1 HUMAN MUTATION 14: (1999) RESEARCH ARTICLE Townes-Brocks Syndrome: Detection of a SALL1 Mutation Hot Spot and Evidence for a Position Effect in One Patient Sandrine Marlin, 1 Stéphane Blanchard, 1 Rima Slim, 1 Didier Lacombe, 2 Françoise Denoyelle, 1,3 Jean-Louis Alessandri, 4 Elisa Calzolari, 5 Valérie Drouin-Garraud, 6 F.G. Ferraz, 7 Alain Fourmaintraux, 8 Nicole Philip, 9 Jean-Edmond Toublanc, 10 and Christine Petit 1 * 1 Unité de Génétique des Déficits Sensoriels, Institut Pasteur, Paris, France 2 Pédiatrie & Génétique Médicale, Hôpital Pellegrin-Enfants, Bordeaux, France 3 Service ORL, Hôpital d Enfants Armand-Trousseau, Paris, France 4 Service de Néonatologie, Hôpital Félix Guyon, St Denis, La Réunion 5 Istituto di Genetica Medica, Universita degli Studi Ferrara, Ferrara, Italy 6 Unité de Génétique Clinique, Hôpital Charles Nicolle, Rouen, France 7 Department of Genetics, Pediatric Hospital D. Estefania, Lisbon, Portugal 8 Unité de Néonatologie, Centre Hospitalier, St Pierre, La Réunion 9 Centre de Génétique Médicale, Hôpital Timone-Enfants, Marseille, France 10 Service Consultations, Hôpital Saint-Vincent de Paul, Paris, France Communicated by Jean-Louis Mandel Townes-Brocks syndrome (TBS) is an autosomal dominant developmental disorder characterized by anal and thumb malformations and by ear anomalies that can affect the three compartments and usually lead to hearing loss. The gene underlying TBS, SALL1, is a human homolog of the Drosophila spalt gene which encodes a transcription factor. A search for SALL1 mutations undertaken in 11 unrelated affected individuals (five familial and six sporadic cases) led to the detection of mutations in nine of them. One nonsense and six different novel frameshift mutations, all located in the second exon, were identified. Together with the previously reported mutations [Kohlhase et al., 1999], they establish that TBS results from haploinsufficiency. The finding of de novo mutations in the sporadic cases is consistent with the proposed complete penetrance of the disease. Moreover, the occurrence of the same 826C>T transition in a CG dimer, in three sporadic cases from the present series and three sporadic cases from the other series [Kohlhase et al., 1999] (i.e., six of the eight mutations identified in sporadic cases), reveals the existence of a mutation hotspot. Six different SALL1 polymorphisms were identified in the course of the present study, three of which are clustered in a particular region of the gene that encodes a stretch of serine residues. Finally, the chromosome 16 breakpoint of a t(5;16)(p15.3;q12.1) translocation carried by a TBS-affected individual was mapped at least 180 kb telomeric to SALL1, thus indicating that a position effect underlies the disease in this individual. Hum Mutat 14: , Wiley-Liss, Inc. KEY WORDS: Townes-Brocks syndrome; mutation; position effect INTRODUCTION In 1972, Townes and Brocks  described a syndrome comprising an imperforate anus, triphalangeal thumbs, external ear anomalies ( satyr ears ) and sensorineural deafness, and which showed an autosomal dominant mode of transmission. The prevalence of Townes-Brocks syndrome (TBS; Received 27 May 1999; accepted revised manuscript 11 August *Correspondence to: Christine Petit, Unité de Génétique des Déficits Sensoriels, CNRS URA 1968, Institut Pasteur, 25 rue du Dr Roux, Paris Cedex 15, France. Grant sponsor: Association Française contre les Myopathies (France). Present address for Rima Slim: Department of Biochemistry, American University, Beirut, Lebanon WILEY-LISS, INC.
