Ectopic acanthosis nigricans occurring in a child after syndactyly repair

Skin grafts from the groin area were used to repair syndactyly of the fourth and fifth fingers in an 8-month-old infant with oculodentodigital dysplasia (ODD). At 12 years of age, he developed hyperpigmented velvety plaques at the repair sites. This patient is the first reported case of acanthosis nigricans (AN) occurring in a graft site after syndactyly repair. We propose the term ectopic acanthosis nigricans to describe the phenomenon of AN occurring in transplanted skin away from the original donor site.

Synpolydactyly and HOXD13 polyalanine repeat: addition of 2 alanine residues is without clinical consequences

BACKGROUND

Type II syndactyly or synpolydactyly (SPD) is clinically very heterogeneous, and genetically three distinct SPD conditions are known and have been designated as SPD1, SPD2 and SPD3, respectively. SPD1 type is associated with expansion mutations in HOXD13, resulting in an addition of > or = 7 alanine residues to the polyalanine repeat. It has been suggested that expansions < or = 6 alanine residues go without medical attention, as no such expansion has ever been reported with the SPD1 phenotype.

METHODS

We describe a large Pakistani and an Indian family with SPD. We perform detailed clinical and molecular analyses to identify the genetic basis of this malformation.

RESULTS

We have identified four distinct clinical categories for the SPD1 phenotype observed in the affected subjects in both families. Next, we show that a milder foot phenotype, previously described as a separate entity, is in fact a part of the SPD1 phenotypic spectrum. Then, we demonstrate that the phenotype in both families segregates with an identical expansion mutation of 21 bp in HOXD13. Finally, we show that the HOXD13 polyalanine repeat is polymorphic, and the expansion of 2 alanine residues, evident in unaffected subjects of both families, is without clinical consequences.

CONCLUSION

It is the first molecular evidence supporting the hypothesis that expansion of < or = 6 alanine residues in the HOXD13 polyalanine repeat is not associated with the SPD1 phenotype.

Fraser syndrome: recurrence in a family

Fraser syndrome is a rare, autosomal recessive condition with classical features of cryptophthalmos, syndactyly, ambiguous genitalia, genitourinary mal-formations and mental retardation. We report a family with affected child where the pregnant woman was referred at 24 weeks of gestation for termination of pregnancy. The aborted fetus showed typical findings suggestive of Fraser syndrome.

Genetic heterogeneity of synpolydactyly: a novel locus SPD3 maps to chromosome 14q11.2-q12

Syndactyly type II or synpolydactyly (SPD) is the second most frequent syndactyly type and is inherited in an autosomal dominant fashion. The cardinal features of this malformation are the cutaneous or bony fusion of third and fourth fingers, and fourth and fifth toes associated with additional digital elements within the web. It shows incomplete penetrance and high inter- and intrafamilial phenotypic variability. Two loci are known for SPD (MIM 186000, MIM 608180) associated with mutations in HOXD13 and FBLN1, respectively. Here, we report further genetic heterogeneity for SDP. Employing a whole genomic screen, we demonstrate, in a large Pakistani kindred, that the classical phenotype of SPD maps on a new locus at chromosome 14q11.2-q12. The highest LOD score (Z(max) = 4.06) was obtained with microsatellite marker D14S264, and the multipoint LOD score reached a maximum of 5.01. Haplotype analysis revealed that the disease interval is flanked by microsatellite markers D14S283 and D14S1060, encompassing a physical distance of 10.72 Mb. We propose to allocate to this locus the symbol SPD3 (synpolydactyly 3), and to name the loci associated with HOXD13 or FBLN1 mutations SPD1 and SPD2, respectively.

A novel mutation of p63 in a Chinese family with inherited syndactyly and adactylism

p63 is a transcription factor homologous to p53 and p73; mutations in this gene have been identified in individuals with several types of developmental abnormalities, including EEC (ectrodactyly, ectodermal dysplasia, facial clefts) syndrome and split-hand/split-foot malformation (SHFM). Several mutations in the p63 gene have previously been shown to be related to SHFM. In this study, we report on a Chinese family with intrafamilial clinical variability of SHFM that have a novel heterozygous mutation in all four affected individuals. The mutation is in exon 8 of p63, 1046G --> A, which predicts an amino acid substitution G310E. SSCP analysis of the segregation pattern of the mutation strongly suggests a causal relationship to the SHFM phenotype in p63. This mutation has not been observed in other countries in the world.

Some oculodentodigital dysplasia-associated Cx43 mutations cause increased hemichannel activity in addition to deficient gap junction channels

Oculodentodigital dysplasia (ODDD) is a dominantly inherited human disorder associated with different symptoms like craniofacial anomalies, syndactyly and heart dysfunction. ODDD is caused by mutations in the GJA1 gene encoding the gap junction protein connexin43 (Cx43). Here, we have characterized four Cx43 mutations (I31M, G138R, G143S and H194P) after stable expression in HeLa cells. In patients, the I31M and G138R mutations showed all phenotypic characteristics of ODDD, whereas G143S did not result in facial abnormalities and H194P mutated patients exhibited no syndactylies. In transfected HeLa cells, these mutations led to lack of the P2 phosphorylation state of the Cx43 protein, complete inhibition of gap junctional coupling measured by neurobiotin transfer and increased hemichannel activity. In addition, altered trafficking and delayed degradation were found in these mutants by immunofluorescence and pulse-chase analyses. In G138R and G143S mutants, the increased hemichannel activity correlated with an increased half-time of the Cx43 protein. However, the I31M mutated protein showed no extended half-time. Thus, the increased hemichannel activity may be directly caused by an altered conformation of the mutated channel forming protein. We hypothesize that increased hemichannel activity may aggravate the phenotypic abnormalities in ODDD patients who are deficient in Cx43 gap junction channels.

