In other species: cattle , pig , goat , rabbit , alpaca , llama

Possibly relevant human trait(s) and/or gene(s) (MIM number): 163700 (trait)

Mendelian trait/disorder: no

Mode of inheritance: Multifactorial

Considered a defect: no

Key variant known: no

Cross-species summary: Also known as Supernumerary teats, multi-nippled, polymastia and hyperthelia

History: Alexander Graeme Bell (1898, 1904, 1912, 1923), of telephone fame, developed by selection a strain of sheep in which most ewes had two to four additional teats. After the death of Bell and his wife, a ram and some ewes from his flock were obtained by the New Hampshire Agricultural Experiment Station. In 1941, the flock was transferred to the United States Morgan Horse Farm, Middlebury, Vermont. The results of Bell and his wife were summarised by Castle (1924). All available data from the Bells and from the subsequent research in New Hampshire and Vermont were summarised by Phillips et al. (1946), who reported estimates of the heritability of teat number ranging from 14% to 26%, consistent with the substantial response to selection achieved by the Bells. Phillips et al. (1946) concluded: "The results . . . indicate that the incidence of the multinipple trait in sheep can be readily affected by selection of sires and dams. There is little indication, however, that this trait has practical value in sheep husbandry, either by association with high fertility or increased milk production. In most flocks this character can safely be disregarded in selection but if the incidence of multinippled individuals becomes high enough to be objectionable it should be possible to bring it under control 'rather quickly by the use of rams with only two rudimentary nipples."

A more recent review of Bell's considerable contributions to science is provided by Stansfield (2005). Among many other things, Bell was very interested in the inheritance of deafness (both his mother and his wife were deaf), which led him to write two papers concerning deaf white cats (see OMIA 000259-9685). As it turns out, in these papers deaf white cats are mentioned only in passing; in both reports, Bell is primarily concerned with deafness and skin colour in humans.

Mapping: Peng et al. 2015) "conducted the first GWAS of the supernumerary nipple phenotype in Wadi sheep, a native Chinese sheep breed, based on Ovine Infinium HD SNP BeadChip genotypes in a total of 144 ewes (75 cases with four teats, including two normal and two supernumerary teats, and 69 control cases with two teats). We detected 63 significant SNPs at the chromosome-wise threshold. Additionally, one candidate region (chr1: 170.723-170.734 Mb) was identified by haplotype-based association tests, with one SNP (rs413490006) surrounding functional genes BBX and CD47 on chromosome 1 being commonly identified as significant by the two mentioned analyses."

Zhao et al. (2022): " ... a genome-wide association study was used to identify genetic markers and genes related to the number of teats in the Hu sheep population, a native Chinese sheep breed. ... We also performed quantitative real-time PCR testing of ... identified [positional] candidate genes, identifying three genes with significantly different expression. Our study suggested that the LHFP, DPYSL2, and TDP-43 genes may be related to the number of teats in sheep."

Breeds: Hu, Wadi.