The major locus for multifactorial nonsyndromic cleft lip maps to mouse chromosome 11

Prevention of cleft lip and/or palate in A/J mice by licorice solution

Cleft lip and/or palate anomalies (CL ± P) are the most frequent birth defects affecting the orofacial region in humans. Although their etiology remains unclear, the involvement of environmental and genetic risk factors is known. This observational study aimed to investigate how the use of  crude drugs with estrogen activity influenced an animal model's ability to prevent CL ± P. A/J mice were randomly divided into six experimental groups. Five of these groups consumed a drink containing crude drug licorice root extract, with the following weights attributed to each group: 3 g in group I, 6 g in group II, 7.5 g in group III, 9 g in group IV, and 12 g in group V, whereas a control group consumed tap water. The effect of licorice extract was examined for fetal mortality and fetal orofacial cleft development compared to the control group. The rates for fetal mortality were 11.28%, 7.41%, 9.18%, 4.94%, and 7.90% in groups I, II, III, IV, and V, respectively, compared to 13.51% in the control group. There were no significant differences in the mean weight of alive fetuses in all five groups compared to the control group (0.63 ± 0.12). Group IV showed the lowest orafacial cleft occurrence of 3.20% (8 fetuses) with statistical significance (p = 0.0048) out of 268 live fetuses, whereas the control group had the occurrence of 8.75% (42 fetuses) among 480 live fetuses. Our study showed that the dried licorice root extract may reduce orofacial birth defects in experimental animal studies.

Role of carotenoids and retinoids during heart development

The nutritional requirements of the developing embryo are complex. In the case of dietary vitamin A (retinol, retinyl esters and provitamin A carotenoids), maternal derived nutrients serve as precursors to signaling molecules such as retinoic acid, which is required for embryonic patterning and organogenesis. Despite variations in the composition and levels of maternal vitamin A, embryonic tissues need to generate a precise amount of retinoic acid to avoid congenital malformations. Here, we summarize recent findings regarding the role and metabolism of vitamin A during heart development and we survey the association of genes known to affect retinoid metabolism or signaling with various inherited disorders. A better understanding of the roles of vitamin A in the heart and of the factors that affect retinoid metabolism and signaling can help design strategies to meet nutritional needs and to prevent birth defects and disorders associated with altered retinoid metabolism. This article is part of a Special Issue entitled Carotenoids recent advances in cell and molecular biology edited by Johannes von Lintig and Loredana Quadro.

A comprehensive review of the genetic basis of cleft lip and palate

Cleft lip and palate (CLP) are birth defects that affect the upper lip and the roof of the mouth. CLP has a multifactorial etiology, comprising both genetic and environmental factors. In this review we discuss the recent data on the etiology of cleft lip and palate. We conducted a search of the MEDLINE database (Entrez PubMed) from January 1986 to December 2010 using the key words: ‘cleft lip,’ ‘cleft palate,’ ‘etiology,’ and ‘genetics.’ The etiology of CLP seems complex, with genetics playing a major role. Several genes causing syndromic CLP have been discovered. Three of them—T-box transcription factor-22 (TBX22), poliovirus receptor-like-1 (PVRL1), and interferon regulatory factor-6 (IRF6)—are responsible for causing X-linked cleft palate, cleft lip/palate–ectodermal dysplasia syndrome, and Van der Woude and popliteal pterygium syndromes, respectively; they are also implicated in nonsyndromic CLP. The nature and functions of these genes vary widely, illustrating the high vulnerability within the craniofacial developmental pathways. The etiological complexity of nonsyndromic cleft lip and palate is also exemplified by the large number of candidate genes and loci. To conclude, although the etiology of nonsyndromic CLP is still largely unknown, mutations in candidate genes have been identified in a small proportion of cases. Determining the relative risk of CLP on the basis of genetic background and environmental influence (including smoking, alcohol use, and dietary factors) will be useful for genetic counseling and the development of future preventive measures.

Genes, environment, and orofacial clefting: N-acetyltransferase and folic acid

Nonsyndromic orofacial clefting has been the subject of intense studies, both genetic and epidemiological. The findings have frequently been controversial because of lack of reproducibility. Mouse models provide the potential both for genetic and environmental uniformity. We have chosen to study the role of genetic susceptibility to teratogen-induced orofacial clefting, using 2 drugs (dilantin and corticosteroid) and 1 nondrug teratogen (6-aminonicotinamide). The strongest single genetic influence we have found is N-acetyltransferase 2. Our recent work and that of others suggest that the influence of this locus is mediated through alterations in folate metabolism. Our results support epidemiological findings in humans and possibly implicate altered cytosine methylation, potentially caused by environmental factors, at least in the A/J model.