2 378 MARLIN ET AL. MIM# ) is unknown. To date, 113 cases have been reported worldwide, 93 of which are familial; the intrafamilial phenotypic expression is variable (for review, see Allanson , and Marlin, in preparation). The typical clinical signs are malformations of the anus (80% of the cases), radial axis (50% of the cases, mainly preaxial polydactyly), and outer ear (65% of the cases) which are often associated with hearing loss (40% of the cases). The hearing loss can be sensorineural, conductive, or mixed [Rossmiller and Pasic, 1994]. Additional anomalies have been reported [for review, see Powell and Michaelis, 1999], namely, renal (19%) [Kurnit et al., 1978; Newman et al., 1997], urogenital (15%) [de Vries-Van der Weerd et al., 1988], skeletal (28%, mainly foot malformations) [Green et al., 1996], and cardiac (15%) [Barakat et al., 1988] anomalies. The diverse anomalies associated with TBS suggest a developmental defect taking place during the organogenesis period, i.e., between embryonic weeks 5 and 10. The gene responsible for TBS has been identified as SALL1 (MIM# ) by the detection of a single basepair deletion and a nonsense mutation in two affected families [Kohlhase et al., 1998]. SALL1 is one of two identified human homologs [Kohlhase et al., 1996] of the Drosophila developmental gene spalt which encodes a transcription factor [Kühnlein et al., 1994]. Spalt mutants exhibit homeotic head and tail transformations [Jürgens, 1988]. Partial or complete cdna sequences of spalt homologs from several species have been characterized, namely msal-1 in mouse [Ott et al., 1996], spalt in medaka fish [Köster et al., 1997], and Xsal-1 in Xenopus [Hollemann et al., 1996]. They encode proteins which contain the typical eight amino acids SAL-box (FTTK- GNLK) [Kühnlein et al., 1994] and a variable number of zinc finger motifs. Patients from 12 unrelated families (five familial cases and seven sporadic cases) who upon careful clinical examination were recognized as presenting the most prominent features for TBS were studied. We report on the molecular analysis of the SALL1 gene, which led us to detect the causative mutations in nine of them. Moreover, the characterization of the chromosome 16 breakpoint present in a TBSaffected individual carrying a 5p16q translocation allowed us to propose that a position effect is responsible for the disease in this patient. Patients SUBJECTS AND METHODS The diagnosis of TBS was based on the occurrence of anal and thumb malformations and ear anomalies. Families TB3, TB4, TB5, TB8, TB11, and TB10 [case report in Marlin et al., 1998] were from France, TB1 and TB9 from Île de la Réunion (Indian Ocean), TB2 from Spain, TB6 from Portugal [case report in Ferraz et al., 1989], and TB7 from Italy [case report in Baldi et al., 1995]. Individual TB12, carrying a t(5;16)(p15.3;q12.1) translocation, was described in Serville et al. . Informed consent for the molecular analysis was obtained from all families. DNA was prepared from whole blood samples by standard phenol/chloroform extraction and ethanol precipitation. Molecular analysis was performed in the propositus and both nonaffected parents of families TB6, TB7, TB8, and TB9, in the propositus and affected mother of families TB1, TB3, and TB4, in the propositus and affected father of family TB5, and only in the propositus of families TB2, TB10, TB11, and TB12. TABLE 1. Primers for PCR Amplification and Sequencing of the SALL1 Exons Amplification Sequencing primers Exon primers Forward (5 3 ) Reverse (5 3 ) 1 Ex1a pex1 a 32 tttattctgccccagctgatg aattacgccgagtggaag 2 TF1 TR2 b gtcctggccccttttctaatc b 414 GCCGCTGCCGCTTTTGTTAG 323 TGGACTGCAGCGACCTTT 862 GGGAACTTAGCGTGGACA 682 GCCCTCATGGAACAACTC 1,242 TCTGCAGTTGTTCCGATGTT 1,102 CCAGCGGTCTCATCATCGTC 1,619 CTGGTGACTGGCTTCTCTGG TF2 TR5 b 1,492 CGCCACAAAGAGAAATACCC 2,015 GCCTTGAACTGCTCGGACAT 1,844 CCACTCTGCCACCCTCTG 2,415 GGACTCAGAGTAGCTGTC 2,255 ACTACAGTGTCCATCGTG 2,780 TGCATGGAAGAGGTAGAC 2,654 TGAAGTCAGTGGAGAATG 3,240 CGAGTTGGCGGGAATCAC 3,098 TTTGCAATCGTGGCTTTTCC ggacagggttgatggagcag b 3 TF5 TR5.1 b gttgccttcactgtcgtcac b tctgaacaggaatgaatgctatg b Primers located in introns and untranslated regions are in lower case, their positions are indicated in italics. a See primer sequences in Subjects and Methods. b Primers reported by Kohlhase et al. .
