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

Split-hand/foot malformation 3 resulting from microduplications in 10q24 region in five patients from India

Split-hand/foot malformation (SHFM) is a genetically heterogeneous congenital limb reduction defect characterized by the deficiencies of central rays of the autopod. Tandem duplications at 10q24 locus account for approximately 20% of all SHFM cases. Here, we report five affected individuals from four unrelated Indian families with SHFM3 caused by microduplication of 10q24 locus showing varied clinical presentations. This report substantiates and extends the current understanding of this rare, multifaceted, and complex condition.

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.

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.

Perspective: Is Random Monoallelic Expression a Contributor to Phenotypic Variability of Autosomal Dominant Disorders?

Several factors have been proposed as contributors to interfamilial and intrafamilial phenotypic variability in autosomal dominant disorders, including allelic variation, modifier genes, environmental factors and complex genetic and environmental interactions. However, regardless of the similarity of genetic background and environmental factors, asymmetric limb or trunk anomalies in a single individual and variable manifestation between monozygotic twins have been observed, indicating other mechanisms possibly involved in expressivity of autosomal dominant diseases. One such example is Holt-Oram syndrome (HOS), which is characterized by congenital cardiac defects and forelimb anomalies, mainly attributed to mutations in the TBX5 gene. We hypothesize that monoallelic expression of the TBX5 gene occurs during embryo development, and, in the context of a mutation, random monoallelic expression (RME) can create discrepant functions in a proportion of cells and thus contribute to variable phenotypes. A hybrid mouse model was used to investigate the occurrence of RME with the Tbx5 gene, and single-cell reverse transcription PCR and restriction digestion were performed for limb bud cells from developing embryos (E11.5) of the hybrid mice. RME of Tbx5 was observed in approximately two-thirds of limb bud cells. These results indicate that RME of the Tbx5 gene occurs frequently during embryo development, resulting in a mosaic expression signature (monoallelic, biallelic, or null) that may provide a potential explanation for the widespread phenotypic variability in HOS. This model will further provide novel insights into the variability of autosomal dominant traits and a better understanding of the complex expressivity of disease conditions.

Molecular Genetic Characterization of a Chinese Family with Severe Split Hand/Foot Malformation

AIMS

Split hand/foot malformation (SHFM) is a congenital limb malformation characterized by underdeveloped or absent central digital rays, clefts of the hands and feet, and variable syndactyly of the remaining digits. SHFM is a genetically heterogeneous disease; the aim of this study was to identify pathogenic variations in a Chinese family with SHFM.

MATERIALS AND METHODS

Haplotype analyses with microsatellite markers covering the five SHFM loci were performed to localize the causative locus. Real-time quantitative polymerase chain reaction (qPCR) assays and inverse PCR were performed to determine the copy number variations and to amplify junction breakpoints in affected individuals. Candidate genes were further screened for mutations through Sanger sequencing.

RESULTS

A potential haplotype in the SHFM3 locus was shared by all affected individuals. qPCR and inverse PCR showed a microduplication at chromosome 10q24 spanning 488,859 bp and encompassing five entire genes, LBX1, BTRC, POLL, DPCD, and FBXW4, that co-segregated with the SHFM phenotype. No coding or splice-site mutations of these genes were found.

CONCLUSION

We determined the molecular basis of SHFM in a Chinese family by haplotype analysis, qPCR, inverse PCR, and Sanger sequencing. Our work extends the clinical spectrum of SHFM3; provides a fine-scale delineation of the chromosomal breakpoints helping to narrow the critical region of SHFM3; and facilitates an understanding of the mechanisms underlying abnormal limb development and extraskeletal anomalies.

The Classification of Swanson for Congenital Anomalies of Upper Limb Modified by the Japanese Society for Surgery of the Hand (JSSH)

The aim of this study is to introduce the classification of Swanson for congenital anomalies of upper limb modified by the Japanese Society for Surgery of the Hand (the JSSH modification) in English. The Swanson classification has been widely accepted by most hand surgeons. However, several authors have suggested that complex cases, particularly those involving the complex spectrum of cleft hand and symbrachydactyly, are difficult to classify into the classification schemes. In the JSSH modification, brachysyndactyly, so-called atypical cleft hand and transverse deficiency are included under the same concept of transverse deficiency. Cleft hand, central polydactyly, and syndactyly are included in the same category of abnormal induction of digital rays. We believe that the JSSH modification system is effective in providing hand surgeons with the clinical features and conditions for congenital anomalies.

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.

A novel homozygous missense mutation in WNT10B in familial split-hand/foot malformation

Split-hand/foot malformation (SHFM) is a rare limb developmental malformation, characterized by variable degree of median clefts of hands and feet due to the absence of central rays of extremities. To date, six different forms of SHFM have been described. Four of these SHFM1, SHFM3, SHFM4 and SHFM5 show autosomal dominant, SHFM6 autosomal recessive and SHFM2 X-linked pattern of inheritance. In this study a large consanguineous Pakistani family, with autosomal recessive SHFM, appeared in the last two generations, was investigated. In total 15 individuals including 9 males and 6 females were affected with the syndrome. Affected members of the family exhibited SHFM phenotype with involvement of hands and feet. Most of the affected members showed syndactyly/polydactyly in hands and feet, dysplastic hand, aplasia of radial ray of hand and cleft foot. Investigating linkage to known autosomal SHFM loci mapped the family to SHFM6 locus on chromosome 12p11.1-q13.13. Mutation screening of the gene WNT10B revealed a novel sequence variant (c.986C>G, p.Thr329Arg) in all affected individuals who were studied. This is the third mutation reported in gene WNT10B causing autosomal recessive SHFM syndrome.