Development of the upper lip: morphogenetic and molecular mechanisms

The vertebrate upper lip forms from initially freely projecting maxillary, medial nasal, and lateral nasal prominences at the rostral and lateral boundaries of the primitive oral cavity. These facial prominences arise during early embryogenesis from ventrally migrating neural crest cells in combination with the head ectoderm and mesoderm and undergo directed growth and expansion around the nasal pits to actively fuse with each other. Initial fusion is between lateral and medial nasal processes and is followed by fusion between maxillary and medial nasal processes. Fusion between these prominences involves active epithelial filopodial and adhering interactions as well as programmed cell death. Slight defects in growth and patterning of the facial mesenchyme or epithelial fusion result in cleft lip with or without cleft palate, the most common and disfiguring craniofacial birth defect. Recent studies of craniofacial development in animal models have identified components of several major signaling pathways, including Bmp, Fgf, Shh, and Wnt signaling, that are critical for proper midfacial morphogenesis and/or lip fusion. There is also accumulating evidence that these signaling pathways cross-regulate genetically as well as crosstalk intracellularly to control cell proliferation and tissue patterning. This review will summarize the current understanding of the basic morphogenetic processes and molecular mechanisms underlying upper lip development and discuss the complex interactions of the various signaling pathways and challenges for understanding cleft lip pathogenesis.

Expression ofWnt9b and activation of canonical Wnt signaling during midfacial morphogenesis in mice

Cleft lip with or without cleft palate (CLP) is the most common craniofacial birth defect in humans. Recently, mutations in the WNT3 and Wnt9b genes, encoding two members of the Wnt family of signaling molecules, were found associated with CLP in human and mice, respectively. To investigate whether Wnt3 and Wnt9b directly regulate facial development, we analyzed their developmental expression patterns and found that both Wnt3 and Wnt9b are expressed in the facial ectoderm at critical stages of midfacial morphogenesis during mouse embryogenesis. Whereas Wnt3 mRNA is mainly expressed in the maxillary and medial nasal ectoderm, Wnt9b mRNA is expressed in maxillary, medial nasal, and lateral nasal ectoderm. During lip fusion, Wnt9b, but not Wnt3, is expressed in the epithelial seam between the fusing medial and lateral nasal processes. Furthermore, we found that expression of TOPGAL, a transgenic reporter of activation of canonical Wnt signaling pathway, is specifically activated in the distal regions of the medial nasal, lateral nasal, and maxillary processes prior to lip fusion. During lip fusion, the epithelial seam between the medial and lateral nasal processes as well as the facial mesenchyme directly beneath the fusing epithelia strongly expresses TOPGAL. These data, together with the CLP lip phenotype in WNT3-/- humans and Wnt9b-/- mutant mice, indicate that Wnt3 and Wnt9b signal through the canonical Wnt signaling pathway to regulate midfacial development and lip fusion.

Investigations of the genomic region that contains the clf1 mutation, a causal gene in multifactorial cleft lip and palate in mice

BACKGROUND

Human nonsyndromic cleft lip and palate, CL(P), is genetically complex, with one contributing gene on chromosome 17q. A potentially homologous gene, clf1 on distal chromosome 11, is part of the digenic cause of the 10-30% CL(P) in the A/WySn mouse strain. Here we report our progress toward identifying the clf1 mutation.

METHODS

Transcription from all of the known and predicted genes in the 1.5-Mb candidate region was examined in A/WySn and control (AXB-4/Pgn) ED10-11 embryo heads. The marker haplotype for 28 inbred strains across the clf1 region was obtained. The entire transcripts of Wnt9b and Wnt3 in A/WySn were sequenced. Using long PCR, the genomic region from Wnt3 throughWnt9b was screened in A/WySn for an inserted retrotransposon.

