Familial isolated clubfoot is associated with recurrent chromosome 17q23.1q23.2 microduplications containing TBX4

Prenatal Counseling for Congenital Clubfoot

Congenital clubfoot is a common deformity that affects 1 in 1000 newborns and is frequently detected prenatally during routine prenatal care. A wide variety of detection methods and testing are used to identify clubfoot and other congenital anomalies in the fetus, including complete ultrasonography, amniocentesis, chorionic villus sampling, or cell-free DNA. Newer studies have associated certain genome sequences to clubfoot specifically. It is important for orthopaedic surgeons to understand the implications of the various tests to provide the appropriate prenatal counseling. Early prenatal detection of clubfoot can help parents prepare for the demands of caring for a child with clubfoot and build trust between families and clinicians, ultimately leading to better, patient-centered care for their children.

Key Concepts

(1)Prompt recognition and treatment of congenital clubfoot is imperative to facilitate optimal treatment.(2)Prenatal diagnosis usually consists of sonography of the plantar surface of both feet at 13-16 weeks' gestation.(3)Additional post-natal testing may be indicated in patients with neurological impairment or syndromic features.(4)Genetic markers such as PITX1, RBM10, HOX, and CASP (among others) have been identified as involved in clubfoot development and have implications on prenatal testing and counseling.

Exome sequencing of 1190 non-syndromic clubfoot cases reveals HOXD12 as a novel disease gene

BACKGROUND

Clubfoot, presenting as a rigid inward and downward turning of the foot, is one of the most common congenital musculoskeletal anomalies. The aetiology of clubfoot is poorly understood and variants in known clubfoot disease genes account for only a small portion of the heritability.

METHODS

Exome sequence data were generated from 1190 non-syndromic clubfoot cases and their family members from multiple ethnicities. Ultra-rare variant burden analysis was performed comparing 857 unrelated clubfoot cases with European ancestry with two independent ethnicity-matched control groups (1043 in-house and 56 885 gnomAD controls). Additional variants in prioritised genes were identified in a larger cohort, including probands with non-European ancestry. Segregation analysis was performed in multiplex families when available.

RESULTS

Rare variants in 29 genes were enriched in clubfoot cases, including PITX1 (a known clubfoot disease gene), HOXD12, COL12A1, COL9A3 and LMX1B. In addition, rare variants in posterior HOX genes (HOX9-13) were enriched overall in clubfoot cases. In total, variants in these genes were present in 8.4% (100/1190) of clubfoot cases with both European and non-European ancestry. Among these, 3 are de novo and 22 show variable penetrance, including 4 HOXD12 variants that segregate with clubfoot.

CONCLUSION

We report HOXD12 as a novel clubfoot disease gene and demonstrate a phenotypic expansion of known disease genes (myopathy gene COL12A1, Ehlers-Danlos syndrome gene COL9A3 and nail-patella syndrome gene LMX1B) to include isolated clubfoot.

Clinical Characteristics and Whole Exome Sequencing Analysis in Serbian Cases of Clubfoot Deformity-Single Center Study

BACKGROUND

Recognized as one of the most serious musculoskeletal deformities, occurring in 1-2 per 1000 newborns, 80% of clubfeet are idiopathic while 20% present with associated malformations. The etiopathogenesis of clubfoot is described as multifactorial, including both genetic and environmental risk factors. The aim of this study was to analyze possible genetic causes of isolated and syndromic clubfoot in Serbian children, as well as to correlate clinical and genetic characteristics that would provide insight into clubfoot etiopathogenesis and possibly contribute to global knowledge about clinical features of different genetically defined disorders.

METHODS

We evaluated 50 randomly selected, eligible children with clubfoot aged 3 to 16 years that were initially hospitalized and treated at University Children's Hospital between November 2006 and November 2022. The tested parameters were gender, age, dominant foot, affected foot, degree of deformity, treatment, neuromuscular disorders, positive family history, and maternal smoking. According to the presence of defined genetic mutation/s by whole exome sequencing (WES), patients were separated into two groups: positive (with genetic mutation/s) and negative (without genetic mutation/s).

