17 2 Genetics of Anorectal Malformations Giuseppe Martucciello Contents blastogenesis often involve two or more progenitor fields. This fact may explain the cause of subgroups 2.1 Introduction . 17 of ARM that form part of complex phenotypes due 2.2 Non-syndromic ARM . 17 to developmental field defects. These complex phe- 2.3 ARM Associated with Other Systemic notypes are considered as end results of pleiotropic Malformations . 18 effects of single causal events that might be chromo- 2.4 Aetiological Classification . 20 somal, monogenic or even teratogenic [72]. 2.4.1 Chromosomal Anomalies Classifying ARM from the genetic point of view is Associated with ARM . 20 2.4.2 Down Syndrome . 20 not easy since they present different forms that are be- 2.4.3 Cat-Eye Syndrome . 20 lieved to be influenced by different factors such as sex 2.4.4 Genetic Syndromes Associated and associated anomalies. ARM can be the only path- with ARM . 21 ological finding (non-syndromic) or as part of a more 2.4.4.1 Townes-Brocks Syndrome . 21 complex phenotype (syndromic), and may occur in a 2.4.4.2 FG Syndrome . 21 single affected individual (sporadic) or in more than 2.4.4.3 Pallister-Hall Syndrome . 21 one individual in the same family (familial) with dif- 2.4.4.4 VACTERL Association (VATER) . 22 ferent modes of inheritance. There are gender differ- 2.4.4.5 Sirenomelia . 22 ences, with remarkably higher preponderance in boys 2.4.4.6 Caudal Regression Syndrome . 23 for more complex ARM forms, while the less severe 2.4.4.7 Currarino Syndrome . 23 types, with perineal or vestibular fistulae, reported 2.5 Mouse Models with ARM . 25 more frequently in girls (Fig. 2.1) [61]. These topics 2.6 Conclusions . 26 will be discussed in detail below. References . 26 2.2 Non-syndromic ARM Sporadic ARM is a frequent clinical finding; however, 2.1 Introduction different modes of inheritance have been reported. Eleven families have been reported with inherited Anorectal malformations (ARM) present an incidence variants, 7 of these families showing autosomal domi- rate ranging from 1:1,500 to 1:5,000 live births [18, nant mode of inheritance. In one family the condition 19, 41, 49, 52, 53, 61, 109, 110, 112], and have vari- was suggestive of autosomal recessive inheritance, able clinical presentations ranging from mild forms with two affected females to healthy-looking parents. that might require only minor surgical interventions In the remaining three families, it was not possible to to more complicated cases that need to be managed differentiate whether the inheritance was autosomal with multi-staged operations [51, 87, 88, 108]. or X-linked recessive (Table 2.1). The cause of ARM is unknown, although arrest Moreover, excluding the isolated autosomal domi- of the descent of the urorectal septum towards the nant low type, ARM can escape diagnosis easily due cloacal membrane between the 4th and 8th weeks of to variable expression, such as presenting with a very gestation was previously considered the basic event mild manifestation such as an anteriorly located anus leading to ARM [31, 32, 55, 71]. Since the molecu- (perineal fistula) [60]. Careful examination of the first- lar determinants during blastogenesis are overlap- degree relatives, particularly the parents, is highly ping for many body systems, and these elements are recommended before calculating the recurrence risk closely related in timing and spacing, so defects in in isolated low ARM due to variable expression [96]. 18 Giuseppe Martucciello Fig. 2.1 Classification of anorec- tal malformations (ARM) Table 2.1 Suggested mode of inheritance for isolated anorectal malformations (ARM) Reports Affected members Suggested inheritance Manny et al. (1973) [68] Father-son Autosomal-dominant Schwoebel et al. (1984) [106] Mother, son and daughter Autosomal-dominant Boocock and Donnai (1987) [12] Three father-son pairs Autosomal-dominant Weinstein (1965) [124] Three families with affected Autosomal- or X-linked recessive sons and healthy parents Winkler and Weinstein (1970) [126] Two daughters, healthy parents Autosomal-recessive Landau et al. (1997) [60] Four members in three generations Autosomal-dominant Robb and Teebi (1998) [100] Father-son Autosomal-dominant 2.3 ARM Associated with Other affected with ARM of whom 58% had additional Systemic Malformations malformations: 68% were male and 32% were female. High-type ARM was found in 58%, but occurred five There is a wide spectrum of possible associations times more frequently in males than in females, while of ARM with various systemic malformations (Ta- low-type ARM occurred twice as often in females ble 2.2). These associations may be well-described than in males. High-type ARM were associated 13 syndromes with various aetiologies or may be just a times more frequently with other congenital malfor- random association with other malformations. In a mations than were low-type ARM. ARM with other recent review, Ratan et al. [94] studied 416 patients anomalies were four times more common among 2 Genetics