RESULTS

Gosr2, Wnt9b, Wnt3, Nsf, Arf2, Crhr1, Mapt, Cdc27, Myl4, Itgb3, chr11_20.152, chr11_20.154, chr11_20.155, and chr11_20.156 are expressed in ED10-11 heads. None is absent or detectably reduced in A/WySn. The ancestral pre-clf1 mutation haplotype was found in CBA/J mice. By a test-cross, CBA/J was confirmed to lack the clf1 mutation. Three single-nucleotide variants in A/WySn (vs. C57BL/6J) were found in each of the 3' untranslated regions (3'UTRs) of Wnt3 and of Wnt9b, respectively; their presence in CBA/J shows that none are the clf1 mutation. An inserted intracisternal A particle (IAP) retrotransposon located 6.6 kb from the 3' end of Wnt9b was found in A/WySn and in all clf1 strains tested. This IAP is absent in C57BL/6J and CBA/J.

CONCLUSIONS

The clf1 mutation is a genomic alteration present in A/WySn and absent in the ancestral chromosomal segment in CBA/J. The IAP retrotransposon insertion near Wnt9b in A/WySn fits this criterion; we predict that interference with Wnt9b function by this IAP is the clf1 mutation.

Experimental aspects of the pathogenesis of Robin sequence

OBJECTIVE

The Pierre Robin Sequence (PRS) is a good example of disturbed embryonic development of the secondary palate involving insufficient mandibular growth, failed forward tongue movement, and, in the case of a cleft, impeded fusion of the secondary palate. Discussion continues regarding which of the involved pathogenetic factors is the primary cause of the induced cascade of signs: insufficient mandibular growth or failed descent of the tongue.

DESIGN

Forty-five randomly selected, 18-day-old formalin-fixed A/WySn mouse fetuses were investigated. The strain is known to have a basic genetic defect and as much as 44% clefts in the offspring. Twenty-four fetuses in the group had a cleft palate. Mandible position was measured relative to the head and to the presence or absence of a cleft. Cleft width and tongue position were also determined. Thirty-eight NMRI mouse fetuses of the same age served as controls.

RESULTS

All A/WySn fetuses showed marked mandibular retrognathia, which was more severe in the cleft group (p < .05), but there was no correlation between the degree of retrognathia and cleft width. The median cleft width was 3.4 mm (1.6 through 6.3 mm). The tongue was in the cleft in all 12 fetuses with wide clefts (>3.4 mm wide), and free in the oral cavity in the other 12. Tongue position did not influence the degree of retrognathia (p < .05). Moreover, the tongue was free in all fetuses with severe retrognathia.

CONCLUSION

The results support the primary role of retroposition of the mandible in the development of cardinal symptoms of Pierre Robin Sequence.

A previously unreported association between Nance-Horan syndrome and spontaneous dental abscesses

Atypical dentofacial structures may be the first indicator of other anomalies linked to a syndrome. This case describes the management of a 9-year-old girl referred for the routine management of supernumerary teeth. The anomalous form of her teeth, together with multiple supernumerary units and a history of congenital cataracts, were suggestive of a diagnosis of Nance-Horan syndrome. This is an X-linked disorder, in which females usually demonstrate mild expression; this case was unusual in respect to the marked phenotype expressed. Unusually, the girl developed 2 spontaneous abscesses of her noncarious upper incisor teeth; a feature never previously described in this syndrome. This report details the patient's dental management and discusses the possible pathogenesis of the dental abscesses, together with the genetic implications of this syndrome.

A digenic cause of cleft lip in A-strain mice and definition of candidate genes for the two loci

BACKGROUND

Nonsyndromic cleft lip with or without cleft palate, CL(P), is a common human birth defect with a complex unknown genetic cause. The mouse model is the "A/-" strains. Our previous studies mapped two loci: clf1 on Chr11 and clf2 on Chr13--with a strong genetic maternal effect on the level of risk. Here we test the hypothesis that CL(P) is digenic and identify candidate genes for clf1 and clf2.

METHODS

We observed E14 CL(P) frequencies in backcross (BC1) embryos from a new cross of A/WySn to AXB-4/Pgn and from test crosses of three new "congenic RI" lines. Using new polymorphic markers from genes and our mapping panels of segregants and RI strains, we identified the candidate genes for clf1 and clf2. We sequenced the coding region of Ptch in A/WySn cDNA.

RESULTS

Seventy new BC1 CL(P) segregants (4%) were obtained, as predicted. All three new congenic RI lines homozygous for both clf1 and clf2 had A/WySn-level CL(P) frequencies (10-30%) in test crosses. The clf1 region contains 10 known genes (Arf2, Cdc27, Crhr1, Gosr2, Itgb3, Mapt, Myl4, Nsf, Wnt3, and Wnt9b). The clf2 region contains 17 known genes with human orthologs. Both regions contain additional potential genes. No causal mutation in Ptch coding sequence was found.

