doi:10.1086/301643 Am. J. Hum. Genet. 61:1405–1412, 1997 1405 Autosomal Dominant Postaxial Polydactyly, Nail Dystrophy, and Dental Abnormalities Map to Chromosome 4p16, in the Region Containing the Ellis–van Creveld Syndrome Locus Timothy D. Howard,1 Alan E. Guttmacher,3,4 Wendy McKinnon,3 Mridula Sharma,1 Victor A. McKusick,2 and Ethylin Wang Jabs1,2 1Departments of Pediatrics and Surgery and 2Department of Medicine, Center for Medical Genetics, Johns Hopkins School of Medicine, Baltimore; and Departments of 3Pediatrics and 4Medicine, Vermont Regional Genetics Center, University of Vermont College of Medicine, Burlington Summary We have studied a four-generation family with features of Weyers acrofacial dysostosis, in which the proband has a more severe phenotype, resembling Ellis–van Crev- eld syndrome. Weyers acrofacial dysostosis is an auto- somal dominant condition with dental anomalies, nail dystrophy, postaxial polydactyly, and mild short stature. Ellis–van Creveld syndrome is a similar condition, with autosomal recessive inheritance and the additional fea- tures of disproportionate dwarfism, thoracic dysplasia, and congenital heart disease. Linkage and haplotype analysis determined that the disease locus in this pedigree resides on chromosome 4p16, distal to the genetic marker D4S3007 and within a 17-cM region flanking the genetic locus D4S2366. This region includes the El- lis–van Creveld syndrome locus, which previously was reported to map within a 3-cM region between genetic markers D4S2957 and D4S827. Either the genes for the condition in our family and for Ellis–van Creveld syn- drome are near one another or these two conditions are allelic with mutations in the same gene. These data also raise the possibility that Weyers acrofacial dysostosis is the heterozygous expression of a mutation that, in ho- mozygous form, causes the autosomal recessive disorder Ellis–van Creveld syndrome. Received June 30, 1997; accepted for publication October 1, 1997; electronically published November 26, 1997. Address for correspondence and reprints: Dr. Ethylin Wang Jabs, Center for Medical Genetics, Johns Hopkins School of Medicine, 600 North Wolfe Street, Baltimore, MD 21287-3914. E-mail: ewjabs@welchlink.welch.jhu.edu � 1997 by The American Society of Human Genetics. All rights reserved. 0002-9297/97/6106-0026$02.00 Introduction Weyers acrofacial dysostosis (Curry-Hall syndrome; OMIM 193530 [http://www.ncbi.nlm.nih.gov/Omim/]) is an autosomal dominant condition characterized by hypotelorism, an abnormal mandible, incisors abnormal in shape and number, a single central incisor, conical teeth, postaxial polydactyly type A or type B, hypo- plastic or dysplastic nails, and short stature. It was first reported in three unrelated cases (Weyers 1952), and three additional families have since been described (Curry and Hall 1979; Roubicek and Spranger 1984; Shapiro et al. 1984). Ellis–van Creveld syndrome (OMIM 225500 [http:// www.ncbi.nlm.nih.gov/Omim/]) (Ellis and van Creveld 1940) is a rare autosomal recessive disproportionate dwarfism that is most prevalent in the Amish population (McKusick et al. 1964). It is characterized by lip defects (oral frenula), dental abnormalities (neonatal teeth, hy- podontia, and premature tooth loss), cardiac malfor- mations (atrial septal defect and single atrium), geni- tourinary anomalies (epispadias and hypospadias), skeletal abnormalities (postaxial polydactyly type A, brachydactyly, fusion of the capitate and hamate, genu valgum, and distal limb shortening), and nail dysplasia (McKusick et al. 1964; Biggerstaff and Mazaheri 1968; Taylor et al. 1984). Weyers acrofacial dysostosis has some features in common with, but is distinct from, Ellis–van Creveld syndrome (table 1) (Gorlin et al. 1990, pp. 201–204). The two syndromes are dissimilar in mode of inheritance and phenotypic severity. Linkage analysis of 12 families with Ellis–van Creveld syndrome previously mapped the locus to a 3-cM region between the genetic loci D4S2957 and D4S827 on chro- mosome 4p16.1 (Polymeropoulos et al. 1996). The max- imum two-point LOD score (Zmax) observed was 6.91 (recombination fraction [v] of .02) with a genetic marker for the MSX1 homeobox gene. Subsequent sequencing of both MSX1 exons in two patients and one obligate carrier of Ellis–van Creveld syndrome ruled out the pos- 1406 Am. J. Hum. Genet. 