Homozygous WNT10b mutation and complex inheritance in Split-Hand/Foot Malformation

Gollop-Wolfgang Complex Is Associated with a Monoallelic Variation in WNT11

Gollop-Wolfgang complex (GWC) is a rare congenital limb anomaly characterized by tibial aplasia with femur bifurcation, ipsilateral bifurcation of the thigh bone, and split hand and monodactyly of the feet, resulting in severe and complex limb deformities. The genetic basis of GWC, however, has remained elusive. We studied a three-generation family with four GWC-affected family members. An analysis of whole-genome sequencing results using a custom pipeline identified the WNT11 c.1015G>A missense variant associated with the phenotype. In silico modelling and an in vitro reporter assay further supported the link between the variant and GWC. This finding further contributes to mapping the genetic heterogeneity underlying split hand/foot malformations in general and in GWC specifically.

Sequence Variants in the WNT10B Underlying Non-Syndromic Split-Hand/Foot Malformation

Introduction

Split hand and foot malformation (SHFM) or ectrodactyly is a rare limb deformity characterized by median cleft of the hand and foot with impaired or missing central rays. It can occur as an isolated anomaly or in association with abnormalities of other body parts.

Methods

After delineating the clinical features of two families (A-B), with non-syndromic SHFM, exome and Sanger sequencing were employed to search for the disease-causing variants.

Results

Analysis of exome and Sanger sequencing data revealed two causative variants in the WNT10B gene in affected members of the two families. This included a novel missense change [c.338G>C; p.(Gly113Ala)] in family A and a previously reported frameshift variant [c.884-896delTCCAGCCCCGTCT; p.(Phe295Cysfs*87)] in family B.

Conclusion

Our findings add a novel variant in WNT10B gene as the underlying cause of SHFM. The finding adds to the growing body of knowledge about the genetic basis of developmental disorders and provides valuable insights into the molecular mechanisms that regulate limb development.

BHLHA9 homozygous duplication in a consanguineous family: A challenge for genetic counseling

Split-hand/foot malformation (SHFM) with long-bone deficiency (SHFLD) is a rare condition characterized by SHFM associated with long-bone malformation usually involving the tibia. It includes three different types; SHFLD1 (MIM % 119,100), SHFLD2 (MIM % 610,685) and SHFLD3 (MIM # 612576). The latter was shown to be the most commonly reported with a duplication in the 17p13.1p13.3 locus that was narrowed down to the BHLHA9 gene. Here, we report a consanguineous Lebanese family with three members presenting with limb abnormalities including tibial hemimelia. One of these patients presented with additional bowing fibula and another with bilateral split hand. CGH array analysis followed by RQ-PCR allowed us to detect the first homozygous duplication on the short arm of chromosome 17p13.3 including the BHLHA9 gene and involved in SHFLD3. Interestingly, one patient with the homozygous duplicated region, carrying thus four BHLHA9 copies presented with long bone deficiency but no SHFM. The incomplete penetrance and the variable expressivity of the disease in this family as well as the presence of the BHLHA9 homozygous duplication rendered genetic counseling extremely challenging and preimplantation genetic diagnosis almost impossible.

The role of WNT10B in physiology and disease: A 10-year update

WNT10B, a member of the WNT family of secreted glycoproteins, activates the WNT/β-catenin signaling cascade to control proliferation, stemness, pluripotency, and cell fate decisions. WNT10B plays roles in many tissues, including bone, adipocytes, skin, hair, muscle, placenta, and the immune system. Aberrant WNT10B signaling leads to several diseases, such as osteoporosis, obesity, split-hand/foot malformation (SHFM), fibrosis, dental anomalies, and cancer. We reviewed WNT10B a decade ago, and here we provide a comprehensive update to the field. Novel research on WNT10B has expanded to many more tissues and diseases. WNT10B polymorphisms and mutations correlate with many phenotypes, including bone mineral density, obesity, pig litter size, dog elbow dysplasia, and cow body size. In addition, the field has focused on the regulation of WNT10B using upstream mediators, such as microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). We also discussed the therapeutic implications of WNT10B regulation. In summary, research conducted during 2012-2022 revealed several new, diverse functions in the role of WNT10B in physiology and disease.

Complete Pseudo-Anodontia in an Adult Woman with Pseudo-Hypoparathyroidism Type 1a: A New Additional Nonclassical Feature?

Pseudo-anodontia consists in the clinical, not radiographic, absence of teeth, due to failure in their eruption. It has been reported as part of an extremely rare syndrome, named GAPO syndrome. Pseudo-hypoparathyroidism type 1a (PHPT-1a) is a rare condition, characterized by resistance to the parathyroid hormone (PTH), as well as to many other hormones, and resulting in hypocalcemia, hyperphosphatemia, and elevated PTH. We report here the case of a 32-year-old woman with a long-standing history of non-treated hypocalcemia, in the context of an undiagnosed PHPT-1a. She had an intellectual disability, showed clinical features of the Albright hereditary osteodystrophy (AHO) and presented signs of multiple hormone resistances. She received treatment for seizures since the age of six. Examination of her mouth revealed a complete absence of teeth. Treatment of hypocalcemia and hormone deficiencies were started only at 29 years of age. Genetic testing demonstrated the presence of a frameshift variant in the GNAS gene in the proband as well as in her mother. A Single Nucleotide Polymorphism (SNP) array analysis failed to demonstrate pathogenic copy number variants (CNVs) but showed several regions with loss of heterozygosity (LOHs) for a final percentage of 1.75%, compatible with a fifth degree of relationship. Clinical exome sequencing (CES) ruled out any damaging variants in all the teeth agenesis-related genes. In conclusion, although we performed an extensive genetic analysis in search of possible additional gene alterations that could explain the presence of the peculiar phenotypic characteristics observed in our patient, we could not find any additional genetic defects. Our results suggest that the association of genetically confirmed PHPT-1a and complete pseudo-anodontia associated with persistent patchy alopecia areata is a new additional nonclassical feature related to the GNAS pathogenic variant.