CONCLUSIONS

In A-strain mice, nonsyndromic CL(P) is digenic, suggesting that nonsyndromic human CL(P) may also be digenic. The orthologous human genes are on 17q (clf1) and 9q, 8q and 5p (clf2), and good candidate genes are WNT3 or WNT9B (17q), and PTCH (9q) or MTRR (5p).

Analysis of polymorphic TGFB1 codons 10, 25, and 263 in a German patient group with non-syndromic cleft lip, alveolus, and palate compared with healthy adults

Background

Clefts of the lip, alveolus, and palate (CLPs) rank among the most frequent and significant congenital malformations. Leu10Pro and Arg25Pro polymorphisms in the precursor region and Thr263Ile polymorphism in the prodomain of the transforming growth factor β1 (TGF-β1) gene have proved to be crucial to predisposition of several disorders.

Methods

In this study, polymorphism analysis was performed by real-time polymerase chain reaction (LightCycler) and TGF-β1 levels determined by enzyme-linked immunosorbent assay.

Results

Only 2/60 Caucasian non-syndromic patients with CLP (3.3%) carried the Arg25Pro and another 2/60 patients (3.3%) the Thr263Ile genotypes, whereas, in a control group of 60 healthy Caucasian blood donors, these heterozygous genotypes were more frequent 16.7% having Arg25Pro (10/60; p < 0.035) and 10,0% having Thr263Ile (6/60), respectively. TGF-β1 levels in platelet-poor plasma of heterozygous Arg25Pro individuals were lower than those of homozygous members (Arg25Arg) in the latter group, but this discrepancy narrowly failed to be significant. Although polymorphisms in codon 10 and 25 were associated with each other, no difference was found between patients and controls concerning the Leu10Pro polymorphism.

Conclusions

The genetic differences in codons 25 and 263 suggest that TGF-β1 could play an important role in occurrence of CLP, however, functional experiments will be required to confirm the mechanisms of disturbed development.

The cleft lip and palate defects in Dancer mutant mice result from gain of function of the Tbx10 gene

Cleft lip and palate (CL/P) is a common disfiguring birth defect with complex, poorly understood etiology. Mice carrying a spontaneous mutation, Dancer (Dc), exhibit CL/P in homozygotes and show significantly increased susceptibility to CL/P in heterozygotes [Deol, M. S. & Lane, P. W. (1966) J. Embryol. Exp. Morphol. 16, 543-558 and Trasler, D. G., Kemp, D. & Trasler, T. A. (1984) Teratology 29, 101-104], providing an animal model for understanding the molecular pathogenesis of CL/P. We genetically mapped Dc to within a 1-cM region near the centromere of chromosome 19. In situ hybridization analysis showed that one positional candidate gene, Tbx10, is ectopically expressed in Dc mutant embryos. Positional cloning of the Dc locus revealed an insertion of a 3.3-kb sequence containing the 5' region of the p23 gene into the first intron of Tbx10, which causes ectopic expression of a p23-Tbx10 chimeric transcript encoding a protein product identical to a normal variant of the Tbx10 protein. Furthermore, we show that ectopic expression of Tbx10 in transgenic mice recapitulates the Dc mutant phenotype, indicating that CL/Pin Dc mutant mice results from the p23 insertion-induced ectopic Tbx10 expression. These results identify gain of function of a T-box transcription factor gene as a mechanism underlying CL/P pathogenesis.

A genome-wide scan for loci predisposing to non-syndromic cleft lip with or without cleft palate in two large Syrian families

Non-syndromic cleft lip with/without cleft palate (CL/P) is a common, usually non-fatal birth defect of complex etiology. Several segregation analyses have demonstrated that genetic factors are important in the pathogenesis of CL/P, most likely through the interaction of several genes of modest effects. The aim of this study was to perform a genome-wide linkage analysis to identify/search for candidate gene loci for CL/P. We conducted a genome-wide search in two large, relatively isolated Syrian families, each one with a large number of cases with CL/P (18 in family 1 and 4 in family 2). A locus with a multipoint LOD score of 2.80 and a 2-point non-parametric MLS LOD of 3.0 was detected on 17p13.1. Other chromosomal regions with multipoint LOD scores > or = 1.2 (P < or = 0.01) included 3p21.2, 4q32.1, and 7q34. These data indicate the possible presence of several susceptibility loci for CL/P and identify a strong candidate locus for this common birth defect on chromosome 17p13.

