Mapping loci causing susceptibility to anal atresia in pigs, using a resource pedigree

Partial urorectal septum malformation sequence in a kitten with disorder of sexual development

A 2-month-old kitten exhibited simultaneously an imperforate anus, hypospadias, rectourethral fistula and genital dysgenesis (penis restricted to the glans, absence of prepuce and bifid scrotum). Surgical correction consisted of separation of the urinary and digestive tracts, perineal urethrostomy and connection of the rectum to the newly made anal opening. Pathological examination of the testes, conventionally removed at 9 months of age, showed no mature spermatozoa and underdevelopment of germ and Leydig cells. In humans, the absence of an anal opening in association with abnormal sexual development defines the urorectal septum malformation sequence. Here, we describe the first case of this syndrome in a kitten with a normal male karyotype (38,XY) and a normal coding sequence for the SRY gene. Both the rectourethral fistula and observed genital abnormalities might have been induced by a disturbance in the hedgehog signalling pathway. However, although four polymorphic sites were identified by DHH gene sequencing, none cosegregated with the malformation.

Anorectal atresia and variants at predicted regulatory sites in candidate genes

Anorectal atresia is a serious birth defect of largely unknown etiology but candidate genes have been identified in animal studies and human syndromes. Because alterations in the activity of these genes might lead to anorectal atresia, we selected 71 common variants predicted to be in transcription factor binding sites, CpG windows, splice sites, and miRNA target sites of 25 candidate genes, and tested for their association with anorectal atresia. The study population comprised 150 anorectal atresia cases and 623 control infants without major malformations. Variants predicted to affect transcription factor binding, splicing, and DNA methylation in WNT3A, PCSK5, TCF4, MKKS, GLI2, HOXD12, and BMP4 were associated with anorectal atresia based on a nominal P value < 0.05. The GLI2 and BMP4 variants are reported to be moderately associated with gene expression changes (Spearman's rank correlation coefficients between -0.260 and 0.226). We did not find evidence for interaction between maternal pre-pregnancy obesity and variants in MKKS, a gene previously associated with obesity, on the risk of anorectal atresia. Our results for MKKS support previously suggested associations with anorectal malformations. Our findings suggest that more research is needed to determine whether altered GLI2 and BMP4 expression is important in anorectal atresia in humans.

Evaluation of an experimental model for anorectal anomalies induced by ethylenethiourea

PURPOSE

To evaluate an experimental model for anorectal anomalies and their principal associated malformations induced by ethylene thiourea (ETU).

METHODS

Rat fetuses were utilized, divided into two groups: experimental group - fetuses from rats that received ETU on the 11th day of gestation at the dose of 125 mg/kg, diluted in distilled water to 1% concentration (12.5 ml/kg); and control group - fetuses from rats that received distilled water alone, at a volume of 12.5 ml/kg. On the 21st day of gestation, the animals were sacrificed by hypoxia in a carbon dioxide chamber, followed by laparotomy to remove the fetuses. These were initially examined externally to determine the sex and whether anorectal anomalies and malformations of the vertebral column and tail were present. Then, with the aid of microscopy, the fetuses underwent exploratory laparotomy to characterize the type of anorectal anomaly and investigate urological malformations.

RESULTS

None of the fetuses in the control group presented anorectal anomaly, vertebral column malformation or urological structural alterations. In the experimental group, 71% presented anorectal anomaly, 80% presented vertebral column alterations and 35% presented urological alterations.

CONCLUSION

The model described was shown to be easy to implement and presented results that allow its use in studying anorectal anomalies and associated malformations.

Molecular genetic analysis of a de novo balanced translocation t(6;17)(p21.31;q11.2) associated with hypospadias and anorectal malformation

We report a young boy with penoscrotal hypospadias, anal atresia (AA) with a recto-urethral fistula, a hypoplastic kidney and a balanced translocation t(6;17)(p21.31;q11.2). Physical mapping of the breakpoints localized the chromosome 6 breakpoint within an intron of the gene lipoma HMGIC fusion partner-like 5 (LHFPL5) whereas the chromosome 17 breakpoint was mapped to the first intron of the 182-FIP gene encoding the Fragile X Mental Retardation Protein Interacting Protein. Sequence analysis across the breakpoints revealed an almost perfectly balanced translocation with a 2 bp deletion on the derivative chromosome 6 and a 7 bp duplication on the derivative chromosome 17. We identified a fusion transcript consisting of the first exon of 182-FIP and the last exon of LHFPL5 in patient-derived cells. Quantitative expression analysis of the genes flanking the breakpoints, revealed increased transcript levels for SFRS protein kinase 1 (SRPK1) and TAO kinase 1 (TAOK1) which suggests a positional effect due to the translocation. We hypothesize that the urogenital and anorectal malformations in the patient result from one or several mechanisms including disruption of the genes 182-FIP and LHFPL5, altered expression of the genes flanking the translocation breakpoints and, a gain of function mechanism mediated by the 182-FIP-LHFPL5 fusion transcript.

