Linkage and sequence analysis indicate that CCBE1 is mutated in recessively inherited generalised lymphatic dysplasia

Abstract

Generalised lymphatic dysplasia (GLD) is chararacterised by extensive peripheral lymphoedema with visceral involvement. In some cases it presents in utero with hydrops fetalis. Autosomal dominant and recessive inheritance has been reported. A large, non-consanguineous family with three affected siblings with generalised lymphatic dysplasia is presented. One child died aged 5 months, one spontaneously miscarried at 17 weeks gestation, and the third has survived with extensive lymphoedema. All three presented with hydrops fetalis. There are seven other siblings who are clinically unaffected.Linkage analysis produced two loci on chromosome 18, covering 22Mb and containing 150 genes, one of which is CCBE1. A homozygous cysteine to serine change in CCBE1 has been identified in the proband, in exon 3, in a residue that is conserved across species. High density SNP analysis revealed homozygosity (a region of 900kb) around the locus for CCBE1 in all three affected cases. This indicates a likely ancestral mutation that is common to both parents; an example of a homozygous mutation representing Identity by Descent (IBD) in this pedigree. Recent studies in zebrafish have shown this gene to be required for lymphangiogenesis and venous sprouting and are therefore supportive of our findings. In view of the conserved nature of the cysteine, the nature of the amino acid change, the occurrence of a homozygous region around the locus, the segregation within the family, and the evidence from zebrafish, we propose that this mutation is causative for the generalised lymphatic dysplasia in this family, and may be of relevance in cases of non-immune hydrops fetalis.Introduction.

Ccbe1 expression marks the cardiac and lymphatic progenitor lineages during early stages of mouse development

“…Moreover, the detection of mCcbe1 protein near Prox1 + LECs further supports the previously raised hypothesis that Ccbe1 protein might act as an extracellular guidance molecule regulating the budding and migration of lymphangioblasts from the anterior cardinal vein . In humans, homozygous and compound heterozygous mutations of hCCBE1 gene have also been shown to result in generalized lymphatic dysplasia associated with the very debilitating and highly deadly Hennekam syndrome (Connell et al, 2009;Alders et al, 2009). Despite the above mentioned and more preeminent defects in sues followed by absence of expression at later stages of heart development suggests that expression of mCcbe1 is limited to multipotent and highly proliferative progenitors and downregulated upon cellular commitment into more specific cardiac phenotypes.…”

“…lymphangiogenesis, cysteine to serine mutation of hCCBE1 gene (C75S) has also been shown to be associated with in hypertrofic cardiomyopathy and congenital heart defects (Connell et al, 2009;Alders et al, 2009). This raises the possibility of a role of Ccbe1 in the organogenesis of the heart from cardiac progenitors of the FHF, SHF and proepicardium where mCcbe1 is now reported to be expressed.…”

“…In humans, CCBE1 gene has also been associated with Hennekam syndrome, a disorder characterized by abnormal lymphatic system development causing generalized lymphedema, intestinal lymphangiectasias and mild to moderate levels of growth and mental retardation. Homozygous cysteine to serine mutation in a human CCBE1 (hCCBE1) gene region (exon 3) highly conserved across vertebrates has been shown to result in a generalized lymphatic dysplasia leading to significant morbidity and high mortality prevalence (Connell et al, 2009;Alders et al, 2009). While the importance of mCcbe1 for the development of the lymphatic system appears to be indisputable, its role in cardiac development has not been investigated despite the increasing evidence of a potential function in cardiogenesis.…”

“…5 (Bos et al, 2011). Furthermore, some of the Hennekam syndrome patients carrying a mutated hCCBE1 gene were shown to possess congenital heart defects including hypertrophic cardiomyopathy and ventricular septal defects (Connell et al, 2009;Alders et al, 2009).…”

Getting out and about: the emergence and morphogenesis of the vertebrate lymphatic vasculature

“…CCBE1 is essential for embryonic lymphangiogenesis in both zebrafish and mice (Hogan et al, 2009a;Bos et al, 2011) and is mutated in the human primary lymphoedema syndrome, Hennekam syndrome (Alders et al, 2009;Connell et al, 2010) (see also Table 1). CCBE1 is a secreted protein and loss-of-function phenotypes closely resemble those of Vegfc and Vegfr3 in zebrafish and VEGFC in mice (Hogan et al, 2009a;Bos et al, 2011).…”