Association between palatal morphogenesis and Pax9 expression pattern in CL/Fr embryos with clefting during palatal development

The CL/Fr mouse strain develops cleft lip and palate (CLP) spontaneously. In this study, Pax9 mRNA expression was investigated in the palatal shelves during palatal morphogenesis to assess the correlation between secondary palatal morphogenesis and Pax9 expression of CL/Fr embryos with spontaneous cleft lip and palate. The expression of Pax9 mRNA was characterised using whole mount in situ hybridisation with a digoxygenin-labelled probe. In the control strain of C57BL/6 and CL/Fr normal embryos, Pax9 was expressed in the palate, especially along the medial edge (ME), on embryonic day 13.5 (E13.5) and E14.5 when the palatal shelves grew vertically down the side of the tongue and subsequently elevated to a horizontal position, and was down regulated on E15.5 when the palatal shelves met and began fusing. In the cleft embryo, Pax9 was expressed in the ME region but was not down regulated on E15.5. Furthermore, whole mount in situ hybridisation was performed after organ culture, using CL/Fr-N and CL/Fr-BCL palatal shelves dissected and approximated by pairs on E13.5. This showed that Pax9 was still expressed in the ME region in separated palatal shelves of CL/Fr-N and CL/Fr-BCL embryos, while Pax9 expression was down regulated in paired palatal shelves. These expression patterns of Pax9 in normal and cleft embryos during palatal fusion indicate that Pax9 expression is altered in spontaneous cleft lip and palate, and concludes that there is a direct correlation between Pax9 expression and palatal fusion.

Recent developments in orofacial cleft genetics

Nonsyndromic cleft of the lip and/or palate (CLP or orofacial cleft) derives from an embryopathy with consequent failure of the nasal process and/or palatal shelves fusion. This severe birth defect is one of the most common malformations among live births. Nonsyndromic CLP is composed of two separate entities: cleft lip and palate (CL+/-P) and cleft palate only (CPO). Both have a genetic background, and environmental factors probably disclose these malformations. In CL+/-P, several loci have been identified, and, in one case, a specific gene has also been found. In CPO, one gene has been identified, but many more are probably involved. Because of the complexity of the genetics of nonsyndromic CLP as a result of the difference between CL+/-P and CPO, heterogeneity of each group caused by the number of involved genes, type of inheritance, and interaction with environmental factors, we discuss the more sound results obtained with different approaches: epidemiological studies, animal models, human genetic studies, and in vitro studies.

Chromosome 17: gene mapping studies of cleft lip with or without cleft palate in Chinese families

OBJECTIVE

Involvement of loci on chromosome 17, including retinoic acid receptor alpha (RARA) in nonsyndromic oral clefts has been reported in Caucasian populations, although never investigated in Asian populations. The purpose of the present study was to investigate several loci on chromosome 17, including RARA, in Chinese families.

PARTICIPANTS

Thirty-six multiplex families (310 individuals), ascertained through nonsyndromic cleft lip with or without cleft palate surgical probands from hospitals in Shanghai, China, participated in the present study. There were 23 families whose probands had cleft lip and cleft palate (CLP) and 13 with cleft lip alone (CL).

RESULTS

Seventeen markers, spanning chromosome 17 and about 10 cM apart were assessed. Logarithm of odds ratio (LOD) scores (two point and multipoint), model-free linkage analyses, and allelic association tests (transmission/disequilibrium, Fisher's exact tests, and chi-square) were performed on the total family sample, families with CLP probands (CLP subgroup), and families with CL probands (CL subgroup). LOD scores from the two-point analyses were inconclusive. Multipoint analyses rejected linkage except for a few regions in the CL subgroup. However, positive results were found using the model-free linkage and association methods (p < .05). The markers with positive results varied across the CL and CLP subgroups. However, the RARA region and loci nearby yielded consistently positive results.

CONCLUSION

Genetic variation within the RARA locus or nearby appears to be involved in the pathogenesis of nonsyndromic oral clefts in this population. Furthermore, based on the differing pattern of results in the CL versus CLP subgroups, it appears that the formation of CL and CLP is because of either differing alleles at the same genetic locus or different but related (and/or linked) genes that modify the severity and expression of oral clefting.