Oculodentodigital dysplasia with mandibular retrognathism and absence of syndactyly: a case report with a novel mutation in the connexin 43 gene

Oculodentodigital dysplasia (ODDD) is a rare, autosomal dominant pleiotropic disorder, caused by mutations in the Connexin 43 (Cx43 or GJA1) gene. Described here is the case of a 10-year-old girl with enamel hypoplasia, typical facies and mental delay, initially thought to be related to an unknown metabolic disorder. Careful clinical re-evaluation revealed a type of ODDD, characterised by the predominance of facial and ophthalmological involvement with mandibular retrognathism, and by the absence of cutaneous hand or foot syndactyly. A novel single-sequence variation (Nt460A>G) in exon 2, resulting in the substitution of alanine for threonine at amino acid 154, was found. These findings confirm once again the highly variable phenotypic expression caused by Cx43 mutations.

A syndactyly type IV locus maps to 7q36

Syndactyly occurs as an isolated abnormality or a part of a malformation syndrome. Syndactyly types I, II, III and V have been mapped to chromosomal regions 2q34-q36, 2q31-q32, 6q21-q23.2 and 2q31-q32, respectively, whereas syndactyly type IV (SD4) is extremely rare, and its gene localization has not yet been assigned. The SD4 manifests complete syndactyly of all fingers accompanied with polydactyly, and flexion of the fingers gives the hand a cup-shaped appearance. We performed a linkage and haplotype analysis of a Chinese pedigree with autosomal dominant, non-syndromic SD4 using a set of 406 microsatellite markers. The analysis gave the maximum two-point LOD score of 1.613 at recombination fraction of 0.00 and penetrance of 1.00. Thus, the SD4 locus in the family was likely assigned to a 17.39-cM region at a segment between markers D7S3070 and D7S559 at 7q36, although the LOD score obtained was not high enough to conclude the localization. Analysis of three candidate genes, LMBR1, SHH and ZRS, failed to identify any pathogenic mutations. Our gene mapping may give a clue to identify the putative SD4 gene and provide a better understanding of normal human limb development.

A t(4;6)(q12;p23) translocation disrupts a membrane-associated O-acetyl transferase gene (MBOAT1) in a patient with a novel brachydactyly-syndactyly syndrome

Here, we report a patient with a novel brachydactyly-syndactyly syndrome and a de novo translocation 46,XY,t(4;6)(q12;p23). We mapped the breakpoint and identified genes in the breakpoint region. One of the genes on chromosome 6, the membrane-associated O-acetyl transferase gene 1 (MBOAT1), was disrupted by the breakpoint. This gene consists of 13 exons and encodes a protein of 495 amino acids. MBOAT1 is predicted to be a transmembrane protein and belongs to the superfamily of membrane-bound O-acyltransferases. These proteins transfer organic compounds, usually fatty acids, onto hydroxyl groups of membrane-embedded targets. Identification of the transferred acyl group and the target may reveal the signaling pathways altered in this novel brachydactyly-syndactyly syndrome.

Skin changes in oculo-dento-digital dysplasia are correlated with C-terminal truncations of connexin 43

Oculo-dento-digital dysplasia (ODDD, OMIM no.164210) is a pleiotropic disorder caused by mutations in the GJA1 gene that codes for the gap junction protein connexin 43. While the gene is highly expressed in skin, ODDD is usually not associated with skin symptoms. We recently described a family with ODDD and palmoplantar keratoderma. Interestingly, mutation carriers had a novel dinucleotide deletion in the GJA1 gene that resulted in truncation of part of the C-terminus. We speculated, that truncation of the C-terminus may be uniquely associated with skin disease in ODDD. Here, we describe a patient with ODDD and palmar hyperkeratosis caused by a novel dinucleotide deletion that truncates most of the connexin 43 C-terminus. Thus, our findings support the notion that such mutations are associated with the occurrence of skin symptoms in ODDD and provide the first evidence for the existence of a genotype-phenotype correlation.

Congenital syndactyly in cattle: four novel mutations in the low density lipoprotein receptor-related protein 4 gene (LRP4)

Background

Isolated syndactyly in cattle, also known as mulefoot, is inherited as an autosomal recessive trait with variable penetrance in different cattle breeds. Recently, two independent mutations in the bovine LRP4 gene have been reported as the primary cause of syndactyly in the Holstein and Angus cattle breeds.

Results

We confirmed the previously described LRP4 exon 33 two nucleotide substitution in most of the affected Holstein calves and revealed additional evidence for allelic heterogeneity by the identification of four new LRP4 non-synonymous point mutations co-segregating in Holstein, German Simmental and Simmental-Charolais families.

Conclusion

We confirmed a significant role of LRP4 mutations in the pathogenesis of congenital syndactyly in cattle. The newly detected missense mutations in the LRP4 gene represent independent mutations affecting different conserved protein domains. However, the four newly described LRP4 mutations do still not explain all analyzed cases of syndactyly.