3 SALL1 MUTATIONS IN TOWNES-BROCKS SYNDROME 379 PCR Amplification and Sequencing of the SALL1 Exons The PCR amplification and sequencing of doublestranded DNA templates (dideoxy chain terminator method using fluorescent dideoxynucleotides) were performed under the same conditions as in Lévy et al. . For exon 1 amplification, the primers used were EX1a (starting in the noncoding part of this exon, 32 bp 5 from the ATG initiation codon) and pex1 (starting 143 bp 3 from the donor splice site of this exon) (Table 1). PCR amplification of exon 2 was carried out in two parts, using primer pairs TF1 TR2 (5 side, 1.5 kb amplicon) and TF2 TR5 (3 side, 2.2 kb amplicon), and that of exon 3, using primer pair TF5 TR5.1 according to Kohlhase et al. . The primers used for sequencing are listed in Table 1. In patient TB5, PCR amplification using primers TF2 (within exon 2) and TR5 (within intron 2) resulted in the normal 2.2 kb band and an additional 1.1 kb band. The latter was separated from the normal one by agarose gel electrophoresis and sequenced. Southern Blot Analysis Ten µg of HindIII-digested genomic DNA were run on a 0.8% agarose gel and blotted onto N+- Hybond filters (Amersham, Arlington Hts., IL). Blots were hybridized in Church buffer overnight at 65 C. Membranes were washed in 0.2x SSC, 0.1% SDS at 65 C. The probes used to analyze each of the SALL1 exons were derived by PCR amplification using the primer pairs EX1A pex1 for exon 1 (see above), TF1 TR5 or TF2 TR5 for exon 2, and TF5 TR5.1 for exon 3 [Kohlhase et al., 1998]. Construction of l Phage Libraries of PAC 4645 and YAC 438H5, and Sequencing DNA from P1 phage artificial chromosome (PAC) 4645 and yeast artificial chromosome (YAC) 438H5 was partially digested with Sau 3AI, and run on a 0.6% agarose gel. Fragments in the kb range were eluted, ligated to λ pgem11 vector (Promega, Madison, WI), and packaged in E. coli KW251 using the Promega Packaging system extract. To construct a contig of λ clones covering PAC 4645 and YAC 438H5, the extremities of this PAC, this YAC, and each subsequently selected λ subclone were sequenced and used as probes (after PCR amplification) to get overlapping new λ clones from the library. The clones covering the entire PAC 4645 and the telomeric 100 kb of YAC 438H5 were sequenced. FIGURE 1. Pedigrees of the five families affected by TBS. The propositus is indicated by an asterisk.
4 TABLE 2. Summary of the Clinical Features Presented by the TBS Patients Patient a Anal malformations Thumb anomalies Ear malformations Hearing loss Other features TB1 (F) Imperforate Bifid thumbs Preauricular tags Sensorineural Bilateral renal hypoplasia mild Persistent ductus arteriosus Foot malformations + abnormal toes TB2 (F) Imperforate Triphalangeal thumbs Preauricular tags Mixed Normal renal ultrasonography Severe Bifid toes TB3 (F) Imperforate Triphalangeal thumbs Microtia Sensorineural Normal renal ultrasonography Perineal fistula Moderate Foot malformation Arachnodactyly TB4 (F) Stenosis Broad thumbs Microtia Unknown Unknown Antepositioned Low set ears TB5 (F) Imperforate Bifid thumbs Preauricular tags Unknown Unilateral renal agenesis Abnormal helix Metacarpal anomalies Low set ears Growth delay TB6 b (S) Imperforate Hexadactyly Satyr ears Mixed Normal renal ultrasonography Perineal fistula Triphalangeal thumb Preauricular tags Mild Uterovaginal hypoplasia Ventricular septal defect Hand syndactylies TB7 c (S) Imperforate Hexadactyly External auditory atresia Sensorineural Bilateral renal hypoplasia Perineal fistula Triphalangeal thumbs Microtia Profound Preauricular tags + pits TB8 (S) Imperforate Hexadactyly External auditory atresia Mixed Renal failure Triphalangeal thumbs Microtia Profound Foot malformations Retinal maculopathy Angioedema d TB9 (S) Vulvar anus Hexadactyly No No Normal renal ultrasonography TB10 e (S) Imperforate Triphalangeal thumbs No No Normal renal ultrasonography Pubertal delay TB11 (S) Imperforate No External ear aplasia Mixed Normal renal ultrasonography Mild Hand + foot syndactylies TB12 f (S) Imperforate Triphalangeal thumbs Preauricular tags No Normal renal ultrasonography Antepositioned Overfolded helix No a F = familial case; S = sporadic