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

Split-Hand/Foot Malformation (SHFM) is a complex limb malformation affecting the central rays of the autopod. We studied a large consanguineous kindred afflicted with autosomal recessive SHFM. Twelve affected members had central feet reductions with or without hand involvement while the remaining one had the mildest phenotype and atypical SHFM. We identified by homozygosity mapping a novel SHFM locus at 12q13.11-q13 with a maximum multipoint lod score of 5.47 and by subsequent candidate gene approach a homozygous missense WNT10b mutation (p.R332W) in all affected individuals but the atypical case plus in an asymptomatic female. We propose that either a second locus contributes to the manifestation of SHFM phenotype or a suppressor locus prevented trait manifestation in the non-penetrant female. We also investigated linkage to the five known SHFM loci. Four of the loci were excluded, while in TP63 [tumor protein p63 (SHFM4)], the only known gene responsible for SHFM, we detected in most affected subjects a rare insertion variant (rs34201045) at the alternate promoter used for transcription of the N-terminal-truncated p63 isotype. This is the first reported WNT10b mutation on the pathogenesis of limb development and recessive mutation in SHFM.

Clinical features and teratogenic mechanisms of congenital absence of digits

To have a better understanding of classification of congenital hand anomalies, clinical features and teratogenic mechanisms of congenital absence of digits including ulnar and radial deficiencies, cleft hand, symbrachydactyly and constriction band were reviewed. There seemed to be four different teratogenic mechanisms of congenital absence of digits. Ulnar and radial deficiencies have the same clinical features and the cause of these deficiencies is closely related to a deficit of mesenchymal cells in the limb-bud due to impairment before the formation of the limb-bud. Cleft hand, central polydactyly and osseous syndactyly were induced by the same treatment at the same developmental stage in rats. Roentgenograms of the clinical cases and skeletal changes of the anomalies in rats appear to demonstrate that cleft hand formation proceeds from osseous syndactylies and central polydactylies. The teratogenic mechanism of a cleft hand seemed to be failure of induction of digital rays in the hand plate. The sequence of anomalies from brachysyndactyly, or the atypical cleft hand, to the congenital amputation, can be regarded as equivalent to the category of transverse deficiency that is bony dysplasia of the hand. Congenital constriction ring syndrome appears after the formation of the digital rays.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

The expanding panorama of split hand foot malformation

The split hand/foot malformation is a developmental defect of the extremities resulting from errors in the initiation and maintenance of the apical ectodermal ridge. The phenotype is genetically heterogeneous, and it can be identified either as an isolated phenotypic manifestation or as a constituent component of a malformation syndrome. This overview describes the clinical phenotype, related animal models, and the evolving genetic heterogeneity of the malformation.

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

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

Frequency of genomic rearrangements involving the SHFM3 locus at chromosome 10q24 in syndromic and non-syndromic split-hand/foot malformation

Split-hand/foot malformation (SHFM), or ectrodactyly, is characterized by underdeveloped or absent central digital rays, clefts of the hands and feet, and variable syndactyly of the remaining digits. SHFM occurs as both an isolated finding and a component of many syndromes. SHFM is a heterogeneous condition caused by multiple loci, including SHFM1 (chromosome region 7q21-q22), SHFM2 (Xq26), SHFM3 (10q24), SHFM4 (3q27), and SHFM5 (2q31). Mutations in TP63 at the SHFM4 locus are known to underlie both syndromic and non-syndromic forms SHFM, but the causes of most non-syndromic SHFM cases remain unknown. The recent identification of submicroscopic tandem chromosome duplications affecting the SHFM3 locus in seven families with non-syndromic SHFM has helped to further unravel the molecular basis of this malformation. In our ongoing studies of the SHFM3 locus in 44 additional cases of syndromic and non-syndromic SHFM, we have identified similar chromosome rearrangements in eight additional cases (18%), using pulsed-field gel electrophoresis (PFGE). We have also utilized real-time quantitative PCR (qPCR) to test for the duplications. Seven of the cases with rearrangements were non-syndromic. The current findings bring the total of SHFM3-associated cases with chromosome rearrangements to 15, which constitute 29% (15 of 51) of the cases screened to date. This includes 9 of 9 cases (100%) with known linkage to the SHFM3 locus, all of whom have non-syndromic SHFM, and 6 of 42 additional cases (14%), four of whom have non-syndromic SHFM. Thus, SHFM3 abnormalities underlie a substantial proportion of SHFM cases and appear to be a more frequent cause of non-syndromic SHFM than mutations in TP63.