A single C to T transition in intron 5 of LMBR1 gene is associated with triphalangeal thumb-polysyndactyly syndrome in a Chinese family

Triphalangeal thumb-polysyndactyly syndrome (TPT-PS) is a type of human hand-foot malformation. In this study, we collected data from a Chinese family with TPT-PS and mapped the disease region to chromosome 7q36. By using a fine mapping study and a haplotype analysis, we narrowed the affected region to 1.7cM between markers D7S2465 and D7S2423, which contains four candidate genes: HLXB9, LMBR1, NOM1, and RNF32. By sequence analysis, we found no sequence alterations, which are specific to the patients in the transcribed regions and in the intron-exon boundaries among the four genes. After closely examining intron 5 of the LMBR1 gene, we discovered a single C to T transition in the affected TPT-PS individuals of the Chinese subject family. The position of this C to T transition is located close to other sequence alterations involved in several preaxial polydactyly (PPD) families, supporting the notion that intron 5 of LMBR1 contains a cis-acting regulator of limb-specific Sonic Hedgehog (SHH). We postulate that the disruption of this cis-regulator via a single C to T transition results in the dysregulation of SHH, which leads to the TPT-PS found in this case.

Mutations in HOXD13 underlie syndactyly type V and a novel brachydactyly-syndactyly syndrome

HOXD13, the homeobox-containing gene located at the most 5' end of the HOXD cluster, plays a critical role in limb development. It has been shown that mutations in human HOXD13 can give rise to limb malformations, with variable expressivity and a wide spectrum of clinical manifestations. Polyalanine expansions in HOXD13 cause synpolydactyly, whereas amino acid substitutions in the homeodomain are associated with brachydactyly types D and E. We describe two large Han Chinese families with different limb malformations, one with syndactyly type V and the other with limb features overlapping brachydactyly types A4, D, and E and mild syndactyly of toes 2 and 3. Two-point linkage analysis showed LOD scores >3 (theta =0) for markers within and/or flanking the HOXD13 locus in both families. In the family with syndactyly type V, we identified a missense mutation in the HOXD13 homeodomain, c.950A-->G (p.Q317R), which leads to substitution of the highly conserved glutamine that is important for DNA-binding specificity and affinity. In the family with complex brachydactyly and syndactyly, we detected a deletion of 21 bp in the imperfect GCN (where N denotes A, C, G, or T) triplet-containing exon 1 of HOXD13, which results in a polyalanine contraction of seven residues. Moreover, we found that the mutant HOXD13 with the p.Q317R substitution was unable to transactivate the human EPHA7 promoter. Molecular modeling data supported these experimental results. The calculated interactions energies were in agreement with the measured changes of the activity. Our data established the link between HOXD13 and two additional limb phenotypes--syndactyly type V and brachydactyly type A4--and demonstrated that a polyalanine contraction in HOXD13, most likely, led to other digital anomalies but not to synpolydactyly. We suggest the term "HOXD13 limb morphopathies" for the spectrum of limb disorders caused by HOXD13 mutations.

Intrafamilial variability in Fraser syndrome

Fraser syndrome (OMIM 219000) is a rare, autosomal recessive disorder characterized by cryptophthalmos, cutanaeous syndactyly, malformations of the larynx and genitourinary tract, craniofacial dysmorphism, orofacial clefting, mental retardation and musculoskeletal anomalies. There is marked interfamilial clinical heterogeneity. However, there is strong phenotypic similarity and concordance of the degree of severity of the disease within a family. We report a family with two cases of Fraser syndrome with marked clinical heterogeneity. One case had lethal phenotype with bilateral renal agenesis, while the other had mild phenotype with normal kidneys. It has not been reported before and highlights the importance of careful screening of pregnancies in families with Fraser syndrome.

Duplication 18q21.31-q22.2

We report on three siblings with mild mental retardation and minor dysmorphic features carrying an interstitial duplication of the long arm of chromosome 18 inherited from a healthy mosaic carrier mother. The duplicated region spanned between 18q21.31 and 18q22.2 for about 12 Mb. The distal duplications of 18q are rare and only a small number of subjects, manifesting quite different clinical outcomes, have been described. However, in most of these cases, molecular characterization was not available. We have reviewed nine patients, including three familial cases, displaying overlapping duplicated regions, and compared them with the present individuals in an attempt to delineate karyotype-phenotype correlation.

A nonclassified and unusual polydactyly of the foot

A rare polydactyly of the foot, mixed central and pre-axial type, is described; no other dysmorphic features were present. Early surgery was performed with good results.

Acro-cardio-facial syndrome associated with neuroepithelial cyst: a case report

Acro-cardio-facial syndrome (ACFS) is a very rare genetic syndrome. Only 5 patients have been reported in the literature so far. A female neonate presented with limb abnormalities, cleft palate and congenital heart disease was diagnosed as ACFS. Her cranial magnetic resonance imaging revealed a huge cerebral neuroepithelial cyst. To our knowledge, this is the first case of ACFS in the literature associated with a neuroepithelial cyst in the brain.

Blepharophimosis, corneal vascularization, deafness, and acroosteolysis: a "new" syndrome?