61:1405–1412, 1997 Table 1 Phenotype of the Family and Related Syndromes Proband (IV:4) Other Affected Family Members Ellis–van Creveld Syndrome Jeune Asphyxiating Thoracic Dysplasia Weyers Acrofa- cial Dysostosis Short stature � Mild � Mild Mild Abnormal frenula � � � � � Natal teeth � � � � � Hypodontia � � � � � Conical teeth � � � ? � Mandibular anomalies � � � � �/� Retinal degeneration � � � � � Postaxial polydactyly Hands and feet Hands and feet Hands; sometimes feet �/�; if present, usu- ally hands and feet Hands and/or feet Onychodystrophy � � � � � Thoracic dysplasia � � � � � Cardiac findings Patent ductus arter- iosus, ventricular septal defect � Atrial septal defect, atrioventricular sep- tal anomaly � � Hepatic/pancreatic abnormalities � � � � � Renal abnormality � � � � � Radiological findings Flat acetabular roof with pointed pel- vic prominence � Fifth carpal in distal row of wrist, multi- ple ossification cen- ters in hamate, flat acetabular roof with pointed pelvic prominence Flat acetabular roof with pointed pelvic prominence � Lethal in newborns � � �/� Often � Inheritance ? Autosomal dominant Autosomal recessive Autosomal recessive Autosomal dominant Chromosomal linkage 4p16 4p16 4p16 ? 4p16? NOTE.—A plus sign (�) indicates present; a minus sign (�) indicates absent; a plus/minus sign (�/�) indicates sometimes present; and a question mark (?) indicates unknown. sibility that mutations in the coding region are causative of this condition (Ide et al. 1996). It has been suggested that isolated postaxial polydac- tyly, which occurs in these two conditions, may be a heterozygous manifestation of Ellis–van Creveld syn- drome (Fryns 1991; Goldblatt et al. 1992). Another sim- ilar condition with postaxial polydactyly as a clinical feature is Jeune syndrome (OMIM 208500 [http:// www.ncbi.nlm.nih.gov/Omim/]) (Jeune et al. 1955; Pir- nar and Neuhauser 1966; Langer 1969). The pelvis and limbs are similar in Ellis–van Creveld and Jeune syn- dromes, but nail dystrophy, abnormal frenula, and car- diac abnormalities are not found in the latter condition. In addition, renal involvement is a frequent feature of Jeune syndrome and is not found in Ellis–van Creveld syndrome. Postaxial polydactyly also has been observed to segregate as a single trait. Linkage of an autosomal dominant form of postaxial polydactyly type A to chro- mosome 7p15-q11.23 recently was reported in a five- generation Indian family with no other clinical findings (Radhakrishna et al. 1997). We have studied a family in which one individual (the proband) had findings that are most typical of Ellis–van Creveld syndrome. The paternal relatives, however, pre- sented with postaxial polydactyly, short stature relative to unaffected sibs, and tooth abnormalities segregating in an autosomal dominant manner. These findings are similar to those reported for Weyers acrofacial dysostosis (Curry and Hall 1979; Roubicek and Spranger 1984; Shapiro et al. 1984). We performed linkage analysis of this condition and mapped it to chromosome 4p16 in a region that encompasses the locus for Ellis–van Creveld syndrome. Patients and Methods Patient Population Genomic DNA was isolated from blood samples or lymphoblast cultures from 19 available family members, by use of the Blood and Cell Culture DNA kit (Qiagen). All these family members were examined