Our study on a kindred of spoon nails found among residents in Wakayama City, shows:
1. The kindred includes 36 affected members extending in five generations (Fig. 1). The seventeen marriages between affected and normal members of the kindred and which have more than two children, produced 29 affected, 16 males and 13 females, and 37 normal children 22 males and 15 females. This 37: 29 ratio falls within the range of the 1: 1 ratio of the affected and normal offspring. The sex ratio of the affected members, 16 males: 13 females, also is about 1:1. Thus, the abnormality seems to be due to a single autosomal dominant gene.
2. The penetrance of the gene in this family is apparently fairly high.
3. Regarding the expressivity of this abnormality, the concavity of nails is not always distinct especially in toes, while the expressivity of the gene in finger nails is more apparent.