Distal limb malformations: underlying mechanisms and clinical associations

Split Hand-Foot and Deafness in a Patient with 7q21.13-q21.3 Deletion Not Including the DLX5/6 Genes

Split Hand-Foot Malformation (SHFM) is a congenital limb defect characterized by a median cleft of the hands and/or feet due to the absence/hypoplasia of the central rays. It may occur as part of a syndromic condition or as an isolated malformation. The most common of the six genetic loci identified for this condition is correlated to SHFM1 and maps in the 7q21q22 region. SHFM1 is characterized by autosomal dominant transmission, incomplete penetrance and variable expressivity. Associated features often include hearing loss, intellectual disability/developmental delay and craniofacial abnormalities. Disruption of the DLX5/DLX6 genes, mapping within the SHFM1 locus, is now known to be responsible for the phenotype. Through SNP array, we analyzed a patient affected by SHFM1 associated with deafness and an abnormality of the inner ear (incomplete partition type I); we identified a deletion in 7q21, not involving the DLX5/6 genes, but including exons 15 and 17 of DYNC1I1, known to act as exonic enhancers (eExons) of the DLX5/6 genes. We further demonstrated the role of DYNC1I1 eExons in regulating DLX5/6 expression by means of showing a reduced expression of the DLX5/6 genes through RT-PCR in a patient-derived lymphoblastoid cell line. Furthermore, our data and a review of published cases do not support the hypothesis that DLX5/6 are imprinted in humans. This work is an example of how the disruption of regulatory elements can be responsible for congenital malformations.

Magnetic resonance imaging of the fetal musculoskeletal system

Diagnosing musculoskeletal pathology requires understanding of the normal embryological development. Intrinsic errors of skeletal development are individually rare but are of paramount clinical importance because anomalies can greatly impact patients' lives. An accurate assessment of the fetal musculoskeletal system must be performed to provide optimal genetic counseling as well as to drive therapeutic management. This manuscript reviews the embryology of skeletal development and the appearance of the maturing musculoskeletal system on fetal MRI. In addition, it presents a comprehensive review of musculoskeletal fetal pathology along with postnatal imaging.

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.

Constant inhibition in congenital lower extremity shortening: does it begin in utero?

BACKGROUND

Limb-length discrepancy (LLD) in children with congenital lower extremity shortening is constant in proportion from birth to skeletal maturity (known as constant inhibition), but its developmental pattern in utero is unknown. The popular prenatal multiplier method to predict LLD at birth assumes constant inhibition in utero to be true. Verifying the in utero developmental pattern of LLD, and thus confirming the validity of the prenatal multiplier method, is crucial for meaningful prenatal parental counseling.

OBJECTIVE

To elucidate the in utero developmental pattern of LLD in fetuses with congenital lower extremity shortening.

MATERIALS AND METHODS

Clinical indications for 3,605 lower extremity radiographs performed on infants (<1 year old) at a large tertiary hospital over a 17-year period were reviewed. Inclusion criteria were (1) diagnosis of congenital lower extremity shortening, (2) bilateral lower limb postnatal radiographs documenting LLD and (3) fetal ultrasound (US) documenting LLD. Available measurements of femoral, tibial and fibular lengths on fetal US and postnatal radiographs were collected. Prenatal and postnatal length ratios of shorter-to-longer bones were calculated and compared.

RESULTS

Eighteen infants met inclusion criteria. Diagnoses were proximal focal femoral deficiency=4, congenital short femur=2, tibial hemimelia=3, posteromedial tibial bowing=6 and fibular hemimelia=3. The correlations between postnatal and prenatal length ratios were high for the femur, tibia and fibula (R>0.98, P<0.0001). The relative differences in the postnatal and prenatal length ratios of these bones were small (|average|<0.026, standard deviation <0.068).

CONCLUSION

Our data indicate that the postnatal and prenatal length ratios were equivalent, supporting the constant inhibition pattern of LLD in utero, thus validating the prenatal multiplier method for predicting LLD.

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.

Deletions of exons with regulatory activity at the DYNC1I1 locus are associated with split-hand/split-foot malformation: array CGH screening of 134 unrelated families

BACKGROUND

A growing number of non-coding regulatory mutations are being identified in congenital disease. Very recently also some exons of protein coding genes have been identified to act as tissue specific enhancer elements and were therefore termed exonic enhancers or "eExons".

METHODS

We screened a cohort of 134 unrelated families with split-hand/split-foot malformation (SHFM) with high resolution array CGH for CNVs with regulatory potential.

