Novel cleft susceptibility genes in chromosome 6q.

Cleft lip/palate is a defect of craniofacial development. In previous reports, chromosome 6q has been suggested as a candidate region for cleft lip/palate. A multipoint posterior probability of linkage analysis of multiplex families from the Philippines attributed an 88% probability of harboring a cleft-susceptibility gene to a narrower region on bands 6q14.2-14.3. We genotyped 2732 individuals from families and unrelated individuals with and without clefts to investigate the existence of possible cleft-susceptibility genes in this region. We found association of PRSS35 and SNAP91 genes with cleft lip/palate in the case-control cohort and in Caucasian families. Haplotype analyses support the individual associations with PRSS35. We found Prss35 expression in the head and palate of mouse embryos at critical stages for palatogenesis, whereas Snap91 was expressed in the adult brain. We provide further evidence of the involvement of chromosome 6q in cleft lip/palate and suggest PRSS35 as a novel candidate gene.

Identification of a Van der Woude syndrome mutation in the cleft palate 1 mutant mouse.

Mutations in Interferon Regulatory Factor 6 (IRF6) have been identified in two human allelic syndromes with cleft lip and/or palate: Van der Woude (VWS) and Popliteal Pterygium syndromes (PPS). Furthermore, common IRF6 haplotypes and single nucleotide polymorphisms (SNP) alleles are strongly associated with nonsyndromic clefting defects in multiple ethnic populations. Mutations in the mouse often provide good models for the study of human diseases and developmental processes. We identified the cleft palate 1 (clft1) mouse mutant in a forward genetic screen for phenotypes modeling human congenital disease. In the clft1 mutant, we have identified a novel missense point mutation in the mouse Irf6 gene, which confers an amino acid alteration that has been found in a VWS family. Phenotypic comparison of clft1 mutants to previously reported Irf6 mutant alleles demonstrates the Irf6(clft1) allele is a hypomorphic allele. The cleft palate seen in these mutants appears to be due to abnormal adhesion between the palate and tongue. The Irf6(clft1) allele provides the first mouse model for the study of an etiologic IRF6 missense mutation observed in a human VWS family.

Matroshka and ectopic polymorphisms: Two new classes of DNA sequence variation identified at the Van der Woude syndrome locus on 1q32-q41.

Van der Woude syndrome (VWS) is an orofacial clefting disorder with an autosomal dominant pattern of inheritance. In our efforts to clone the VWS gene, 900 kb of genomic sequence from the VWS candidate region at chromosome 1q32-q41 was analyzed for new DNA sequence variants. We observed that in clone CTA-321i20 a 7922 bp sequence is absent relative to the sequence present in PAC clone RP4-782d21 at positions 1669-9590, suggesting the presence of a deletion/insertion (del/ins) polymorphism. Embedded in this 7922 bp region was a TTCC short tandem repeat (STR). Genotype analysis showed that both the internal STR and the (del/ins) mutation were true polymorphisms. This is a novel example of intraallelic variation, a polymorphism within a polymorphism, and we suggest that it be termed a "Matroshka" polymorphism. Further genetic and DNA sequence analysis indicated that the ancestral state of the 1669-9590 del/ins polymorphism was the insertion allele and that the original deletion mutation probably occurred only once. A second class of novel DNA sequence variation was discovered on chromosome 5 that shared a 328 bp identical sequence with this region on chromosome 1. A single nucleotide polymorphism (SNP) was detected by SSCP using a pair of primers derived from the chromosome 1 sequence. Surprisingly, these primers also amplified the identical locus on chromosome 5, and the SNP was only located on chromosome 5. Since the probe unexpectedly detected alleles from another locus, we suggest that this type of sequence variant be termed an "ectopic" polymorphism. These two novel classes of DNA sequence polymorphisms have the potential to confound genetic and DNA sequence analysis and may also contribute to variation in disease phenotypes.

A preliminary gene map for the Van der Woude syndrome critical region derived from 900 kb of genomic sequence at 1q32-q41.

Van der Woude syndrome (VWS) is a common form of syndromic cleft lip and palate and accounts for approximately 2% of all cleft lip and palate cases. Distinguishing characteristics include cleft lip with or without cleft palate, isolated cleft palate, bilateral lip pits, hypodontia, normal intelligence, and an autosomal-dominant mode of transmission with a high degree of penetrance. Previously, the VWS locus was mapped to a 1.6-cM region in 1q32-q41 between D1S491 and D1S205, and a 4.4-Mb contig of YAC clones of this region was constructed. In the current investigation, gene-based and anonymous STSs were developed from the existing physical map and were then used to construct a contig of sequence-ready bacterial clones across the entire VWS critical region. All STSs and BAC clones were shared with the Sanger Centre, which developed a contig of PAC clones over the same region. A subset of 11 clones from both contigs was selected for high-throughput sequence analysis across the approximately 1.1-Mb region; all but two of these clones have been sequenced completely. Over 900 kb of genomic sequence, including the 350-kb VWS critical region, were analyzed and revealed novel polymorphisms, including an 8-kb deletion/insertion, and revealed 4 known genes, 11 novel genes, 9 putative genes, and 3 psuedogenes. The positional candidates LAMB3, G0S2, HIRF6, and HSD11 were excluded as the VWS gene by mutation analysis. A preliminary gene map for the VWS critical region is as follows: [see text] 41-TEL. The data provided here will help lead to the identification of the VWS gene, and this study provides a model for how laboratories that have a regional interest in the human genome can contribute to the sequencing efforts of the entire human genome.

Microdeletions at chromosome bands 1q32-q41 as a cause of Van der Woude syndrome.

Van der Woude syndrome (VWS) is an autosomal dominant disorder comprising cleft lip and/or cleft palate and lip pits. We reported previously a family whose underlying mutation is a 500-800 kb deletion localized to chromosome bands 1q32-q41 [Sander et al., 1994: Hum Mol Genet 3:576-578]. Along with cleft lip/palate and lip pits, affected relatives exhibit developmental delays, suggesting that the function of a gene nearby may also be disrupted. To further localize the VWS gene we searched for other deletions that cause VWS. An allele loss assay was performed using a novel highly polymorphic marker, D1S3753. From a panel of 37 unrelated individuals, we detected an allele loss in one family, indicating the presence of a deletion. In this family, the phenotype in three generations of affected individuals was confined to the cardinal signs of VWS. Surprisingly, mapping of the new deletion showed that it extended 0.2-1 Mb beyond the proximal breakpoint for the deletion described previously. No deletions were detected in seven cases of popliteal pterygia syndrome, 76 cases of mixed syndromic forms of cleft lip and palate, and 178 cases of nonsyndromic cleft lip and palate. These observations suggest that genetic searches for microdeletions should be routine in screening patients for causes of VWS and may facilitate the positional cloning efforts of the VWS gene and of a nearby gene or genes that may be involved in brain development.