Fine mapping of the split-hand/split-foot locus (SHFM3) at 10q24: evidence for anticipation and segregation distortion

The prenatal diagnosis and genetic counseling of chromosomal micro-duplication on 10q24.3 in a fetus: A case report and a brief review of the literature

RATIONALE

Split-hand/split-foot malformation (SHFM), also known as ectrodactyly, is a congenital limb malformation affecting the central rays of the autopod extending to syndactyly, median clefts of the hands and feet, aplasia/hypoplasia of phalanges, metacarpals and metatarsals. Duplication of this 10q24 region is associated with SHFM3. While the clinical and genetic heterogeneity of SHFM makes the prenatal diagnosis and genetic counseling more challenging and difficult.

PATIENT CONCERNS

A physically normal pregnant woman had a systemic ultrasound at the second trimester, only identified the deformity of both hands and feet on the fetus.

DIAGNOSES

The fetus was diagnosed as sporadic SHFM3.

INTERVENTIONS

After seeking advice from genetic counseling, she decided to terminate the pregnancy. The induction of infant was done after appearance of bipedal clefts, lobster-claw appearance and partial loss of phalanges and metacarpals, leaving behind 2nd finger in the left hand and the 5th in the right hand. Furthermore, collection of umbilical cord is recommended to this fetus for genome-wide detection.

OUTCOMES

An outcome of the gene detection from abortion shows that there is variation in copy number in genome of chromosome 1 and chromosome 10.

LESSONS

This case study confirms an association between SHFM3 and chromosomal micro-duplication on 10q24.3, and the extension of clinical spectrum of SHFM3. It also proposes some prenatal diagnosis and genetic counseling to help in planning and management in affected pregnancy. This will reduce the congenital and development abnormalities in birth rate, as well as relive the economic, psychological, and physical burden to the affected families.

FBXW4 Acts as a Protector of FOLFOX-Based Chemotherapy in Metastatic Colorectal Cancer Identified by Co-Expression Network Analysis

Background

FOLFOX chemotherapy is one of the most commonly used treatments for colorectal cancer (CRC) patients. However, the efficacy and tolerance of FOLFOX therapy varies between patients. The purpose of this study was to explore hub genes associated with primary chemotherapy-resistance and to explore the possible mechanisms involved from non-European patients.

Method

A weighted gene co-expression network was constructed to identify gene modules associated with chemotherapy resistance in mCRC from China.

Results

A Gene Array Chip was used to detect mRNA expression in 11 mCRC patients receiving preoperative FOLFOX chemotherapy. The immune response was associated with chemotherapy-resistance in microarray data. Through the use of WGCNA, we demonstrated that the crucial functions enriched in chemotherapy-resistance modules were cell proliferation, MAPK signaling pathways, and PI3K signaling pathways. Additionally, we identified and validated FBXW4 as a new effective predictor for chemotherapy sensitivity and a prognostic factor for survival of CRC patients by using our own data and GSE69657. Furthermore, a meta-analysis of 15 Gene Expression Omnibus–sourced datasets showed that FBXW4 messenger RNA levels were significantly lower in CRC tissues than in normal colon tissues. An analysis of the data from the R2: Genomics Analysis and Visualization Platform showed that low FBXW4 expression was correlated with a significantly worse event- and relapse-free survival. Gene set enrichment analysis showed that the mechanism of FBXW4-mediated chemotherapy resistance may involve the DNA replication signal pathway and the cell cycle.

Conclusion

FBXW4 is associated with chemotherapy resistance and prognosis of CRC probably by regulating DNA replication signaling pathways and the cell cycle.

Homozygous sequence variants in the WNT10B gene underlie split hand/foot malformation

Split-hand/split-foot malformation (SHFM), also known as ectrodactyly is a rare genetic disorder. It is a clinically and genetically heterogeneous group of limb malformations characterized by absence/hypoplasia and/or median cleft of hands and/or feet. To date, seven genes underlying SHFM have been identified. This study described four consanguineous families (A-D) segregating SHFM in an autosomal recessive manner. Linkage in the families was established to chromosome 12p11.1-q13.13 harboring WNT10B gene. Sequence analysis identified a novel homozygous nonsense variant (p.Gln154*) in exon 4 of the WNT10B gene in two families (A and B). In the other two families (C and D), a previously reported variant (c.300_306dupAGGGCGG; p.Leu103Argfs*53) was detected. This study further expands the spectrum of the sequence variants reported in the WNT10B gene, which result in the split hand/foot malformation.