RESULTS

Seven patients were found to be positive, i.e., with genetic mutation/s. A statistically significant difference between categorical variables was found for families with a history of clubfoot, where more than half (57.14%) of patients with confirmed genetic mutation/s also had a family history of genetic mutation/s (p = 0.023).

CONCLUSIONS

The results from this study further expand the genetic epidemiology of clubfoot. This study contributes to the establishment of genetic diagnostic strategies in pediatric patients with this condition, which can lead to more efficient genetic diagnosis.

COL1A1 regulates the apoptosis of embryonic stem cells by mediating the PITX1/TBX4 signaling

PURPOSE

The purpose of this study is to explore the regulatory function of COL1A1 against the apoptosis of embryonic stem cells (ESCs) and the potential function in congenital talipes equinovarus (CTEV).

METHODS

Muscle tissues were collected from 20 children with CTEV and 20 children without CTEV, followed by detecting the expression of COL1A1 using the RT-PCR method. COL1A1 was knocked down in H1 and H9 human ESCs using the RNA interference technology, followed by determining the level of COL1A1, PITX1, TBX4, HOXD10, Fas, FasL, and Bax using the Western blotting assay.

RESULTS

COL1A1 was found markedly upregulated in muscle tissues of CTEV children. In H1 and H9 human ESCs, compared to the empty vector, COL1A1, PITX1, TBX4, HOXD10, Fas, FasL, and Bax were found notably downregulated after transfected with the siRNA targeting COL1A1.

CONCLUSION

COL1A1 induced the apoptosis of ESCs by mediating the PITX1/TBX4 signaling and might be a potential target for treating CTEV.

Incidence and prevalence of congenital clubfoot in Apulia: a regional model for future prospective national studies

BACKGROUND

Congenital clubfoot is a fairly common and severe congenital malformation, most often of idiopathic origin. A smaller percentage of cases is related to chromosomal abnormalities and genetic syndromes. It is estimated that 0.5/1000 newborns are affected worldwide, with a male to female ratio of 2:1 and greater distribution in developing countries (80%). The "European Surveillance of Congenital Anomalies (EUROCAT)" reported clubfoot prevalence in European newborns, but data regarding Italy are missing or poor. We aim to provide detailed data on clubfoot incidence according to the Apulian Regional Registry on Congenital Malformations and to report current knowledge on clubfoot genetic factors.

METHODS

We extrapolated data from the Regional Registry of Congenital Malformations to evaluate incidence and prevalence of congenital clubfoot in Apulia, Italy over a period of four years (2015-2018). We also performed a narrative review focusing on genetic mutations leading to congenital clubfoot.

RESULTS

Over the period from 2015 to 2018 in Apulia, Italy, 124,017 births were recorded and 209 cases of clubfoot were found, accounting for an incidence rate of 1.7/1,000 and a prevalence rate of 1.6/1,000. Six families of genes have been reported to have an etiopathogenetic role on congenital clubfoot.

CONCLUSIONS

Incidence and prevalence of congenital clubfoot in Apulia, Italy, are comparable with those reported in the other Italian regions but higher than those reported in previous studies from Europe. Genetic studies to better classify congenital clubfoot in either syndromic or isolated forms are desirable.

Molecular Function and Contribution of TBX4 in Development and Disease

Over the past decade, recognition of the profound impact of the TBX4 (T-box 4) gene, which encodes a member of the evolutionarily conserved family of T-box-containing transcription factors, on respiratory diseases has emerged. The developmental importance of TBX4 is emphasized by the association of TBX4 variants with congenital disorders involving respiratory and skeletal structures; however, the exact role of TBX4 in human development remains incompletely understood. Here, we discuss the developmental, tissue-specific, and pathological TBX4 functions identified through human and animal studies and review the published TBX4 variants resulting in variable disease phenotypes. We also outline future research directions to fill the gaps in our understanding of TBX4 function and of how TBX4 disruption affects development.