case. b The mutation identified in this patient [described in Ferraz et al., 1989], was not detected in either of her parents, thus leading to the conclusion that the deafness and other mild symptoms affecting the grandfather (and his own grandfather and granduncle) [see pedigree in Ferraz et al., 1989] cannot be ascribed to TBS. c Described in Baldi et al. . d A mutation in the gene coding for the C1 inhibitor has been identified in this individual and other family members who suffered from angioedema [Verpy et al., 1996]; none of the latter presented with TBS anomalies. e Described in Marlin et al. . f Described in Serville et al. . This patient carries a t(5;16)(p15.3;q12.1) chromosomal translocation. 380 MARLIN ET AL.
5 SALL1 MUTATIONS IN TOWNES-BROCKS SYNDROME 381 Fluorescence In Situ Hybridization (FISH) Analysis Metaphase chromosome spreads from individual TB12 (t(5;16)(p15.3;q12.1)) were prepared and hybridized, as described previously [Vincent et al., 1994], with probes corresponding to the entire YAC 438H5, the entire PAC 4645, and each of its λ subclones. RESULTS Search for SALL1 Mutations in TBS Affected Individuals The cdna sequence corresponding to SALL1 first exon, obtained as a result of 5 RACE-PCR (not shown) (GenBank accession number AF074949), and the genomic structure that we established in parallel were entirely consistent with those reported in the meantime [Kohlhase et al., 1999] (GenBank accession number Y18265). Eleven unrelated individuals affected by TBS, without any detectable karyotypic anomaly, were studied. They consist of five familial (families TB1 to TB5, pedigrees in Fig. 1) and six sporadic (individuals TB6 to TB11) cases. The clinical features of the patients are described in Table 2 and Figure 1. The three SALL1 coding exons were PCR-amplified and sequenced in the proband and in both parents whenever possible. For that purpose, specific primer pairs were designed for the first two exons (see Table 1), whereas the previously described primers were used to explore the third exon [Kohlhase et al., 1998]. Mutations were identified in nine patients. They consist of seven different mutations: one nonsense mutation, three microdeletions, two microinsertions, and one large complex deletion (Table 3a, and see Figs. 2 and 3). All are located in the second exon and result in premature protein truncation. No SALL1 mutation was detected in patients TB10 and TB11; Southern blot analysis, using probes corresponding to each of the three SALL1 exons, failed to detect any gross DNA rearrangement in these patients either (see Fig. 3; and data not shown). In addition to the aforementioned mutations, six nucleotide changes were identified, of which two are silent polymorphisms, two lead to an amino acid change (S159G, G1265E), and two result in the insertion (S ins) or deletion (S164del) of a serine residue (Table 3b). The latter four mutations were considered as asymptomatic polymorphisms since three of them were present in both the propositus and an unaffected parent or relative, and the remaining one (S ins, in family TB4) was present simultaneously with the 1565delC frameshift mutation (Table 3a), supposed to be responsible for the disease in this family. Characterization of the Chromosome 16 Breakpoint in a TBS Individual Carrying a 5p;16q Translocation: Evidence for a Position Effect The occurrence of a balanced translocation t(5;16)(p15.3;q12.1) in a TBS-affected child (TB12) has permitted the assignment of the causative gene to 16q12.1 [Serville et al., 1993]. No SALL1 modification was detected in TB12, either by DNA sequencing or by Southern blot analysis (Fig. 3). A PAC library and a YAC library were screened with sequence tagged sites (STSs) of the paracentromeric region of chromosome 16. The clones so selected were characterized by FISH on the patient s chromosomes. We thereby identified PAC 4645, encompassing the 16q breakpoint, and YAC 438H5 (180 kb, located centromeric to the breakpoint) (not shown). PAC 4645 (Fig. 4a) was subcloned into λ phages which were ordered into a contig (see Subjects and Methods). The λ 12.6 subclone spanning the breakpoint was identified by FISH (Fig. 4b). According to the contig