Congenital hypogonadotropic hypogonadism with split hand/foot malformation: a clinical entity with a high frequency of FGFR1 mutations

PURPOSE

Congenital hypogonadotropic hypogonadism (CHH) and split hand/foot malformation (SHFM) are two rare genetic conditions. Here we report a clinical entity comprising the two.

METHODS

We identified patients with CHH and SHFM through international collaboration. Probands and available family members underwent phenotyping and screening for FGFR1 mutations. The impact of identified mutations was assessed by sequence- and structure-based predictions and/or functional assays.

RESULTS

We identified eight probands with CHH with (n = 3; Kallmann syndrome) or without anosmia (n = 5) and SHFM, seven of whom (88%) harbor FGFR1 mutations. Of these seven, one individual is homozygous for p.V429E and six individuals are heterozygous for p.G348R, p.G485R, p.Q594*, p.E670A, p.V688L, or p.L712P. All mutations were predicted by in silico analysis to cause loss of function. Probands with FGFR1 mutations have severe gonadotropin-releasing hormone deficiency (absent puberty and/or cryptorchidism and/or micropenis). SHFM in both hands and feet was observed only in the patient with the homozygous p.V429E mutation; V429 maps to the fibroblast growth factor receptor substrate 2α binding domain of FGFR1, and functional studies of the p.V429E mutation demonstrated that it decreased recruitment and phosphorylation of fibroblast growth factor receptor substrate 2α to FGFR1, thereby resulting in reduced mitogen-activated protein kinase signaling.

CONCLUSION

FGFR1 should be prioritized for genetic testing in patients with CHH and SHFM because the likelihood of a mutation increases from 10% in the general CHH population to 88% in these patients.

Exome sequencing reveals a heterozygous DLX5 mutation in a Chinese family with autosomal-dominant split-hand/foot malformation

Split-hand/foot malformation (SHFM) is a congenital limb deformity due to the absence or dysplasia of central rays of the autopod. Six SHFM loci have already been identified. Here we describe a Chinese family with autosomal-dominant SHFM1 that has previously been mapped to 7q21.2-21.3. The two affected family members, mother and son, showed deep median clefts between toes, ectrodactyly and syndactyly; the mother also showed triphalangeal thumbs. Exome sequencing and variant screening of candidate genes in the six loci known to be responsible for SHFM revealed a novel heterozygous mutation, c.558G>T (p.(Gln186His)), in distal-less homeobox 5 (DLX5). As DLX5 encodes a transcription factor capable of transactivating MYC, we also tested whether the mutation could affect DLX5 transcription acitivity. Results from luciferase reporter assay revealed that a mutation in DLX5 compromised its transcriptional activity. This is the first report of a mutation in DLX5 leading to autosomal-dominant SHFM1.

Clinical, genetic, and molecular aspects of split-hand/foot malformation: an update

We here provide an update on the clinical, genetic, and molecular aspects of split-hand/foot malformation (SHFM). This rare condition, affecting 1 in 8,500-25,000 newborns, is extremely complex because of its variability in clinical presentation, irregularities in its inheritance pattern, and the heterogeneity of molecular genetic alterations that can be found in affected individuals. Both syndromal and nonsyndromal forms are reviewed and the major molecular genetic alterations thus far reported in association with SHFM are discussed. This updated overview should be helpful for clinicians in their efforts to make an appropriate clinical and genetic diagnosis, provide an accurate recurrence risk assessment, and formulate a management plan.