Whole exome sequencing improves genetic diagnosis of fetal clubfoot

OBJECTIVE

This retrospective study aimed to investigate the value of whole exome sequencing (WES) for clubfoot (CF) fetuses with or without other structural abnormalities and to further explore the genetic causes of fetal CF.

METHODS

this study included 83 singleton pregnancies diagnosed with fetal CF referred to our center between January 2016 and March 2022; cases were divided into two groups: isolated CF and non-isolated CF. After excluding cases with positive karyotyping and chromosomal microarray analysis results, WES was performed for the eligible fetuses and parents. Monogenic variants detected by WES and perinatal outcomes were recorded and evaluated at postnatal follow-up.

RESULTS

overall, clinically significant variations were identified in 12.0% (10/83) of fetuses, and the detection rate was significantly higher in the non-isolated than in the isolated CF group (8/36, 22.2% vs. 2/47, 4.3%, p = 0.031). We additionally detected eight (9.6%) fetuses harboring variants of unknown significance. We identified 11 clinically significant variations correlating with clinical phenotypes in nine genes from ten fetuses, with KLHL40 being the most frequent (n = 2). Furthermore, we observed a significant difference in termination and survival rates between isolated and non-isolated CF cases (27.6 vs. 77.8% and 59.6 vs. 19.4%, p < 0.001 for both).

CONCLUSION

our data indicate that WES has a high additional diagnostic yield for the molecular diagnosis of fetal CF, markedly enhancing existing prenatal diagnostic capabilities and expanding our understanding of intrauterine genetic disorders, thus assisting us to better interpret fetal phenotype in the future.

What Is the Exact Contribution of PITX1 and TBX4 Genes in Clubfoot Development? An Italian Study

Congenital clubfoot is a common pediatric malformation that affects approximately 0.1% of all births. 80% of the cases appear isolated, while 20% can be secondary or associated with complex syndromes. To date, two genes that appear to play an important role are PTIX1 and TBX4, but their actual impact is still unclear. Our study aimed to evaluate the prevalence of pathogenic variants in PITX1 and TBX4 in Italian patients with idiopathic clubfoot. PITX1 and TBX4 genes were analyzed by sequence and SNP array in 162 patients. We detected only four nucleotide variants in TBX4, predicted to be benign or likely benign. CNV analysis did not reveal duplications or deletions involving both genes and intragenic structural variants. Our data proved that the idiopathic form of congenital clubfoot was rarely associated with mutations and CNVs on PITX1 and TBX4. Although in some patients, the disease was caused by mutations in both genes; they were responsible for only a tiny minority of cases, at least in the Italian population. It was not excluded that other genes belonging to the same TBX4-PITX1 axis were involved, even if genetic complexity at the origin of clubfoot required the involvement of other factors.

Whole Exome Sequencing in Individuals with Idiopathic Clubfoot Reveals a Recurrent Filamin B (FLNB) Deletion

BACKGROUND

Clubfoot, a congenital deformity that presents as a rigid, inward turning of the foot, affects approximately 1 in 1000 infants and occurs as an isolated birth defect in 80% of patients. Despite its high level of heritability, few causative genes have been identified, and mutations in known genes are only responsible for a small portion of clubfoot heritability.

QUESTIONS/PURPOSES

(1) Are any rare gene variants enriched (that is, shared) in unrelated patients with isolated clubfoot? (2) Are there other rare variants in the identified gene (Filamin B) in these patients with clubfoot?

METHODS

Whole-exome sequence data were generated from a discovery cohort of 183 unrelated probands with clubfoot and 2492 controls. Variants were filtered with minor allele frequency < 0.02 to identify rare variants as well as small insertions and deletions (indels) resulting in missense variants, nonsense or premature truncation, or in-frame deletions. A candidate deletion was then genotyped in another cohort of 974 unrelated patients with clubfoot (a replication cohort). Other rare variants in the candidate gene were also investigated. A segregation analysis was performed in multigenerational families of individuals with clubfoot to see if the genotypes segregate with phenotypes. Single-variant association analysis was performed using the Fisher two-tailed exact test (exact p values are presented to give an indication of the magnitude of the association).