clinically by one of the authors (A.E.G.). Howard et al.: Polydactyly Maps to Chromosome 4p16 1407 Case Presentation The proband (fig. 1; individual IV:4 in fig. 2) was the 7-lb 8-oz male product of an uncomplicated term preg- nancy of a 29-year-old mother and her nonconsanguin- eous 28-year-old husband. The initial physical exami- nation of the newborn was significant for a narrow chest, four-extremity postaxial polydactyly type A, short limbs, and swelling secondary to forceps delivery because of face presentation. As this swelling receded, examination of the upper lip revealed multiple frenula with shallow sulcus. Neonatal cardiology evaluation demonstrated a large patent ductus arteriosus that closed spontaneously at age 5 d and a small muscular ventricular septal defect. Radiographs were remarkable for short ribs and a flat acetabular roof with pointed pelvic prominence. The proband was ventilator dependent for the first month of life but otherwise had an uncomplicated new- born course. He remained on oxygen supplementation by nasal cannula until 10 mo of age. At ∼2 mo of age, the proband developed a hemangioma over the left chest that began to involute after his first birthday. By ∼3 years of age, his fingernails and toenails had become dys- trophic. He has decreased range of motion of the distal interphalangeal joints of his hands, and his thumbs ap- pear to be mildly digitalized. Dental evaluation has re- vealed a number of symmetrically absent primary teeth and dental pitting. Renal evaluation demonstrated no structural or functional abnormalities. He generally has enjoyed excellent health and normal development. Height has been at slightly below but paralleling the 5th percentile, weight has been at approximately the 10th percentile, and head circumference has been at the 25th–50th percentile. The proband’s father has a history of postaxial poly- dactyly type A, radial fifth-digit clinodactyly, and ony- chodystrophy, as do at least seven other of the father’s relatives (see fig. 2). Chromosome analysis was per- formed on the affected father (III:8 in fig. 2) and revealed a normal 46,XY karyotype. In the affected individuals, the polydactyly involves all four extremities, with the extra digits on the feet usually more fully formed than those on the hands. The individuals also may be slightly shorter in stature than their sibs. For instance, the pro- band’s father (III:8) is 5 feet 9 inches tall, and his affected brothers are 5 feet 8 inches (III:4) and 5 feet 11 inches (III:6), whereas their unaffected brothers are 6 feet 2 inches (III:2) and 6 feet 4 inches (III:3) and their unaf- fected sister (III:1) is 5 feet 11 inches. Some of these affected individuals have unusual labial frenula or shal- low labial sulci. Several, but not all, of the affected family members have had dental abnormalities: the paternal great-aunt (II:4) is reported to have conical-shaped teeth; the proband’s father (III:8) has tooth agenesis; a paternal uncle (III:4) had a pear-shaped tooth that was removed; and a first cousin (IV:2) has bilateral fusion of primary mandibular canine and lateral incisors and several con- ical-shaped primary teeth. The same cousin also has a prominent raphe extending over the middle of her phil- trum, from vermilion border to nasal root. The family history includes the proband’s mother (III:9) being 5 feet 6 inches tall and having a history of urinary reflux. Her family’s history is negative for short stature, polydactyly, onychodystrophy, congenital heart disease, or dental abnormalities. PCR Amplification and Sequence Analysis For the nine genetic markers listed in table 2, PCR was performed with DNA from each family member, in 10-ml reactions consisting of 100 ng genomic DNA, 50 mM KCl, 10 mM Tris-HCl, 200 mM each dNTP, 1.5 mM MgCl2, 0.1 mg BSA/ml, 0.6 mmol each primer, 5–10 ng one