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Lawson JM, Shilton CA, Lindsay-McGee V, Psifidi A, Wathes DC, Raudsepp T, de Mestre AM. Does inbreeding contribute to pregnancy loss in Thoroughbred horses? Equine Vet J 2024; 56:711-718. [PMID: 38221707 DOI: 10.1111/evj.14057] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2023] [Accepted: 12/29/2023] [Indexed: 01/16/2024]
Abstract
BACKGROUND Excessive inbreeding increases the probability of uncovering homozygous recessive genotypes and has been associated with an increased risk of retained placenta and lower semen quality. No genomic analysis has investigated the association between inbreeding levels and pregnancy loss. OBJECTIVES To compare genetic inbreeding coefficients (F) of naturally occurring Thoroughbred Early Pregnancy Loss (EPLs), Mid and Late term Pregnancy Loss (MLPL) and Controls. The F value was hypothesised to be higher in cases of pregnancy loss (EPLs and MLPLs) than Controls. STUDY DESIGN Observational case-control study. METHODS Allantochorion and fetal DNA from EPL (n = 37, gestation age 14-65 days), MLPL (n = 94, gestational age 70 days-24 h post parturition) and Controls (n = 58) were genotyped on the Axiom Equine 670K SNP Genotyping Array. Inbreeding coefficients using Runs of Homozygosity (FROH) were calculated using PLINK software. ROHs were split into size categories to investigate the recency of inbreeding. RESULTS MLPLs had significantly higher median number of ROH (188 interquartile range [IQR], 180.8-197.3), length of ROH (3.10, IQR 2.93-3.33), and total number of ROH (590.8, IQR 537.3-632.3), and FROH (0.26, IQR 0.24-0.28) when compared with the Controls and the EPLs (p < 0.05). There was no significant difference in any of the inbreeding indices between the EPLs and Controls. The MLPLs had a significantly higher proportion of long (>10 Mb) ROH (2.5%, IQR 1.6-3.6) than the Controls (1.7%, IQR 0.6-2.5), p = 0.001. No unique ROHs were found in the EPL or MLPL populations. MAIN LIMITATIONS SNP-array data does not allow analysis of every base in the sequence. CONCLUSIONS This first study of the effect of genomic inbreeding levels on pregnancy loss showed that inbreeding is a contributor to MLPL, but not EPL in the UK Thoroughbred population. Mating choices remain critical, because inbreeding may predispose to MLPL by increasing the risk of homozygosity for specific lethal allele(s).
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Affiliation(s)
- Jessica M Lawson
- Department of Pathobiology and Population Sciences, The Royal Veterinary College, University of London, Hatfield, UK
| | - Charlotte A Shilton
- Department of Comparative Biomedical Sciences, The Royal Veterinary College, University of London, London, UK
| | - Victoria Lindsay-McGee
- Department of Clinical Science and Services, The Royal Veterinary College, University of London, London, UK
| | - Androniki Psifidi
- Department of Clinical Science and Services, The Royal Veterinary College, University of London, London, UK
| | - D Claire Wathes
- Department of Pathobiology and Population Sciences, The Royal Veterinary College, University of London, Hatfield, UK
| | - Terje Raudsepp
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, Texas, USA
| | - Amanda M de Mestre
- Department of Comparative Biomedical Sciences, The Royal Veterinary College, University of London, London, UK
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Steensma MJ, Doekes HP, Pook T, Derks MFL, Bakker N, Ducro BJ. Evaluation of breeding strategies to reduce the inbreeding rate in the Friesian horse population: Looking back and moving forward. J Anim Breed Genet 2024. [PMID: 38745529 DOI: 10.1111/jbg.12872] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2024] [Revised: 04/29/2024] [Accepted: 05/01/2024] [Indexed: 05/16/2024]
Abstract
In the past, small population sizes and unequal ancestor contributions have resulted in high inbreeding rates (ΔF) in the Friesian horse. Two decades ago, the studbook implemented a mating quota and started publishing individual kinships and reduced ΔF below 1% per generation. However, since then, the breeding population size has decreased and this raises the question whether current breeding strategies are sufficient to keep ΔF below desired rates. The aim of this study was to (1) reflect on past inbreeding trends and their main determinants, using pedigree analysis and (2) evaluate the effectiveness of the current and additional breeding strategies using stochastic simulations. We estimated the current ΔF (2013-2022) at 0.72% per generation. While the total contribution of the top 10 sires to the number of offspring per year has decreased from 75% in 1980 to 35% in 2022, this was mainly due to an increased number of approved studbook sires, and not due to more equalized contributions among sires. Of the simulated breeding strategies, selecting only breeding stallions with a below average mean kinship (i.e., "mean kinship selection") was most effective to decrease ΔF (from 0.66% to 0.33%). Increasing the number of breeding sires only had an effect when also a mating quota was applied. However, its effect remained limited. For example, a ~1.5 fold increase, combined with a mating quota of 80 offspring per sire per year, reduced ΔF from 0.55% to 0.51%. When increasing the number of breeding mares, a practically unfeasible large increase was needed for a meaningful reduction in ΔF (e.g. twice as many mares were needed to reduce ΔF from 0.66% to 0.56%). Stratified mating quotas, a novel approach in which we assigned each sire a mating quota (of 60, 80, 100 or 120 offspring per year) based on its mean kinship to recently born foals, resulted in a lower ΔF (0.43%) than a general mating quota of 90 offspring per sire per year (0.55%). Overall, while the current ΔF is below 1%, we recommend to implement additional strategies to further reduce ΔF below 0.5% in the Friesian horse population. For this breed and similar populations, we recommend to focus on breeding strategies based on kinship levels to effectively reduce ΔF.
