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Anal atresia/stenosis is the absence, closure, or constriction of the rectum or anus. It includes the diagnosis of imperforate anus. This condition is one of the more common defects of the gastrointestinal tract (Forrester 2002). Anal atresia/stenosis is usually diagnosed shortly after delivery.

While anal atresia/stenosis can occur as an isolated defect, it is often associated with other birth defects (Forrester 2002, Garne 2002, Haeusler 2002, Stoll 1996, Harris 1995, Castilla1990). Anal atresia/stenosis is often associated with a group of defects called the VACTERL syndrome; this syndrome causes vertebral, anal, cardiac, trachea, esophageal, renal, and limb abnormalities (Moore 1998). This defect can also be associated with chromosomal abnormalities, particularly trisomy 21 (Haeusler 2002, Bianco 2000, Torfs 1998, Stoll 1997, Kallen 1996, Harris 1995).


While some studies failed to find a significant association between race/ethnicity and anal atresia/stenosis (Stoll 1997, Yang 1994), several studies have reported the anal atresia/stenosis rate to be slightly lower in African-Americans (Harris 1995, Chavez 1988), and another reported the rate of rectal/anal atresia to be higher in Europeans and South Asians than in Caribbeans (Leck 1995). A New York study found atresia/stenosis of the anus or rectum to be significantly lower among Mexican-born Hispanic women when compared with Hispanic mothers born in the U.S., Cuba, or Central/South America (Zhu 2006).

More than one investigation found no secular trend for anal atresia/stenosis (Forrester 2002, Spouge 1986), while another investigation reported an increase in the rate of the defects over time (Yang 1994). Anal atresia/stenosis does not appear to demonstrate seasonal variation (Stoll 1997, Castilla 1990).

Geographic location does not affect risk for anal atresia/stenosis (Stoll et al., 1997), except that one investigation identified an increased risk of the defects with higher altitude (Castilla 1999).

The association between anal atresia/stenosis and maternal age has been reported to be U-shaped (Harris 1995, Yang 1994) or to increase with increasing maternal age (Myers 2001), although another study found no association between maternal age and the condition (Stoll 1997). However, one confounding factor is that advanced maternal age is associated with an increase in chromosomal abnormalities (which often produce multiple defects); there is limited data available for non-chromosomal or isolated anal atresia/stenosis (Forrester 2002, Cuschieri 2001). Paternal age does not appear to influence anal atresia/stenosis risk (Stoll 1997, McIntosh 1995).

Infant sex may influence anal atresia/stenosis risk, with the condition being more common among males (Lisi 2005, Haeusler 2002, Lary 2001, Myers 2001, Cuschieri 2001, Riley 1998, Harris 1995, Spouge 1986), although several studies found no relationship between sex and anal atresia/stenosis (Stoll 1997, Yang 1994).

Anal atresia/stenosis risk increases with lower birth weight (Riley 1998, Stoll 1997, Mili 1991) but is not associated with large for gestational age (Lapunzina 2002). Anal atresia/stenosis risk is elevated with prematurity (Rasmussen 2001). Large intestinal atresia has been associated with intrauterine growth retardation (Khoury 1988). Various investigations found a decrease in risk of these defects with increasing parity and an increase in risk with multiple gestation pregnancy (Mastroiacovo 1999, Riley 1998, Harris 1995, Doyle 1991, Kallen 1986); however, a different investigation reported no such associations (Stoll 1997). Anorectal malformations have been associated when assisted reproductive techniques were used in conception of the fetus (Midrio 2006).

One study identified higher risk of anal atresia/stenosis with consanguinity (Stoll 1997) while another study found no association (Rittler 2001). A small percentage of cases with anal atresia/stenosis have a family history of the same defect (Stoll 1997, Spouge 1986).


Maternal education does not appear to affect risk for anal atresia/stenosis (Stoll 1997). One investigation identified no significant association between maternal nursing occupation and risk of atresia/stenosis of the colon, rectum, or anus (Matte 1993). Paternal occupations of printing or sales do not appear to increase risk of rectal atresia (Irgens 2000). A review article noted increased risk of anal atresia/stenosis with paternal occupation of vehicle manufacturer (Chia 2002).