g[32P]-dATP end-labeled primer, and 1.0 U Taq DNA polymerase (Boehringer Mannheim). Amplifica- tion parameters were as follows: 3 min at 94�C; 10 cycles of 40 s at 94�C, 40 s at the annealing temperature, and 40 s at 72�C; followed by 15 cycles of 40 s at 92�C, 40 s at the annealing temperature, and 40 s at 72�C; and a final extension of 3 min at 72�C. The annealing tem- perature for each genetic marker was as described in the Genome Database (http://www.gdb.org/), with the ex- ceptions that the temperature for D4S827 was increased from 62�C to 65�C and that for D4S412 was decreased from 55�C to 50�C. The PCR products were separated on a 6.0% polyacrylamide sequencing gel and were de- tected by autoradiography. The MSX1 gene was sequenced by, first, amplification of both exons with two sets of PCR primers derived from the published sequence (Hewitt et al. 1991). To amplify exon 1, the forward primer 5′-CTGCTGACA- TGACTTCTTTGC-3′ and the reverse primer 5′-TGG- GTTCTGGCTACTACCTG-3′, which amplify a 477-bp fragment, were used. PCR reactions for exon 1 were performed in 50-ml volumes consisting of 100–500 ng genomic DNA, 10 mM Tris-HCl (pH 8.3), 50 mM KCl, 1.5 mM MgCl2, 200 mM each dNTP, 0.5 mM each pri- mer, 5% dimethyl sulfoxide, and 1.25 U Taq DNA poly- merase (Boehringer Mannheim). PCR parameters were 35 cycles of 1 min at 94�C, 1 min at 60�C, and 1 min at 72�C. Exon 2 was amplified with the forward primer 5′-GGCTGATCATGCTCCAATGCTT-3′ and the re- verse primer 5′-TACAGCACCAGGGCTGGAGG-3′, yielding a 561-bp fragment. PCR reactions were per- formed as described for exon 1, with cycling parameters of 1 min at 95�C, 1 min at 66�C, and 2 min at 72�C. PCR products were run on 2% NuSieve gels (FMC BioProducts) and were extracted. The DNA, isolated with the Gel Extraction Kit (Qiagen), was directly se- Figure 1 Clinical photographs of affected family members. A, Proband (IV:4 in fig. 2), front and lateral view. Note the short stature, abnormal configuration of the chest, hands with nail dysplasia of the thumbs (bottom right), and postaxial polydactyly in infancy (bottom left). B, Father of the proband (III:8 in fig. 2), front and lateral view. Note the proportional stature, normal chest, and onychodystrophy. His postaxial polydactyly had been surgically removed. Howard et al.: Polydactyly Maps to Chromosome 4p16 1409 Figure 2 Linkage- and haplotype-analysis data for the studied family with features of Weyers acrofacial dysostosis and Ellis–van Creveld syndrome. For each individual evaluated, the alleles for the genetic markers are given below the symbol; individuals without as- signed alleles were not available for analysis. The proband is indicated with an arrow. The boxed areas include the alleles that are either certainly or possibly inherited from an affected parent and show the largest possible region in which the disease locus may lie. Table 2 Linkage Analysis of Postaxial Polydactyly, Nail Dystrophy, and Dental Abnormalities to Chromosome 4p16 MARKER LOD SCORE AT v � Zmax vmax.00 .01 .05 .10 .20 .30 .40 D4S412 2.46 2.44 2.33 2.17 1.77 1.23 .59 2.46 .00 D4S2957 �.04 �.04 �.03 �.03 �.02 �.01 .00 .00 .50 D4S432 .25 .25 .25 .24 .20 .15 .08 .25 .04 MSX1 1.14 1.14 1.11 1.06 .90 .68 .38 1.14 .00 D4S827 3.22 3.16 2.93 2.63 1.98 1.27 .53 3.22 .00 D4S431 1.62 1.59 1.46 1.29 .92 .52 .16 1.62 .00 D4S2366 4.09 4.02 3.74 3.37 2.57 1.69 .75 4.09 .00 D4S3007 �� .26 .81 .92 .81 .54 .20 .92 .11 D4S394 �� 1.73 2.20 2.19 1.82 1.27 .60 2.22 .07 quenced by the Johns Hopkins Genetic Resources Core Facility, by use of the specific PCR primers. Linkage and Haplotype Analysis Nine genetic markers, spanning 10 cM (Polymero- poulos et al. 1996), were used for linkage analysis (table 2). The ILINK and MLINK options of the LINKAGE software package (version 5.1) (Ott 1991) were used to calculate LOD scores by use of an IBM personal