RESULTS

In three families with an autosomal dominant non-syndromic SHFM phenotype we detected microdeletions encompassing the exonic enhancer (eExons) 15 and 17 of DYNC1I1. In a fourth family, who had hearing loss in addition to SHFM, we found a larger deletion of 510 kb including the eExons of DYNC1I1 and, in addition, the human brain enhancer hs1642. Exons 15 and 17 of DYNC1I1 are known to act as tissue specific limb enhancers of DLX5/6, two genes that have been shown to be associated with SHFM in mice. In our cohort of 134 unrelated families with SHFM, deletions of the eExons of DYNC1I1 account for approximately 3% of the cases, while 17p13.3 duplications were identified in 13% of the families, 10q24 duplications in 12%, and TP63 mutations were detected in 4%.

CONCLUSIONS

We reduce the minimal critical region for SHFM1 to 78 kb. Hearing loss, however, appears to be associated with deletions of a more telomeric region encompassing the brain enhancer element hs1642. Thus, SHFM1 as well as hearing loss at the same locus are caused by deletion of regulatory elements. Deletions of the exons with regulatory potential of DYNC1I1 are an example of the emerging role of exonic enhancer elements and their implications in congenital malformation syndromes.

Insulin-like growth factors in embryonic and fetal growth and skeletal development (Review)

The insulin-like growth factors (IGF)-I and -II have a predominant role in fetal growth and development. IGFs are involved in the proliferation, differentiation and apoptosis of fetal cells in vitro and the IGF serum concentration has been shown to be closely correlated with fetal growth and length. IGF transcripts and peptides have been detected in almost every fetal tissue from as early in development as pre‑implantation to the final maturation stage. Furthermore, IGFs have been demonstrated to be involved in limb morphogenesis. However, although ablation of Igf genes in mice resulted in growth retardation and delay in skeletal maturation, no impact on outgrowth and patterning of embryonic limbs was observed. Additionally, various molecular defects in the Igf1 and Igf1r genes in humans have been associated with severe intrauterine growth retardation and impaired skeletal maturation, but not with truncated limbs or severe skeletal dysplasia. The conflicting data between in vitro and in vivo observations with regard to bone morphogenesis suggests that IGFs may not be the sole trophic factors involved in fetal skeletal growth and that redundant mechanisms may exist in chondro- and osteogenesis. Further investigation is required in order to elucidate the functions of IGFs in skeletal development.

DLX5, FGF8 and the Pin1 isomerase control ΔNp63α protein stability during limb development: a regulatory loop at the basis of the SHFM and EEC congenital malformations

Ectrodactyly, or Split-Hand/Foot Malformation (SHFM), is a congenital condition characterized by the loss of central rays of hands and feet. The p63 and the DLX5;DLX6 transcription factors, expressed in the embryonic limb buds and ectoderm, are disease genes for these conditions. Mutations of p63 also cause the ectodermal dysplasia–ectrodactyly–cleft lip/palate (EEC) syndrome, comprising SHFM. Ectrodactyly is linked to defects of the apical ectodermal ridge (AER) of the developing limb buds. FGF8 is the key signaling molecule in this process, able to direct proximo-distal growth and patterning of the skeletal primordial of the limbs. In the limb buds of both p63 and Dlx5;Dlx6 murine models of SHFM, the AER is poorly stratified and FGF8 expression is severely reduced. We show here that the FGF8 locus is a downstream target of DLX5 and that FGF8 counteracts Pin1–ΔNp63α interaction. In vivo, lack of Pin1 leads to accumulation of the p63 protein in the embryonic limbs and ectoderm. We show also that ΔNp63α protein stability is negatively regulated by the interaction with the prolyl-isomerase Pin1, via proteasome-mediated degradation; p63 mutant proteins associated with SHFM or EEC syndromes are resistant to Pin1 action. Thus, DLX5, p63, Pin1 and FGF8 participate to the same time- and location-restricted regulatory loop essential for AER stratification, hence for normal patterning and skeletal morphogenesis of the limb buds. These results shed new light on the molecular mechanisms at the basis of the SHFM and EEC limb malformations.

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.

Overexpression and ratio disruption of ΔNp63 and TAp63 isoform equilibrium in endometrial adenocarcinoma: correlation with obesity, menopause, and grade I/II tumors

PURPOSE

p63 plays an important role in several intracellular processes such as transcription activation and apoptosis. p63 has two N-terminal isoforms, TAp63 and ΔNp63. TAp63 isoform has p53-like functions, while ΔNp63 acts as a dominant negative inhibitor of the p53 family and is considered oncogenic. Although p63 and its isoforms are overexpressed in a wide variety of human malignancies such as cervical, head and neck, and lung cancer, their role in endometrial carcinoma has not been investigated.

METHODS

We measured by quantitative real-time polymerase chain reaction the mRNA expression of TAp63 and ΔNp63 in a series of 20 endometrioid adenocarcinomas paired with adjacent normal tissue.