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Affiliation(s)
- Marije J Steensma
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
- Koninklijke Vereniging het Friesch Paarden-Stamboek, Drachten, The Netherlands
| | - Harmen P Doekes
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
| | - Torsten Pook
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
| | - Martijn F L Derks
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
| | - Nynke Bakker
- Koninklijke Vereniging het Friesch Paarden-Stamboek, Drachten, The Netherlands
| | - Bart J Ducro
- Animal Breeding and Genomics, Wageningen University & Research, Wageningen, The Netherlands
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De Coster T, Zhao Y, Tšuiko O, Demyda-Peyrás S, Van Soom A, Vermeesch JR, Smits K. Genome-wide equine preimplantation genetic testing enabled by simultaneous haplotyping and copy number detection. Sci Rep 2024; 14:2003. [PMID: 38263320 PMCID: PMC10805710 DOI: 10.1038/s41598-023-48103-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2023] [Accepted: 11/22/2023] [Indexed: 01/25/2024] Open
Abstract
In different species, embryonic aneuploidies and genome-wide errors are a major cause of developmental failure. The increasing number of equine embryos being produced worldwide provides the opportunity to characterize and rank or select embryos based on their genetic profile prior to transfer. Here, we explored the possibility of generic, genome-wide preimplantation genetic testing concurrently for aneuploidies (PGT-A) and monogenic (PGT-M) traits and diseases in the horse, meanwhile assessing the incidence and spectrum of chromosomal and genome-wide errors in in vitro-produced equine embryos. To this end, over 70,000 single nucleotide polymorphism (SNP) positions were genotyped in 14 trophectoderm biopsies and corresponding biopsied blastocysts, and in 26 individual blastomeres from six arrested cleavage-stage embryos. Subsequently, concurrent genome-wide copy number detection and haplotyping by haplarithmisis was performed and the presence of aneuploidies and genome-wide errors and the inherited parental haplotypes for four common disease-associated genes with high carrier frequency in different horse breeds (GBE1, PLOD1, B3GALNT2, MUTYH), and for one color coat-associated gene (STX17) were compared in biopsy-blastocyst combinations. The euploid (n = 12) or fully aneuploid (n = 2) state and the inherited parental haplotypes for 42/45 loci of interest of the biopsied blastocysts were predicted by the biopsy samples in all successfully analyzed biopsy-blastocyst combinations (n = 9). Two biopsies showed a loss of maternal chromosome 28 and 31, respectively, which were confirmed in the corresponding blastocysts. In one of those biopsies, additional complex aneuploidies not present in the blastocyst were found. Five out of six arrested embryos contained chromosomal and/or genome-wide errors in most of their blastomeres, demonstrating their contribution to equine embryonic arrest in vitro. The application of the described PGT strategy would allow to select equine embryos devoid of genetic errors and pathogenetic variants, and with the variants of interest, which will improve foaling rate and horse quality. We believe this approach will be a gamechanger in horse breeding.
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Affiliation(s)
- T De Coster
- Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Merelbeke, Belgium.
- Department of Human Genetics, KU Leuven, Leuven, Belgium.
| | - Y Zhao
- Department of Human Genetics, KU Leuven, Leuven, Belgium
| | - O Tšuiko
- Department of Human Genetics, KU Leuven, Leuven, Belgium
| | - S Demyda-Peyrás
- Department of Genetics, University of Córdoba, Córdoba, Spain
- Department of Animal Production, Veterinary School, National University of La Plata, La Plata, Argentina
| | - A Van Soom
- Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Merelbeke, Belgium
| | - J R Vermeesch
- Department of Human Genetics, KU Leuven, Leuven, Belgium
| | - K Smits
- Department of Internal Medicine, Reproduction and Population Medicine, Ghent University, Merelbeke, Belgium.
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Shilton CA, Kahler A, Roach JM, Raudsepp T, de Mestre AM. Lethal variants of equine pregnancy: is it the placenta or foetus leading the conceptus in the wrong direction? Reprod Fertil Dev 2022; 35:51-69. [PMID: 36592981 DOI: 10.1071/rd22239] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Embryonic and foetal loss remain one of the greatest challenges in equine reproductive health with 5-10% of established day 15 pregnancies and a further 5-10% of day 70 pregnancies failing to produce a viable foal. The underlying reason for these losses is variable but ultimately most cases will be attributed to pathologies of the environment of the developing embryo and later foetus, or a defect intrinsic to the embryo itself that leads to lethality at any stage of gestation right up to birth. Historically, much research has focused on the maternal endometrium, endocrine and immune responses in pregnancy and pregnancy loss, as well as infectious agents such as pathogens, and until recently very little was known about the both small and large genetic variants associated with reduced foetal viability in the horse. In this review, we first introduce key aspects of equine placental and foetal development. We then discuss incidence, risk factors and causes of pregnancy loss, with the latter focusing on genetic variants described to date that can impact equine foetal viability.