map, λ 12.6 was located at approximately 40 kb from the centromeric end of PAC Since sequencing of this PAC as well as PCR amplification of the TABLE 3. Nucleotide Changes in SALL1 and Predicted Modifications of the Protein (a) Nucleotide Amino acid Patient* change change TB1 (F) delCA frameshift TB2 (F) insA frameshift TB3 (F) insAG frameshift TB4 (F) 1565delC frameshift TB5 (F) 1487del562 frameshift 2056del588 TB6, TB7, TB8 (S) 826C>T** R276X TB9 (S) 1966del10 frameshift (b) Nucleotide Amino acid Exon change change 2 475A>G** S159G insAGC** S ins delAGC S164del G>A no T>C no G>A G1265E (a) Mutations in TBS affected patients. *F = familial, S = sporadic. In patient TB5, PCR amplification of the 3 part of exon 2 revealed a band of the expected size (2.2 kb), and a smaller additional band (1.1 kb) which was sequenced (not shown). This allowed us to identify a 1.1 kb complex deletion within which a short segment of 6 bp was preserved. This deletion predicts the loss of a HindIII restriction site in exon 2 which was performed by Southern blot analysis (see Fig. 3). (b) Polymorphisms. **These nucleotide changes have also been reported in Kohlhase et al. . Nomenclature according to Beaudet and Tsui  modified by Antonarakis .
6 382 MARLIN ET AL. adjacent YAC 438H5 failed to detect any SALL1 sequence within this interval, we undertook a physical mapping of this chromosomal region. We first selected a bacterial artificial chromosome (BAC 230e15) containing the three SALL1 exons. The distal end of YAC 438H5 was found to overlap approximately 30 kb of PAC 4645, and its proximal end about 10 kb of BAC 230e15 (Fig. 4a; FIGURE 2. Electrophoretograms showing the mutations in six TBS individuals. In each case, the corresponding normal graph (wt) is presented in parallel. For three mutations, the sequence of the DNA strand which is presented is complementary to that of the cdna, and the direct sequence has been added on top of the normal electrophoretogram.
7 SALL1 MUTATIONS IN TOWNES-BROCKS SYNDROME 383 FIGURE 3. Southern blot analysis of SALL1 exon 2 in TBS individuals. HindIII-digested genomic DNA from BAC 230e15 (lane 1), patients TB12 (t(5;16)(p15.3;q12.1)) (lane 2), TB10 (lane 3) and TB11 (lane 6) (two sporadic TBS cases with no detected point mutation), TB5 (1.1 kb deletion) (lane 4), and one control individual (lane 5) were hybridized with a PCR product obtained using primers TF2 TR5, corresponding to the 3 part of exon 2 (see Subjects and Methods). This probe detects two SALL1 specific bands (2.5 kb and 3 kb) in all individuals except TB5 (lane 4), who carries a heterozygous 1.1 kb deletion which results in the loss of an HindIII restriction site and gives rise to the additional 4 kb band. The two other bands detected by this probe are indicative of a yet-unidentified SAL gene or pseudogene. see Subjects and Methods). These results show that the chromosomal breakpoint in TB12 is located at a minimal distance of 180 kb from SALL1. The present data establish that TBS in this patient results from a position effect [for review, see Kleinjan and van Heyningen 1998], the mechanism of which awaits further characterization. In particular, in the absence so far of characterization of the SALL1 regulatory elements, the disruption of a remote one should be considered. DISCUSSION In this series, the causative mutations or chromosomal rearrangement were detected in 10 out of 12 unrelated TBS-affected individuals. No SALL1 mutation or karyotypic anomaly was detected in patients TB10 and TB11. The possibility of a misdiagnosis for these patients seems unlikely, as they both present with classical clinical features of TBS (see Table 2). As there is no evidence for genetic heterogeneity in TBS, TB10, and TB11 presumably carry a mutation in the unexplored regions of SALL1, i.e., the promoter, introns, and 5 and 3 untranslated regions. Alternatively, TBS in these patients might result from a position effect associated with a chromosomal rearrangement undetected by the karyotypic analysis. None of the four mutations identified in the sporadic cases (TB6, TB7, TB8, and TB9) was detected in either of the parents, demonstrating that these mutations occurred de novo. Together