RESULTS

TAp63 isoform exhibited 1.8-fold overexpression in malignant samples, while ΔNp63 was 4.3-fold overexpressed in cancer specimens. Further analysis revealed that the ΔN/TA isoform ratio shifted from 0.5 in normal samples to 1.2 in tumor specimens. Statistical analysis also revealed an association of TAp63 expression with high body mass index (p = 0.034), late menopause (p = 0.020), and lower tumor grade (p = 0.034). ΔNp63 was also correlated with grade I/II tumors (p = 0.044).

CONCLUSIONS

These results indicate that both p63 isoforms and especially ΔNp63 play an important role in the development and progression of grade I/II endometrial adenocarcinoma, especially in obese and late-menopause women.

Congenital anomalies of the hand: an overview

Of the 1% to 2% of newborns that are born with congenital defects, 10% of these are born with upper extremity malformations. Although many classification systems have been developed, the most widely used classification system was developed by Swanson. This system categorizes the congenital upper extremity malformations according to the embryonic process that has failed to develop. Congenital hand malformation is a broad category that is broken down into 7 subclasses. This review will focus on congenital hand defects and their associated craniofacial syndromes. The topics will include failure of formation, failure of differentiation, duplication, overgrowth, undergrowth, constriction band syndromes, and generalized skeletal abnormalities.

Regulation of Dlx5 and Dlx6 gene expression by p63 is involved in EEC and SHFM congenital limb defects

The congenital malformation Split Hand-Foot Malformation (SHFM, or ectrodactyly) is characterized by a medial cleft of hands and feet, and missing central fingers. Five genetically distinct forms are known in humans; the most common (type-I) is linked to deletions of DSS1 and the distalless-related homeogenes DLX5 and DLX6. As Dlx5;Dlx6 double-knockout mice show a SHFM-like phenotype, the human orthologs are believed to be the disease genes. SHFM-IV and Ectrodactyly-Ectodermal dysplasia-Cleft lip (EEC) are caused by mutations in p63, an ectoderm-specific p53-related transcription factor. The similarity in the limb phenotype of different forms of SHFM may underlie the existence of a regulatory cascade involving the disease genes. Here, we show that p63 and Dlx proteins colocalize in the nuclei of the apical ectodermal ridge (AER). In homozygous p63- (null) and p63EEC (R279H) mutant limbs, the AER fails to stratify and the expression of four Dlx genes is strongly reduced; interestingly, the p63+/EEC and p63+/- hindlimbs, which develop normally and have a normally stratified AER, show reduced Dlx gene expression. The p63+/EEC mutation combined with an incomplete loss of Dlx5 and Dlx6 alleles leads to severe limb phenotypes, which are not observed in mice with either mutation alone. In vitro, DeltaNp63alpha induces transcription from the Dlx5 and Dlx6 promoters, an activity abolished by EEC and SHFM-IV mutations, but not by Ankyloblepharon-Ectodermal defects-Cleft lip/palate (AEC) mutations. ChIP analysis shows that p63 is directly associated with the Dlx5 and Dlx6 promoters. Thus, our data strongly implicate p63 and the Dlx5-Dlx6 locus in a pathway relevant in the aetio-pathogenesis of SHFM.

Split hand malformation, hypospadias, microphthalmia, distinctive face and short stature in two brothers suggest a new syndrome

Split hand/foot malformation (SHFM) is a genetically heterogeneous limb malformation that may be isolated or associated with other malformations. More than 50 recognizable entities with SHFM have been described and at least 5 mapped genetic loci have been implicated. Two brothers with intrauterine growth retardation, short stature, distinctive face, microphthalmia, genital anomalies, and SHFM are described. Molecular analyses of TP63, HOXA13, and HOXD13 genes were normal. We propose this pattern to be a newly recognized SHFM syndrome.

p63 gene analysis in Mexican patients with syndromic and non-syndromic ectrodactyly

Ectrodactyly is a congenital limb malformation that involves a central reduction defect of the hands and/or feet which is frequently associated with other phenotypic abnormalities. The condition appears to be genetically heterogeneous and recently it has been demonstrated that mutations in the p63 gene, a homologue of the tumor suppressor gene p53, are the cause of at least four autosomal dominant genetic syndromes which feature ectrodactyly: ectrodactyly, ectodermal dysplasia, and facial clefting (EEC), split hand/split foot malformation (SHFM), limb-mammary syndrome (LMS), and acro-dermato-ungual-lacrimal-tooth syndrome (ADULT). In this study, genetic analysis of the p63 gene in a group of 13 patients with ectrodactyly (syndromic and isolated) was performed. Four patients with syndromic ectrodactyly had p63 heterozygous point mutations that affect the DNA binding domain of the protein. One of these subjects exhibited the typical features of EEC syndrome as well as ankyloblepharon being, to our knowledge, the first case combining these traits. This finding supports the view of a clinical overlap in this group of autosomal dominant syndromes caused by p63 mutations and demonstrates that there are exceptions in the previously established p63 genotype-phenotype correlation.

