INHA Gene Variant Linked to Litter Size in Kreishi Ewes

A single-letter change in the INHA gene is strongly associated with litter size in Kreishi ewes, according to a study published in Molecular Biology Reports. In a flock of 100 ewes aged three to four years, researchers led by Siraj A. Hashem, Mervan Bayraktar and Tahreer M. Al-Thuwaini identified a variant at position 425 of the gene, where a cytosine is replaced by thymine. This substitution alters the encoded protein at amino acid 142, swapping a serine for a phenylalanine, a change designated p.Ser142Phe. Ewes carrying certain versions of this variant were far more likely to bear twins than single lambs, although the finding is an association in one population and does not establish that the variant causes higher fertility.

The team divided the animals by reproductive record into two groups: 46 ewes that had carried a single lamb and 54 that had carried twins. Using polymerase chain reaction amplification followed by bidirectional Sanger sequencing, they genotyped the INHA variant and found three genotypes in the flock, labelled CC, CT and TT. The distribution of these genotypes differed markedly between the single-bearing and twin-bearing groups, with a chi-square statistic of 30.87 and a P value below 0.0001. In plain terms, the probability of seeing such a skewed pattern by chance alone is extremely small, though the result still reflects correlation rather than a demonstrated biological mechanism.

Binary logistic regression quantified the strength of the association. Compared with ewes carrying the TT genotype, those with the CT genotype had roughly sixfold higher odds of twin birth, with an odds ratio of 6.77 and a 95 percent confidence interval spanning 1.59 to 28.72. The CC genotype showed an even larger estimated association, with an odds ratio of 16.51 and a confidence interval of 5.56 to 49.08. Confidence intervals this wide, particularly for the CT genotype, indicate considerable statistical uncertainty in the smaller genotype groups, a limitation the authors acknowledge by calling for validation in larger, independent populations before the variant is used as a molecular marker for reproductive selection.

INHA is a candidate gene involved in reproductive regulation, which is why it was examined for links to litter size in sheep. To probe what the p.Ser142Phe substitution might do to the protein, the researchers applied four computational tools. SIFT predicted the amino acid change to be deleterious, PolyPhen-2 rated it as potentially damaging, and DynaMut2 predicted a destabilizing effect on protein stability. Visualization with PyMOL suggested that the overall protein fold remains conserved, with localized structural changes around residue 142. These are model-based predictions about protein structure and function, not measurements of reproductive outcomes in the animals themselves.

The study’s scope is worth keeping in view. It involved a single breed, one flock of 100 animals, and a binary classification of litter size rather than a full range of litter sizes. The genotypes were recorded alongside reproductive history, so the analysis cannot distinguish whether the variant influences ovulation rate, embryo survival, or some other linked genetic factor in the same breed. Environmental and management influences on twinning were not the focus of the association analysis. What the work delivers is a precisely characterized variant, a statistically significant genotype frequency difference between single- and twin-bearing ewes, and in silico evidence that the substitution may affect protein structure, all of which together justify follow-up studies in larger and genetically independent sheep populations. If the association holds up under validation, the authors conclude, the variant could eventually serve as a molecular marker for reproductive selection; for now, that step remains unproven.

Subject of Research: Association of an INHA missense polymorphism with litter size in Kreishi ewes

Article Title: Association of INHA polymorphism with fertility in Kreishi ewes

Article References: Hashem, S. A., Bayraktar, M., & Al-Thuwaini, T. M. (2026). Association of INHA polymorphism with fertility in Kreishi ewes. Molecular Biology Reports, 53(1), Article 1814. https://doi.org/10.1007/s11033-026-13058-1

Image Credits: AI Generated

DOI: 10.1007/s11033-026-13058-1

Keywords: INHA gene, Kreishi sheep, litter size, twinning, polymorphism, missense variant, Sanger sequencing, logistic regression, sheep fertility, molecular marker, in silico prediction, Association