Omphalocele in half-siblings

Genome-wide linkage and copy number variation analysis reveals 710 kb duplication on chromosome 1p31.3 responsible for autosomal dominant omphalocele

BACKGROUND

Omphalocele is a congenital birth defect characterised by the presence of internal organs located outside of the ventral abdominal wall. The purpose of this study was to identify the underlying genetic mechanisms of a large autosomal dominant Caucasian family with omphalocele.

METHODS AND FINDINGS

A genetic linkage study was conducted in a large family with an autosomal dominant transmission of an omphalocele using a genome-wide single nucleotide polymorphism (SNP) array. The analysis revealed significant evidence of linkage (non-parametric NPL = 6.93, p=0.0001; parametric logarithm of odds (LOD) = 2.70 under a fully penetrant dominant model) at chromosome band 1p31.3. Haplotype analysis narrowed the locus to a 2.74 Mb region between markers rs2886770 (63014807 bp) and rs1343981 (65757349 bp). Molecular characterisation of this interval using array comparative genomic hybridisation followed by quantitative microsphere hybridisation analysis revealed a 710 kb duplication located at 63.5-64.2 Mb. All affected individuals who had an omphalocele and shared the haplotype were positive for this duplicated region, while the duplication was absent from all normal individuals of this family. Multipoint linkage analysis using the duplication as a marker yielded a maximum LOD score of 3.2 at 1p31.3 under a dominant model. The 710 kb duplication at 1p31.3 band contains seven known genes including FOXD3, ALG6, ITGB3BP, KIAA1799, DLEU2L, PGM1, and the proximal portion of ROR1. Importantly, this duplication is absent from the database of genomic variants.

CONCLUSIONS

The present study suggests that development of an omphalocele in this family is controlled by overexpression of one or more genes in the duplicated region. To the authors' knowledge, this is the first reported association of an inherited omphalocele condition with a chromosomal rearrangement.

Familial abdominal wall defects

We report 2 families, each having multiple sibs with abdominal wall defects. In family 1, normal parents gave birth to identical (monochorionic, diamniotic) twins. This is the first reported case of gastroschisis occurring in monozygotic twins. In family 2, a normal mother gave birth to a son with omphalocele. Two subsequent pregnancies with a different husband resulted in a stillborn girl with partial atresia of the colon and a liveborn girl with gastroschisis. In neither case were there any associated anomalies. In neither of the 2 families was there consanguinity or history of other abdominal wall defects. The familial occurrence of these defects suggests that 1) multifactorial determination should be considered in at least some cases of abdominal wall defects, 2) the bowel atresias that occasionally accompany gastroschisis may also have a genetic (multifactorial) cause, and 3) some cases of gastroschisis and omphalocele may have the same genetic cause.

Cloacal exstrophy and related abdominal wall defects in Manitoba: incidence and demographic factors

A retrospective descriptive study of omphalocele and exstrophic defects of the abdominal wall was carried out in Manitoba to determine the prevalence of these defects, changes in birth incidence with time and their etiologic heterogeneity. The incidence of isolated omphalocele was similar to that reported in other series but the overall incidence of other types of abdominal wall defects was high. Cloacal exstrophy, bladder exstrophy and amnion disruption defects contributed significantly to the number of cases ascertained and emphasized the heterogeneity of abdominal wall defects. There were fluctuations in birth incidence with time with cloacal exstrophy especially apparently being more common in 1980-81. No specific demographic or environmental factors were documented in the cases seen in 1980-81 which could explain the high incidence in these years. Cloacal exstrophy is, however, now appreciated to be much more common than first realized. Studied directed at elucidation of the causes of apparent changes in incidence of malformations such as omphalocele or exstrophic defects will have to take into account both the fluctuations in background incidence of these defects and the considerable diversity in their etiology.