Consideration of VACTERL association in patients with trisomy 21

A Network of Anomalies Prompting VACTERL Workup in a Trisomy 21 Newborn

VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities) association is a condition defined by having at least three of the following congenital malformations: vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities. While diagnosing the VACTERL association is rare, the conditions that make up the VACTERL core-component features among other congenital abnormalities are even more unique. We present a case of a 34-week-old premature infant with trisomy 21 in addition to esophageal atresia, tracheoesophageal fistula, laryngeal cleft, vascular ring, Hirschsprung’s disease, atrioventricular canal defect, ventricular septal defect, and other related conditions diagnosed at birth. To our knowledge, this case represents the first of its kind in relation to the constellation of anomalies diagnosed in one individual at birth of which may or may not be related to Down syndrome, and the associated interventions necessary to continue postnatal living.

Embryonic hypocellularity, blastogenetic malformations, and fetal growth restriction

An association between congenital malformations and fetal growth restriction (FGR) can be largely explained by a relationship with early embryonic hypocellularity. The malformations include the VACTERL association, which is exceptional as a Mendelian syndrome, but is commonly associated with monozygotic twinning, maternal diabetes, and some forms of aneuploidy, all characterized by a small embryo early in development. Parsimony suggests that these different links to VACTERL are related to the hypocellularity as a single common factor, rather than as an expression of three independent pathogenetic processes. A distinct non-genetic pathogenesis is further supported by increased frequencies in the same conditions of a single umbilical artery (SUA), which is also unusual in Mendelian disorders. SUA often involves the atrophy of one artery, which may be facilitated by altered hemodynamics in a smaller embryo, providing a direct link to hypocellularity. Hypocellularity may also explain a possible connection between VACTERL and certain mitochondrial disorders, where reduced energy might slow early cell division and growth, reducing the size of the embryo. © 2016 Wiley Periodicals, Inc.

VACTERL Association Etiology: The Impact of de novo and Rare Copy Number Variations

Copy number variations (CNVs), either DNA gains or losses, have been found at common regions throughout the human genome. Most CNVs neither have a pathogenic significance nor result in disease-related phenotypes but, instead, reflect the normal population variance. However, larger CNVs, which often arise de novo, are frequently associated with human disease. A genetic contribution has long been suspected in VACTERL (Vertebral, Anal, Cardiac, TracheoEsophageal fistula, Renal and Limb anomalies) association. The anomalies observed in this association overlap with several monogenetic conditions associated with mutations in specific genes, e.g. Townes Brocks (SALL1), Feingold syndrome (MYCN) or Fanconi anemia. So far VACTERL association has typically been considered a diagnosis of exclusion. Identifying recurrent or de novo genomic variations in individuals with VACTERL association could make it easier to distinguish VACTERL association from other syndromes and could provide insight into disease mechanisms. Sporadically, de novo CNVs associated with VACTERL are described in literature. In addition to this literature review of genomic variation in published VACTERL association patients, we describe CNVs present in 68 VACTERL association patients collected in our institution. De novo variations (>30 kb) are absent in our VACTERL association cohort. However, we identified recurrent rare CNVs which, although inherited, could point to mechanisms or biological processes contributing to this constellation of developmental defects.

Mitochondrial Factors and VACTERL Association-Related Congenital Malformations

VACTERL/VATER association is a group of congenital malformations characterized by at least 3 of the following findings: vertebral defects, anal atresia, cardiac defects, tracheo-esophageal fistula, renal anomalies, and limb abnormalities. To date, no unifying etiology for VACTERL/VATER association has been established, and there is strong evidence for causal heterogeneity. VACTERL/VATER association has many overlapping characteristics with other congenital disorders that involve multiple malformations. In addition to these other conditions, some of which have known molecular causes, certain aspects of VACTERL/VATER association have similarities with the manifestations of disorders caused by mitochondrial dysfunction. Mitochondrial dysfunction can result from a number of distinct causes and can clinically manifest in diverse presentations; accurate diagnosis can be challenging. Case reports of individuals with VACTERL association and confirmed mitochondrial dysfunction allude to the possibility of mitochondrial involvement in the pathogenesis of VACTERL/VATER association. Further, there is biological plausibility involving mitochondrial dysfunction as a possible etiology related to a diverse group of congenital malformations, including those seen in at least a subset of individuals with VACTERL association.

Clinical characteristics of neonates with VACTERL association

BACKGROUND

The VACTERL association (VA) is the non-random co-occurrence of vertebral anomalies, anal atresia, cardiovascular malformations, tracheoesophageal fistula and/or esophageal atresia, renal anomalies, and/or limb anomalies, and is referred to by the first letters of its components. Studies investigating the clinical characteristics of VA patients and probing of the observed current six component types are limited, and none of them is focused on neonates. We investigated the clinical characteristics of our patients diagnosed as having VA in the newborn period.

METHODS

We retrospectively reviewed the neonates whose final diagnosis was VACTERL association. Presence of at least three components of previously reported six anomalies was accepted as VACTERL association. Sex, birthweight, gestational age, postnatal age, anomalies of the systems that are included in VA, and the other features were recorded.

RESULTS

There was a male predominance (14/11) of 28 patients; and there were three patients with ambiguous genitalia. The most common observed VACTERL component was vertebral anomalies (n= 26), followed by anal atresia (n= 19), tracheoesophageal fistula/esophageal atresia (n= 17), renal anomalies (n= 15), limb anomalies (n= 15) and cardiac anomalies (n= 14). The most frequent combination was VCTL (n= 4). Fifteen (57%) patients had non-VACTERL anomalies and the most frequent of these was ambiguous genitalia (n= 3).

CONCLUSION

VA patients may have different clinical characteristics in different populations, and clinicians may miss some component features if the patients are evaluated after the neonatal period.

Analysis of FOXF1 and the FOX gene cluster in patients with VACTERL association

VACTERL association, a relatively common condition with an incidence of approximately 1 in 20,000 -35,000 births, is a non-random association of birth defects that includes vertebral defects (V), anal atresia (A), cardiac defects (C), tracheo-esophageal fistula (TE), renal anomalies (R) and limb malformations (L). Although the etiology is unknown in the majority of patients, there is evidence that it is causally heterogeneous. Several studies have shown evidence for inheritance in VACTERL, implying a role for genetic loci. Recently, patients with component features of VACTERL and a lethal developmental pulmonary disorder, alveolar capillary dysplasia with misalignment of pulmonary veins (ACD/MPV), were found to harbor deletions or mutations affecting FOXF1 and the FOX gene cluster on chromosome 16q24. We investigated this gene through direct sequencing and high-density SNP microarray in 12 patients with VACTERL association but without ACD/MPV. Our mutational analysis of FOXF1 showed normal sequences and no genomic imbalances affecting the FOX gene cluster on chromosome 16q24 in the studied patients. Possible explanations for these results include the etiologic and clinical heterogeneity of VACTERL association, the possibility that mutations affecting this gene may occur only in more severely affected individuals, and insufficient study sample size.