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Affiliation(s)
- Charlotte A Shilton
- Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Herts, AL9 7TA, UK
| | - Anne Kahler
- Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Herts, AL9 7TA, UK
| | - Jessica M Roach
- Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Herts, AL9 7TA, UK
| | - Terje Raudsepp
- Department of Veterinary Integrative Biosciences, Texas A&M University, College Station, TX 77843-4458, USA
| | - Amanda M de Mestre
- Department of Comparative Biomedical Sciences, The Royal Veterinary College, Hawkshead Lane, Herts, AL9 7TA, UK
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Hang J, Wang J, Lu M, Xue Y, Qiao J, Tao L. Protein O-mannosylation across kingdoms and related diseases: From glycobiology to glycopathology. Biomed Pharmacother 2022; 148:112685. [PMID: 35149389 DOI: 10.1016/j.biopha.2022.112685] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 01/29/2022] [Accepted: 02/01/2022] [Indexed: 11/18/2022] Open
Abstract
The post-translational glycosylation of proteins by O-linked α-mannose is conserved from bacteria to humans. Due to advances in high-throughput mass spectrometry-based approaches, a variety of glycoproteins are identified to be O-mannosylated. Various proteins with O-mannosylation are involved in biological processes, providing essential necessity for proper growth and development. In this review, we summarize the process and regulation of O-mannosylation. The multi-step O-mannosylation procedures are quite dynamic and complex, especially when considering the structural and functional inspection of the involved enzymes. The widely studied O-mannosylated proteins in human include α-Dystroglycan (α-DG), cadherins, protocadherins, and plexin, and their aberrant O-mannosylation are associated with many diseases. In addition, O-mannosylation also contributes to diverse functions in lower eukaryotes and prokaryotes. Finally, we present the relationship between O-mannosylation and gut microbiota (GM), and elucidate that O-mannosylation in microbiome is of great importance in the dynamic balance of GM. Our study provides an overview of the processes of O-mannosylation in mammalian cells and other organisms, and also associated regulated enzymes and biological functions, which could contribute to the understanding of newly discovered O-mannosylated glycoproteins.
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Affiliation(s)
- Jing Hang
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing 100191, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), Beijing 100191, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, Beijing 100191, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, Beijing 100191, China
| | - Jinpeng Wang
- Department of Orthopedics, First Hospital of China Medical University, Shenyang 110001, China
| | - Minzhen Lu
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing 100191, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), Beijing 100191, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, Beijing 100191, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, Beijing 100191, China
| | - Yuchuan Xue
- The First Department of Clinical Medicine, China Medical University, Shenyang 110001, China
| | - Jie Qiao
- Center for Reproductive Medicine, Department of Obstetrics and Gynecology, Peking University Third Hospital, Beijing 100191, China; National Clinical Research Center for Obstetrics and Gynecology (Peking University Third Hospital), Beijing 100191, China; Key Laboratory of Assisted Reproduction (Peking University), Ministry of Education, Beijing 100191, China; Beijing Key Laboratory of Reproductive Endocrinology and Assisted Reproductive Technology, Beijing 100191, China.
| | - Lin Tao
- Department of Orthopedics, First Hospital of China Medical University, Shenyang 110001, China.
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6
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Diaphragmatic hernia with focal megaoesophagus: An extremely rare combination. EQUINE VET EDUC 2021. [DOI: 10.1111/eve.13358] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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7
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Fernandes TJ, David F, Samper JC, Vinardell T. Theriogenology Question of the Month. J Am Vet Med Assoc 2021; 258:1345-1347. [PMID: 34061614 DOI: 10.2460/javma.258.12.1345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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8
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De Coster T, Velez DA, Van Soom A, Woelders H, Smits K. Cryopreservation of equine oocytes: looking into the crystal ball. Reprod Fertil Dev 2021; 32:453-467. [PMID: 32172776 DOI: 10.1071/rd19229] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2019] [Accepted: 11/14/2019] [Indexed: 12/18/2022] Open
Abstract
Invitro embryo production has evolved rapidly in the horse over the past decade, but blastocyst rates from vitrified equine oocytes remain quite poor and further research is needed to warrant application. Oocyte vitrification is affected by several technical and biological factors. In the horse, short exposure of immature oocytes to the combination of permeating and non-permeating cryoprotective agents has been associated with the best results so far. High cooling and warming rates are also crucial and can be obtained by using minimal volumes and open cryodevices. Vitrification of invivo-matured oocytes has yielded better results, but is less practical. The presence of the corona radiata seems to partially protect those factors that are necessary for the construction of the normal spindle and for chromosome alignment, but multiple layers of cumulus cells may impair permeation of cryoprotective agents. In addition to the spindle, the oolemma and mitochondria are also particularly sensitive to vitrification damage, which should be minimised in future vitrification procedures. This review presents promising protocols and novel strategies in equine oocyte vitrification, with a focus on blastocyst development and foal production as most reliable outcome parameters.
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Affiliation(s)
- Tine De Coster
- Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium; and Corresponding authors. ;
| | - Daniel Angel Velez
- Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium; and Corresponding authors. ;
| | - Ann Van Soom
- Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
| | - Henri Woelders
- Wageningen Livestock Research, Wageningen University and Research, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands
| | - Katrien Smits
- Department of Reproduction, Obstetrics and Herd Health, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium
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McKnight I, Hart C, Park IH, Shim JW. Genes causing congenital hydrocephalus: Their chromosomal characteristics of telomere proximity and DNA compositions. Exp Neurol 2021; 335:113523. [PMID: 33157092 PMCID: PMC7750280 DOI: 10.1016/j.expneurol.2020.113523] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2020] [Revised: 10/10/2020] [Accepted: 10/30/2020] [Indexed: 01/06/2023]
Abstract
Congenital hydrocephalus (CH) is caused by genetic mutations, but whether factors impacting human genetic mutations are disease-specific remains elusive. Given two factors associated with high mutation rates, we reviewed how many disease-susceptible genes match with (i) proximity to telomeres or (ii) high adenine and thymine (A + T) content in human CH as compared to other disorders of the central nervous system (CNS). We extracted genomic information using a genome data viewer. Importantly, 98 of 108 genes causing CH satisfied (i) or (ii), resulting in >90% matching rate. However, such a high accordance no longer sustained as we checked two factors in Alzheimer's disease (AD) and/or familial Parkinson's disease (fPD), resulting in 84% and 59% matching, respectively. A disease-specific matching of telomere proximity or high A + T content predicts causative genes of CH much better than neurodegenerative diseases and other CNS conditions, likely due to sufficient number of known causative genes (n = 108) and precise determination and classification of the genotype and phenotype. Our analysis suggests a need for identifying genetic basis of both factors before human clinical studies, to prioritize putative genes found in preclinical models into the likely (meeting at least one) and more likely candidate (meeting both), which predisposes human genes to mutations.