We report on a patient with blepharophimosis who after unsuccessful surgery developed progressive corneal vascularization. The patient had conductive hearing loss, acroosteolysis of the phalanges, arthropathy, loss of subcutaneous fat of the hands, feet and face, and oligospermia. He had had spontaneous pneumothorax four times. We have found no similar case reports in the literature and suggest that this is a new syndrome, which must be differentiated from hereditary mucoepithelial dysplasia, mandibuloacral dysplasia, keratitis-ichthyosis-deafness syndrome, Hajdu-Cheney syndrome, Penttinen syndrome, and mucopolysaccharidoses.

Synpolydactyly of the foot in homozygotes

In 2002, we reinvestigated a large synpolydactyly kindred first described in 1995. It was found to have expanded with an increase in number of homozygous offspring. These homozygotes had severe hypoplasia, with synpolydactyly of their hands and feet. We present the clinical, genetic, and surgical findings of this deformity and the histologic findings of the removed bones of the heterozygous and homozygous members. There were 125 affected individuals (113 heterozygotes and 12 homozygotes) of 245 members of the past five generations. We identified seven marriages in which both spouses were affected. Twelve offspring from these marriages had homozygote genetic patterns, hypoplastic synpolydactyly of the hands, and a distinctive foot deformity, with a prominent great toe and syndactylized hypoplastic minor toes. From clinical and surgical perspectives, their hand and foot deformities were different from those of their parents. We surgically treated both feet of four individuals with this deformity, which we called "homozygote foot synpolydactyly." Clinically, the deformity consisted of a supinated prominent great toe, hypoplastic and severely synpolydactylized minor toes, and secondary problems. Radiographically, the bones were underdeveloped, unshaped, and largely fused. Abundant cartilage covering the bones was observed surgically and histologically. Genetically, analysis of HOXD13 identified a 27-base pair duplication with a homozygote pattern. The foot deformity of the homozygotes was so distinctive and complicated that it should be considered a separate foot synpolydactyly type--homozygote foot synpolydactyly.

Loss of Nidogen-1 and -2 Results in Syndactyly and Changes in Limb Development

Nidogens are two ubiquitous basement membrane proteins produced mainly by mesenchymal cells. Nidogen-mediated interactions, in particular with laminin, collagen IV, and perlecan have been considered important in the formation and maintenance of the basement membrane. However, whereas mice lacking both nidogen isoforms or carrying mutations in the high affinity nidogen-binding site upon the laminin gamma1 chain have specific basement membrane defects in certain organs, particularly in the lung, characterization of these mice has also shown that basement membrane formation per se does not need nidogens or the laminin-nidogen interaction. Limb development requires the complex interplay of numerous growth factors whose expression is dependent upon the apical ectodermal ridge. Here, we show that lack of nidogen-1 and -2 results in a specific and time-limited failure in the ectodermal basement membrane of the limb bud. The absence of this basement membrane leads to aberrant apical ectodermal ridge formation. It also causes altered distribution of growth factors, such as fibroblast growth factors and leads to a fully penetrant soft tissue syndactyly caused by the dysregulation of interdigital apoptosis. Further, in certain animals more severe changes in bone formation occur, providing evidence for the interplay between growth factors and the extracellular matrix.

The bovine aristaless-like homeobox 4 (ALX4) as a candidate gene for syndactyly

The ALX4 (aristaless-like homeobox 4) gene encodes a paired-type homeodomain transcriptional activator and plays a major role in anterior-posterior pattern formation during limb development. Here, the cloning, genomic structure and expression of the bovine ortholog of the ALX4 gene are reported. The bovine ALX4 gene consists of four exons and is located on BTA15q28-->q29 in a region syntenic to HSA11p11.2. The transcribed ALX4 mRNA encodes a 397-amino-acid protein showing a paired-type homeodomain and a C-terminal stretch of amino acids known as the OAR- or aristaless domain. The predicted protein shares 92.5% identity to human and mouse ALX4 proteins and all three species share almost complete identity in the conserved domains. ALX4 expression was detected by reverse transcriptase polymerase chain reaction in bovine fetal limb bones. The ALX4 gene was evaluated as a candidate gene for bovine syndactyly which has been mapped on the telomeric region of cattle chromosome 15. Sequencing of the four exons with flanking sequences of the bovine ALX4 gene from a panel of 14 affected animals belonging to German Holstein, German Fleckvieh and crossbreds, and 27 unaffected individuals from German Holstein revealed five silent SNPs within the coding region out of eleven SNPs in total. Four SNPs were polymorphic in the affected animals, but in comparison to the genotyped unaffected individuals the genotype distribution showed no evidence for an association to the phenotype. Therefore our data indicate that the ALX4 gene can probably be excluded as candidate gene for bovine syndactyly in the examined animals.