The novel ubiquitin ligase complex, SCF(Fbxw4), interacts with the COP9 signalosome in an F-box dependent manner, is mutated, lost and under-expressed in human cancers

Identification of novel proteins that can potentially contribute to carcinogenesis is a requisite venture. Herein, we report the first biochemical characterization of the novel F-box and WD40 containing protein, FBXW4. We have identified interacting protein partners and demonstrated that FBXW4 is part of a ubiquitin ligase complex. Furthermore, the Fbxw4 locus is a common site of proviral insertion in a variety of retroviral insertional mutagenesis murine cancer models and Fbxw4 mRNA is highly expressed in the involuting murine mammary gland. To begin to characterize the biochemical function of Fbxw4, we used proteomic analysis to demonstrate that Fbxw4 interacts with Skp1 (SKP1), Cullin1 (CUL1), Ring-box1 (RBX1) and all components of the COP9 signalosome. All of these interactions are dependent on an intact F-box domain of Fbxw4. Furthermore, Fbxw4 is capable of interacting with ubiquitinated proteins within cells in an F-box dependent manner. Finally, we demonstrate that FBXW4 is mutated, lost and under-expressed in a variety of human cancer cell lines and clinical patient samples. Importantly, expression of FBXW4 correlates with survival of patients with non-small cell lung cancer. Taken together, we suggest that FBXW4 may be a novel tumor suppressor that regulates important cellular processes.

Discontinuous microduplications at chromosome 10q24.31 identified in a Chinese family with split hand and foot malformation

Background

Split hand/foot malformation (SHFM) is a congenital disorder characterized by a cleft of the hands and/or feet due to dificiency of central rays. Genomic rearrangement at 10q24 has been found to cause nonsyndromic SHFM (SHFM3).

Methods

Four patients and fourteen unaffected individuals from a four-generation Chinese pedigree with typical SHFM3 phenotypes were recruited for this study. After informed consent was obtained, genome-wide copy number analysis was performed on all patients and two normal family members using the Affymetrix Cytogenetics Whole-Genome 2.7M Array. The results were then confirmed by real-time quantitative polymerase chain reaction in all available individuals of this pedigree. Candidate genes were further screened for mutation through sequence analyses.

Results

Copy number analysis showed a microduplication at chromosome 10q24.31-q24.32 co-segregating with the SHFM phenotype. Compared to other known genomic duplications for SHFM3, the duplication described here contains two discontinuous DNA fragments. The minimal centromeric duplicated segment of 259 kb involves LBX1, POLL and a disrupted BTRC. The minimal telomeric duplication of 114 kb encompasses DPCD and one part of FBXW4. No coding and splice-site mutations of candidate genes in the region were found.

Conclusions

Genomic duplications at chromosome 10q24.3, which were identified in the current study, provide further evidence for limb-specific cis-regulatory sequences in this region, highlighting the importance of chromosome 10q24.31-q24.32 in limb development and SHFM pathogenesis.

Familial ectrodactyly syndrome in a nigerian child: a case report

Ectrodactyly, also known as Split-Hand/Split-Foot Malformation (SHFM) is a rare genetic condition characterized by defects of the central elements of the autopod. It has a prevalence of 1:10,000-1:90,000 worldwide. The X-linked and autosomal dominant types have been described. It can occur as an isolated malformation or in combination with other anomalies, such as tibial aplasia, craniofacial defects, and genitourinary abnormalities. Ectrodactyly-ectodermal dysplasia-clefting syndrome (EEC) is an example of ectrodactyly syndrome accompanied by multiple organ defects. Ectrodactyly has been reported in Africa, especially in several families in remote areas of central Africa but there has not been any published work on ectrodactyly in Nigeria. A baby was born in Ilorin, North Central Zone of Nigeria, with an uneventful prenatal and delivery history but was noticed to have malformation of the two hands and the two lower limbs at birth which are replica of the father's malformation. We present this case to highlight familial ectrodactyly in Nigeria and prepare us to improve upon simple prenatal diagnosis and management of the challenges associated with patients with congenital malformation in Nigeria and other developing countries.

