Anorectal malformations (ARMs) represent a wide spectrum of congenital anus and rectum anomalies that arise in early embryonic development[
1].Their incidence is estimated at 1 in 5,000 live births[
2]. The most common malformations include anal atresia (
Human Phenotype Ontology HP:0002023), imperforate anus (
Monarch Initiative MONDO:0001046), anteriorly placed anus (HP:0001545), persistent cloaca (HP:0012621), and anoperineal fistula (HP:0005218)[
3]. More than 50% of ARMs are associated to other malformations (syndromic ARMs)[
4,
5]. The majority of non-syndromic ARMs are identified after birth, while syndromic ARMs are more often detected by foetal ultrasound during pregnancy[
6]. The causes of ARMs are heterogeneous and still poorly known. Both genetic and environmental factors are thought to be implicated[
1,
2]. Notably, ARMs is a common feature of the VACTERL malformative sequence that accounts for about 15% of ARMs cases, and is typically of unknown etiology[
5]. Chromosomal causes of ARMs represent 5 to 15% of the cases. They include aneuploidies (in particular trisomy 21 found approximately in 2% of ARM) and Copy Number Variations (CNV, approximately found in 3% of ARM)[
5,
7]. Monogenic variants explain up to 1/3 of syndromic ARMs, and are very heterogeneous[
8]. The genes involved in syndromic ARMs include but are not limited to:
ADNP (Helsmoortel-van der Aa syndrome),
BBS1 (Bardet-Biedl syndrome 1),
CHD7 (CHARGE syndrome),
CREBBP (Rubinstein-Taybi syndrome 1),
EP300 (Rubinstein-Taybi syndrome 2),
FANCC (Fanconi anemia group C),
GLI3 (Pallister–Hall syndrome),
KDM6A ( Kabuki syndrome 2),
MID1 (Opitz G/BBB syndrome),
MNX1 (Currarino syndrome),
SALL1 (Townes–Brocks syndrome),
SALL4 (Duane-radial ray syndrome ), and
SETD2 (SETD2-related disorders)[
1,
9,
10]
Coffin-Siris syndrome (CSS) is a well-known genetic disorder characterized by developmental delay and/or intellectual disability, hypoplastic to absent fifth fingernails and fifth distal phalanges, coarse facial appearance, and other variable features including hypotonia, slow growth, hypertrichosis, sparse scalp hair, feeding difficulties, and organ malformations[
11]. CSS is caused by heterozygous variants in genes involved in chromatin remodeling, especially those coding for subunits of the BAF (BRG1-associated factor) complex. Of the 12 genes responsible for CSS,
ARID1B is by far the most prevalent (~60% of molecularly diagnosed cases).
SMARCB1, SMARCA4 are among the next most common (~10%), following with
ARID1A (~7%)[
12,
13].