The molecular genetics of human appendicular skeleton

Disorders that result from de-arrangement of growth, development and/or differentiation of the appendages (limbs and digit) are collectively called as inherited abnormalities of human appendicular skeleton. The bones of appendicular skeleton have central role in locomotion and movement. The different types of appendicular skeletal abnormalities are well described in the report of "Nosology and Classification of Genetic skeletal disorders: 2019 Revision". In the current article, we intend to present the embryology, developmental pathways, disorders and the molecular genetics of the appendicular skeletal malformations. We mainly focused on the polydactyly, syndactyly, brachydactyly, split-hand-foot malformation and clubfoot disorders. To our knowledge, only nine genes of polydactyly, five genes of split-hand-foot malformation, nine genes for syndactyly, eight genes for brachydactyly and only single gene for clubfoot have been identified to be involved in disease pathophysiology. The current molecular genetic data will help life sciences researchers working on the rare skeletal disorders. Moreover, the aim of present systematic review is to gather the published knowledge on molecular genetics of appendicular skeleton, which would help in genetic counseling and molecular diagnosis.

Monoallelic and biallelic variants in LEF1 are associated with a new syndrome combining ectodermal dysplasia and limb malformations caused by altered WNT signaling

PURPOSE

LEF1 encodes a transcription factor acting downstream of the WNT-β-catenin signaling pathway. It was recently suspected as a candidate for ectodermal dysplasia in 2 individuals carrying 4q35 microdeletions. We report on 12 individuals harboring LEF1 variants.

METHODS

High-throughput sequencing was employed to delineate the genetic underpinnings of the disease. Cellular consequences were characterized by immunofluorescence, immunoblotting, pulldown assays, and/or RNA sequencing.

RESULTS

Monoallelic variants in LEF1 were detected in 11 affected individuals from 4 unrelated families, and a biallelic variant was detected in an affected individual from a consanguineous family. The phenotypic spectrum includes various limb malformations, such as radial ray defects, polydactyly or split hand/foot, and ectodermal dysplasia. Depending on the type and location of LEF1 variants, the inheritance of this novel Mendelian condition can be either autosomal dominant or recessive. Our functional data indicate that 2 molecular mechanisms are at play: haploinsufficiency or loss of DNA binding are responsible for a mild to moderate phenotype, whereas loss of β-catenin binding caused by biallelic variants is associated with a severe phenotype. Transcriptomic studies reveal an alteration of WNT signaling.

CONCLUSION

Our findings establish mono- and biallelic variants in LEF1 as a cause for a novel syndrome comprising limb malformations and ectodermal dysplasia.

Wnt Pathway Extracellular Components and Their Essential Roles in Bone Homeostasis

The Wnt pathway is involved in several processes essential for bone development and homeostasis. For proper functioning, the Wnt pathway is tightly regulated by numerous extracellular elements that act by both activating and inhibiting the pathway at different moments. This review aims to describe, summarize and update the findings regarding the extracellular modulators of the Wnt pathway, including co-receptors, ligands and inhibitors, in relation to bone homeostasis, with an emphasis on the animal models generated, the diseases associated with each gene and the bone processes in which each member is involved. The precise knowledge of all these elements will help us to identify possible targets that can be used as a therapeutic target for the treatment of bone diseases such as osteoporosis.

A Human Pleiotropic Multiorgan Condition Caused by Deficient Wnt Secretion

BACKGROUND

Structural birth defects occur in approximately 3% of live births; most such defects lack defined genetic or environmental causes. Despite advances in surgical approaches, pharmacologic prevention remains largely out of reach.

METHODS

We queried worldwide databases of 20,248 families that included children with neurodevelopmental disorders and that were enriched for parental consanguinity. Approximately one third of affected children in these families presented with structural birth defects or microcephaly. We performed exome or genome sequencing of samples obtained from the children, their parents, or both to identify genes with biallelic pathogenic or likely pathogenic mutations present in more than one family. After identifying disease-causing variants, we generated two mouse models, each with a pathogenic variant "knocked in," to study mechanisms and test candidate treatments. We administered a small-molecule Wnt agonist to pregnant animals and assessed their offspring.

RESULTS

We identified homozygous mutations in WLS, which encodes the Wnt ligand secretion mediator (also known as Wntless or WLS) in 10 affected persons from 5 unrelated families. (The Wnt ligand secretion mediator is essential for the secretion of all Wnt proteins.) Patients had multiorgan defects, including microcephaly and facial dysmorphism as well as foot syndactyly, renal agenesis, alopecia, iris coloboma, and heart defects. The mutations affected WLS protein stability and Wnt signaling. Knock-in mice showed tissue and cell vulnerability consistent with Wnt-signaling intensity and individual and collective functions of Wnts in embryogenesis. Administration of a pharmacologic Wnt agonist partially restored embryonic development.

CONCLUSIONS

Genetic variations affecting a central Wnt regulator caused syndromic structural birth defects. Results from mouse models suggest that what we have named Zaki syndrome is a potentially preventable disorder. (Funded by the National Institutes of Health and others.).

The Emerging Mechanisms of Wnt Secretion and Signaling in Development

Wnts are highly-conserved lipid-modified secreted proteins that activate multiple signaling pathways. These pathways regulate crucial processes during various stages of development and maintain tissue homeostasis in adults. One of the most fascinating aspects of Wnt protein is that despite being hydrophobic, they are known to travel several cell distances in the extracellular space. Research on Wnts in the past four decades has identified several factors and uncovered mechanisms regulating their expression, secretion, and mode of extracellular travel. More recently, analyses on the importance of Wnt protein gradients in the growth and patterning of developing tissues have recognized the complex interplay of signaling mechanisms that help in maintaining tissue homeostasis. This review aims to present an overview of the evidence for the various modes of Wnt protein secretion and signaling and discuss mechanisms providing precision and robustness to the developing tissues.