RESULTS

There were no recurrent variants in the known genes causing clubfoot in this study. A three-base pair in-frame codon deletion of Filamin B (FLNB) (p.E1792del, rs1470699812) was identified in 1.6% (3 of 183) of probands with clubfoot in the discovery cohort compared with 0% of controls (0 of 2492) (odds ratio infinity (inf) [95% CI 5.64 to inf]; p = 3.18 x 10-5) and 0.0016% of gnomAD controls (2 of 125,709) (OR 1.01 x 103 [95% CI 117.42 to 1.64 x 104]; p = 3.13 x 10-8). By screening a replication cohort (n = 974 patients), we found two probands with the identical FLNB deletion. In total, the deletion was identified in 0.43% (5 of 1157) of probands with clubfoot compared with 0% of controls and 0.0016% of gnomAD controls (OR 268.5 [95% CI 43.68 to 2.88 x 103]; p = 1.43 x 10-9). The recurrent FLNB p.E1792del variant segregated with clubfoot, with incomplete penetrance in two families. Affected individuals were more likely to be male and have bilateral clubfoot. Although most patients had isolated clubfoot, features consistent with Larsen syndrome, including upper extremity abnormalities such as elbow and thumb hypermobility and wide, flat thumbs, were noted in affected members of one family. We identified 19 additional rare FLNB missense variants located throughout the gene in patients with clubfoot. One of these missense variants, FLNB p.G2397D, exhibited incomplete penetrance in one family.

CONCLUSION

A recurrent FLNB E1792 deletion was identified in 0.43% of 1157 isolated patients with clubfoot. Given the absence of any recurrent variants in our discovery phase (n = 183) for any of the known genes causing clubfoot, our findings support that novel and rare missense variants in FLNB in patients with clubfoot, although rare, may be among the most commonly known genetic causes of clubfoot. Patients with FLNB variants often have isolated clubfoot, but they and their family members may be at an increased risk of having additional clinical features consistent with Larsen syndrome.

CLINICAL RELEVANCE

Identification of FLNB variants may be useful for determining clubfoot recurrence risk and comorbidities.

Exacerbation of mild lung disorders to lethal pulmonary hypoplasia by a noncoding hypomorphic SNV in a lung-specific enhancer in trans to the frameshifting TBX4 variant

Variants involving TBX4 are associated with a wide variety of disorders, including pulmonary arterial hypertension, ischiocoxopodopatellar syndrome (ICPPS)/small patella syndrome (SPS), lethal lung developmental disorders (LLDDs) in neonates, heart defects, and prenatally lethal posterior amelia with pelvic and pulmonary hypoplasia syndrome. The objective of our study was to elucidate the wide variable phenotypic expressivity and incomplete penetrance in a three-generation family with a truncating variant in TBX4. In addition to exome and genome sequencing analyses, a candidate noncoding regulatory single nucleotide variant (SNV) within the lung-specific TBX4 enhancer was functionally tested using an in vitro luciferase reporter assay. A heterozygous frameshift variant c.1112dup (p.Pro372Serfs*14) in TBX4 was identified in patients with mild interstitial lung disease (1), bronchiolitis obliterans (1), recurrent pneumothorax (1), ICPPS/SPS (1), LLDD (2), and in unaffected individuals (4). In two deceased neonates with LLDD, we identified a noncoding SNV rs62069651-C located in trans to the mutated TBX4 allele that reduced the TBX4 promoter activity by 63% in the reporter assay. Our findings provide a functional evidence for the recently reported model of complex compound inheritance in which both TBX4 coding and in trans noncoding hypomorphic variants in the lung-specific enhancer of TBX4 contribute to LLDD.

Muscle volume evaluation using 3DCT for congenital clubfoot

Background

In congenital clubfoot, the lower leg is very thin and the calf muscles are hypoplasic. However, there are few studies reporting real muscle volume.