Zoom-in comparative genomic hybridisation arrays for the characterisation of variable breakpoint contiguous gene syndromes

Contiguous gene syndromes cause disorders via haploinsufficiency for adjacent genes. Some contiguous gene syndromes (CGS) have stereotypical breakpoints, but others have variable breakpoints. In CGS that have variable breakpoints, the extent of the deletions may be correlated with severity. The Greig cephalopolysyndactyly contiguous gene syndrome (GCPS-CGS) is a multiple malformation syndrome caused by haploinsufficiency of GLI3 and adjacent genes. In addition, non-CGS GCPS can be caused by deletions or duplications in GLI3. Although fluorescence in situ hybridisation (FISH) can identify large deletion mutations in patients with GCPS or GCPS-CGS, it is not practical for identification of small intragenic deletions or insertions, and it is difficult to accurately characterise the extent of the large deletions using this technique. We have designed a custom comparative genomic hybridisation (CGH) array that allows identification of deletions and duplications at kilobase resolution in the vicinity of GLI3. The array averages one probe every 730 bp for a total of about 14,000 probes over 10 Mb. We have analysed 16 individuals with known or suspected deletions or duplications. In 15 of 16 individuals (14 deletions and 1 duplication), the array confirmed the prior results. In the remaining patient, the normal CGH array result was correct, and the prior assessment was a false positive quantitative polymerase chain reaction result. We conclude that high-density CGH array analysis is more sensitive than FISH analysis for detecting deletions and provides clinically useful results on the extent of the deletion. We suggest that high-density CGH array analysis should replace FISH analysis for assessment of deletions and duplications in patients with contiguous gene syndromes caused by variable deletions.

Adams-Oliver syndrome and isolated aplasia cutis congenita in two siblings

Adams-Oliver syndrome is a rare congenital anomaly complex characterized by aplasia cutis congenita (ACC) and terminal transverse limb defects. We present a 9-year-old girl with a large, congenital scalp defect on her vertex, without underlying bone defect. Brachydactyly and syndactylia of her toes were also evident. Her 13-year-older brother had an 8 x 5 cm scalp defect without any limb defects (isolated ACC).

FGFR1 Pfeiffer syndrome without craniosynostosis: an additional case report

Pfeiffer syndrome is an autosomal dominant condition classically encompassing both craniosynostosis and digital abnormalities of the hands and feet. Individuals with Pfeiffer syndrome may have mutations within either fibroblast growth factor receptor 1 gene (FGFR1) or FGFR2. FGFR1 mutations often result in less severe craniofacial involvement and hand abnormalities. We report a four-generation family with an FGFR1 P252R mutation, who have typical hand and feet skeletal features of Pfeiffer syndrome without craniofacial involvement. This is the third family in the literature in which no family members have craniofacial features of Pfeiffer syndrome. The absence of craniosynostosis should not preclude the consideration of FGFR mutation analysis in cases in which digital features are characteristic of the craniosynostosis syndromes.

Myofibrillar myopathy with congenital cataract and skeletal anomalies without mutations in the desmin, alphaB-crystallin, myotilin, LMNA or SEPN1 genes

Myofibrillar myopathies are genetically heterogeneous. We present a sporadic case of an 8-year-old boy with unusual combination of congenital skeletal muscle myopathy, cataract and poly/syndactyly. Muscle pathology revealed a mild myopathic picture with hyaline plaques, showing dark green staining in modified trichrome reaction, and strong immunoreactivity for alphaB-crystallin, desmin and dystrophin. Analysis of the coding sequences of the desmin, alphaB-crystallin, SEPN1, lamin A/C genes and of exon 2 of the myotilin gene showed no abnormalities in the patient. Presented case expands the wide clinical spectrum of myofibrillar myopathies, reinforcing the need for further exploration of genetic causes for this group of disorders.

Defective splicing of Megf7/Lrp4, a regulator of distal limb development, in autosomal recessive mulefoot disease

Mulefoot disease (MFD) is an autosomal recessive disorder of phenotypically variable expression that causes syndactyly in certain strains of cows. MFD maps to a narrow interval on bovine chromosome 15 that is syntenic to human chromosome 11p12-p11.2. This region contains MEGF7/LRP4 (approved gene symbol LRP4), a gene that encodes a member of the multifunctional low-density lipoprotein receptor gene family. Targeted and naturally occurring mutations in the murine Megf7/Lrp4 gene, a putative coreceptor in the Wnt signaling pathway, cause polysyndactyly in the rodent. Thus, Megf7/Lrp4 is a strong candidate for the MFD mutation. Using PCR analysis of tissue samples and sperm from confirmed homozygous MFD carriers, we have identified a functional single base pair mutation in the affected animals. We show that a G --> A transition at the first nucleotide in the splice donor site of intron 37 completely disables this splice site. The abnormal splicing that is caused by this mutation predicts the generation of a dysfunctional membrane-anchored receptor lacking the normal cytoplasmic domain. These findings confirm that autosomal recessive loss-of-function mutations in Megf7/Lrp4 result in phenotypically similar forms of syndactyly in different mammalian species and that such mutations are the cause of MFD in bovines.

Acro-dermato-ungual-lacrimal-tooth-like syndrome: report of a family with variable expression

We report the case of a young boy with fine hair, mild nail dysplasia, blocked nasolacrimal ducts, absence of central incisors, bilateral oligodactyly of feet and anal stenosis. His father showed the same spectrum of anomalies with mild expression. He had mild nail dysplasia, blocked nasolacrimal ducts, inferior dental cysts with consequent premature tooth loss, frequent dental decays consequent to enamel abnormality and cutaneous syndactyly of the second and third right toe. The acro-dermato-ungual-lacrimal-tooth syndrome was suspected and molecular analysis of the P63 gene was performed, but no mutation was found. Although P63 gene analysis was negative, we think that both cases show clinical overlap with the acro-dermato-ungual-lacrimal-tooth syndrome and confirm the wide expression of this condition, even in the same family.