Atresia Ani in the Dog: A Retrospective Study

Congenital anomalies of the rectum and anus are rare in dogs. The most frequently reported anomaly is atresia ani. Four types of atresia ani have been reported, including congenital anal stenosis (Type I); imperforate anus alone (Type II) or combined with more cranial termination of the rectum as a blind pouch (Type III); and discontinuity of the proximal rectum with normal anal and terminal rectal development (Type IV). An increased incidence was found in females and in several breeds, including miniature or toy poodles and Boston terriers. Surgical repair is the treatment of choice, but postoperative complications can occur, including fecal incontinence and colonic atony secondary to prolonged preoperative distension.

Genomewide scan for anal atresia in swine identifies linkage and association with a chromosome region on Sus scrofa chromosome 1

Anal atresia is a rare and severe disorder in swine occurring with an incidence of 0.1-1.0%. A whole-genome scan based on affected half-sibs was performed to identify susceptibility loci for anal atresia. The analysis included 27 families with a total of 95 animals and 65 affected piglets among them. Animals were genotyped for 126 microsatellite markers distributed across the 18 autosomal porcine chromosomes and the X chromosome, covering an estimated 2080 cM. Single-point and multipoint nonparametric linkage scores were calculated using the computer package ALLEGRO 1.0. Significant linkage results were obtained for chromosomes 1, 3, and 12. Markers on these chromosomes and additionally on chromosomes for which candidate genes have been postulated in previous studies were subjected to the transmission disequilibrium test (TDT). The test statistic exceeded the genomewide significance level for adjacent markers SW1621 (P = 7 x 10(-7)) and SW1902 (P = 3 x 10(-3)) on chromosome 1, supporting the results of the linkage analysis. A specific haplotype associated with anal atresia that could prove useful for selection against the disorder was revealed. Suggestive linkage and association were also found for markers S0081 on chromosome 9 and SW957 on chromosome 12.

Genetic analysis of anal atresia in pigs: evidence for segregation at two main loci

Anal atresia is a relatively common congenital malformation that occurs in about 1 out of 5000 infants, caused by abnormal hindgut development of the embryo, often associated with other developmental anomalies (e.g., Currarino, Townes-Brock, Pallister-Hall syndromes, and VATER association). Genetic analysis in human families is exceedingly difficult due to the multifactorial nature of the trait. In pigs, anal atresia occurs at a higher incidence (0.18%) than in humans. A complete genome scan (165 microsatellite markers) was performed using a backcross pedigree previously obtained by crossing affected animals from a partially inbred line, selected for a high incidence of anal atresia, with an unaffected male of a different breed (Meishan). The data set was analyzed with classical linkage (TWOPOINT) and nonparametric genetic methods (NPL, Non-Parametric Linkage, and TDT, Transmission Disequilibrium Test). Both methods support association of the trait with two loci on Chromosomes 9 and 15. GLI2 (GLI-Kruppel family member GLI2) was identified as a positional candidate gene based on comparative mapping; radiation hybrid mapping confirmed that this locus is located within the QTL region.

A proposed mechanism for intermediate atresia ani (AA), based on a porcine case of AA and hypospadias

BACKGROUND

Atresia Ani (AA) is one of the most common malformations of the lower gastrointestinal tract. It occurs in 1 in 1500 to 1 in 5000 human births. These patients suffer physically and psychologically from this disorder, and thus there is a research interest in the condition. There are 3 subcategories of AA: high, intermediate, and low. Each of these forms is likely related to separate etiological processes.

METHODS

An anatomical study was performed on a porcine case of AA with a urorectal fistula and malformed urethra.

RESULTS

This animal was found to have the intermediate form of AA.

CONCLUSIONS

A new mechanism is hypothesized, distinct from that described for the high and low forms of AA. This proposed mechanism involves the persistence of the cloacal membrane. Evidence to support this hypothesis includes: location of the urorectal fistula in the region of the embryonic cloacal duct, the lack of anomalies usually seen in conjunction with AA associated with mutations of the Sonic Hedgehog gene, and the presence of a malformed urethra, which is significantly correlated to intermediate AA. This form of AA could be related to a failure of the cloacal membrane to break down at the appropriate time during urorectal separation.