Phenotypic and molecular analyses of A/WySn mice

OBJECTIVE

Since its first description, the A strain of mice have been utilized extensively as models to study the processes involved in clefting of the midfacial region. Of the A substrains, the A/WySn has a spontaneous rate of clefting of the lip of about 20% to 30%. The A/WySn mouse model was utilized in this study to analyze and compare the phenotypic and molecular changes in the midfacial region of embryos with and without cleft.

RESULTS

Scanning electron microscopy and skeletal and cartilage preparations of newborn A/WySn pups showed the presence of bilateral and unilateral clefts of the lips and the disruption of the skeletal and cartilaginous components of the mice with clefts of the lip. The expression of the msx1 homeobox gene was analyzed by whole mount in situ hybridization of A/WySn embryos at different stages of midfacial development. The results showed that there was misregulation of the expression of the msx1 gene in embryos with cleft, with a persistence of expression in the distal growing tips of the midfacial processes and in areas that have fused in normal embryos without cleft.

CONCLUSIONS

Although the genetic defect in A/WySn mice is not known, a possible candidate gene has been mapped to a corresponding human chromosome carrying retinoic acid receptor alpha, and there exists a possibility that msx1 is in the same genetic pathway affected by the mutation of the gene in A/WySn.

The impact of molecular genetics on oral health paradigms

As a result of our increased understanding of the human genome, and the functional interrelationships of gene products with each other and with the environment, it is becoming increasingly evident that many human diseases are influenced by heritable alterations in the structure or function of genes. Significant advances in research methods and newly emerging partnerships between private and public sector interests are creating new possibilities for utilization of genetic information for the diagnosis and treatment of human diseases. The availability and application of genetic information to the understanding of normal and abnormal human growth and development are fundamentally changing the way we approach the study of human diseases. As a result, the issues and principles of medical genetics are coming to bear across all disciplines of health care. In this review, we discuss some of the potential applications of human molecular genetics for the diagnosis and treatment of oral diseases. This discussion is presented in the context of the ongoing technological advances and conceptual changes that are occurring in the field of medical genetics. To realize the promise of this new molecular genetics, we must be prepared to foresee the possibilities and to incorporate these newly emergent technologies into the evolving discipline of dentistry. By using examples of human conditions, we illustrate the broad application of this emerging technology to the study of simple as well as complex genetic diseases. Throughout this paper, we will use the following terminology: Penetrance--In a population, defined as the proportion of individuals possessing a disease-causing genotype who express the disease phenotype. When this proportion is less than 100%, the disease is said to have reduced or incomplete penetrance. Polymerase chain reaction (PCR)--A technique for amplifying a large number of copies of a specific DNA sequence flanked by two oligonucleotide primers. The DNA is alternately heated and cooled in the presence of DNA polymerase and free nucleotides, so that the specified DNA segment is denatured, hybridized with primers, and extended by DNA polymerase. MIM--Mendelian Inheritance in Man catalogue number from V. McKusick's Mendelian Inheritance in man (OMIM, 1998).

Characterization of a novel gene disrupted by a balanced chromosomal translocation t(2;19)(q11.2;q13.3) in a family with cleft lip and palate

Cleft lip with or without cleft palate is a common birth defect that is genetically complex. The nonsyndromic forms have been studied genetically using linkage and candidate-gene association studies with only partial success in defining the loci responsible for orofacial clefting. Loci for nonsyndromic cases have been suggested on 2p13, 4q31, 6p24, 17q21-q24, and 19q13.2. Recently, we identified a family in which cleft lip and palate segregated in two of three generations with a balanced chromosomal translocation t(2;19)(q11. 2;q13.3). We used a positional-cloning strategy to identify a novel gene disrupted by the translocation on chromosome 19. Eight rare (q < 0.01) and nine common (q > 0.01) variants of this gene were detected in the DNA of 74 unrelated cases of cleft lip and/or cleft palate; no variants associated significantly with clefting, suggesting that this gene is not a major contributor to abnormal craniofacial development. This gene, CLPTM1, was ubiquitously expressed on Northern blots containing RNA from adult tissues and in whole-mount in situ hybridization of day 10 to 12 mouse embryos. CLPTM1 encodes a transmembrane protein and has strong homology to two Caenorhabditis elegans genes, suggesting that CLPTM1 may belong to a new gene family.