Purpose

The purpose of this study is to assay the muscle volume in congenital clubfoot using 3DCT and to quantify the degree of the hypoplasia.

Material and methods

From January 2015 to December 2016, nine consecutive patients, seven male and two female, with unilateral congenital clubfeet were recruited for CT scans. Axial transverse sectional CT scans were acquired from the delineation of the fibular head to the tibial plafond. From the data, we rendered the entire muscle in 3D for muscle volume assay, and further segmented the posterior musculature for comparison between the normal and affected sides.

Results

The whole muscle volume on the normal side was 291.23 cm³ (181.23–593.49) and that on the affected side was 225.08 cm³ (120.71–429.08), for an affected side to normal side ratio of 0.79 (0.72–0.9), which was significantly smaller (p < .01). Posterior muscle volume on the normal side was 175.81 cm³ (103.72–376.32) and that on the affected side was 106.52 cm³ (58.3–188.39). The ratio of posterior muscle to whole muscle on the normal side was 0.62 (0.46–0.75), and that on the affected side was 0.48 (0.4–0.55), such that the affected side was significantly smaller (p < .01)

Conclusion

This study contributes quantitative data supporting the longstanding observations that the posterior calf muscles are significantly smaller on the affected side compared to the normal side in congenital clubfoot, and further underscores the importance of the extending the excursion of these muscles.

Genotype-phenotype correlation in clubfoot (talipes equinovarus)

Clubfoot (talipes equinovarus) is a congenital malformation affecting muscles, bones, connective tissue and vascular or neurological structures in limbs. It has a complex aetiology, both genetic and environmental. To date, the most important findings in clubfoot genetics involve PITX1 variants, which were linked to clubfoot phenotype in mice and humans. Additionally, copy number variations encompassing TBX4 or single nucleotide variants in HOXC11, the molecular targets of the PITX1 transcription factor, were linked to the clubfoot phenotype. In general, genes of cytoskeleton and muscle contractile apparatus, as well as components of the extracellular matrix and connective tissue, are frequently linked with clubfoot aetiology. Last but not least, an equally important element, that brings us closer to a better understanding of the clubfoot genotype/phenotype correlation, are studies on the two known animal models of clubfoot-the pma or EphA4 mice. This review will summarise the current state of knowledge of the molecular basis of this congenital malformation.

Congenital Abdominal Wall Defects: A Topic Review and a Case Report of a Lethal Polymalformation Syndrome with a Giant Abdominoschisis

Abdominal wall defects (AWDs) represent a wide spectrum of congenital anomalies which are characterized by a herniation of abdominal organs through a pathologic opening in the abdominal region. The author describes a 29-year-old pregnant woman who was prenatally found to have a living female fetus with a giant omphalocele and a spinal deformation in the lumbosacral region. An evisceration of the abdominal contents into the amnionic cavity was visible. Based on USG findings the limb-body wall complex was suggested. An amniocentesis was performed and a genetic testing identified a chromosome 17q23.1–q23.2 duplication. As the fetal anomaly was considered incompatible with life, a medical termination of the pregnancy was carried out. Postmortem examination of the fetus revealed a huge abdominoschisis with a complete evisceration of the liver, stomach, small and large intestines, spleen, and the right kidney. A severe left-sided scoliosis deformity of the spine with crooked trunk was evident. The gross findings shared the features of omphalocele and limb-body wall complex with no postnatal life expectancy. Most fetal AWDs have poor prognosis. The pathology of these conditions differ greatly and require specific prenatal evaluation and pregnancy management for each entity. Accurate assessment of AWDs will allow the identification of isolated forms with better clinical outcomes compared to associated multiple malformations with chromosomal anomalies or genetic syndromes.

