Holt-Oram syndrome (HOS) is an autosomal dominant hearthand syndrome characterized by congenital heart disease (CHD) and upper limb deformity, and caused by mutations in the TBX5 gene. To date, the sensitivity of TBX5 genetic testing for HOS has been unclear. We now report mutational analyses of a nongenetically selected population of 54 unrelated individuals who were consecutively referred to our center with a clinical diagnosis of HOS. TBX5 mutational analyses were performed in all individuals, and clinical histories and findings were reviewed for each patient without reference to the genotypes. Twenty-six percent of the complete cohort was shown to have mutations of the TBX5 gene. However, among those subjects for whom clinical review demonstrated that their presentations met strict diagnostic criteria for HOS, TBX5 mutations were identified in 74%. No mutations were identified in those subjects who did not meet these criteria. Thus, these studies validate our clinical diagnostic criteria for HOS including an absolute requirement for preaxial radial ray upper limb malformation. Accordingly, TBX5 genotyping has high sensitivity and specificity for HOS if stringent diagnostic criteria are used in assigning the clinical diagnosis. HOS is the most common of the heart-hand syndromes. It segregates in an autosomal dominant fashion and is estimated to occur in at least 1/100,000 live births (1). HOS is characterized by upper limb anomalies involving the preaxial radial ray and CHD (2,3). Upper limb deformity may be bilateral but asymmetric or even unilateral. The most common forms of CHD associated with HOS are ASD, usually of the ostium secundum variety, and VSD, usually occurring in the muscular trabeculated septum. Cardiac conduction disease may also occur, regardless of the presence or absence of structural cardiac disease (3

Podocyte-derived vascular endothelial growth factor (VEGF) is upregulated in diabetes and may contribute to albuminuria. Although believed to act upon the glomerular endothelium, VEGF may have pronounced effects on the podocyte itself. The functionality of this VEGF autocrine loop was investigated in conditionally immortalized mouse podocytes. Exogenous VEGF164 increased the production of α3(IV) collagen, an integral component of the glomerular basement membrane (GBM); this effect was completely prevented by SU5416, a pan-VEGF receptor inhibitor. The VEGF inhibitor also partially prevented the stimulation of α3(IV) collagen by transforming growth factor (TGF)-β1, establishing a novel role for endogenous VEGF. However, VEGF did not influence the production of another novel chain of collagen IV, α5(IV) collagen, and SU5416 failed to reverse the known inhibitory effect of TGF-β1 on α5(IV) collagen production. Cultured mouse podocytes possess at least the VEGFR-1 receptor, confirmed by RT-PCR, immunoblotting, and immunocytochemistry. By these techniques, however, VEGFR-2 is absent. VEGF signaling proceeds via autophosphorylation of VEGFR-1 and activation of the phosphatidylinositol 3-kinase (PI3K) pathway. Thus, podocyte-derived VEGF operates in an autocrine loop, likely through VEGFR-1 and PI3K, to stimulate α3(IV) collagen production. The TGF-β1–stimulated endogenous VEGF may have significant implications for podocyte dysfunction in diabetic glomerulopathy, manifesting as GBM thickening and altered macromolecular permeability.

AngII stimulates the podocyte to produce alpha3(IV) collagen protein via mechanisms involving TGF-beta and VEGF signalling. Alterations in alpha3(IV) collagen production may contribute to GBM thickening and perhaps proteinuria in diabetes.

In tubular epithelial cells, TGF-beta1 mediates the hypertrophic and fibronectin-stimulatory effects of high glucose, confirming the role of the TGF-beta1 isoform in the pathogenesis of diabetic tubular hypertrophy and fibronectin overexpression.