Homozygous nonsense mutation of WNT10B gene in a Moroccan family with split-hand foot malformation identified by exome sequencing: a case report

Split-hand foot malformation (SHFM) is a clinically heterogeneous congenital limb defect affecting predominantly the central rays of hands and/or feet. The clinical expression varies in severity between patients as well between the limbs in the same individual. SHFM might be non-syndromic with limb-confined manifestations or syndromic with extra-limb manifestations. Isolated SHFM is a rare condition with an incidence of about 1 per 18,000 live born infants and accounts for 8-17 % of all limb malformations. To date, many chromosomal loci and genes have been described as associated with isolated SHFM, i.e., SHFM1 to 6. SHFM6 is one of the rarest forms of SHFM, and is caused by mutations in WNT10B gene. Less than ten pathogenic variants have been described. We have investigated a large consanguineous Moroccan family with three affected members showing feet malformations with or without split hand malformation phenotypes. Using an exome sequencing approach, we identified a homozygous nonsense variant p.Arg115* of WNT10B gene retaining thereby the diagnosis of SHFM6. This homozygous nonsense mutation identified by exome sequencing in a large family of split hand foot malformation highlights the importance of exome sequencing in genetically heterogeneous entities.

A Novel Missense Variant of TP63 Heterozygously Present in Split-Hand/Foot Malformation

Background

Split-hand/foot malformation (SHFM) is a severe congenital disability mainly characterized by the absence or hypoplasia of the central ray of the hand/foot. To date, several candidate genes associated with SHFM have been identified, including TP63, DLX5, DLX6, FGFR1, and WNT10B. Herein, we report a novel variant of TP63 heterozygously present in affected members of a family with SHFM.

Methods

This study investigated a Chinese family, in which the proband and his son suffered from SHFM. The peripheral blood sample of the proband was used to perform whole-exome sequencing (WES) to explore the possible genetic causes of this disease. Postsequencing bioinformatic analyses and Sanger sequencing were conducted to verify the identified variants and parental origins on all family members in the pedigree.

Results

By postsequencing bioinformatic analyses and Sanger sequencing, we identified a novel missense variant (NM_003722.4:c.948G>A; p.Met316Ile) of TP63 in this family that results in a substitution of methionine with isoleucine, which is probably associated with the occurrence of SHFM.

Conclusion

A novel missense variant (NM_003722.4:c.948G>A; p.Met316Ile) of TP63 in SHFM was thus identified, which may enlarge the spectrum of known TP63 variants and also provide new approaches for genetic counselling of families with SHFM.

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.

Sequence Variants in the WNT10B and TP63 Genes Underlying Isolated Split-Hand/Split-Foot Malformation

Aims: Split-hand/split-foot malformation (SHFM) is a developmental and congenital limb malformation characterized by variable degrees of medial clefting or absence of one or more digits in hands and/or feet. The aim of this study was to identify the underlying cause of three consanguineous Pakistani families showing various types of SHFM-related features. Materials and Methods: Standard molecular methods, including whole-genome sequencing (WGS), whole-exome sequencing (WES), microsatellite markers-based genotyping, and Sanger sequencing were performed to search for the likely causative variants. Results: In family A, WES revealed a novel homozygous missense variant [c.338G>A, p.(Gly113Asp)] in the WNT10B gene. In family B, microsatellite-based genotyping followed by Sanger sequencing revealed a novel homozygous 13 base pairs deletion [c.884-896delTCCAGCCCCGTCT, p.(Phe295Cysfs*87)] in the same gene. In family C, WGS divulged a previously reported heterozygous missense variant [c.956G>A, p.(Arg319His)] in the TP63 gene. Conclusions: Mapping and sequencing genes and variants for severe skeletal disorders, such as SHRM, will facilitate establishing specific genotype-phenotype correlations and providing genetic counseling for the families suffering from such conditions.

Rare missense variant p.Ala505Ser in the ZAK protein observed in a patient with split-hand/foot malformation from a non-consanguineous pedigree

Objective

Split-hand/foot malformation (SHFM) is a rare, often debilitating, congenital limb malformation. A single nucleotide polymorphism within the leucine zipper containing kinase AZK (ZAK) gene was recently associated with SHFM in two consanguineous Pakistani pedigrees. We hypothesized that additional unrelated patients with the phenotype may carry a pathogenic mutation in ZAK.

Methods

DNA samples were collected from 38 patients with SHFM and associated hearing loss for Sanger DNA sequencing and in silico analysis.

Results

Two missense mutations within ZAK were detected in 11 patients, but only one missense variant, p.Ala505Ser, occurred with a presumed rare allele frequency. In silico modeling of the ZAK protein with the p.Ala505Ser substitution indicated a negative binding free energy change (mean ΔΔG = −0.9), representing destabilization of the ZAK tertiary structure. Additional laboratory analysis demonstrated a chromosome region 7q21.3-q22.1 deletion. This locus contains the SHFM-1 causative genes SHFM1, DLX5, and DLX6 (distal-less homeobox-5 and -6).

Conclusions

We report a novel and rare missense variant, ZAK p.Ala505Ser, in one patient with SHFM from a non-consanguineous pedigree. This variant mildly destabilizes the ZAK tertiary structure. Although this mutation involved a deletion at the SHFM1 locus (7q21.3-q22.1), ZAK signaling destabilization may have contributed to the phenotype, which included hearing loss.

A Novel Homozygous Nonsense Mutation p.Cys366* in the WNT10B Gene Underlying Split-Hand/Split Foot Malformation in a Consanguineous Pakistani Family

Split hand/split foot malformation (SHFM) or ectrodactyly is characterized by a deep median cleft of the hand or foot, hypoplasia or aplasia of the metacarpals, metatarsals, and phalanges. It is a clinically and genetically heterogeneous group of limb malformations. This study aimed to identify the pathogenic variant in a consanguineous Pakistani family with autosomal recessive SHFM. Peripheral blood samples were obtained, DNA was extracted, WNT10B coding and noncoding regions were PCR amplified and Sanger sequencing was performed using workflow suggested by Thermo Fisher Scientific. A novel homozygous nonsense variant (c.1098C>A; p.Cys366*) was identified in the WNT10B gene in the index patients, which probably explains SHFM type 6 in this family in comparison with similar data from the literature.

Novel missense alteration in LRP4 gene underlies Cenani-Lenz syndactyly syndrome in a consanguineous family

BACKGROUND

Syndactyly is a clinical feature of split-hand foot malformation (SHFM), ectodermal-dysplasia-syndactyly (EDSS1) and Cenani-Lenz syndactyly syndromes (CLSS). In EDSS1, only cutaneous syndactyly is observed, with sparse hair, abnormal nails and dentition. In SHFM, bony syndactyly may vary from hypoplasia of one phalanx to aplasia of central digits, extending to complete fusion of all fingers and toes in CLSS. Several genes have been assigned to these syndromes. Performing a single step molecular diagnostics becomes a challenge when a phenotype has overlaps with several syndromes or when some of the clinical features are not fully expressed in patients.

