Ing the rare variants identified by sequencing with those catalogued in the public databases bmjopen-2016-011824 demonstrates that some of the rare variants may be of etiologic importance. The observation that three (P108A, W203R, and F284L) of the four rare missense variants not found in either the 1000GP [28,29] or the NHLBI_ESP [30] data were predicted to affect the function of the receptor protein particularly merits further attention. These results suggest that rare OXTR coding variants appear to make some contribution to the genetic risk of prematurity, but larger studies will be needed to measure their combined as well as individual impact more accurately and determine the diagnostic or therapeutic relevance of the findings. We studied the role of maternal OXTR genotype in PTB in more PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/744568 depth using maternal grandparent-mother triads. Transmission disequilibrium analysis revealed no significant transmission distortion of the OXTR coding variants examined when the analysis was performed on all GA cases or stratified into 3 GA groups. However, two missense SNPs (rs4686302 and rs237902) showed nominal associations in the U.S. triads for the sliding window GA subgroups primarily involving 24?2 weeks of gestation. These results suggest GA-specific effects of maternal genotypes of these OXTR SNPs on susceptibility to PTB. We characterized the effects of three mutations of potential functional significance with in vitro assays. Our radioligand binding assay revealed that P108A and W203R mutant-transfected cells display significantly diminished levels of [3H]OXT specific binding, compared to wild-type-transfected cells. Although it should be further clarified if the mutations affect OXTR protein expression, ligand binding affinity, or both, our results indicate the importance of these residues in receptor function and support previous findings that the first and second extracellular loops of OXTR, where P108 and W203 residues, respectively, are located, are important for agonist binding and selectivity [38]. Despite theirimportant biological effects, it is yet unclear how the mutations may contribute to the disease as it is counterintuitive that attenuated OXT signaling leads to PTB. However, it is possible that the variants may act indirectly to stimulate uterine contractions. Given that the regulation of OXTR function is dependent on steroids such as estradiol, progesterone, and its metabolites [39-41], it is probable that the mutations may affect receptor-hormone interaction in a way that interferes with the timely onset of labor. Another mutation, F284L, also exhibited a reduced level of specific binding, but the result did not quite reach statistical significance. An earlier mutagenesis study has shown that when two transmembrane residues Y209 and F284 are mutated to F and Y residues, respectively, arginine vasopressin (AVP), a partial agonist of the OXTR, becomes a full PubMed ID:https://www.ncbi.nlm.nih.gov/pubmed/3971254 agonist [8,42]. The finding indicates that these residues may be critical for modulation of the receptor response to AVP. Given the N-BOC-3-Fluoro-D-phenylalanine uterotonic action of AVP [43], an investigation into the sensitivity of the F284 as well as the other two mutants to other agonists like AVP could possibly provide an explanation about the pathogenic effects of those mutations. Our study has certain limitations. First of all, the sample size of our association study may not be large enough Ethyl 5-bromo-6-chloropicolinate to provide sufficient statistical power for the analysis of rare variants with small effects. Second, the functional assa.