Identification and mapping of human histone acetylation modifier gene homologues

The products of histone acetyltransferase and deacetyltransferase genes regulate histone acetylation in eukaryotes, thereby regulating access of transcription factors to chromatin and modulating gene expression. Histone acetylation modifiers have been found to participate as cofactors in diverse mammalian transcriptional complexes involved in regulation of cellular proliferation and differentiation. A role for histone acetylase has been implicated in leukemias and developmental disorders. To gain insight into a role of additional potential histone acetylation modifier genes in human disease, we identified six histone acetyl-transferase or deacetyltransferase homologues using the dbEST database, and we mapped, using high-resolution FISH, a total of five family members to 1p34.3, 6q21-q22, 5q31, 3p24, and 17q21. We then identified human genetic disorders for which candidate genes are not yet known and that have been mapped to the same chromosomal regions as the histone acetylation modifiers. This analysis may help identify new candidate genes for human diseases that involve disturbances of histone acetylation.

Complex traits and polygenic inheritance in the mouse

Polygenic inheritance has recently become an increasingly active field of research due to the availability of techniques allowing in-depth screening of genetic markers across the entire genome. The mouse is being used both in its own right and as a model system for certain human traits. The advantages and disadvantages of the mouse for such studies are outlined and in this context, the adequacy of the mouse as a model for polygenic traits in humans is discussed. A detailed overview of the approaches and methods used in the analysis of polygenic inheritance in the mouse is presented.

Application of transmission disequilibrium tests to nonsyndromic oral clefts: including candidate genes and environmental exposures in the models

Extensive epidemiological and genetic studies of the cause of oral clefts have demonstrated strong familial aggregation but have failed to yield definitive evidence of any single genetic mechanism. We used the transmission/disequilibrium test (TDT) to investigate the relationship between oral clefts and markers associated with five candidate genes by utilizing 160 parent-offspring trios. Conditional logistic regression models extended the TDT to include covariates as effect modifiers, thus permitting tests for gene-environment interactions. For four of these candidates [transforming growth factor alpha (TGFA), transforming growth factor beta 3 (TGFB3), retinoic acid receptor (RARA), and the proto-oncogene BCL3], we detected modestly elevated odds ratios for the transmission of one marker allele to cleft probands when all the trios were analyzed together. These odds ratios increased when information on type of cleft, race, family history, or maternal smoking were incorporated as effect modifiers. We detected significant interaction between maternal smoking and the transmission of alleles for markers near TGFA and TGFB3; excess transmission of allele 3 at BCL3 was most significant among cleft lip probands; and the odds ratios for transmission of alleles at D19S178 and THRA1 were significant when ethnic group was included in the model. We suggest that utilizing an analytical strategy that allows for stratification of data and incorporating environmental effects into a single analysis may be more effective for detecting genes of small effect.

Genome scan for teratogen-induced clefting susceptibility loci in the mouse: evidence of both allelic and locus heterogeneity distinguishing cleft lip and cleft palate

Nonsyndromic clefting of the lip and palate in humans has a highly complex etiology, with both multiple genetic loci and exposure to teratogens influencing susceptibility. Previous studies using mouse models have examined only very small portions of the genome. Here we report the findings of a genome-wide search for susceptibility genes for teratogen-induced clefting in the AXB and BXA set of recombinant inbred mouse strains. We compare results obtained using phenytoin (which induces cleft lip) and 6-aminonicotinamide (which induces cleft palate). We use a new statistical approach based on logistic regression suitable for these categorical data to identify several chromosomal regions as possible locations of clefting susceptibility loci, and we review candidate genes located within each region. Because cleft lip and cleft palate do not frequently co-aggregate in human families and because these structures arise semi-independently during development, these disorders are usually considered to be distinct in etiology. Our data, however, implicate several of the same chromosomal regions for both forms of clefting when teratogen-induced. Furthermore, different parental strain alleles are usually associated with clefting of the lip versus that of the palate (i.e., allelic heterogeneity). Because several other chromosomal regions are associated with only one form of clefting, locus heterogeneity also appears to be involved. Our findings in this mouse model suggest several priority areas for evaluation in human epidemiological studies.

Embryologic features of term fetuses and newborns in CL/Fr mice with special reference to cyanosis

OBJECTIVE

The objective of this study was to clarify the embryologic features of CL/Fr mice in relation to cyanosis.