with the four de novo mutations from the other series [Kohlhase et al., 1998, 1999], the present results bring the total number of de novo mutations to 8 out of 20 identified SALL1 mutations. Assuming the absence of a recruitment bias in the two series of patients, this indicates that a high proportion of TBS cases are due to de novo mutations. The finding of de novo mutations in sporadic cases is consistent with the proposed full penetrance of the disease [Arroyo Carrera et al., 1996]. So far, only one phenotypically normal individual was found to carry a SALL1 mutation. In this case, however, the likely mosaic state of the mutation would account for the absence of TBS features [Kohlhase et al., 1999]. The six novel SALL1 mutations from the present study together with the seven reported by Kohlhase et al. [1998, 1999], make a total of 15 different identified mutations in TBS. All are located in the second exon (see Fig. 5) and predicted to lead to a truncated protein. So far, only one mutation, namely the C to T transition at position 826, has been detected in several unrelated patients (Table 3a, Fig. 5). In the present series, this mutation was detected in three out of four sporadic cases with identified SALL1 mutations. The same mutation has been observed in three out of four sporadic cases with identified mutations in the other series [Kohlhase et al., 1999]. The CG dimer where this transition occurs thus represents a hotspot of mutations that can be attributed to uncorrected spontaneous deamination of a methylcytosine [Duncan and Miller, 1980]. This mechanism has been proposed to represent the most frequent source of mutations in humans [Barker et al., 1984]. It is noteworthy that the 826C>T nonsense mutation, which largely accounts for the observed high proportion of de novo mutations in TBS, has never been found in familial cases. It is therefore tempting to speculate that this particular mutation does not allow fertility. This hypothesis could not be put to the test so far because the three affected females of the present
8 384 MARLIN ET AL. FIGURE 4. Analysis of the breakpoint present in a TBS-affected individual. A: Physical map of the TBS region. BAC 230e15 contains the entire SALL1 coding sequence. The 3 5 orientation of SALL1 with regard to YAC 438H5 (180 kb) was not determined. PAC 4645 encompasses the translocation breakpoint in patient TB12. B: FISH analysis of individual TB12 carrying the t(5;16)(p15.3;q12.1) translocation. Metaphase chromosome spreads were hybridized with a probe derived from the λ 12.6 subclone of PAC 4645 (see A). A signal is detected on the normal chromosome 16 and on both the der5 and der16 translocated chromosomes. study are still too young and the age of the three affected males from the report by Kohlhase et al.  was not mentioned. Among the six sequence polymorphisms identified in the present study, three, namely S159G, S ins, and S164del, deserve further comment. These polymorphisms are located in a particular region of SALL1 (amino acid residues 150 to 166) which is characterized by a stretch of 10 serine residues, encoded by an (AGC)10 repeat, followed by four glycine residues encoded by a (GGC)4 repeat and three serine residues, the first of which (S164) is also encoded by an AGC codon. The S159G mutation is located at the last position of the stretch of 10 serine residues, S ins is located in the same stretch of serine residues, and S164del involves the serine immediately following the glycine repeat. These mutations
9 SALL1 MUTATIONS IN TOWNES-BROCKS SYNDROME 385 FIGURE 5. Schematic representation of the human SALL1 protein and localization of the mutations identified thus far. The protein comprises five zinc finger domains (dotted rectangles), including a vertebrate-specific C 2 HC motif, three double C 2 H 2 motifs, plus an additional one [Kohlhase et al., 1996]. The stretch of serine residues (aa ) is indicated by a stippled rectangle. The two exon intron limits are indicated by gray triangles. The sites of the mutations so far identified in TBS patients are indicated by arrows. The 826C>T transition has been detected in six sporadic cases (three from each series) and therefore