, but those few animals that are somewhat less severely affected may live for a short time. No effect was seen on birth weight or litter size. Inheritance of vestigial pulmonary arterial trunk appears to be due to two autosomal recessive factors both of which must be homozygous for the expression of the condition. We propose the symbols vpt-1 and vpt-2 for the genes responsible for vestigial pulmonary arterial trunk and its related abnormalities.