p73 can suppress the proliferation of cells that express mutant p53

Mutation of the p53 tumor suppressor gene is the most common genetic alteration in human cancer. p73, a member of the p53 family, has been found to exhibit activity similar to that of p53, including the ability to induce growth arrest and apoptosis. p53 and p73 have a high percentage of similarity at several domains, including the DNA binding domain. This domain in p53 is the location of missense mutations in many human cancers. Mutant p53, which cannot suppress cell proliferation, has been found to have a dominant-negative activity that inactivates wild-type p53. To determine the effects of mutant p53 on wild-type p73, we have established cell lines expressing both mutant p53 and wild-type p73 in a dual-inducible system. This system expresses mutant p53 in a tetracycline-repressible system and p73beta in an ecdysone-inducible system in a p53-null lung carcinoma parental cell line. We have found that wild-type p73beta, in the presence of mutant p53, retains the ability to transactivate p21 and suppresses cell growth through induction of both cell cycle arrest and apoptosis. In addition, in cell lines expressing wild-type p53 and wild-type p73beta, we have found that these proteins cooperate to additively transactivate p21 and suppress cell proliferation.

Differentiation of cartilaginous anlagen in entire embryonic mouse limbs cultured in a rotating bioreactor

Mechanisms involved in development of the embryonic limb have remained the same throughout eons of genetic and environmental evolution under Earth gravity (1 g). During the spaceflight era it has been of interest to explore the ancient theory that form of the skeleton develops in response to gravity, and that changes in gravitational forces can change the developmental pattern of the limb. This has been shown in vivo and in vitro, allowing the hypergravity of centrifugation and microgravity of space to be used as tools to increase our knowledge of limb development. In recapitulations of spaceflight experiments, premetatarsals were cultured in suspension in a bioreactor, and found to be shorter and less differentiated than those cultured in standard culture dishes. This study only measured length of the metatarsals, and did not account for possible changes due to the skeletal elements having a more in vivo 3D shape while in suspension vs. flattened tissues compressed by their own weight. A culture system with an outcome closer to in vivo and that supports growth of younger limb buds than traditional systems will allow studies of early Hox gene expression, and contribute to the understanding of very early stages of development. The purpose of the current experiment was to determine if entire limb buds could be cultured in the bioreactor, and to compare the growth and differentiation with that of culturing in a culture dish system. Fore and hind limbs from E11-E13 ICR mouse embryos were cultured for six days, either in the bioreactor or in center-well organ culture dishes, fixed, and embedded for histology. E13 specimens grown in culture dishes were flat, while bioreactor culture specimens had a more in vivo-like 3D limb shape. Sections showed excellent cartilage differentiation in both culture systems, with more cell maturation, and hypertrophy in the specimens cultured in the bioreactor. Younger limb buds fused together during culture, so an additional set of E11.5 limb buds was cultured with and without encapsulation in alginate prior to culturing in the bioreactor. Encapsulated limbs grown in the bioreactor did not fuse together, but developed only the more proximal elements while limbs grown in culture dishes formed proximal and distal elements. Alginate encapsulation may have reduced oxygenation to the progress zone of the developing limb bud resulting in lack of development of the more distal elements. These results show that the bioreactor supports growth and differentiation of skeletal elements in entire E13 limb buds, and that a method to culture younger limb buds without fusing together needs to be developed if any morphometric analysis is to be performed.

Limb anomalies: Developmental and evolutionary aspects

In this review we describe the developmental mechanisms involved in the making of a limb, by focusing on the nature and types of interactions of the molecules that play a part in the regulation of limb patterning and characterizing clinical conditions that are known to result from the abnormal function of these molecules. The latter subject is divided into sections dealing with syndromal and nonsyndromal deficiencies, polydactylies, and brachydactylies. Conditions caused by mutations in homeobox genes and fibroblast growth factors and their receptor genes are listed separately. Since the process of limb development has been conserved for more than 300 millions years, with all the necessary adaptive modifications occurring throughout evolution, we also take into consideration the evolutionary aspects of limb development in terms of genetic repertoire, molecular pathways, and morphogenetic events.

Mouse model of split hand/foot malformation type I

Split hand/foot malformation type I (SHFM1) disease locus maps to chromosome 7q21.3-q22, a region that includes the distal-less-related (dll) genes DLX5 and DLX6. However, incomplete penetrance, variable expressivity, segregation distortion, and syndromic association with other anomalies have so far prevented the identification of the SHFM1 gene(s) in man. Here we show that the targeted double inactivation of Dlx5 and Dlx6 in the mouse causes in homozygous mutant animals bilateral ectrodactyly with a severe defect of the central ray of the hindlimbs, a malformation typical of SHFM1. This is the first evidence that the role of dll/Dlx genes in appendage development is conserved from insects to mammals and proves their involvement in SHFM1.