Genetic association and characterization of FSTL5 in isolated clubfoot

Talipes equinovarus (clubfoot, TEV) is a congenital rotational foot deformity occurring in 1 per 1000 births with increased prevalence in males compared with females. The genetic etiology of isolated clubfoot (iTEV) remains unclear. Using a genome-wide association study, we identified a locus within FSTL5, encoding follistatin-like 5, significantly associated with iTEV. FSTL5 is an uncharacterized gene whose potential role in embryonic and postnatal development was previously unstudied. Utilizing multiple model systems, we found that Fstl5 was expressed during later stages of embryonic hindlimb development, and, in mice, expression was restricted to the condensing cartilage anlage destined to form the limb skeleton. In the postnatal growth plate, Fstl5 was specifically expressed in prehypertrophic chondrocytes. As Fstl5 knockout rats displayed no gross malformations, we engineered a conditional transgenic mouse line (Fstl5LSL) to overexpress Fstl5 in skeletal osteochondroprogenitors. We observed that hindlimbs were slightly shorter and that bone mineral density was reduced in adult male, but not female, Prrx1-cre;Fstl5LSL mice compared with control. No overt clubfoot-like deformity was observed in Prrx1-cre;Fstl5LSL mice, suggesting FSTL5 may function in other cell types to contribute to iTEV pathogenesis. Interrogating published mouse embryonic single-cell expression data showed that Fstl5 was expressed in cell lineage subclusters whose transcriptomes were associated with neural system development. Moreover, our results suggest that lineage-specific expression of the Fstl genes correlates with their divergent roles as modulators of transforming growth factor beta and bone morphogenetic protein signaling. Results from this study associate FSTL5 with iTEV and suggest a potential sexually dimorphic role for Fstl5 in vivo.

Rare and de novo duplications containing SHOX in clubfoot

Introduction

Congenital clubfoot is a common birth defect that affects at least 0.1% of all births. Nearly 25% cases are familial and the remaining are sporadic in inheritance. Copy number variants (CNVs) involving transcriptional regulators of limb development, including PITX1 and TBX4, have previously been shown to cause familial clubfoot, but much of the heritability remains unexplained.

Methods

Exome sequence data from 816 unrelated clubfoot cases and 2645 in-house controls were analysed using coverage data to identify rare CNVs. The precise size and location of duplications were then determined using high-density Affymetrix Cytoscan chromosomal microarray (CMA). Segregation in families and de novo status were determined using qantitative PCR.

Results

Chromosome Xp22.33 duplications involving SHOX were identified in 1.1% of cases (9/816) compared with 0.07% of in-house controls (2/2645) (p=7.98×10⁻⁵, OR=14.57) and 0.27% (38/13592) of Atherosclerosis Risk in Communities/the Wellcome Trust Case Control Consortium 2 controls (p=0.001, OR=3.97). CMA validation confirmed an overlapping 180.28 kb duplicated region that included SHOX exons as well as downstream non-coding regions. In four of six sporadic cases where DNA was available for unaffected parents, the duplication was de novo. The probability of four de novo mutations in SHOX by chance in a cohort of 450 sporadic clubfoot cases is 5.4×10^–10.

Conclusions

Microduplications of the pseudoautosomal chromosome Xp22.33 region (PAR1) containing SHOX and downstream enhancer elements occur in ~1% of patients with clubfoot. SHOX and regulatory regions have previously been implicated in skeletal dysplasia as well as idiopathic short stature, but have not yet been reported in clubfoot. SHOX duplications likely contribute to clubfoot pathogenesis by altering early limb development.

Prenatal clubfoot increases the risk for clinically significant chromosomal microarray results - Analysis of 269 singleton pregnancies

OBJECTIVE

To examine the detection rate of clinically significant chromosomal microarray analysis (CMA) results in singleton pregnancies with clubfoot.

METHODS

Data from all CMA tests in singleton pregnancies with sonographic diagnosis of clubfoot (talipes equinovarus) performed between January 2013 and September 2017 were retrospectively obtained from the Israeli Ministry of Health computerized database. The rates of clinically significant CMA results in fetuses with clubfoot were compared to the general population risk, based on a local cohort of 5541 pregnancies with no major sonographic anomalies.