com- puter. The disease was modeled as an autosomal dom- inant, fully penetrant disorder. The allele frequencies for each marker were set as equal. For the haplotype anal- ysis, the order of the genetic markers was determined from the publicly available YAC physical map from the Stanford University Genome Center (ftp:// shgc.stanford.edu/pub/hgmc/YAC�data) and from the order described elsewhere (Polymeropoulos et al. 1996). Results Phenotype of Family Members As table 1 indicates, the proband and a number of his paternal relatives have features similar to those observed in Weyers acrofacial dysostosis, Ellis–van Creveld syn- drome, and Jeune syndrome. Of these conditions, the proband most closely fits Ellis–van Creveld syndrome, on the basis of his short stature, four-extremity postaxial polydactyly type A, dystrophic nails, abnormal labial frenula and sulcus, hypodontia with poor enamel, tho- racic dysplasia, congenital heart disease, neonatal pelvic x-ray significant for flat acetabular roof with pointed pelvic prominence, and survival postinfancy. If one as- sesses the family when the proband is excluded, however, the autosomal dominant mild short stature, four-extrem- ity postaxial polydactyly type A, onychodystrophy, hy- podontia, and abnormal frenula, with which the affected members present, closely resemble Weyers acrofacial dysostosis. Linkage to Chromosome 4p16 and Haplotype Analysis The proband in this family has features most consis- tent with Ellis–van Creveld syndrome. Therefore, we evaluated this family by using nine genetic markers from near the Ellis–van Creveld locus on chromosome 4p16.1 (table 2) (Polymeropoulos et al. 1996). Evidence for link- age to this region was observed, with LOD scores 13.00 and no recombination for two of the markers, D4S827 and D4S2366. The highest two-point LOD score was 4.09 with the genetic marker D4S2366. One recombi- nation event, between the genetic markers D4S2366 and D4S3007, was detected in individual III:10 (fig. 2), de- fining the most proximal boundary for the region con- taining the disease locus. Recombinants that would have indicated the most distal boundary for the location of the gene were not detected within this 10-cM region. Using the LOD score 4.09, we calculated the 95% con- fidence interval for the disease locus to be 14 cM prox- imal and distal of D4S2366. However, the genetic dis- tance between D4S431 and D4S3007, which flank D4S2366, is only 3 cM (Polymeropoulos et al. 1996); thus, the recombinant (detected in individual III:10) lim- its the proximal boundary to a maximum of 3 cM from 1410 Am. J. Hum. Genet. 61:1405–1412, 1997 D4S2366. Therefore, the region most likely to contain the gene is a 17-cM interval. This region encompasses the 3-cM critical region, between D4S2957 and D4S827, for the Ellis–van Creveld syndrome locus, re- ported elsewhere (Polymeropoulos et al. 1996). Hap- lotype analysis provided similar results, with the critical region found to reside distal to D4S3007 on the basis of recombination events detected in individual III:10 (fig. 2). Sequencing of the MSX1 Candidate Gene A candidate gene that maps within the critical region is the homeobox gene MSX1. The mouse homologue, Hox-7, is expressed in the neural crest, the developing mandible and teeth, the embryonic heart, and the limb buds (Robert et al. 1989), all of which are developmental regions affected in Ellis–van Creveld syndrome. In ad- dition, a mutation in MSX1 was recently reported in a family with selective tooth agenesis (Vastardis et al. 1996), which may be relevant to the dental abnormalities observed in both Ellis–van Creveld syndrome and Wey- ers acrofacial dysostosis. Both exons of MSX1 from the proband (IV:4) and his affected paternal uncle (III:6) were sequenced. No mutations were detected, suggesting that changes in the MSX1 coding region are not