ALK2 mutation in a patient with Down's syndrome and a congenital heart defect

Down's syndrome (DS), resulting from an additional copy of chromosome 21 (trisomy 21), is frequently associated with congenital heart defects (CHDs). Although the increased dosage of chromosome 21 sequences is likely to be part of the etiology of cardiac defects, only a proportion of DS patients exhibit a congenital heart defect (birth prevalence 40–60%). Through a large-candidate gene-sequencing screen in patients with atrioventricular septal defects, substitutions were identified in bone morphogenetic protein (BMP) type I receptor ALK2 and two other genes in a patient with DS and a primum-type atrial septal defect. Structural modeling of the cytoplasmic domain of the ALK2 receptor suggests that H286 is in close proximity to the nucleotide-binding site of the kinase domain. We investigated whether this p.His286Asp substitution altered ALK2 function by using both in vitro as well as in vivo assays. The p.His286Asp variant demonstrated impaired functional activity as measured by BMP-specific transcriptional response assays. Furthermore, mild dominant-interfering activity was observed in vivo compared with wild-type ALK2 as determined by RNA injection into zebrafish embryos. These data indicate that in the context of a DS background, ALK2-mediated reduction of BMP signaling may contribute to CHDs

Dominant-negative ALK2 allele associates with congenital heart defects

BACKGROUND: Serious congenital heart defects occur as a result of improper atrioventricular septum (AVS) development during embryogenesis. Despite extensive knowledge of the genetic control of AVS development, few genetic lesions have been identified that are responsible for AVS-associated congenital heart defects. METHODS AND RESULTS: We sequenced 32 genes known to be important in AVS development in patients with AVS defects and identified 11 novel coding single-nucleotide polymorphisms that are predicted to impair protein function. We focused on variants identified in the bone morphogenetic protein receptor, ALK2, and subjected 2 identified variants to functional analysis. The coding single-nucleotide polymorphisms R307L and L343P are heterozygous missense substitutions and were each identified in single individuals. The L343P allele had impaired functional activity as measured by in vitro kinase and bone morphogenetic proteinspecific transcriptional response assays and dominant-interfering activity in vivo. In vivo analysis of zebrafish embryos injected with ALK2 L343P RNA revealed improper atrioventricular canal formation. CONCLUSION: These data identify the dominant-negative allele ALK2 L343P in a patient with AVS defects