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Affiliation(s)
- Ian McKnight
- Department of Biomedical Engineering, Marshall University, Huntington, WV 25755, USA
| | - Christoph Hart
- Department of Biomedical Engineering, Marshall University, Huntington, WV 25755, USA
| | - In-Hyun Park
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06519, USA
| | - Joon W Shim
- Department of Biomedical Engineering, Marshall University, Huntington, WV 25755, USA.
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Hisey EA, Hermans H, Lounsberry ZT, Avila F, Grahn RA, Knickelbein KE, Duward-Akhurst SA, McCue ME, Kalbfleisch TS, Lassaline ME, Back W, Bellone RR. Whole genome sequencing identified a 16 kilobase deletion on ECA13 associated with distichiasis in Friesian horses. BMC Genomics 2020; 21:848. [PMID: 33256610 PMCID: PMC7706231 DOI: 10.1186/s12864-020-07265-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2020] [Accepted: 11/23/2020] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND Distichiasis, an ocular disorder in which aberrant cilia (eyelashes) grow from the opening of the Meibomian glands of the eyelid, has been reported in Friesian horses. These misplaced cilia can cause discomfort, chronic keratitis, and corneal ulceration, potentially impacting vision due to corneal fibrosis, or, if secondary infection occurs, may lead to loss of the eye. Friesian horses represent the vast majority of reported cases of equine distichiasis, and as the breed is known to be affected with inherited monogenic disorders, this condition was hypothesized to be a simply inherited Mendelian trait. RESULTS A genome wide association study (GWAS) was performed using the Axiom 670 k Equine Genotyping array (MNEc670k) utilizing 14 cases and 38 controls phenotyped for distichiasis. An additive single locus mixed linear model (EMMAX) approach identified a 1.83 Mb locus on ECA5 and a 1.34 Mb locus on ECA13 that reached genome-wide significance (pcorrected = 0.016 and 0.032, respectively). Only the locus on ECA13 withstood replication testing (p = 1.6 × 10- 5, cases: n = 5 and controls: n = 37). A 371 kb run of homozygosity (ROH) on ECA13 was found in 13 of the 14 cases, providing evidence for a recessive mode of inheritance. Haplotype analysis (hapQTL) narrowed the region of association on ECA13 to 163 kb. Whole-genome sequencing data from 3 cases and 2 controls identified a 16 kb deletion within the ECA13 associated haplotype (ECA13:g.178714_195130del). Functional annotation data supports a tissue-specific regulatory role of this locus. This deletion was associated with distichiasis, as 18 of the 19 cases were homozygous (p = 4.8 × 10- 13). Genotyping the deletion in 955 horses from 54 different breeds identified the deletion in only 11 non-Friesians, all of which were carriers, suggesting that this could be causal for this Friesian disorder. CONCLUSIONS This study identified a 16 kb deletion on ECA13 in an intergenic region that was associated with distichiasis in Friesian horses. Further functional analysis in relevant tissues from cases and controls will help to clarify the precise role of this deletion in normal and abnormal eyelash development and investigate the hypothesis of incomplete penetrance.
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Affiliation(s)
- E A Hisey
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA
| | - H Hermans
- Department of Clinical Sciences, Utrecht University, Yalelaan 112-114, NL-3584, CM, Utrecht, The Netherlands
| | - Z T Lounsberry
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA
| | - F Avila
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA
| | - R A Grahn
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA
| | - K E Knickelbein
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA
- Veterinary Medical Teaching Hospital, University of California-Davis, Davis, CA, USA
| | - S A Duward-Akhurst
- Department of Veterinary Population Medicine, University of Minnesota, Saint Paul, MN, USA
| | - M E McCue
- Department of Veterinary Population Medicine, University of Minnesota, Saint Paul, MN, USA
| | - T S Kalbfleisch
- Department of Veterinary Science, Gluck Equine Research Center, University of Kentucky, Lexington, KY, USA
| | - M E Lassaline
- Department of Clinical Sciences and Advanced Medicine, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - W Back
- Department of Clinical Sciences, Utrecht University, Yalelaan 112-114, NL-3584, CM, Utrecht, The Netherlands
- Department of Surgery and Anaesthesia of Domestic Animals, Ghent University, Merelbeke, Belgium
| | - R R Bellone
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA.
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, USA.
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11
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Abstract
Neurologic disease in horses can be particularly challenging to diagnose and treat. These diseases can result in economic losses, emotional distress to owners, and injury to the horse or handlers. To date, there are 5 neurologic diseases caused by known genetic mutations and several more are suspected to be heritable: lethal white foal syndrome, lavender foal syndrome, cerebellar abiotrophy, occipitoatlantoaxial malformation, and Friesian hydrocephalus. Genetic testing allows owners, breeders, and veterinarians to make informed decisions when selecting dams and sires for breeding or deciding the treatment or prognosis of a neurologic animal.