represents a mutation hot spot. define a particularly unstable region prone to DNA modifications, most of which are likely to result from DNA polymerase slippage. Such a mechanism would also account for the S150del polymorphism reported by Kohlhase et al. . All the mutations detected so far [Kohlhase et al., 1998, 1999; this study] indicate that TBS results from SALL1 haploinsufficiency. This syndrome is to be added to the long list of dominant developmental diseases that are caused by haploinsufficiency of a gene encoding a transcription factor, such as aniridia (PAX6 [Fantes et al., 1995]), Waardenburg syndrome types I and II (PAX3 and MITF, respectively [reviewed in Read and Newton, 1997]), Pallister-Hall and Greig syndromes (GLI3 [Kang et al., 1997]), a form of Rieger syndrome (RIEG [Flomen et al., 1998]). In such diseases, different threshold levels of the protein are believed to be critical for each of the associated developmental processes, which likely accounts for the variable phenotypic expressivity [for review, see Fisher and Scambler, 1994]. Accordingly, considerable variability of the clinical features was noted among the TBS-affected patients in our series (see Table 2), even within a given family (see Fig. 1). The molecular diagnosis of TBS by direct sequencing on genomic DNA is simple, as there are only three SALL1 coding exons to be analyzed, and it allows the detection of a high proportion of the mutations (i.e., in 9 out of 11 patients analyzed in the present study). This test should prove potentially helpful in medical practice since the clinical features of TBS are sometimes difficult to distinguish from those of other syndromes [for reviews, see Kotzot et al., 1992; Allanson, 1995] (Marlin, unpublished observations); in particular, the VACTERL association (MIM# ) [Khoury et al., 1983]. In addition, the present characterization of a normal SALL1 coding sequence in a TBS patient carrying a 16q12 chromosomal rearrangement indicates performing a karyotype, in case a typical TBS with no SALL1 mutation is identified. An improvement in genetic counseling for TBS-affected families is expected from these genetic investigations. ACKNOWLEDGMENTS We thank the families for participation in this study. We thank Dominique Weil for helpful advice, Michel Salmon for preliminary physical mapping, Jean-Pierre Hardelin, Viki Kalatzis, and Jacqueline Levilliers for contributions to the writing and for critical reading of the manuscript, and Ana Baroncini (Ferrara) for clinical examination of patient TB7. The technical assistance of Fabienne Levi-Acobas in subcloning and of Stéphane Douglay in sequencing is acknowledged. REFERENCES Allanson J Genetic hearing loss associated with external ear abnormalities. In: Gorlin RJ, Toriello HV, Cohen MM, editors. Hereditary hearing loss and its syndromes, vol. 28. New York, Oxford: Oxford University Press. p Antonarakis SE, Nomenclature Working Group A suggested nomenclature for designating mutations. Hum Mutat 11:1 3. Arroyo Carrera I, Lopez Cuesta MJ, Garcia Garcia MJ, Lozano Rodriguez JA, Carretero Diaz V Sindrome de Townes- Brocks. An Esp Pediatr 44: Baldi F, Baroncini A, Ricci G, Specchia F, Tampieri M, Comellini L, Masi M Sindrome di Townes-Brocks: descrizione di un caso. Riv Ital Pediatr 21: Barakat A, Butler MG, Salter JE, Fogo A Townes-Brocks syndrome: report of three additional patients with previously undescribed renal and cardiac abnormalities. Dysmorphol Clin Genet 2: Barker D, Schafer M, White R Restriction sites containing CpG show a higher frequency of polymorphism in human DNA. Cell 36: Beaudet AL, Tsui L-C A suggested nomenclature for designating mutations. Hum Mutat 2: de Vries-Van der Weerd MA, Willems PJ, Mandema HM, ten Kate LP A new family with the Townes-Brocks syndrome. Clin Genet 34: Duncan BK, Miller JH Mutagenic deamination of cytosine residues in DNA. Nature 287: Fantes J, Redeker B, Breen M, Boyle S, Brown J, Fletcher J, Jones S, Bickmore W, Fukushima Y, Mannens M, Danes S, van Heyningen V, Hanson I Aniridia-associated cytogenetic rearrangements suggest that a position effect may cause the mutant phenotype. Hum Mol Genet 4:
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