We identified mutations in the VSX1 homeobox gene for two distinct inherited corneal dystrophies; posterior polymorphous dystrophy (PPD) and keratoconus. One of the mutation (R166W) responsible for keratoconus altered the homeodomain and impaired DNA binding. Two other sequence changes (L159M and G160D) were associated with keratoconus and PPD, respectively, and involved a region adjacent to the homeodomain. The G160D substitution, and a fourth defect affecting the highly conserved CVC domain (P247R), occurred in a child with very severe PPD who required a corneal transplant at 3 months of age. In this family, relatives with the G160D change alone had mild to moderate PPD, while P247R alone caused no corneal abnormalities. However, with either the G160D or P247R mutation, electroretinography detected abnormal function of the inner retina, where VSX1 is expressed. These data define the molecular basis of two important corneal dystrophies and reveal the importance of the CVC domain in the human retina.

In the Chx10-null ocular retardation (or J ) mouse, retinal progenitor cell (RPC) proliferation is impaired, and bipolar neurons, a late born cell type, fail to differentiate. It is unclear whether Chx10 is required to maintain proliferation throughout retinogenesis or whether the bipolar cell defect is an indirect effect of growth arrest. We show that Chx10 is dispensable for late-stage RPC proliferation but is essential to promote bipolar cell genesis in place of rods. Ectopic Chx10 expression drove bipolar instead of rod cell differentiation without affecting division. Converting Chx10 to an activator impaired bipolar cell differentiation, implying that repression is important for Chx10 activity. In the Chx10 null or J retina, only a small fraction of cells expressing mutated Chx10 mRNA were rods, but this fraction increased after p27 Kip1 inactivation, which partially rescues proliferation. Most significantly, acute Chx10 knockdown in the postnatal retina promoted rods in place of bipolar neurons without affecting division. Thus, Chx10 directly controls bipolar cell genesis by inhibiting rod differentiation independent of its temporally limited early effect on RPC proliferation.CVC domain ͉ homeobox ͉ homeodomain ͉ short-hairpin RNA

The glutamatergic signaling pathway represents an ideal candidate susceptibility system for attention-deficit/ hyperactivity disorder (ADHD). Disruption of specific Nmethyl-D-aspartate-type glutamate receptor subunit genes (GRIN1, 2A-D) in mice leads to significant alterations in cognitive and/or locomotor behavior including impairments in latent learning, spatial memory tasks and hyperactivity. Here, we tested for association of GRIN2B variants with ADHD, by genotyping nine single nucleotide polymorphisms (SNPs) in 205 nuclear families identified through probands with ADHD. Transmission of alleles from heterozygous parents to affected offspring was examined using the transmission/disequilibrium test. Quantitative trait analyses for the ADHD symptom dimensions [inattentive (IA) and hyperactive/impulsive (HI)] and cognitive measures of verbal working memory and verbal short-term memory were performed using the FBAT program. Three SNPs showed significantly biased transmission (P < 0.05), with the strongest evidence of association found for rs2284411 (x 2 5 7.903, 1 degree of freedom, P 5 0.005). Quantitative trait analyses showed associations of these markers with both the IA and the HI symptom dimensions of ADHD but not with the cognitive measures of verbal short-term memory or verbal working memory. Our data suggest an association between variations in the GRIN2B subunit gene and ADHD as measured categorically or as a quantitatively distributed trait.

Chx10 and VSX1 are transcription factors that share a homeodomain (HD), 1 and a CVC motif, named after CHX10, VSX1, and ceh-10 (1-3). CHX10 is expressed early in development in dividing retinal progenitor cells (RPCs) and is also expressed in mature bipolar neurons and a subset of Mü ller glia (2, 4). Null mutations results in microphthalmia in humans (5) and mice (6), and antisense Chx10 RNA injected into zebrafish embryos impairs retinal development (7). Recessive mutations identified in patients with microphthalmia that modified residues in helix III of the CHX10 HD (R200P and R200Q) ablated DNA binding in vitro (5). The ocular retardation (or J ) mouse carries a mutation that generates a premature stop codon in helix