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Affiliation(s)
- Lisa Edwards
- Department of Veterinary Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, Room 4206 Vet Med 3A One Shields Avenue, Davis, CA 95616, USA
| | - Carrie J Finno
- Department of Veterinary Population Health and Reproduction, School of Veterinary Medicine, University of California Davis, Room 4206 Vet Med 3A One Shields Avenue, Davis, CA 95616, USA.
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12
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Abstract
The sequencing and assembly of a reference genome for the horse has been revolutionary for investigation of horse health and performance. Next-generation sequencing (NGS) methods represent a second revolution in equine genomics. Researchers can align and compare DNA and RNA sequencing data to the reference genome to explore variation that may contribute or be attributed to disease. NGS has also facilitated the translation of research discovery to clinically relevant applications. This article discusses the history and development of NGS, details some of the available sequencing platforms, and describes currently available applications in the context of both discovery and clinical settings.
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13
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Dini P, Bartels T, Revah I, Claes AN, Stout TAE, Daels P. A retrospective study on semen quality parameters from four different Dutch horse breeds with different levels of inbreeding. Theriogenology 2020; 157:18-23. [PMID: 32768723 DOI: 10.1016/j.theriogenology.2020.07.017] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2020] [Revised: 07/15/2020] [Accepted: 07/15/2020] [Indexed: 01/04/2023]
Abstract
A high degree of inbreeding has been reported to negatively impact semen quality in Friesian horses and Shetland ponies. Both breeds are characterized by a closed studbook, small population size, and high incidence of inbreeding. The Dutch Warmblood studbook (KWPN: Koninklijk Warmblood Paardenstamboek Nederland) is a much larger studbook with two distinct populations: the KWPN-Riding horses, managed as an 'open' studbook, and the KWPN-Harness horses, representing a much smaller subpopulation within the KWPN breed and managed as an 'almost closed' studbook. It was recently reported that the degree of inbreeding in KWPN-Harness horses has increased in recent decades due to the small gene pool; however, the degree of inbreeding is still lower than that of Friesian horses and Shetland ponies. We hypothesized that a high or rising degree of inbreeding might negatively impact semen quality. In the present study, we retrospectively compared semen quality parameters of stallions from four different breeds or types (Friesian Horses, Shetland Ponies, KWPN-Riding horses, and KWPN-Harness horses), each reported with different degrees of inbreeding. Semen concentration, and percentages of motile, morphologically normal and live spermatozoa, and the total number of morphologically normal, progressive motile spermatozoa per ejaculate (TNM) were analyzed for 2832 semen evaluations performed over a 15-year period. KWPN-Harness horses had a significantly lower sperm concentration, % motile spermatozoa and % live spermatozoa than KWPN-Riding horses but the % motile and % morphologically normal spermatozoa and TNM in both KWPN-Harness and KWPN-Riding horses were significantly higher than in Friesian horses and Shetland ponies. These results suggest a lower semen quality in KWPN-Harness than KWPN-Riding horses, potentially as a result of a higher coefficient of inbreeding. The negative trend observed in the KWPN-Harness horses may be a warning sign, and breeders or stud books should monitor the degree of inbreeding carefully to avoid a further reduction in semen quality, to the levels observed in Friesian horses and Shetland ponies.
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Affiliation(s)
- Pouya Dini
- Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium
| | - Tara Bartels
- Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium
| | - Irma Revah
- Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium
| | - Anthony N Claes
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112, 3584CM, Utrecht, the Netherlands
| | - Tom A E Stout
- Department of Clinical Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112, 3584CM, Utrecht, the Netherlands
| | - Peter Daels
- Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820, Merelbeke, Belgium.
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14
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Abstract
Genetic testing in horses began in the 1960s, when parentage testing using blood group markers became the standard. In the 1990s, parentage testing shifted from evaluating blood groups to DNA testing. The development of genetics and genomics in both human and veterinarian medicine, along with continued technological advances in the last 2 decades, has helped unravel the causal variants for many horse traits. Genetic testing is also now possible for a variety of phenotypic and disease traits and is used to assist in breeding and clinical management decisions. This article describes the genetic tests that are currently available for horses.
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Affiliation(s)
- Rebecca R Bellone
- Department of Population Health and Reproduction Davis, CA 95616, USA; Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
| | - Felipe Avila
- Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA
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15
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Raudsepp T, Finno CJ, Bellone RR, Petersen JL. Ten years of the horse reference genome: insights into equine biology, domestication and population dynamics in the post-genome era. Anim Genet 2019; 50:569-597. [PMID: 31568563 PMCID: PMC6825885 DOI: 10.1111/age.12857] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/09/2019] [Indexed: 12/14/2022]
Abstract
The horse reference genome from the Thoroughbred mare Twilight has been available for a decade and, together with advances in genomics technologies, has led to unparalleled developments in equine genomics. At the core of this progress is the continuing improvement of the quality, contiguity and completeness of the reference genome, and its functional annotation. Recent achievements include the release of the next version of the reference genome (EquCab3.0) and generation of a reference sequence for the Y chromosome. Horse satellite‐free centromeres provide unique models for mammalian centromere research. Despite extremely low genetic diversity of the Y chromosome, it has been possible to trace patrilines of breeds and pedigrees and show that Y variation was lost in the past approximately 2300 years owing to selective breeding. The high‐quality reference genome has led to the development of three different SNP arrays and WGSs of almost 2000 modern individual horses. The collection of WGS of hundreds of ancient horses is unique and not available for any other domestic species. These tools and resources have led to global population studies dissecting the natural history of the species and genetic makeup and ancestry of modern breeds. Most importantly, the available tools and resources, together with the discovery of functional elements, are dissecting molecular causes of a growing number of Mendelian and complex traits. The improved understanding of molecular underpinnings of various traits continues to benefit the health and performance of the horse whereas also serving as a model for complex disease across species.