Clinical phenotype associated with homozygosity for a HOXD13 7-residue polyalanine tract expansion

Synpolydactyly (SPD) is an autosomal dominant malformation of the distal limbs caused by mutations in the homeobox gene HOXD13 located on chromosome 2q31. We detail the clinical findings in a consanguineous Pakistani family segregating a HOXD13 7-residue polyalanine tract expansion. Three members of this pedigree were heterozygotes with features typical of SPD. Two further members demonstrate a more severe phenotype consistent with homozygosity for the familial mutation. We also report a child from a consanguineous Somali family homozygous for the same molecular lesion. Characteristic changes include a complex central polydactyly in the hands, abnormal modelling of the metacarpals and metatarsals, an increased number of carpal bones with abnormal shapes, hypoplasia or absence of the fifth digital rays in the feet, hypoplasia of the middle phalanges and abnormally long proximal phalanges in hands and feet. These cases illustrate the distinct phenotype associated with homozygosity for a HOXD13 mutation and also highlight the importance of considering homozygosity for a dominant mutation in consanguineous pedigrees.

Gene mutations and genomic rearrangements in the mouse as a result of transposon mobilization from chromosomal concatemers

Previous studies of the Sleeping Beauty (SB) transposon system, as an insertional mutagen in the germline of mice, have used reverse genetic approaches. These studies have led to its proposed use for regional saturation mutagenesis by taking a forward-genetic approach. Thus, we used the SB system to mutate a region of mouse Chromosome 11 in a forward-genetic screen for recessive lethal and viable phenotypes. This work represents the first reported use of an insertional mutagen in a phenotype-driven approach. The phenotype-driven approach was successful in both recovering visible and behavioral mutants, including dominant limb and recessive behavioral phenotypes, and allowing for the rapid identification of candidate gene disruptions. In addition, a high frequency of recessive lethal mutations arose as a result of genomic rearrangements near the site of transposition, resulting from transposon mobilization. The results suggest that the SB system could be used in a forward-genetic approach to recover interesting phenotypes, but that local chromosomal rearrangements should be anticipated in conjunction with single-copy, local transposon insertions in chromosomes. Additionally, these mice may serve as a model for chromosome rearrangements caused by transposable elements during the evolution of vertebrate genomes.

Perhaps the greatest challenge for biomedical research in the post-genomics era will be to assign functions to the human set of ~25,000 genes. The classical method for discovering the gene function is mutation. Thus, technologies that can mutate genes in mammalian genetic models like the mouse are under development in hopes of creating an efficient method to complete this task. One such technology, the Sleeping Beauty (SB) transposon system, was developed for this purpose in 2001. This mobile DNA element is highly active in transgenic mice and has been shown to disrupt mouse genes efficiently. Geurts et al. describe a novel attempt to use the SB transposon in a forward-genetic screen using an insertional mutagen, the first attempt of its kind. They discovered that the process of transposon mobilization in mouse chromosomes can lead to dramatic effects on local genomic sequences. Indeed, transposons like SB can cause genomic rearrangements including deletions, inversions and translocations, involving tens of thousands to tens of millions of base pairs. This discovery has important implications for using transposable elements for mouse germline mutagenesis and, at the same time, may provide a model for studying genomic rearrangements that have helped shape vertebrate genomes during evolution.

Paediatric phenotype of Kallmann syndrome due to mutations of fibroblast growth factor receptor 1 (FGFR1)

Kallmann syndrome characterised by hypogonadotropic hypogonadism (HH) and anosmia is genetically heterogeneous with X-linked, autosomal dominant and autosomal recessive forms. The autosomal dominant form due to loss of function mutation in the fibroblast growth factor receptor 1 (FGFR1) accounts for about 10% of cases. We report here three paediatric cases of Kallmann syndrome with unusual phenotype in two unrelated patients with severe ear anomalies (hypoplasia or agenesis of external ear) associated with classical features, such as cleft palate, dental agenesis, syndactylia, micropenis and cryptorchidism. We found de novo mutation in these two patients (Cys178Ser and Arg622Gly, respectively), and one inherited Arg622Gln mutation with intrafamilial variable phenotype. These genotype-phenotype correlations indicate that paediatric phenotypic expression of FGFR1 loss of function mutations is highly variable, the severity of the oro-facial malformations at birth does not predict gonadotropic function at the puberty and that de novo mutations of FGFR1 are relatively frequent.

Identification of a doublet missense substitution in the bovine LRP4 gene as a candidate causal mutation for syndactyly in Holstein cattle

Syndactyly in Holstein cattle is an autosomal recessive abnormality characterized by the fusion of the functional digits. This disorder has been previously mapped to the telomeric part of bovine chromosome 15. Here, we describe the fine-mapping of syndactyly in Holstein cattle to a 3.5-Mb critical interval using a comparative mapping approach and an extended pedigree generated by embryo transfer. We report genetic evidence for the exclusion of two genes previously suggested as candidates (EXT2 and ALX4) and describe the identification of a doublet mutation in complete linkage disequilibrium with syndactyly in one gene of the critical interval: LRP4. Finally, based on recent discoveries concerning the mouse mutants dan and mdig and a mouse knockout for Lrp4, we present solid evidence that the subsequent substitution in LRP4 exon 33 is a strong candidate causal mutation for syndactyly in Holstein cattle.