Genetically regulated epigenetic transcriptional activation of retrotransposon insertion confers mouse dactylaplasia phenotype

Dactylaplasia, characterized by missing central digital rays, is an inherited mouse limb malformation that depends on two genetic loci. The first locus, Dac, is an insertional mutation around the dactylin gene that is inherited as a semidominant trait. The second locus is an unlinked modifier, mdac/Mdac, that is polymorphic among inbred strains. Mdac dominantly suppresses the dactylaplasia phenotype in mice carrying Dac. However, little is known about either locus or the nature of their interaction. Here we show that Dac is a LTR retrotransposon insertion caused by the type D mouse endogenous provirus element (MusD). This insertion exhibits different epigenetic states and spatiotemporally expresses depending on the mdac/Mdac modifier background. In dactylaplasia mutants (Dac/+ mdac/mdac), the LTRs of the insertion contained unmethylated CpGs and active chromatin. Furthermore, MusD elements expressed ectopically at the apical ectodermal ridge of limb buds, accompanying the dactylaplasia phenotype. On the other hand, in Dac mutants carrying Mdac (Dac/+ Mdac/mdac), the 5' LTR of the insertion was heavily methylated and enriched with inactive chromatin, correlating with inhibition of the dactylaplasia phenotype. Ectopic expression was not observed in the presence of Mdac, which we refined to a 9.4-Mb region on mouse chromosome 13. We report a pathogenic mutation caused by MusD. Our findings indicate that ectopic expression from the MusD insertion correlates with the dactylaplasia phenotype and that Mdac acts as a defensive factor to protect the host genome from pathogenic MusD insertions.

Triphalangeal thumb in association with split hand/foot: A phenotypic marker for SHFM3?

BACKGROUND

At least five distinct loci have been implicated in split hand foot malformation (SHFM). Establishing genotype/phenotype correlations at the chromosomal level may elucidate responsible developmental genes and improve patient management. In our analysis of previously published genetically mapped SHFM cases, preaxial hand involvement was a significant discriminating variable, most commonly seen at the SHFM3 locus (OMIM 600095) at 10q24. Of the 47 SHFM3 patients analyzed, 15 (31.9%) had triphalangeal thumb (TPT), a limb finding not reported at any other locus.

METHODS

The association of TPT/split foot, in particular, prompted us to review the literature for similar cases.

RESULTS

We ascertained a number of unmapped familial and sporadic cases with TPT/split foot, including a group of patients with triphalangeal thumb-brachyectrodactyly syndrome. Certain trends were similar in both SHFM3 and these unmapped literature cases. With respect to gender, 7/12 (58%) of mapped SHFM3 cases with TPT/split foot were male whereas 5/12 (42%) were female, compared with 22/50 (44%) males and 28/50 (56%) females among unmapped cases (P=0.3715). Individuals in both groups usually had bilateral involvement, with 67 and 60% showing bilateral TPT among mapped and literature cases, respectively (P=0.6714). Bilateral involvement of the feet was even more striking (83% of SHFM3 patients and 96% of literature cases; P=0.0808).

CONCLUSIONS

Patients with TPT/split foot may in fact represent SHFM3 cases and should be evaluated for genomic rearrangements at 10q24. TPT may be identified only by radiographic analysis, emphasizing the importance of imaging these patients and their family members.

Split-hand/split-foot malformation 3 (SHFM3) at 10q24, development of rapid diagnostic methods and gene expression from the region

Split-hand/split-foot malformation (SHFM, also called ectrodactyly) is a clinically variable and genetically heterogeneous group of limb malformations. Several SHFM loci have been mapped, including SHFM1 (7q21), SHFM2 (Xq26), SHFM3 (10q24), SHFM4 (3q27) and SHFM5 (2q31). To date, mutations in a gene (TP63) have only been identified for SHFM4. SHFM3 has been shown by pulsed-field gel electrophoresis to be caused by an approximately 500 kb DNA rearrangement at 10q24. This region contains a number of candidate genes for SHFM3, though which gene(s) is (are) involved in the pathogenesis of SHFM3 is not known. Our aim in this study was to improve the diagnosis of SHFM3, and to begin to understand which genes are involved in SHFM3. Here we show, using two different techniques, FISH and quantitative PCR that SHFM3 is caused by a minimal 325 kb duplication containing only two genes (BTRC and POLL). The data presented provide improved methods for diagnosis and begin to elucidate the pathogenic mechanism of SHFM3. Expression analysis of 13 candidate genes within and flanking the duplicated region shows that BTRC (present in three copies) and SUFU (present in two copies) are overexpressed in SHFM3 patients compared to controls. Our data suggest that SHFM3 may be caused by overexpression of BTRC and SUFU, both of which are involved in beta-catenin signalling.