re- sponsible for the clinical phenotype of this family. This result is consistent with the recent report that no mu- tations were detected in either of the two MSX1 exons in patients with Ellis–van Creveld syndrome (Ide et al. 1996). Discussion We have studied a four-generation family segregating a condition with features of both Weyers acrofacial dy- sostosis and Ellis–van Creveld syndrome. The disorder in affected members of this family, including in the pro- band, demonstrated linkage to a chromosome 4p16 re- gion estimated to be 17 cM and defined by recombi- nation only proximally between loci D4S3007 and D4S2366. The linkage-analysis data clearly show that, in this family, the candidate region for the condition encompasses the Ellis–van Creveld gene. The mapping of these two diseases to the same chromosomal region might represent any one of several phenomena. One pos- sibility is that all affected members of this family have either an unreported autosomal dominant condition or Weyers acrofacial dysostosis with variable expression, with the proband being the most severely affected. Thus, the proband’s condition would be a genocopy for El- lis–van Creveld syndrome. A second possibility is that the proband is a double heterozygote, with a mutation for the condition inherited from his father and a mu- tation for Weyers acrofacial dysostosis, Ellis–van Cre- veld syndrome, or Jeune syndrome inherited from his mother. A final possibility is that the proband has Ellis–van Creveld syndrome and that his “affected” paternal rel- atives are symptomatic heterozygotes. Although some have questioned this interpretation (see OMIM 225500 [http://www.ncbi.nlm.nih.gov/Omim/]) because no het- erozygous effects of Ellis–van Creveld syndrome were observed in the Amish population (McKusick et al. 1964), reports exist of several families in which heter- ozygotes exhibit findings similar to those in the family reported here (Fryns 1991; Goldblatt et al. 1992; Spran- ger and Tariverdian 1995). In fact, a similar family, con- sisting of a proband with Ellis–van Creveld syndrome and her father, who had features of Weyers acrofacial dysostosis (mild short stature, nail dysplasia, and teeth abnormalities but no polydactyly), has been reported (Spranger and Tariverdian 1995). The features observed in our proband’s paternal relatives could be the phe- notype resulting from one specific allele of the Ellis–van Creveld syndrome gene, an allele that differs from the allele affected in the Amish population. The proband may have inherited this allele from his father and a dif- ferent mutant allele from his mother, leading to the full Ellis–van Creveld phenotype. Although no mutations were detected in the coding region of MSX1 in the two members of this family who were tested, it is conceivable that mutations in the MSX1 regulatory elements may be responsible for the condition in this family and, perhaps, for Ellis–van Creveld syndrome. Previous studies, using deletion analysis of the mouse Msx1 promoter, identified regions that were important for distinct spatial and tem- poral expression patterns (MacKenzie et al. 1997). Another candidate gene in the critical region for the condition in our family is that for fibroblast growth- factor receptor 3 (FGFR3). Mutations in FGFR3 have been reported in patients with achondroplasia (Rousseau et al. 1994; Shiang et al. 1994), hypochondroplasia (Bel- lus et al. 1995), thanatophoric dysplasia (Tavormina et al. 1995; Rousseau et al. 1996), and craniofacial and limb abnormalities resembling Crouzon, Pfeiffer, or Sae- thre-Chotzen syndromes (Meyers et al. 1995; Bellus et al. 1996). FGFR3 maps to chromosome 4p16.3 (Thompson et al. 1991) and is a potential candidate gene for the condition in this family or for Weyers acrofacial dysostosis, but it is distal to the critical region for the Ellis–van Creveld