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Affiliation(s)
- T Raudsepp
- Department of Veterinary Integrative Biosciences, College of Veterinary Medicine and Biomedical Research, Texas A&M University, College Station, TX, 77843, USA
| | - C J Finno
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA
| | - R R Bellone
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.,School of Veterinary Medicine, Veterinary Genetics Laboratory, University of California-Davis, Davis, CA, 95616, USA
| | - J L Petersen
- Department of Animal Science, University of Nebraska, Lincoln, NE, 68583-0908, USA
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16
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Origin and Evolution of Deleterious Mutations in Horses. Genes (Basel) 2019; 10:genes10090649. [PMID: 31466279 PMCID: PMC6769756 DOI: 10.3390/genes10090649] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 08/24/2019] [Accepted: 08/26/2019] [Indexed: 01/04/2023] Open
Abstract
Domestication has changed the natural evolutionary trajectory of horses by favoring the reproduction of a limited number of animals showing traits of interest. Reduced breeding stocks hampered the elimination of deleterious variants by means of negative selection, ultimately inflating mutational loads. However, ancient genomics revealed that mutational loads remained steady during most of the domestication history until a sudden burst took place some 250 years ago. To identify the factors underlying this trajectory, we gather an extensive dataset consisting of 175 modern and 153 ancient genomes previously published, and carry out the most comprehensive characterization of deleterious mutations in horses. We confirm that deleterious variants segregated at low frequencies during the last 3500 years, and only spread and incremented their occurrence in the homozygous state during modern times, owing to inbreeding. This independently happened in multiple breeds, following both the development of closed studs and purebred lines, and the deprecation of horsepower in the 20th century, which brought many draft breeds close to extinction. Our work illustrates the paradoxical effect of some conservation and improvement programs, which reduced the overall genomic fitness and viability.
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17
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The Genomic Makeup of Nine Horse Populations Sampled in the Netherlands. Genes (Basel) 2019; 10:genes10060480. [PMID: 31242710 PMCID: PMC6627704 DOI: 10.3390/genes10060480] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2019] [Revised: 06/11/2019] [Accepted: 06/22/2019] [Indexed: 11/16/2022] Open
Abstract
The spectrum of modern horse populations encompasses populations with a long history of development in isolation and relatively recently formed types. To increase our understanding of the evolutionary history and provide information on how to optimally conserve or improve these populations with varying development and background for the future, we analyzed genotype data of 184 horses from 9 Dutch or common horse populations in the Netherlands: The Belgian draft horse, Friesian horse, Shetland pony, Icelandic horse, Gelder horse, Groninger horse, harness horse, KWPN sport horse and the Lipizzaner horse population. Various parameters were estimated (e.g., runs of homozygosity and FST values) to gain insight into genetic diversity and relationships within and among these populations. The identified genomic makeup and quantified relationships did mostly conform to the development of these populations as well as past and current breeding practices. In general, populations that allow gene-flow showed less inbreeding and homozygosity. Also, recent bottlenecks (e.g., related to high selective pressure) caused a larger contribution of long ROHs to inbreeding. Maintaining genetic diversity through tailor-made breeding practices is crucial for a healthy continuation of the investigated, mostly inbred and (effectively) small sized horse populations, of which several already experience inbreeding related issues.
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18
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Kolb DS, Klein C. Congenital hydrocephalus in a Belgian draft horse associated with a nonsense mutation in B3GALNT2. THE CANADIAN VETERINARY JOURNAL = LA REVUE VETERINAIRE CANADIENNE 2019; 60:197-198. [PMID: 30705458 PMCID: PMC6340252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Congenital hydrocephalus has been reported for a number of horse breeds, and for Friesian horses this condition has been associated with a nonsense mutation of B3GALNT2. We report the first case of congenital hydrocephalus associated with the said mutation in a Belgian draft horse. Genetic testing and consideration of the testing results in breeding programs are warranted.
