Rieger syndrome (RIEG) is an autosomal-dominant human disorder that includes anomalies of the anterior chamber of the eye, dental hypoplasia and a protuberant umbilicus. We report the human cDNA and genomic characterization of a new homeobox gene, RIEG, causing this disorder. Six mutations in RIEG were found in individuals with the disorder. The cDNA sequence of Rieg, the murine homologue of RIEG, has also been isolated and shows strong homology with the human sequence. In mouse embryos Rieg mRNA localized in the periocular mesenchyme, maxillary and mandibular epithelia, and umbilicus, all consistent with RIEG abnormalities. The gene is also expressed in Rathke's pouch, vitelline vessels and the limb mesenchyme. RIEG characterization provides opportunities for understanding ocular, dental and umbilical development and the pleiotropic interactions of pituitary and limb morphogenesis.

Nonsyndromic cleft lip with or without cleft palate (CL/P) and nonsyndromic cleft palate only (CPO) are common congenital anomalies with significant medical, psychological, social, and economic ramifications. Both CL/P and CPO are examples of complex genetic traits. There exists sufficient evidence to hypothesize that disease loci for CL/P and CPO can be identified by a candidate-gene linkage-disequilibrium (LD) strategy. Candidate genes for clefting, including TGFA, BCL3, DLX2, MSX1, and TGFB3, were screened for LD with either CL/P or CPO in a predominantly Caucasian population, with both case-control- and nuclear-family-based approaches. Previously reported LD for TGFA with both CL/P and CPO could not be confirmed, except in CL/P patients with a positive family history. Also, in contrast to previous studies, no LD was found between BCL3 and either CL/P or CPO. Significant LD was found between CL/P and both MSX1 and TGFB3 and between CPO and MSX1, suggesting that these genes are involved in the pathogenesis of clefting. In addition, a mutation search in the genes DLX2, MSX1, and TGFB3 was performed in 69 CPO patients and in a subset of the CL/P patients. No common mutations were found in the coding regions of these genes; however, several rare variants of MSX1 and TGFB3 were found that may alter the latters' normal function. These results form the basis for future research, including (a) mutation searches in the MSX1 and TGFB3 genes in Caucasian CL/P patients and (b) extension of the search for MSX1 mutations in CPO patients to the noncoding regions.

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.

Signaling molecules such as Activin, Sonic hedgehog, Nodal, Lefty, and Vg1 have been found to be involved in determination of left-right (L-R) asymmetry in the chick, mouse, or frog. However, a common signaling pathway has not yet been identified in vertebrates. We report that Pitx2, a bicoid-type homeobox gene expressed asymmetrically in the left lateral plate mesoderm, may be involved in determination of L-R asymmetry in both mouse and chick. Since Pitx2 appears to be downstream of lefty-1 in the mouse pathway, we examined whether mouse Lefty proteins could affect the expression of Pitx2 in the chick. Our results indicate that a common pathway from lefty-1 to Pitx2 likely exists for determination of L-R asymmetry in vertebrates.

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