METHODS

Whole exome sequencing (WES) analysis on one sample derived from a consanguineous family was performed. A causative variant in WES data was prioritized via standard bioinformatics tools. The selected variant was Sanger sequenced in all the available family members for autosomal recessive segregation.

RESULTS

A novel missense variant (c.1151A>G; p.Tyr384Cys) was identified in the LRP4 gene. Sanger validation confirmed that all affected individuals were homozygous and the obligate carriers were heterozygous for this variant. The variant is neither reported in 1000 human genomes, nor in 60 706 exomes databases, and is predicted as "pathogenic" by SIFT, Polyphen-2 and MutationTaster software.

CONCLUSIONS

The present study broadens the pathogenic spectrum of the LRP4 gene in syndactyly syndromes. WES is a powerful tool for genetic analysis in research and can be readily used as a first-line diagnostic test in syndactyly and related phenotypes.

WNT Signaling and Bone: Lessons From Skeletal Dysplasias and Disorders

Skeletal dysplasias are a diverse group of heritable diseases affecting bone and cartilage growth. Throughout the years, the molecular defect underlying many of the diseases has been identified. These identifications led to novel insights in the mechanisms regulating bone and cartilage growth and homeostasis. One of the pathways that is clearly important during skeletal development and bone homeostasis is the Wingless and int-1 (WNT) signaling pathway. So far, three different WNT signaling pathways have been described, which are all activated by binding of the WNT ligands to the Frizzled (FZD) receptors. In this review, we discuss the skeletal disorders that are included in the latest nosology of skeletal disorders and that are caused by genetic defects involving the WNT signaling pathway. The number of skeletal disorders caused by defects in WNT signaling genes and the clinical phenotype associated with these disorders illustrate the importance of the WNT signaling pathway during skeletal development as well as later on in life to maintain bone mass. The knowledge gained through the identification of the genes underlying these monogenic conditions is used for the identification of novel therapeutic targets. For example, the genes underlying disorders with altered bone mass are all involved in the canonical WNT signaling pathway. Consequently, targeting this pathway is one of the major strategies to increase bone mass in patients with osteoporosis. In addition to increasing the insights in the pathways regulating skeletal development and bone homeostasis, knowledge of rare skeletal dysplasias can also be used to predict possible adverse effects of these novel drug targets. Therefore, this review gives an overview of the skeletal and extra-skeletal phenotype of the different skeletal disorders linked to the WNT signaling pathway.

Nonsyndromic Split-Hand/Foot Malformation: Recent Classification

Split-hand/foot malformation (SHFM) is a genetic limb anomaly disturbing the central rays of the autopod. SHFM is a genetically heterogeneous disorder with variable expressivity inherited as syndromic and nonsyndromic forms. We provide an update of the clinical and molecular aspects of nonsyndromic SHFM. This rare condition is highly complex due to the clinical variability and irregular genetic inheritance observed in the affected individuals. Nonsyndromic SHFM types have been reviewed in terms of major molecular genetic alterations reported to date. This updated overview will assist researchers, scientists, and clinicians in making an appropriate molecular diagnosis, providing an accurate recurrence risk assessment, and developing a management plan.

A classification system for split-hand/ foot malformation (SHFM): A proposal based on 3 pedigrees with WNT10B mutations

SHFM6 (OMIM 225300) is caused by WNT10B pathogenic variants (12q13.12). It is one of the rarest forms of SHFM; with only seven pathogenic variants described in the world literature. Furthermore, it has not been determined if SHFM6 has specific phenotypic characteristics. In this paper, we present a case series of three unrelated families with SHFM6 caused by three novel WNT10B pathogenic variants. The index patient of the first family was homozygous for the nonsense variant c.676C > T (p.Arg226*) in the WNT10B gene. The index case of the second family had a homozygous splice variant c.338-1G > C in the WNT10B gene. Finally, the index case of the third family carried two different variants in the WNT10B gene: A nonsense variant (p.Arg226*), and a missense variant (p.Gln86Pro). The latter represents the first compound heterozygous pathogenic variant related to SHFM6. We also offer a classification system for the hand/foot defects to illustrate the specific phenotypic characteristics of SHFM6. Based on this classification and a review of all previously reported cases, we demonstrate that SHFM6 caused by WNT10B pathogenic variants have the following characteristics: more severe feet defects (compared to the hand defects), polydactyly, severe flexion digital contractures, and phalangeal dysplasia.

WNT10B variants in split hand/foot malformation: Report of three novel families and review of the literature

Split-hand/foot malformation (SHFM) is a genetically heterogeneous congenital limb malformation typically limited to a defect of the central rays of the autopod, presenting as a median cleft of hands and feet. It can be associated with long bone deficiency or included in more complex syndromes. Among the numerous genetic causes, WNT10B homozygous variants have been recently identified in consanguineous families, but remain still rarely described (SHFM6; MIM225300). We report on three novel SHFM families harboring WNT10B variants and review the literature, allowing us to highlight some clinical findings. The feet are more severely affected than the hands and there is a frequent asymmetry without obvious side-bias. Syndactyly of third-fourth fingers was a frequent finding (62%). Polydactyly, which was classically described in SHFM6, was only present in 27% of patients. No genotype-phenotype correlation is delineated but heterozygous individuals might have mild features of SHFM, suggesting a dose-effect of the WNT10B loss-of-function.