Genotype-phenotype correlations in mapped split hand foot malformation (SHFM) patients

Split hand foot malformation (SHFM) also known as central ray deficiency, ectrodactyly and cleft hand/foot, is one of the most complex of limb malformations. SHFM can occur as an isolated malformation or in association with other malformations, as in the ectrodactyly-ectodermal dysplasia-clefting (EEC) syndrome and other autosomal dominant conditions with long bone involvement, all showing variable expressivity and reduced penetrance. The deficiency in SHFM patients can also be accompanied by other distal limb anomalies including polydactyly and/or syndactyly. This variability causes the phenotypic classification of SHFM to be far from straightforward and genetic heterogeneity, with at least five loci identified to date, further complicates management of affected patients and their families. Although genotypic-phenotypic correlations have been proposed at the molecular level for SHFM4 patients who have mutations in the P63 gene, phenotypic correlations at the chromosomal level have not been thoroughly documented. Using descriptive epidemiology, Chi square and discriminant function analyses, our laboratory has identified phenotypic patterns associated with the mapped genetic SHFM loci. These findings can assist in classification, provide insight into responsible developmental genes and assist in directing mapping efforts and targeted genetic testing, resulting in more accurate information for family members in the clinical setting. Comparison with relevant animal models is discussed.

Evidence for an additional locus for split hand/foot malformation in chromosome region 8q21.11–q22.3

We identified a family where five members had nonsyndromic ectrodactyly. There were three known instances of nonpenetrance. Although four individuals had unilateral cleft hand, one individual had more severe, bilateral and asymmetric absence of the digits. None had foot abnormalities. After exclusion of linkage of SHFM in this family to five known loci, a genome wide scan was performed with DNA from 5 affected and 15 unaffected members of this family. Suggestive evidence for linkage of ectrodactyly to 8q was obtained on the basis of a maximum LOD score of 2.54 at theta (max) = 0 with GAAT1A4. Critical recombinants place the ectrodactyly gene in this family in a 16 cM (21 Mb) interval between D8S1143 and D8S556. Mutational analysis of two candidate genes (FZD6, GDF6) did not identify any mutations in affected members of this family. Our data indicate further genetic heterogeneity for ectrodactyly and suggest the presence of an additional SHFM locus in chromosome region 8q21.11-q22.3.

Clinical and epidemiological findings in patients with central ray deficiency: Split hand foot malformation (SHFM) in Manitoba, Canada

We conducted a clinical population study to examine the incidence and epidemiology of split hand foot-malformation (SHFM) in Manitoba from 1957 to 2003. The total number of births during this period was 850,742. Forty-three patients with SHFM were identified, resulting in an incidence of 1 in 19,784 births. Most patients were ascertained through referrals to the Section of Genetics and Metabolism at the Children's Hospital, Winnipeg, Manitoba. Overall, 22 (51.2%) of affected individuals were females and 21 (48.8%) were male. The left upper limb (LUL) was the most frequently affected, (in 46.5% of patients). The right hand was involved in 39.5%. In 4 patients (9.3%) all four limbs were affected. SHFM is classified as a failure of formation of parts according to the International Federation of Surgical Societies of the Hand (IFSSH) and has also been categorized as Typical or Atypical. Individuals in the Manitoba cohort were classified into two main categories: Typical (29 cases) and Atypical (3 cases). However, 11 patients were not easily placed into either group and comprised a distinct category termed "difficult to classify." Patients in the three groups were then further subdivided depending on whether or not they had additional congenital anomalies. These complex patients included those with single gene disorders in which SHFM has been reported (e.g., ectodermal dysplasia Ectrodactyly Clefting (EEC), tibial aplasia with SHFM, fibular aplasia with SHFM), as well as those with other recognized or unknown patterns of anomalies. Two had deletions involving 9q and 5p respectively. Unlike some other studies, we did not find an excess of males or right-sided defects and only two of the cases--two sisters--were related.