locus (Polymeropoulos et al. 1996). Other genes located on human chromosome 4p16 (those for dopamine receptor D1B [DRD1B], zinc finger pro- tein–141 [ZNF-141], dopamine receptor D5 [DRD5], and protein S-100P [S100P]; the myosin light-chain reg- ulatory gene [MYL5]; and homeobox gene H6 [HMX1]), identified in the syntenic region of mouse chromosome 5 (those for phosphodiesterase 6B, cGMP- specific, rod, beta [PDEB]; diacylglycerol kinase, delta Howard et al.: Polydactyly Maps to Chromosome 4p16 1411 [DAGK4]; iduronidase, alpha-L [IDUA]; LDL-related protein-associated protein 1 [LRPAP1; alpha-2-macro- globulin receptor-associated protein]; G-protein-coupled receptor kinase-2 [Drosophila]–like [GPRK2L]; alpha- 2C-adrenergic receptor [ADRA2C]; adducin, alpha subunit [ADD1]; huntingtin [HD]; and casein, beta [CSN2]) (DeBry and Seldin 1996; http:// www.ncbi.nlm.nih.gov/Omim/Homology/), or associ- ated with relevant mouse models are not obvious can- didates, because their developmental expression pat- terns, function, or phenotypic effects differ significantly from the features present in the affected members of the family in this study. The concept of a single gene causing both dominant and recessive conditions, as is possibly the case reported here, is not uncommon. Mutations in the genes for rho- dopsin (Rosenfeld et al. 1992), von Willebrand factor (Zimmerman and Ruggeri 1987), thyroid hormone re- ceptor–beta (Takeda et al. 1992), globin-beta (Thein et al. 1990), and collagen types 1A1 (Pruchno et al. 1991), 1A2 (De Paepe et al. 1997), and 7A1 (Christiano et al. 1993, 1994) have been found in both autosomal dom- inant and recessive diseases. For example, a much more severe osteogenesis imperfecta phenotype was found in two sibs homozygous for mutations in the collagen type 1A2 gene than was found in their heterozygous parents or sibs (De Paepe et al. 1997). This finding is similar to those for the family studied here, in which the hetero- zygous carriers are affected more mildly than the pre- sumed homozygote (the proband). A potential mecha- nism for different mutations in the same gene, causing autosomal dominant and recessive inheritance patterns, is that certain mutations in the dominant form lead to dominant-negative effects, as is the case in generalized resistance to thyroid hormone (Takeda et al. 1992; Hay- ashi et al. 1994). In our family, a mutation in one gene may have a dominant-negative effect in the heterozy- gotes, leading to Weyers-acrofacial-dysostosis–like fea- tures, but this mutation in combination with a second mutation would lead to loss of function in the homo- zygote, resulting in the Ellis–van Creveld phenotype. Ex- pression analysis and examination of the regulatory re- gion of MSX1 and of other candidate genes that later may be mapped to chromosome 4p16 in affected mem- bers of this family will help to determine the etiology of this condition. 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Genomics 11:1133–1142 Vastardis H, Karimbux N, Guthua SW, Seidman JG, Seidman CE (1996) A human MSX1 homeodomain missense muta- tion causes selective tooth agenesis. Nat Genet 13:417–421 Weyers H (1952) Ueber eine korrelierte Missbildung der Kiefer und Extremitatenakren (Dysostosis acro-facialis). Fortschr Geb Roentgenstrahlen Nuklear Med 77:562–567 Zimmerman TS, Ruggeri ZM (1987) von Willebrand disease. Hum Pathol 18:140–152 Autosomal Dominant Postaxial Polydactyly, Nail Dystrophy, and Dental Abnormalities Map to Chromosome 4p16, in the Region Containing the Ellis–van Creveld Syndrome Locus Introduction Patients and Methods Patient Population Case Presentation PCR Amplification and Sequence Analysis Linkage and Haplotype Analysis Results Phenotype of Family Members Linkage to Chromosome 4p16 and Haplotype Analysis Sequencing of the MSX1 Candidate Gene Discussion Acknowledgments References