Genetic regulatory pathways of split-hand/foot malformation

Split-hand/foot malformation (SHFM) is caused by mutations in TP63, DLX5, DLX6, FGF8, FGFR1, WNT10B, and BHLHA9. The clinical features of SHFM caused by mutations of these genes are not distinguishable. This implies that in normal situations these SHFM-associated genes share an underlying regulatory pathway that is involved in the development of the central parts of the hands and feet. The mutations in SHFM-related genes lead to dysregulation of Fgf8 in the central portion of the apical ectodermal ridge (AER) and subsequently lead to misexpression of a number of downstream target genes, failure of stratification of the AER, and thus SHFM. Syndactyly of the remaining digits is most likely the effects of dysregulation of Fgf-Bmp-Msx signaling on apoptotic cell death. Loss of digit identity in SHFM is hypothesized to be the effects of misexpression of HOX genes, abnormal SHH gradient, or the loss of balance between GLI3A and GLI3R. Disruption of canonical and non-canonical Wnt signaling is involved in the pathogenesis of SHFM. Whatever the causative genes of SHFM are, the mutations seem to lead to dysregulation of Fgf8 in AER cells of the central parts of the hands and feet and disruption of Wnt-Bmp-Fgf signaling pathways in AER.

A double dealing tale of p63: an oncogene or a tumor suppressor

As a member of tumor suppressor p53 family, p63, a gene encoding versatile protein variant, has been documented to correlate with cancer formation and progression, though it is rarely mutated in cancer patients. However, it has long been controversial on whether p63 is an oncogene or a tumor suppressor. Here, we comprehensively reviewed reports on roles of p63 in development, tumorigenesis and tumor progression. According to data from molecular cell biology, genetic models and clinic research, we conclude that p63 may act as either an oncogene or a tumor suppressor gene in different scenarios: TA isoforms of p63 gene are generally tumor-suppressive through repressing cell proliferation, survival and metastasis; ΔN isoforms, however, may initiate tumorigenesis via promoting cell proliferation and survival, but inhibit tumor metastasis and progression; effects of p63 on tumor formation and progression depend on the context of the whole p53 family, and either amplification or loss of p63 gene locus can break the balance to cause tumorigenesis.

Split hand-foot malformation and a novel WNT10B mutation

We report an Indian girl with split-hand/foot malformation (SHFM), sparse hair, and interrupted eyebrows, who carries a novel homozygous deletion c.695_697delACA in WNT10B. The variant is deduced to cause an in-frame deletion of Asn residue 232 (p.Asn232del). According to the protein model, this single amino acid deletion at the critical position in the protein structure is likely to severely affect the protein structure and function. This deletion is likely to lead decreased lifetime and make it unable to bind to its receptors and other ligands. The patient and all family members had normal bone density and they were not obese like some of the patients with WNT10B variants. Here we report a patient with SHFM6 who carried a novel WNT10B mutation. Sparse hair and interrupted eyebrows may be associated findings of SHFM6.

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.

A Novel Heterozygous Intragenic Sequence Variant in DLX6 Probably Underlies First Case of Autosomal Dominant Split-Hand/Foot Malformation Type 1

Split-hand and foot malformation (SHFM; MIM 183600) is a rare human genetic limb malformation. It is characterized by missing digital rays in the hands and feet. SHFMs vary in severity from mild abnormalities affecting a single limb to acute malformations involving all 4 limbs. It is inherited, as part of both a syndromic and nonsyndromic disorder, in an autosomal recessive, autosomal dominant, and X-linked patterns. So far, 9 loci of hand and foot malformation have been mapped on human chromosomes. The present study describes a family with 2 affected individuals segregating SHFM in an autosomal dominant fashion. Sanger sequencing of the genes involved in SHFM was performed to identify the disease-causing variant. Sequence analysis revealed the first heterozygous missense variant (c.632T>A, p.Val211Glu) in the distal-less homeobox 6 (DLX6) gene, located in chromosome 7q21, causing SHFM in the present family. This study supports the evidence of DLX6 as an SHFM-causing gene.

Ectrodactyly and Lethal Pulmonary Acinar Dysplasia Associated with Homozygous FGFR2 Mutations Identified by Exome Sequencing

Ectrodactyly/split hand-foot malformation is genetically heterogeneous with more than 100 syndromic associations. Acinar dysplasia is a rare congenital lung lesion of unknown etiology, which is frequently lethal postnatally. To date, there have been no reports of combinations of these two phenotypes. Here, we present an infant from a consanguineous union with both ectrodactyly and autopsy confirmed acinar dysplasia. SNP array and whole-exome sequencing analyses of the affected infant identified a novel homozygous Fibroblast Growth Factor Receptor 2 (FGFR2) missense mutation (p.R255Q) in the IgIII domain (D3). Expression studies of Fgfr2 in development show localization to the affected limbs and organs. Molecular modeling and genetic and functional assays support that this mutation is at least a partial loss-of-function mutation, and contributes to ectrodactyly and acinar dysplasia only in homozygosity, unlike previously reported heterozygous activating FGFR2 mutations that cause Crouzon, Apert, and Pfeiffer syndromes. This is the first report of mutations in a human disease with ectrodactyly with pulmonary acinar dysplasia and, as such, homozygous loss-of-function FGFR2 mutations represent a unique syndrome.

Exome sequencing and CRISPR/Cas genome editing identify mutations of ZAK as a cause of limb defects in humans and mice

The CRISPR/Cas technology enables targeted genome editing and the rapid generation of transgenic animal models for the study of human genetic disorders. Here we describe an autosomal recessive human disease in two unrelated families characterized by a split-foot defect, nail abnormalities of the hands, and hearing loss, due to mutations disrupting the SAM domain of the protein kinase ZAK. ZAK is a member of the MAPKKK family with no known role in limb development. We show that Zak is expressed in the developing limbs and that a CRISPR/Cas-mediated knockout of the two Zak isoforms is embryonically lethal in mice. In contrast, a deletion of the SAM domain induces a complex hindlimb defect associated with down-regulation of Trp63, a known split-hand/split-foot malformation disease gene. Our results identify ZAK as a key player in mammalian limb patterning and demonstrate the rapid utility of CRISPR/Cas genome editing to assign causality to human mutations in the mouse in <10 wk.