Genomic rearrangement at 10q24 in non-syndromic split-hand/split-foot malformation

Split-hand/split-foot malformation (SHFM) is a congenital limb malformation characterized by a median cleft of hand and/or foot due to the absence of central rays. Five loci for syndromic and non-syndromic SHFM, termed SHFM1-5, have been mapped to date. Recently, a 0.5 Mb tandem genomic duplication was found at chromosome 10q24 in SHFM3 families. To refine the minimum duplicated region and to further characterize the SHFM3 locus, we screened 28 non-syndromic SHFM families for tandem genomic duplication of 10q24 by Southern blot and sequence analysis of the dactylin gene. Of 28 families, only two showed genomic rearrangements. Representative patients from the two families exhibit typical SHFM, with symmetrically affected hands and feet. One patient is a familial case with a 511,661 bp tandem duplication, whereas the second is a sporadic case arising from a de novo, 447,338 bp duplication of maternal origin. The smaller duplication in the second patient contained the LBX1, BTRC, POLL, and DPCD genes and a disrupted extra copy of the dactylin gene, and was nearly identical to the smallest known duplicated region of SHFM3. Our results indicate that genomic rearrangement of SHFM3 is rare among non-syndromic SHFM patients and emphasize the importance of screening for genomic rearrangements even in sporadic cases of SHFM.

Discrepancies in upper and lower limb patterning in split hand foot malformation

Discrepancies in upper and lower limb patterning in split hand foot malformation. Split hand foot malformation (SHFM) is genetically heterogeneous with five loci mapped to date. Highly variable in presentation, it can occur as an isolated finding or with other anomalies. The genetic heterogeneity and clinical variability make genetic counselling of SHFM families challenging. By establishing genotype/phenotype correlations, one can provide insight into responsible developmental genes and help to direct mapping efforts and target genetic testing, ultimately providing more accurate information for family members. Preaxial involvement of the upper extremities was a significant discriminating limb-specific variable in our analysis of genetically mapped SHFM cases. This finding, which was originally identified through descriptive epidemiology, was subsequently confirmed by discriminant function analysis (p < 0.0001) to be a significant locus discriminator. Preaxial involvement of the upper extremities was most commonly seen at the SHFM3 locus mapped to chromosome 10q24 (OMIM 600095) and consisted of proximally placed thumbs and/or triphalangeal thumbs (TPT), preaxial polydactyly and/or absence of the first ray. These patients' feet, however, tended to show a classical central longitudinal deficiency without a significant preaxial component. This article discusses this discrepant clefting pattern between the upper and lower extremities and proposes potential mechanisms.

Fine mapping of the X-linked split-hand/split-foot malformation (SHFM2) locus to a 5.1-Mb region on Xq26.3 and analysis of candidate genes

Split-hand/split-foot malformation (SHFM) is a genetically heterogeneous disorder, with five known loci, that causes a lack of median digital rays, syndactyly, and aplasia or hypoplasia of the phalanges, metacarpals, and metatarsals. In the only known SHFM2 family, affected males and homozygous females exhibit monodactyly or bidactyly of the hands and lobster-claw feet. This family (1) was revisited to include additional subjects and genealogical data. All 39 affected males and three females fully expressed the SHFM, while 13 carrier females examined exhibited partial expression of SHFM. We narrowed the previously linked 22-Mb genetic interval on Xq24-q26 (2), by analyzing additional family members and typing additional markers. The results define a 5.1-Mb region with a new centromeric boundary at DXS1114 and a telomeric boundary at DXS1192. We did not identify mutations in the exons and exon/intron boundaries of 19 candidate genes. These data suggest that the mutation may lie in a regulatory region of one of these candidate genes or in another gene within the SHFM2 region with unclear role in limb development.