METHOD

Orofacial examinations were conducted on 18-day-old term fetuses and newborns. Except for open eyelids in a few cases, all of the external abnormalities in this strain were cleft lip and/or palate (CLP).

RESULTS

The CLP incidence in term fetuses was 28.4%. The body and placental weights were not different between CLP(+) and CLP(-) fetuses. Several types of CLP were found; the most frequent was bilateral complete CLP (60%) followed by left complete (16%). Bilateral complete CL, which is the most severe CL type, was associated with poorly developed secondary palate and wide cleft. In newborns, 39.4 % of CLP(+) mice showed cyanosis, where no CLP(-) mice had such signs. The body weight of cyanotic mice with CLP was significantly lighter than that of noncyanotic mice with CLP. Cyanotic mice had severe types of CLP and unelevated palatal shelves.

CONCLUSION

We suggest that mechanical airway obstruction may be one of the causes of cyanosis in newborn CL/Fr mice.

Cloning and characterization of a novel bicoid-related homeobox transcription factor gene, RIEG, involved in Rieger syndrome

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.

Genetics of nonsyndromic oral clefts revisited

Nonsyndromic oral clefts are among the most common birth defects, affecting approximately 1 in 1000 Caucasian newborns. In recent decades, many investigators have used genetic and epidemiologic methods to identify etiologic factors, but results have often been inconclusive or contradictory. Etiologic heterogeneity is undoubtedly a major component in these birth defects, and there may not be a single answer to this problem. Here, we describe the main features of published studies pointing out their strengths and limitations. Additionally, we give insight into current methods for detecting the presence of interaction between genetic markers and environmental exposures in the etiology of oral clefts.

Molecular basis of familial cleft lip and palate

Cleft lip and palate (CLP) is one of the commonest congenital malformations and although the aetiology is still very unclear, a familial genetic component is considered to be an important factor in certain individuals. Molecular biology techniques are being used to identify the genes involved and this paper reviews current knowledge and the advances that have already been made. Recent evidence suggests a potential major gene on 6p, and a modifying role for transforming growth factor alpha (TGFA). Moreover retinoic acid receptor alpha (RARA) (17q), MSXI (4p), 4q and BCL3 (19q) could all be implicated in certain CLP families. In addition, the potential modifying role of various genes with the environment are considered to be important areas of research in the future. The identification of a genetic locus associated with this disease would be an important advance in CLP genetic counselling and lead to a better understanding of the genetic basis of CLP.

The lidgap-Gates (lgGa) mutation for open eyelids at birth maps to mouse chromosome 13

Complex nonadditive interactions between specific alleles at multiple loci may underlie many so-called multifactorial threshold birth defects. The open-eyelids-at-birth defect in mice is a good model for these defects, and an understanding of its genetic complexity begins with mapping the participating loci. The open-eyelids defect can be part of a syndrome or can occur with no other obvious phenotypic effects. Of the latter nonsyndromic forms, the lidgap series includes four extant mutations that are considered to be alleles based on complementation tests. All show genetic complexity in segregation ratios. None has been mapped previously. On the basis of a strategy of mapping the mutation with the simplest inheritance pattern first, we generated an extensive exclusion map for lidgap-Gates, lgGa, using morphological and protein polymorphisms. We then screened the non-excluded regions in a congenic strain, AEJ.LGG-lgGa, for SSLP markers and located the differential chromosome segment containing the lgGa locus in a region near the distal end of mouse Chromosome (Chr) 13. This linkage was confirmed and refined by typing SSLPs in 64 F2 and 74 BC1 progeny of a cross of LGG/Bc (lgGa/lgGa) to SWV/Bc. The lgGa mutation maps to a 1- to 2-cM region between D13Mit76 and D13Mit53. Integrin alpha 1 and integrin alpha 2, which map to the same general region, are possible candidate loci, based on their embryonic expression and cellular function. Evidence is also presented for a common unlinked recessive suppressor of the open eyelids trait caused by lgGa.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGF alpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of the mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome (FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis. Poorly co-ordinated control of form and size of structures, or groups of structures (e.g., teeth and jaws), by regulatory genes should do much to explain the very frequent "mismatches" found in malocclusions and other dentofacial "deformities". Future directions for research, including possibilities for prevention, are discussed.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGFalpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome(FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis.(ABSTRACT TRUNCATED AT 400 WORDS)