The apical ectodermal ridge of the mouse model of ectrodactyly Dlx5;Dlx6-/- shows altered stratification and cell polarity, which are restored by exogenous Wnt5a ligand

The congenital malformation split hand/foot (SHFM) is characterized by missing central fingers and dysmorphology or fusion of the remaining ones. Type-1 SHFM is linked to deletions/rearrangements of the DLX5–DLX6 locus and point mutations in the DLX5 gene. The ectrodactyly phenotype is reproduced in mice by the double knockout (DKO) of Dlx5 and Dlx6. During limb development, the apical ectodermal ridge (AER) is a key-signaling center responsible for early proximal–distal growth and patterning. In Dlx5;6 DKO hindlimbs, the central wedge of the AER loses multilayered organization and shows down-regulation of FGF8 and Dlx2. In search for the mechanism, we examined the non-canonical Wnt signaling, considering that Dwnt-5 is a target of distalless in Drosophila and the knockout of Wnt5, Ryk, Ror2 and Vangl2 in the mouse causes severe limb malformations. We found that in Dlx5;6 DKO limbs, the AER expresses lower levels of Wnt5a, shows scattered β-catenin responsive cells and altered basolateral and planar cell polarity (PCP). The addition of Wnt5a to cultured embryonic limbs restored the expression of AER markers and its stratification. Conversely, the inhibition of the PCP molecule c-jun N-terminal kinase caused a loss of AER marker expression. In vitro, the addition of Wnt5a on mixed primary cultures of embryonic ectoderm and mesenchyme was able to confer re-polarization. We conclude that the Dlx-related ectrodactyly defect is associated with the loss of basoapical and PCP, due to reduced Wnt5a expression and that the restoration of the Wnt5a level is sufficient to partially reverts AER misorganization and dysmorphology.

Japanese founder duplications/triplications involving BHLHA9 are associated with split-hand/foot malformation with or without long bone deficiency and Gollop-Wolfgang complex

Background

Limb malformations are rare disorders with high genetic heterogeneity. Although multiple genes/loci have been identified in limb malformations, underlying genetic factors still remain to be determined in most patients.

Methods

This study consisted of 51 Japanese families with split-hand/foot malformation (SHFM), SHFM with long bone deficiency (SHFLD) usually affecting the tibia, or Gollop-Wolfgang complex (GWC) characterized by SHFM and femoral bifurcation. Genetic studies included genomewide array comparative genomic hybridization and exome sequencing, together with standard molecular analyses.

Results

We identified duplications/triplications of a 210,050 bp segment containing BHLHA9 in 29 SHFM patients, 11 SHFLD patients, two GWC patients, and 22 clinically normal relatives from 27 of the 51 families examined, as well as in 2 of 1,000 Japanese controls. Families with SHFLD- and/or GWC-positive patients were more frequent in triplications than in duplications. The fusion point was identical in all the duplications/triplications and was associated with a 4 bp microhomology. There was no sequence homology around the two breakpoints, whereas rearrangement-associated motifs were abundant around one breakpoint. The rs3951819-D17S1174 haplotype patterns were variable on the duplicated/triplicated segments. No discernible genetic alteration specific to patients was detected within or around BHLHA9, in the known causative SHFM genes, or in the exome.

Conclusions

These results indicate that BHLHA9 overdosage constitutes the most frequent susceptibility factor, with a dosage effect, for a range of limb malformations at least in Japan. Notably, this is the first study revealing the underlying genetic factor for the development of GWC, and demonstrating the presence of triplications involving BHLHA9. It is inferred that a Japanese founder duplication was generated through a replication-based mechanism and underwent subsequent triplication and haplotype modification through recombination-based mechanisms, and that the duplications/triplications with various haplotypes were widely spread in Japan primarily via clinically normal carriers and identified via manifesting patients. Furthermore, genotype-phenotype analyses of patients reported in this study and the previous studies imply that clinical variability is ascribed to multiple factors including the size of duplications/triplications as a critical factor.

Electronic supplementary material

The online version of this article (doi:10.1186/s13023-014-0125-5) contains supplementary material, which is available to authorized users.

Heterozygous DLX5 nonsense mutation associated with isolated split-hand/foot malformation with reduced penetrance and variable expressivity in two unrelated families

BACKGROUND

Split-hand/foot malformation (SHFM) is a clinically and genetically heterogeneous limb abnormality characterized by the absence or hypoplasia of the central rays of the autopod. SHFM1, which is one out of seven known SHFM loci, maps to 7q21.2-q21.3. SHFM1 is usually inherited as an autosomal dominant trait with reduced penetrance, although recessive inheritance has been described for a single family carrying a homozygous DLX5 missense variant. In most cases, SHFM1 results from heterozygous deletions encompassing DLX5/DLX6 genes or from inversions and translocations separating the genes from their limb specific enhancers. Recently, a single Chinese family with dominant SHFM1 was shown to result from a heterozygous DLX5 missense mutation.

METHODS

In this study, we report on four male individuals from two unrelated Polish families (one sporadic and one familial case) presenting with isolated SHFM. We tested both probands for known molecular causes of SHFM, including TP63, WNT10B, DLX5 mutations and copy number changes using 1.4 M array CGH.

RESULTS

Sanger sequencing of DLX5 revealed a novel heterozygous nonsense mutation c.G115T(p.E39X) in both index patients. Segregation studies demonstrated that the variant was present in all affected family members but also in three apparently healthy relatives (two females and one male).

CONCLUSION

This is the first report of a heterozygous DLX5 nonsense mutation resulting in incompletely penetrant autosomal dominant isolated SHFM1. Data shown here provides further evidence for the contribution of DLX5 point mutations to the development of ectrodactyly and suggest the possibility of sex-related segregation distortion with an excess of affected males.

Sp6 and Sp8 transcription factors control AER formation and dorsal-ventral patterning in limb development

The formation and maintenance of the apical ectodermal ridge (AER) is critical for the outgrowth and patterning of the vertebrate limb. The induction of the AER is a complex process that relies on integrated interactions among the Fgf, Wnt, and Bmp signaling pathways that operate within the ectoderm and between the ectoderm and the mesoderm of the early limb bud. The transcription factors Sp6 and Sp8 are expressed in the limb ectoderm and AER during limb development. Sp6 mutant mice display a mild syndactyly phenotype while Sp8 mutants exhibit severe limb truncations. Both mutants show defects in AER maturation and in dorsal-ventral patterning. To gain further insights into the role Sp6 and Sp8 play in limb development, we have produced mice lacking both Sp6 and Sp8 activity in the limb ectoderm. Remarkably, the elimination or significant reduction in Sp6;Sp8 gene dosage leads to tetra-amelia; initial budding occurs, but neither Fgf8 nor En1 are activated. Mutants bearing a single functional allele of Sp8 (Sp6^−/−;Sp8^+/−) exhibit a split-hand/foot malformation phenotype with double dorsal digit tips probably due to an irregular and immature AER that is not maintained in the center of the bud and on the abnormal expansion of Wnt7a expression to the ventral ectoderm. Our data are compatible with Sp6 and Sp8 working together and in a dose-dependent manner as indispensable mediators of Wnt/βcatenin and Bmp signaling in the limb ectoderm. We suggest that the function of these factors links proximal-distal and dorsal-ventral patterning.

