X-linked cardiac valvular dysplasia is a rare form of male-specific congenital heart defect mainly characterized by myxomatous degeneration of the atrioventricular valves with variable hemodynamic consequences. It is caused by genetic defects in FLNA-encoded filamin A, a widely expressed actin-binding protein that regulates cytoskeleton organization. Filamin A loss of function has also been associated with often concurring neurologic and connective tissue manifestations, with mutations in the first half of the Rod 1 domain apparently expressing the full cardiac phenotype. We contribute to previous genotype-phenotype correlations with a multidisciplinary approach in a newly-described family. Cardiologic, dysmorphologic, and genetic evaluation of available members were complemented with transcriptional and X-chromosome inactivation studies. A novel FLNA mutation c.1066-3C>G cosegregated with a male-expressed, apparently isolated, cardiac phenotype with no skewed X-inactivation pattern in female carriers. This variant was shown to result in an in-frame deletion of 8 amino acid residues near the N-terminal region of the protein. A nonimprinted, partial loss of function of filamin A proximal Rod 1 domain seems to be the pathogenetic mechanism of cardiac valvular dysplasia, with some cases occasionally expressing associated extracardiac manifestations.

The underlying molecular aetiology of congenital heart defects is largely unknown. The aim of this study was to explore the genetic basis of non-syndromic severe congenital valve malformations in two unrelated families. Whole-exome analysis was used to identify the mutations in five patients who suffered from severe valvular malformations involving the pulmonic, tricuspid and mitral valves. The significance of the findings was assessed by studying sporulation of yeast carrying a homologous Phospholipase D (PLD1) mutation, in situ hybridisation in chick embryo and echocardiography and histological examination of hearts of PLD1 knockout mice. Three mutations, p.His442Pro, p.Thr495fs32* and c.2882+2T>C, were identified in the PLD1 gene. The mutations affected highly conserved sites in the PLD1 protein and the p.His442Pro mutation produced a strong loss of function phenotype in yeast homologous mutant strain. Here we show that in chick embryos PLD1 expression is confined to the forming heart (E2-E8) and homogeneously expressed all over the heart during days E2-E3. Thereafter its expression decreases, remaining only adjacent to the atrioventricular valves and the right ventricular outflow tract. This pattern of expression follows the known dynamic patterning of apoptosis in the developing heart, consistent with the known role of PLD1 in the promotion of apoptosis. In hearts of PLD1 knockout mice, we detected marked tricuspid regurgitation, right atrial enlargement, and increased flow velocity, narrowing and thickened leaflets of the pulmonic valve. The findings support a role for PLD1 in normal heart valvulogenesis.

Polyvalvar myxomatous valve degeneration is a clinical pathology rarely encountered during cardiac anesthesia, but, when present, most commonly occurs in the context of a connective tissue disorder. Filamin A mutations have begun to be recognized as a source of progressive myxomatous mitral and tricuspid valve degeneration. These lesions can be diagnosed by echo, but their clinical presentation can be equivocal. We present a patient with significant echocardiographic findings of mitral and tricuspid valvar regurgitation, aortic dilatation, and intraoperative findings of aortic ectasia. In our case, a detailed family history led to a preoperative echocardiogram revealing myxomatous mitral and tricuspid valve degeneration with significant regurgitation and aortic dilatation. Genetic evaluation led to the diagnosis of a Filamin A mutation. Pre- and postrepair echocardiographic assessments of valvar function played a key role in the management of this patient. Continued surveillance of his aortic dilation and evaluation of postrepair valve function warrants close follow-up with a high likelihood for further surgical intervention.