Split hand foot malformation is associated with a reduced level of Dactylin gene expression

Split hand foot malformation (SHFM) is a congenital limb malformation presenting with a median cleft of the hand and/or foot, syndactyly and polydactyly. SHFM is genetically heterogeneous with four loci mapped to date. Murine Dactylaplasia (Dac) is phenotypically similar, and it has been mapped to a syntenic region of 10q24, where SHFM3 has been localized. Structural alterations of the gene-encoding dactylin, a constituent of the ubiquitinization pathway, leading to reduced levels of transcript have been identified in Dac. Here, we report a significant decrease of Dactylin transcript in several individuals affected by SHFM. This observation supports a central role for dactylin in the pathogenesis of SHFM.

About face: signals and genes controlling jaw patterning and identity in vertebrates

The embryonic vertebrate face is composed of similarly sized buds of neural crest-derived mesenchyme encased in epithelium. These buds or facial prominences grow and fuse together to give the postnatal morphology characteristic of each species. Here we review the role of neural crest cells and foregut endoderm in differentiating facial features. We relate the developing facial prominences to the skeletal structure of the face and review the signals and genes that have been shown to play an important role in facial morphogenesis. We also examine two experiments one at the genetic level and one at the signal level in which transformation of facial prominences and subsequent change of jaw identity was induced. We propose that signals such as retinoids and BMPs and downstream transcription factors such as Distal-less related genes specify jaw identity.

The 10q24-linked split hand/split foot syndrome (SHFM3): Narrowing of the critical region and confirmation of the clinical phenotype

In this communication we describe the clinical and molecular genetic findings in a family with a variable ectrodactyly linked to SHFM3. This is only the second detailed report of the clinical features of the SHFM3 linked syndrome in a large pedigree. Within this family the expressivity of the condition ranges from the classical ectrodactyly deformity to partial absence of the thumb and agenesis of the distal tip of the index finger. There is discordant limb severity, with the feet more severely affected than the hands. Two individuals have a nail dysplasia indicating the presence of a minor ectodermal component. A cleft palate was present in one individual. Radiological features of family members include short metacarpals with rounded proximal heads, agenesis of the radial ray, epiphysial coning, and an unusual supernumerary ossicle opposed to the distal phalanx of the left thumb. Genetic mapping studies in this family exclude p63 involvement and demonstrate that ectrodactyly in this pedigree is linked to the SHFM3 region on chromosome 10q24. A meiotic recombination event enabled exclusion of a maximum of 1.9 Mb of DNA from the previously known critical region thereby narrowing the critical interval to between D10S1265 and D10S222, with the minimal critical region being between D10S1240 and D10S1267. Further investigations are in progress to identify the gene within the SHFM3 critical region responsible for ectrodactyly.

Sorting nexin 3 (SNX3) is disrupted in a patient with a translocation t(6;13)(q21;q12) and microcephaly, microphthalmia, ectrodactyly, prognathism (MMEP) phenotype

A patient with microcephaly, microphthalmia, ectrodactyly, and prognathism (MMEP) and mental retardation was previously reported to carry a de novo reciprocal t(6;13)(q21;q12) translocation. In an attempt to identify the presumed causative gene, we mapped the translocation breakpoints using fluorescence in situ hybridisation (FISH). Two overlapping genomic clones crossed the breakpoint on the der(6) chromosome, locating the breakpoint region between D6S1594 and D6S1250. Southern blot analysis allowed us to determine that the sorting nexin 3 gene (SNX3) was disrupted. Using Inverse PCR, we were able to amplify and sequence the der(6) breakpoint region, which exhibited homology to a BAC clone that contained marker D13S250. This clone allowed us to amplify and sequence the der(13) breakpoint region and to determine that no additional rearrangement was present at either breakpoint, nor was another gene disrupted on chromosome 13. Therefore, the translocation was balanced and SNX3 is probably the candidate gene for MMEP in the patient. However, mutation screening by dHPLC and Southern blot analysis of another sporadic case with MMEP failed to detect any point mutations or deletions in the SNX3 coding sequence. Considering the possibility of positional effect, another candidate gene in the vicinity of the der(6) chromosome breakpoint may be responsible for MMEP in the original patient or, just as likely, the MMEP phenotype in the two patients results from genetic heterogeneity.