In this report we examined the functional roles of Sp6 and Sp8 during limb development using compound loss-of-function mutants. Sp6 and Sp8, two members of the Sp gene family, are expressed in the limb bud ectoderm and function downstream of WNT/βcatenin signaling for Fgf8 induction. The analysis of the allelic series shows that the progressive reduction in the dose of Sp6 and Sp8 gene products leads to predictable morphology, from syndactyly, to split hand/foot malformation, oligodactyly, truncation and finally amelia, indicating that these two factors act in a complementary manner. The molecular characterization of the mutant limbs reveal that Sp6/Sp8 are required in a dose-dependent manner for Fgf8 and En1 induction, thereby placing them as an important link between the induction of the AER and the establishment of dorsal-ventral patterning during limb development.

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.

Novel homozygous mutations in the WNT10B gene underlying autosomal recessive split hand/foot malformation in three consanguineous families

Split-hand/split-foot malformation (SHFM), representing variable degree of median clefts of hands and feet, is a genetically heterogeneous group of limb malformations with seven loci mapped on different human chromosomes. However, only 3 genes (TP63, WNT10B, DLX5) for the seven loci have been identified. The study, presented here, described three consanguineous Pakistani families segregating SHFM in autosomal recessive manner. Linkage in the families was searched by genotyping microsatellite markers and mutation screening of candidate gene was performed by Sanger DNA sequencing. Clinical features of affected members of these families exhibited SHFM phenotype with involvement of hands and feet. Genotyping using microsatellite markers mapped the families to WNT10B gene at SHFM6 on chromosome 12q13.11-q13. Subsequently, sequence analysis of WNT10B gene revealed a novel 4-bp deletion mutation (c.1165_1168delAAGT) in one family and 7-bp duplication (c.300_306dupAGGGCGG) in two other families. Structure-based analysis showed a significant conformational shift in the active binding site of mutated WNT10B (p.Lys388Glufs*36), influencing binding with Fzd8. The mutations identified in the WNT10B gene extend the body of evidence implicating it in the pathogenesis of SHFM.

Split-hand/foot malformation - molecular cause and implications in genetic counseling

Split-hand/foot malformation (SHFM) is a congenital limb defect affecting predominantly the central rays of the autopod and occurs either as an isolated trait or part of a multiple congenital anomaly syndrome. SHFM is usually sporadic, familial forms are uncommon. The condition is clinically and genetically heterogeneous and shows mostly autosomal dominant inheritance with variable expressivity and reduced penetrance. To date, seven chromosomal loci associated with isolated SHFM have been described, i.e., SHFM1 to 6 and SHFM/SHFLD. The autosomal dominant mode of inheritance is typical for SHFM1, SHFM3, SHFM4, SHFM5. Autosomal recessive and X-linked inheritance is very uncommon and have been noted only in a few families. Most of the known SHFM loci are associated with chromosomal rearrangements that involve small deletions or duplications of the human genome. In addition, three genes, i.e., TP63, WNT10B, and DLX5 are known to carry point mutations in patients affected by SHFM. In this review, we focus on the known molecular basis of isolated SHFM. We provide clinical and molecular information about each type of abnormality as well as discuss the underlying pathways and mechanism that contribute to their development. Recent progress in the understanding of SHFM pathogenesis currently allows for the identification of causative genetic changes in about 50 % of the patients affected by this condition. Therefore, we propose a diagnostic flow-chart helpful in the planning of molecular genetic tests aimed at identifying disease causing mutation. Finally, we address the issue of genetic counseling, which can be extremely difficult and challenging especially in sporadic SHFM cases.

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.

Mutation analysis of WNT10B in obese children, adolescents and adults

Wingless-type MMTV integration site family, member 10B (WNT10B) is an activator of the Wnt pathway. The Wnt pathway is known to play an important role in maintenance and differentiation of stem cells and has been implicated in the origination of obesity. To evaluate the role of genetic variation in WNT10B in obesity further, we performed a mutation analysis on Belgian obese patients and control subjects. A mutation analysis of WNT10B by means of high-resolution melting curve analysis and direct sequencing was performed on 546 obese children and adolescents (mean Z-score of 2.6 ± 0.6 and 2.5 ± 0.4 respectively), 86 morbidly obese adults (mean BMI of 48.0 ± 0.4 kg/m(2)) and 447 lean, healthy controls (mean BMI of 22.1 ± 1.7 kg/m(2)). A total of five novel non-synonymous variants were identified. R228Q was the only coding, non-synonymous variant that was exclusively found in patients, but the variant did not co-segregate with obesity in the three investigated siblings. The remaining four variants were either found both in cases and in control samples (G181D) or only in control samples (A108P, S187R and P315S). The frequency of non-synonymous variants in lean individuals (0.9 %) was higher than in obese individuals (0.3 %) and familial co-segregation of the most promising variant in patients could not be demonstrated. Therefore, we conclude that variations in WNT10B do not contribute to human monogenic obesity in our population.

A homozygous 237-kb deletion at 1p31 identified as the locus for midline cleft of the upper and lower lip in a consanguineous family

Orofacial clefts are congenital defects that vary widely in type and severity, and can occur in isolation or in association with a variety of other defects. Herein, we describe a consanguineous family afflicted with a unique form of orofacial clefting manifesting as a facial midline defect that also involves mandibular and maxillary structures. All four affected sibs had median clefts of the upper and lower lips, tooth misalignment, and poor oral hygiene. Linkage analysis of 17 family members identified a 15.3-Mb pair recessive locus at 1p31 with a LOD score of 3.63. To the best of our knowledge, this is, to date, the first locus reported for facial midline clefting and the first recessive locus for an isolated orofacial defect. The locus harboured a novel intergenic deletion of 273 164 bp, for which all fully affected sibs were homozygous. We did not note any potentially pathogenic gene variant at the 1p31 locus via exome-sequencing analysis. The identified deletion could be harbouring a regulatory element for the gene associated with the orofacial defect. The best candidate for the putative target gene is LHX8, located 49 149 bp upstream of the deletion. The gene is known to be associated with facial development in several animals. Four other family members had a subclinical phenotype--a simple notch in the lower lip or an increase in the interdental distance between the lower incisors--indicative of very low-level expression of the trait.