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Affiliation(s)
- David Scott Kolb
- Lodi Veterinary Care, 705 North Main Street, Lodi, Wisconsin 53555, USA (Kolb); University of Calgary, Faculty of Veterinary Medicine, 3280 Hospital Drive NW, Calgary, Alberta T2N 4Z6 (Klein)
| | - Claudia Klein
- Lodi Veterinary Care, 705 North Main Street, Lodi, Wisconsin 53555, USA (Kolb); University of Calgary, Faculty of Veterinary Medicine, 3280 Hospital Drive NW, Calgary, Alberta T2N 4Z6 (Klein)
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19
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Alberi C, Hisey E, Lassaline M, Atilano A, Kalbfleisch T, Stoppini R, Hermans H, Back W, Mienaltowski MJ, Bellone RR. Ruling out BGN variants as simple X-linked causative mutations for bilateral corneal stromal loss in Friesian horses. Anim Genet 2018; 49:656-657. [PMID: 30246344 DOI: 10.1111/age.12726] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/21/2018] [Indexed: 11/30/2022]
Affiliation(s)
- Coral Alberi
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.,Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA
| | - Erin Hisey
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.,Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA
| | - Mary Lassaline
- Department of Surgical & Radiological Sciences, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA
| | - Alyssa Atilano
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.,Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA
| | - Theodore Kalbfleisch
- Biochemistry and Molecular Biology, School of Medicine, University of Louisville, Louisville, KY, 402925, USA
| | - Riccardo Stoppini
- Clinica Veterinaria Equina Cascina Gufa, Strada Provinciale 201 Km 3, 26833, Merlino, LO, Italy
| | - Hanneke Hermans
- Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112-114, NL-3584 CM, Utrecht, The Netherlands
| | - Willem Back
- Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112-114, NL-3584 CM, Utrecht, The Netherlands
| | - Michael J Mienaltowski
- Department of Animal Science, College of Agricultural and Environmental Sciences, University of California-Davis, Davis, CA, 95616, USA
| | - Rebecca R Bellone
- Department of Population Health and Reproduction, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA.,Veterinary Genetics Laboratory, School of Veterinary Medicine, University of California-Davis, Davis, CA, 95616, USA
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20
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Affiliation(s)
- E. N. Adam
- Gluck Equine Research Center; University of Kentucky; Lexington USA
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21
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Saey V, Tang J, Ducatelle R, Croubels S, De Baere S, Schauvliege S, van Loon G, Chiers K. Elevated urinary excretion of free pyridinoline in Friesian horses suggests a breed-specific increase in collagen degradation. BMC Vet Res 2018; 14:139. [PMID: 29699546 PMCID: PMC5921786 DOI: 10.1186/s12917-018-1454-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2017] [Accepted: 04/12/2018] [Indexed: 11/10/2022] Open
Abstract
Background Friesian horses are known for their high inbreeding rate resulting in several genetic diseases such as hydrocephaly and dwarfism. This last decade, several studies focused on two other presumed hereditary traits in Friesian horses: megaoesophagus and aortic rupture. The pathogenesis of these diseases remains obscure but an important role of collagen has been hypothesized. The purpose of this study was to examine possible breed-related differences in collagen catabolism. Urinary specimens from Friesian (n = 17, median age 10 years old) and Warmblood horses (n = 17, median age 10 years old) were assessed for mature collagen cross-links, i.e. pyridinoline (PYD) (=hydroxylysylpyridinoline/HP) and deoxypyridinoline (DPD) (lysylpyridinoline /LP). Solid-phase extraction was performed, followed by reversed-phase ion-paired liquid chromatography prior to tandem mass spectrometry (MS/MS) detection. Results Mean urinary concentrations of free PYD, expressed as fPYD/creatinine ratio, were significantly higher in Friesian horses compared to Warmblood horses (28.5 ± 5.2 versus 22.2 ± 9.6 nmol/mmol, p = 0.02) while mean fDPD/creatinine ratios were similar in both horse breeds (3.0 ± 0.7 versus 4.6 ± 3.7 nmol/mmol, p = 0.09). Conclusions Since DPD is considered a specific bone degradation marker and PYD is more widely distributed in connective tissues, the significant elevation in the mean PYD/DPD ratio in Friesian versus Warmblood horses (9.6 ± 1.6 versus 5.7 ± 1.8, p < 0.0001) suggests a soft tissue origin for the increased fPYD levels. Considering that a previous study found no differences in total collagen content between Friesian and Warmblood horses for tendon and aortic tissue, this indicates a higher rate of collagen degradation. The latter might, at least in part, explain the predisposition of Friesians to connective tissue disorders.
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Affiliation(s)
- Veronique Saey
- Laboratory of Veterinary Pathology, Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium.
| | - Jonathan Tang
- Bioanalytical Facility, Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich, NR4 7UQ, UK
| | - Richard Ducatelle
- Laboratory of Veterinary Pathology, Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Siska Croubels
- Department of Pharmacology, Toxicology and Biochemistry, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Siegrid De Baere
- Department of Pharmacology, Toxicology and Biochemistry, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Stijn Schauvliege
- Deparment of Surgery and anaesthesiology of domestic animals, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Gunther van Loon
- Department of Large Animal Internal Medicine, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
| | - Koen Chiers
- Laboratory of Veterinary Pathology, Department of Pathology, Bacteriology and Avian Diseases, Faculty of Veterinary Medicine, Ghent University, Merelbeke, Belgium
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22
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Ayala-Valdovinos MA, Galindo-García J, Sánchez-Chiprés D, Duifhuis-Rivera T. Genotyping of friesian horses to detect a hydrocephalus-associated c.1423C>T mutation in B3GALNT2 using PCR-RFLP and PCR-PIRA methods: Frequency in stallion horses in México. Mol Cell Probes 2016; 32:69-71. [PMID: 28011345 DOI: 10.1016/j.mcp.2016.12.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2016] [Revised: 11/13/2016] [Accepted: 12/19/2016] [Indexed: 02/02/2023]
Abstract
Hydrocephalus in Friesian horses is an autosomal recessive hereditary disease that can result in an abortion, a stillbirth, or euthanization of a newborn foal. Here, the hydrocephalus-associated c.1423C > T mutation in B3GALNT2 gene was detected with PCR-RFLP and PCR-PIRA methods for horse genotyping. A preliminary genotyping survey was performed on 83 randomly selected Friesian stallion horses to determine the current allele frequency in Mexico. The frequency of the mutant T allele was 9.6%.