Maternal diabetes may increase risk for anal atresia/stenosis (Aberg 2001, Bianchi 2000, Stoll 1997, Becerra 1990), although one investigation reported no association between imperforate anus and diabetes (Ramos-Arroyo 1992). There is no apparent association between anal atresia/stenosis and maternal epilepsy, hypertension, fever, flu, hypothyroidism, or hyperthyroidism (Stoll 1997, Khoury 1989).

Anal atresia/stenosis has been reported in infants whose mothers took thalidomide during pregnancy (Bianchi 2000). One study observed no association between maternal use of the antibiotic oxytetracycline during pregnancy and rectal-anal atresia/stenosis (Czeizel 2000 and others found no relationship between cephalosporin antibiotics, nalidixic acid, ampicillin, or the benzodiazepines nitrazepam, medazepam, tofisopam, alprazolum, and clonazepam and recto-anal atresia or stenosis (Eros 2002, Czeizel 2001a, Czeizel 2001b, Czeizel 2001c). However, first trimester maternal exposure to lorazepam does increase the risk for anal atresia; while bromazepam was associated with other digestive system anomalies (Bonnot 2001). There is also an apparent association between anti-asthmatic drugs and anal atresia (Kallen 2007).

While there is limited data on the effects of illicit drugs on fetal development, the use of marijuana does not increase the risk of anal atresia/stenosis (Fried 2002). The use of cocaine also has not been shown to increase the risk of anal atresia/stenosis (Chavez 1989).

Investigations into the association between alcohol and anal atresia/stenosis are mixed (Bianchi 2000; Stoll 1997). Maternal smoking and exposure to X-rays do not appear to cause anal atresia/stenosis (Honein 2001, Stoll 1997, Yuan 1995, Van Den Eeden 1990, Shiono 1986), although one investigation observed increased risk of atresia of rectum, anal canal, and large intestine with maternal smoking (Cornel 1996).

There appears to be higher rates of all non-chromosomal anomalies within groups with low socioeconomic status (Vrijheid 2000). Living in proximity to hazardous waste sites has not been found to affect risk of anal atresia (Dolk 1998). An investigation failed to identify any significant association between anal atresia and proximity to various types of industry (Castilla 2000). Anal atresia does not appear to be related to water chlorination (Kallen and Robert, 2000), maternal exposure to organic solvents (Wennborg 2005), or maternal exposure to indoor pesticides (Berkowitz 2003). One study reported no increased risk of skin-covered anus in regions of Belarus contaminated after the Chernobyl accident (Feshchenko 2002).

No association between maternal folic acid use and anal atresia was found by one study (Czeizel 1996), while another more recent investigation identified reduced risk of imperforate anus with maternal use of folic acid (Myers 2001). Furthermore, a study that examined co-trimoxazole, a combination of trimethoprim and sulfamethoxazole that is a folic acid antagonist, failed to find any association between the medication and anal-rectal atresia/stenosis (Czeizel 1990).


Birth prevalence in the United States for anal atresia/stenosis ranges between 1.04 and 7.89 per 10,000 live births ( National Center on Birth Defects and Developmental Disabilities 2006). The rate in Texas among 1999-2003 deliveries was 5.23 cases per 10,000 live births (includes atresia or stenosis of the large intestine) (Texas Department of State Health Services 2006). Differences in prevalence may be due to differences in case inclusion criteria.


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Please Note: The primary purpose of this report is to provide background necessary for conducting cluster investigations. It summarizes literature about risk factors associated with this defect. The strengths and limitations of each reference were not critically examined prior to inclusion in this report. Consumers and professionals using this information are advised to consult the references given for more in-depth information. This report is for information purposes only and is not intended to diagnose, cure, mitigate, treat, or prevent disease or other conditions and is not intended to provide a determination or assessment of the state of health. Individuals affected by this condition should consult their physician and when appropriate, seek genetic counseling.


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