of Anorectal Malformations 19 males than females. These findings are in contrast (HD), is another interesting field, since several caus- with isolated ARM, for which there is no sex differ- ative genes for HD are known. The incidence of this ence and, more surprisingly, the isolated low-type combination varies widely from one study to another, ARM is twice as common as the high type. Ratan et al. ranging from 3.4% [54] to 60% [86]. Lerone et al. sug- [94] also found that boys with high ARM had more gested that this variability depends on whether suit- vertebral and gastrointestinal tract anomalies, espe- able techniques for diagnosing intestinal innervation cially for congenital short megacolon, while the boys were used or not [61]. Enzymohistochemical tech- with low ARM had a higher incidence of genital mal- niques studying cryostat sections from biopsy speci- formations. On the other hand, girls with high ARM mens of the fistula and rectal pouch demonstrated an have more skeletal anomalies (other than vertebral) abnormal innervation in 96% of ARM patients [61, and urinary tract malformations. Girls affected with 44]. Classical aganglionosis was found in 31% of rec- low ARM frequently suffered from vesicoureteric re- tal pouch specimens, hypoganglionosis in 38%, and flux. The percentages of patients affected by ARM and intestinal neuronal dysplasia type B in 14%; unclas- 2,3, or 4 other body system anomalies were 50%, 29%, sified dysganglionosis was found in 10%. These data and 16% respectively. demonstrate that ARM and dysganglionoses are not The analysis of associated malformations plays an uncommon, and suggest the importance of mutation important role in the genetic study of ARM, because analysis of HD genes in ARM-affected individuals diagnosing the associated anomalies can identify [61]. specific genes that may represent a starting point for more detailed investigations. Studies have thus fo- cussed on the most frequently associated anomalies, 2.4 Aetiological Classification namely the vertebral, genitourinary and gastrointesti- nal malformations [61]. The frequent association of ARM with common chro- A condition that is commonly associated with mosomal anomalies is well known (e.g. Down syn- ARM is hypospadias (found in 6.5% of cases) [40]. drome, trisomy 18, 13q-, cat-eye syndrome (CEM), or Moreover, one out of five cases of congenital urethral genetic syndromes such as Currarino syndrome, FG fistula – a rare condition – is associated with ARM. In syndrome, VATER association and others [14, 17, 22, a study on rectal innervation in patients with ARM, 35, 39, 42, 48, 75, 80, 82, 85, 95, 98, 99, 111, 115, 123]. enteric nervous system anomalies ranged from 79 to Teratogenic effects of certain agents such as thalido- 100% of cases depending on the ARM type [61]. mide, oestrogen and ethanol intake has also been well The combination of both ARM and intestinal dys- described [8, 61, 89]. ganglionoses, particularly Hirschsprung’s disease Table 2.2 Systemic malformations associated with ARM. US Ultrasound, IVU intravenous urethrogram, MCU micturating cysto- urethrogram, MRI magnetic resonance imaging, ECG electrocardiogram Anomalies Incidence in literature (%) Investigations Notes Urologic 25–55% US, IVU Hoekstra, Ratan, Mittal Vesicoureteric reflux 20–47% US, MCU Hassink, Narasimharao, Rickwood, Ratan Genital 3–18% (boys) Hoekstra, Metts, Cortes 26–39% (girls) Vertebral 25–38% X-ray, MRI Hassink, Carson, Mittal, Ratan Other skeletal 13–16% X-ray Hassink, Ratan, Mittal Spinal-cord-related 8–67% X-ray, MRI Rivosecchi, Walton, Ratan, Mittal Cardiac 10–17% ECG, echocardiography Mittal, Greenwood, Ratan Gastrointestinal 7–10% X-ray, biopsy Ratan, Mittal, Hassink Tracheoesophageal 6–8% Hassink, Ratan Others 4–5% Ratan 20 Giuseppe Martucciello 2.4.1 Chromosomal Anomalies Associated 2.4.3 Cat-Eye Syndrome with ARM CES is characterised by ARM, coloboma of the iris In a study of 1,846 babies with ARM [24], chromo- (total or rarely partial, unilateral or bilateral), colo- somal anomalies were found in 11%, the most fre- boma of the choroid and/or optic nerve, microph- quent form being perineal fistula. The frequencies of thalmia (usually unilateral) and variable external ear trisomy 21, 13, and 18 among babies with ARM were deformities ranging from unilateral auricular reduc- 15, 30, and 90 times higher, respectively, in compari- tion defects to several tags, mostly with atresia of the son to neonates in the general population (Table 2.3). external auditory canal. These anomalies can be as- sociated with mental retardation in half of the cases; dysmorphic features are the leading signs for the di- 2.4.2 Down Syndrome agnosis, including hypertelorism, downward-slant- ing palpebral fissures and low root of the nose. Con- The ARM occurs more frequently with Down syn- genital heart disease can also be associated with this drome than in the general population and there is a syndrome, especially septal defects and anomalous higher rate of deformities without fistula [11, 116].