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Affiliation(s)
- Miguel Angel Ayala-Valdovinos
- Departamento de Producción Animal, División de Ciencias Veterinarias, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, A.P. 218 Zapopan 1, C.P. 45101, Zapopan, Jalisco, Mexico.
| | - Jorge Galindo-García
- Departamento de Producción Animal, División de Ciencias Veterinarias, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, A.P. 218 Zapopan 1, C.P. 45101, Zapopan, Jalisco, Mexico
| | - David Sánchez-Chiprés
- Departamento de Producción Animal, División de Ciencias Veterinarias, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, A.P. 218 Zapopan 1, C.P. 45101, Zapopan, Jalisco, Mexico
| | - Theodor Duifhuis-Rivera
- Departamento de Producción Animal, División de Ciencias Veterinarias, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, A.P. 218 Zapopan 1, C.P. 45101, Zapopan, Jalisco, Mexico
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23
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Leegwater PA, Vos-Loohuis M, Ducro BJ, Boegheim IJ, van Steenbeek FG, Nijman IJ, Monroe GR, Bastiaansen JWM, Dibbits BW, van de Goor LH, Hellinga I, Back W, Schurink A. Dwarfism with joint laxity in Friesian horses is associated with a splice site mutation in B4GALT7. BMC Genomics 2016; 17:839. [PMID: 27793082 PMCID: PMC5084406 DOI: 10.1186/s12864-016-3186-0] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2016] [Accepted: 10/22/2016] [Indexed: 02/08/2023] Open
Abstract
BACKGROUND Inbreeding and population bottlenecks in the ancestry of Friesian horses has led to health issues such as dwarfism. The limbs of dwarfs are short and the ribs are protruding inwards at the costochondral junction, while the head and back appear normal. A striking feature of the condition is the flexor tendon laxity that leads to hyperextension of the fetlock joints. The growth plates of dwarfs display disorganized and thickened chondrocyte columns. The aim of this study was to identify the gene defect that causes the recessively inherited trait in Friesian horses to understand the disease process at the molecular level. RESULTS We have localized the genetic cause of the dwarfism phenotype by a genome wide approach to a 3 Mb region on the p-arm of equine chromosome 14. The DNA of two dwarfs and one control Friesian horse was sequenced completely and we identified the missense mutation ECA14:g.4535550C > T that cosegregated with the phenotype in all Friesians analyzed. The mutation leads to the amino acid substitution p.(Arg17Lys) of xylosylprotein beta 1,4-galactosyltransferase 7 encoded by B4GALT7. The protein is one of the enzymes that synthesize the tetrasaccharide linker between protein and glycosaminoglycan moieties of proteoglycans of the extracellular matrix. The mutation not only affects a conserved arginine codon but also the last nucleotide of the first exon of the gene and we show that it impedes splicing of the primary transcript in cultured fibroblasts from a heterozygous horse. As a result, the level of B4GALT7 mRNA in fibroblasts from a dwarf is only 2 % compared to normal levels. Mutations in B4GALT7 in humans are associated with Ehlers-Danlos syndrome progeroid type 1 and Larsen of Reunion Island syndrome. Growth retardation and ligamentous laxity are common manifestations of these syndromes. CONCLUSIONS We suggest that the identified mutation of equine B4GALT7 leads to the typical dwarfism phenotype in Friesian horses due to deficient splicing of transcripts of the gene. The mutated gene implicates the extracellular matrix in the regular organization of chrondrocyte columns of the growth plate. Conservation of individual amino acids may not be necessary at the protein level but instead may reflect underlying conservation of nucleotide sequence that are required for efficient splicing.
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Affiliation(s)
- Peter A Leegwater
- Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, PO Box 80154, NL-3508 TD, Utrecht, The Netherlands.
| | - Manon Vos-Loohuis
- Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, PO Box 80154, NL-3508 TD, Utrecht, The Netherlands
| | - Bart J Ducro
- Animal Breeding and Genomics Centre, Wageningen University, PO Box 338, NL-6700 AH, Wageningen, The Netherlands
| | - Iris J Boegheim
- Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, PO Box 80154, NL-3508 TD, Utrecht, The Netherlands.,Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112-114, NL-3584 CM, Utrecht, The Netherlands
| | - Frank G van Steenbeek
- Department of Clinical Sciences of Companion Animals, Faculty of Veterinary Medicine, Utrecht University, PO Box 80154, NL-3508 TD, Utrecht, The Netherlands
| | - Isaac J Nijman
- Department of Medical Genetics, University Medical Center Utrecht, PO Box 85090, NL-3508 AB, Utrecht, The Netherlands
| | - Glen R Monroe
- Department of Medical Genetics, University Medical Center Utrecht, PO Box 85090, NL-3508 AB, Utrecht, The Netherlands
| | - John W M Bastiaansen
- Animal Breeding and Genomics Centre, Wageningen University, PO Box 338, NL-6700 AH, Wageningen, The Netherlands
| | - Bert W Dibbits
- Animal Breeding and Genomics Centre, Wageningen University, PO Box 338, NL-6700 AH, Wageningen, The Netherlands
| | - Leanne H van de Goor
- Dr. van Haeringen Laboratorium B.V., PO Box 408, NL-6700 AK, Wageningen, The Netherlands
| | - Ids Hellinga
- Koninklijke Vereniging "het Friesch Paarden-Stamboek", PO Box 624, NL-9200 AP, Drachten, The Netherlands
| | - Willem Back
- Department of Equine Sciences, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 112-114, NL-3584 CM, Utrecht, The Netherlands.,Department of Surgery and Anaesthesiology of Domestic Animals, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, B-9820, Merelbeke, Belgium
| | - Anouk Schurink
- Animal Breeding and Genomics Centre, Wageningen University, PO Box 338, NL-6700 AH, Wageningen, The Netherlands
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