Ectodermal dysplasia, ectrodactyly, cleft lip/palate syndrome without ectrodactyly

The ectodermal dysplasia, ectrodactyly, cleft lip/palate syndrome (EEC syndrome) is an autosomal dominant dysplasia syndrome, whose pleiotropic effects involve mainly ectodermal structures. The most common clinical manifestations are ectodermal dysplasia, ectrodactyly , cleft lip/palate, and tear-duct anomalies. Very rarely the ectrodactyly may be absent, and skeletal abnormalities may be subtle. We present a 44-month-old girl who had features of EEC syndrome but without the classic ectrodactyly.

Mutations in the gene encoding the low-density lipoprotein receptor LRP4 cause abnormal limb development in the mouse

Positional cloning of two recessive mutations of the mouse that cause polysyndactyly (dan and mdig-Chr 2) confirmed that the gene encoding MEGF7/LRP4, a member of the low-density lipoprotein receptor family, plays an essential role in the process of digit differentiation. Pathologies observed in the mutant mice provide insight into understanding the function(s) of LRP4 as a negative regulator of the Wnt-beta-catenin signaling pathway and may help identify the genetic basis for common human disorders with similar phenotypes.

Genetic analysis of syndactyly in German Holstein cattle

Congenital syndactyly with a variable number of affected feet was observed in eight black and white German Holstein calves. Analysis of the pedigree data revealed that all affected individuals could be traced back to a single founder. The pedigree was consistent with monogenic autosomal recessive inheritance and variable expressivity. Bovine syndactyly or "mulefoot" has been previously shown to map on the telomeric end of bovine chromosome 15 and we performed PCR genotyping of microsatellite markers spanning 27 cM of this chromosomal region to test the new cases for genetic linkage with the phenotype. The haplotype segregation confirmed the suggested inheritance pattern of the mulefoot mutation in this family and markers RM004, BM848 and BMS820 showed significant linkage to the phenotype. The results confirmed the chromosomal location of the mulefoot gene in this pedigree. Furthermore the study demonstrated that although marker testing has been available for nearly a decade the use of mulefoot carriers in cattle breeding remains uncontrolled. The presented family provides a resource for positional cloning of the causative mutation.

Mutation analysis of theFRAS1 gene demonstrates new mutations in a propositus with Fraser syndrome

Fraser syndrome (OMIM 219000) is a rare, autosomal recessive condition with classical features of cryptophthalmos, syndactyly, ambiguous genitalia, laryngeal, and genitourinary malformations, oral clefting and mental retardation. Mutations causing loss of function of the FRAS1 gene have been demonstrated in five patients with Fraser syndrome. However, no phenotype-genotype correlation was established and there was evidence for genetic heterogeneity. Fraser syndrome is rare and the FRAS1 gene has 75 exons, complicating mutation screening in affected patients. We have screened two patients who fulfilled the diagnostic criteria for Fraser syndrome and three patients with related phenotypes (two patients with Manitoba oculotrichoanal syndrome and one patient with unilateral cryptophthalmos and labial fusion) for mutations in FRAS1 to increase the molecular genetic data in patients with Fraser syndrome and related conditions. We report two new mutations in a patient with Fraser syndrome, a frameshift mutation and a deletion of two amino acids that we consider pathogenic as both alter the NG2-like domain of the protein. Although we are still unable to clarify a phenotype-genotype relationship in Fraser syndrome, our data add to the list of mutations associated with this syndrome.

Ectrodactyly, ectodermal dysplasia, macular degeneration syndrome: a further contribution

EEM syndrome is a rare condition characterised by ectodermal dysplasia, ectrodactyly and macular dystrophy. Additional abnormalities such as alopecia, cataract, absent eyebrows, and oligodontia may occur. We report two brothers and a sister born to consanguineous parents with EEM syndrome. EEM syndrome differs from other ectrodactly syndromes by the characteristic findings in the ocular fundus showing extensive retinochoroidal atrophy with diffuse retinal pigmentation and mild arteriolar attenuation at the posterior pole. In contrast to other ectrodactyly syndromes autosomal recessive inheritance is most likely.

A Gja1 missense mutation in a mouse model of oculodentodigital dysplasia

Oculodentodigital dysplasia (ODDD) is an autosomal dominant disorder characterized by pleiotropic developmental anomalies of the limbs, teeth, face and eyes that was shown recently to be caused by mutations in the gap junction protein alpha 1 gene (GJA1), encoding connexin 43 (Cx43). In the course of performing an N-ethyl-N-nitrosourea mutagenesis screen, we identified a dominant mouse mutation that exhibits many classic symptoms of ODDD, including syndactyly, enamel hypoplasia, craniofacial anomalies and cardiac dysfunction. Positional cloning revealed that these mice carry a point mutation in Gja1 leading to the substitution of a highly conserved amino acid (G60S) in Cx43. In vivo and in vitro studies revealed that the mutant Cx43 protein acts in a dominant-negative fashion to disrupt gap junction assembly and function. In addition to the classic features of ODDD, these mutant mice also showed decreased bone mass and mechanical strength, as well as altered hematopoietic stem cell and progenitor populations. Thus, these mice represent an experimental model with which to explore the clinical manifestations of ODDD and to evaluate potential intervention strategies.

A novel mutation in the GJA1 gene in a family with oculodentodigital dysplasia

OBJECTIVES

To describe a Brazilian family with oculodentodigital dysplasia (ODDD) and to screen for mutations in the gap junction protein alpha 1 (GJA1) gene in this family.