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.

A Comprehensive Overview of Skeletal Phenotypes Associated with Alterations in Wnt/β-catenin Signaling in Humans and Mice

The Wnt signaling pathway plays key roles in differentiation and development and alterations in this signaling pathway are causally associated with numerous human diseases. While several laboratories were examining roles for Wnt signaling in skeletal development during the 1990s, interest in the pathway rose exponentially when three key papers were published in 2001-2002. One report found that loss of the Wnt co-receptor, Low-density lipoprotein related protein-5 (LRP5), was the underlying genetic cause of the syndrome Osteoporosis pseudoglioma (OPPG). OPPG is characterized by early-onset osteoporosis causing increased susceptibility to debilitating fractures. Shortly thereafter, two groups reported that individuals carrying a specific point mutation in LRP5 (G171V) develop high-bone mass. Subsequent to this, the causative mechanisms for these observations heightened the need to understand the mechanisms by which Wnt signaling controlled bone development and homeostasis and encouraged significant investment from biotechnology and pharmaceutical companies to develop methods to activate Wnt signaling to increase bone mass to treat osteoporosis and other bone disease. In this review, we will briefly summarize the cellular mechanisms underlying Wnt signaling and discuss the observations related to OPPG and the high-bone mass disorders that heightened the appreciation of the role of Wnt signaling in normal bone development and homeostasis. We will then present a comprehensive overview of the core components of the pathway with an emphasis on the phenotypes associated with mice carrying genetically engineered mutations in these genes and clinical observations that further link alterations in the pathway to changes in human bone.

Analysis of large phenotypic variability of EEC and SHFM4 syndromes caused by K193E mutation of the TP63 gene

EEC (ectrodactyly, ectodermal dysplasia, clefting; OMIM 604292) is an autosomal dominant developmental disorder resulting mainly from pathogenic mutations of the DNA-binding domain (DBD) of the TP63 gene. In this study, we showed that K193E mutation in nine affected individuals of a four-generation kindred with a large degree of phenotypic variability causes four different syndromes or TP63-related disorders: EEC, Ectrodactyly-ectodermal dysplasia (EE), isolated ectodermal dysplasia, and isolated Split Hand/Foot Malformation type 4 (SHFM4). Genotype-phenotype and DBD structural modeling analysis showed that the K193-located loop L2-A is associated with R280 through hydrogen bonding interactions, while R280 mutations also often cause large phenotypic variability of EEC and SHFM4. Thus, we speculate that K193 and several other DBD mutation-associated syndromes may share similar pathogenic mechanisms, particularly in the case of the same mutation with different phenotypes. Our study and others also suggest that the phenotypic variability of EEC is attributed, at least partially, to genetic and/or epigenetic modifiers.

The molecular basis of human congenital limb malformations

This review focuses predominantly on the human congenital malformations caused by alterations affecting the morphoregulatory gene networks that control early limb bud patterning and outgrowth. Limb defects are among the most frequent congenital malformations in humans that are caused by genetic mutations or teratogenic effects resulting either in abnormal, loss of, or additional skeletal elements. Spontaneous and engineered mouse models have been used to identify and study the molecular alterations and disrupted gene networks that underlie human congenital limb malformations. More recently, mouse genetics has begun to reveal the alterations that affect the often-large cis-regulatory landscapes that control gene expression in limb buds and cause devastating effects on limb bud development. These findings have paved the way to identifying mutations in cis-regulatory regions as causal to an increasing number of congenital limb malformations in humans. In these cases, no mutations in the coding region of a presumed candidate were previously detected. This review highlights how the current understanding of the molecular gene networks and interactions that control mouse limb bud development provides insight into the etiology of human congenital limb malformations.

The role of WNT10B in physiology and disease

Wnt10b is a member of the Wnt ligand gene family that encodes for secreted proteins, which activate the ancient and highly conserved Wnt signalling cascade. The Wnt pathway has been shown to be essential for embryonic development, tissue integrity, and stem cell activity, but if deregulated, also causes disease such as cancer. Although the 19 different Wnt ligands found in both human and mouse can activate several branches of the Wnt pathway, WNT10B specifically activates canonical Wnt/β-catenin signalling and thus triggers β-catenin/LEF/TCF-mediated transcriptional programs. In this review, we highlight the unique functions of WNT10B and mechanisms of how WNT10B acts in the immune system, mammary gland, adipose tissue, bone and skin. In these organs, WNT10B has been well established to be involved in signalling networks controlling stemness, pluripotency and cell fate decisions. Deregulation of these processes causes diseases such as breast cancer, obesity and osteoporosis. Compelling evidence suggests that WNT10B is a valuable candidate for the development of therapeutic regimens for human diseases.

17p13.3 microduplications are associated with split-hand/foot malformation and long-bone deficiency (SHFLD)

Split-hand/foot malformation with long-bone deficiency (SHFLD) is a relatively rare autosomal-dominant skeletal disorder, characterized by variable expressivity and incomplete penetrance. Although several chromosomal loci for SHFLD have been identified, the molecular basis and pathogenesis of most SHFLD cases are unknown. In this study we describe three unrelated kindreds, in which SHFLD segregated with distinct but overlapping duplications in 17p13.3, a region previously linked to SHFLD. In a large three-generation family, the disorder was found to segregate with a 254 kb microduplication; a second microduplication of 527 kb was identified in an affected female and her unaffected mother, and a 430 kb microduplication versus microtriplication was identified in three affected members of a multi-generational family. These findings, along with previously published data, suggest that one locus responsible for this form of SHFLD is located within a 173 kb overlapping critical region, and that the copy gains are incompletely penetrant.