Ectrodactyly and Germany's eugenics law of 14 July 1933

The family reported herein serves as a genetically and historically important vignette on the issues of nonpenetrance (versus germinal mosaicism) in nonsyndromic autosomal dominant ectrodactyly and the Eugenics Law of Germany of 14 July 1933, which was used to coerce the sterilization of the propositus despite infertility in his first marriage. In a sibship of seven children (with normal parents), three boys were affected. The propositus (adoptive grandfather of the author) was the patient of Paul Leopold Friedrich and Georg Perthes, who published their observations on the propositus. Except for an adopted daughter, the propositus was childless. His two affected brothers each had an affected child, and the father- to son transmission confirmed the hypothesis of autosomal dominant inheritance. The issue of nonpenetrance versus germinal mosaicism in ectrodactyly was debated by Auerbach [1956:Ann Hum Genet 20:266-269] and Vogel [1958:Ann Hum Genet 22:132-137], and remains unresolved.

Genomic organization and embryonic expression of Suppressor of Fused, a candidate gene for the split-hand/split-foot malformation type 3

The genes for human and mouse Suppressor of Fused (SU(FU)/Su(Fu)) in the Hedgehog signaling pathway were characterized and found to contain 12 exons. Human SU(FU) localized on chromosome 10q24-25 between the markers D10S192 and AFM183XB12. We detected three additional SU(FU) isoforms, two of which have lost their ability to interact with the transcription factor GLI1. Expression analysis using whole mount in situ hybridization revealed strong expression of Su(Fu) in various mouse embryonic tissues. SU(FU) was considered a candidate gene for the split-hand/split-foot malformation type 3 (SHFM3). However, no alterations in the SU(FU) gene were found in SHFM3 patients.

Distal limb malformations: underlying mechanisms and clinical associations

Congenital malformations of the extremities are conspicuous and have been described through the ages. Over the past decade, a wealth of knowledge has been generated regarding the genetic regulation of limb development and the underlying molecular mechanisms. Recent studies have identified several of the signaling molecules, growth factors, and transcriptional regulators involved in the initiation and maintenance of the apical ectodermal ridge (AER) as well as the molecular markers defining the three axes of the developing limb. Studies of abnormal murine phenotypes have uncovered the role played by genes such as p63 and Dactylin in the maintenance of AER activity. These phenotypes resemble human malformations and in this review we describe the underlying mechanisms and clinical associations of split hand/foot malformation and ectrodactyly-ectodermal dysplasia-cleft lip/palate syndrome, which have both been associated with mutations in the p63 gene.

Split-hand/split-foot malformation is caused by mutations in the p63 gene on 3q27

Split-hand/split-foot malformation (SHFM), a limb malformation involving the central rays of the autopod and presenting with syndactyly, median clefts of the hands and feet, and aplasia and/or hypoplasia of the phalanges, metacarpals, and metatarsals, is phenotypically analogous to the naturally occurring murine Dactylaplasia mutant (Dac). Results of recent studies have shown that, in heterozygous Dac embryos, the central segment of the apical ectodermal ridge (AER) degenerates, leaving the anterior and posterior segments intact; this finding suggests that localized failure of ridge maintenance activity is the fundamental developmental defect in Dac and, by inference, in SHFM. Results of gene-targeting studies have demonstrated that p63, a homologue of the cell-cycle regulator TP53, plays a critically important role in regulation of the formation and differentiation of the AER. Two missense mutations, 724A-->G, which predicts amino acid substitution K194E, and 982T-->C, which predicts amino acid substitution R280C, were identified in exons 5 and 7, respectively, of the p63 gene in two families with SHFM. Two additional mutations (279R-->H and 304R-->Q) were identified in families with EEC (ectrodactyly, ectodermal dysplasia, and facial cleft) syndrome. All four mutations are found in exons that fall within the DNA-binding domain of p63. The two amino acids mutated in the families with SHFM appear to be primarily involved in maintenance of the overall structure of the domain, in contrast to the p63 mutations responsible for EEC syndrome, which reside in amino acid residues that directly interact with the DNA.