METHODS

Twelve members of a 3-generation family with ODDD underwent screening for mutations of the GJA1 gene and a comprehensive ophthalmic examination. We defined ODDD on the basis of clinical characteristics described in this syndrome (microdontia, caries, enamel hypoplasia, thin nose, and syndactyly) and eye abnormalities such as microphthalmos, iris atrophy, and glaucoma. Direct sequencing of the GJA1 gene was performed using DNA collected from peripheral blood. A control group of 60 healthy individuals underwent evaluation by means of enzyme digestion.

RESULTS

Among the 8 members of this family who were characterized as having ODDD, 2 showed chronic angle-closure glaucoma, and 1 had open-angle glaucoma. A new mutation in the GJA1 gene was identified, consisting of a change from proline to histidine at codon 59. This mutation segregated through members with the ODDD phenotype. Analysis of the control group by means of restriction fragment length polymorphism (MvaI enzyme) did not disclose this mutation.

CONCLUSION

Our results demonstrate a new mutation (P59H) in the GJ1A gene, identified in a family with ODDD syndrome. Clinical Relevance The presence of different forms of glaucoma in families with ODDD may indicate a new mutation in the GJA1 gene.

Foot polydactyly and polysyndactyly: genetic implications in two families

The purpose of this study was to determine the genetic characteristics of foot polydactyly and identify its inheritance pattern by analyzing familial pedigree. Five cases from 2 Korean families were studied: 1 is a family whose members have been affected for 4 generations and the other for 2 generations. Using peripheral blood samples, we performed chromosomal analysis using the banding technique with Giemsa stain and karyotyping. We investigated the shape and structure of 46 chromosomes, looking for translation, deletion, inversion, ring chromosome, and isochromosome abnormalities. All peripheral blood samples demonstrated no chromosomal abnormalities, though the genetic nature of foot polydactyly and a new genetic locus was identified recently by other studies. Familial pedigree analysis suggested that polydactyly was inherited as an autosomal dominant trait in the first family. The mode of inheritance for the second family could not be determined due to an insufficient number of family members. The result of this study brought us to the conclusion that, while genetic factors play a major role in polydactyly, other factors may contribute to its occurrence.

Abnormal development of the apical ectodermal ridge and polysyndactyly in Megf7-deficient mice

Megf7/Lrp4 is a member of the functionally diverse low-density lipoprotein receptor gene family, a class of ancient and highly conserved cell surface receptors with broad functions in cargo transport and cellular signaling. To gain insight into the as yet unknown biological role of Megf7/Lrp4, we have disrupted the gene in mice. Homozygous Megf7-deficient mice are growth-retarded, with fully penetrant polysyndactyly in their fore and hind limbs, and partially penetrant abnormalities of tooth development. The reason for this developmental abnormality is apparent as early as embryonic day 9.5 when the apical ectodermal ridge (AER), the principal site of Megf7 expression at the distal edge of the embryonic limb bud, forms abnormally in the absence of Megf7. Ectopic expression and aberrant signaling of several molecules involved in limb patterning, including Fgf8, Shh, Bmp2, Bmp4 and Wnt7a, as well as the Wnt- and Bmp-responsive transcription factors Lmx1b and Msx1, result in reduced apoptosis and symmetrical dorsal and ventral expansions of the AER. Abnormal signaling from the AER precedes ectopic chondrocyte condensation and subsequent fusion and duplication of digits in the Megf7 knockouts. Megf7 can antagonize canonical Wnt signaling in vitro. Taken together, these findings are consistent with a role of Megf7 as a modulator of cellular signaling pathways involving Wnts, Bmps, Fgfs and Shh. A similar autosomal recessive defect may also occur in man, where polysyndactyly, in combination with craniofacial abnormalities, is also part of a common genetic syndrome.

Evidence for clinical and genetic heterogeneity of syndactyly type I: the phenotype of second and third toe syndactyly maps to chromosome 3p21.31

There is good evidence from the medical literature that type I syndactyly, the most common form of the nonsyndromic syndactylies, is clinically heterogeneous. We therefore propose to group the condition into four subtypes, which are all autosomal dominantly inherited. Subtype 1, zygodactyly (cutaneous webbing of second and third toe without hand involvement) is the mildest and most common form. The phenotype varies from unilateral minor impression of webbing to bilateral complete webbing of second and third toe including a fusion of nails. Bony involvement is never observed. Subtype 2 is characterized by bilateral cutaneous and/or bony webbing of third and fourth finger, and second and third toe. The phenotype maps on chromosome 2q34-q36 and was designated as SD1 (ie syndactyly 1). The hallmark of subtype 3 is bilateral cutaneous or bony webbing of third and fourth finger, while subtype 4 shows bilateral cutaneous webbing of fourth and fifth toe. Both, subtype 3 and 4, are rare entities. Here, we present clinical and molecular data of a large Pakistani family with zygodactyly that was mapped to a new locus on chromosome 3p21.31 by genome-wide linkage analysis. The highest LOD score (Zmax=3.38) was obtained with microsatellite marker D3S2409. The disease interval is flanked by markers Chr3_4919 and Chr3_4940 encompassing about 0.20 Mb. Since the same phenotype appears not to be linked to this locus in a German family, we predict genetic heterogeneity in zygodactyly and propose to designate the 3p21.31 locus as ZD1 (i.e., zygodactyly 1).