RESULTS

Of the 5750 CMA tests, a total of 269 (4.7%) were performed due to demonstration of fetal clubfoot. Of the 229 cases with isolated deformity, nine (3.9%) clinically significant CMA results were detected. This detection rate is significantly increased compared to the control population (RR 2.7 (95% CI 1.4-5.0)). In the 40 pregnancies with non-isolated clubfoot, seven (17.5%) clinically significant CMA results were detected, a significantly higher frequency compared to the control population and to isolated clubfoot cases.

DISCUSSION

Sonographic diagnosis of clubfoot, whether isolated or associated with additional sonographic defects, increases the risk for abnormal CMA findings. Thus, CMA analysis, in conjunction with thorough sonographic anatomic survey, should be recommended in such pregnancies.

Whole‑exome sequencing study identifies two novel rare variations associated with congenital talipes equinovarus

Congenital talipes equinovarus (CTEV) is a common birth defect with an unclear genetic pathogenesis that results from both genetic and environmental factors. The present study aimed to identify novel variants in patients with CTEV using whole‑exome sequencing (WES) and to investigate the genetic factors responsible for the development of CTEV.A cohort of nine neonates/infants with suspected CTEV was recruited. Subsequently, sequential tests, including chromosome karyotyping and WES, were performed for each of the participants. Familial validation was performed using Sanger sequencing and low‑coverage copy‑number variation (CNV) sequencing. A novel CNV containing the mediator complex subunit 13L gene at 12q24.21‑q24.23 was detected by WES and further investigated by CNVseq. Additionally, a novel de novo missense variation, transforming growth factor‑β receptor 2: c.1280T>C, was identified by WES and further investigated by Sanger sequencing. The two identified variations were hypothesized to be causative genetic factors for the development of CTEV in the two cases the variations were identified in. In the present study, two pathogenic variations (one CNV and one single‑base variation) were detected in two Chinese families with CTEV. The results of the present study may aid in investigating the molecular basis of CTEV; however, further investigation is required.

A newly recognized multiple malformation syndrome with caudal regression associated with a biallelic c.402G>A variant in TBX4

The T-box4 (TBX4) gene (OMIM *601719) belongs to the T-box family of transcription regulators that share a conserved homology domain and are expressed at specific sites during various stages of embryonic development. Tbx4 has been found to be a crucial transcriptional regulator in embryonic hindlimb development in animal models. Monoallelic variants in the TBX4 gene are reported to be associated with skeletal defects of the pelvis and lower limbs. We report here a fetus with a novel multiple malformation syndrome associated with sacrococcygeal agenesis, bilateral lower limb aplasia, hypoplastic left heart, bilateral lung hypoplasia, hydroureteronephrosis, and nonimmune fetal hydrops, found to have a homozygous nonsense variant in the TBX4 gene. We propose that biallelic variants in the TBX4 gene are associated with a severe syndromic phenotype of sacrococcygeal agenesis and lower limb reduction defects.

The genetics of isolated and syndromic clubfoot

PURPOSE

Congenital clubfoot is a serious birth defect that affects nearly 0.1% of all births. Though there is strong evidence for a genetic basis of isolated clubfoot, aside from a handful of associations, much of the heritability remains unexplained.

METHODS

By systematically examining the genes involved in syndromic clubfoot, we may find new candidate genes and pathways to investigate in isolated clubfoot.

RESULTS

In addition to the expected enrichment of extracellular matrix and transforming growth factor beta (TGF-β) signalling genes, we find many genes involved in syndromic clubfoot encode peroxisomal matrix proteins, as well as enzymes necessary for sulfation of proteoglycans, an important part of connective tissue. Further, the association of Filamin B with isolated clubfoot as well as syndromic clubfoot is an encouraging finding.

CONCLUSION

We should examine these categories for enrichment in isolated clubfoot patients to increase our understanding of the underlying biology and pathophysiology of this deformity. Understanding the spectrum of syndromes that have clubfoot as a feature enables a better understanding of the underlying pathophysiology of the disorder and directs future genetic screening efforts toward certain genes and genetic pathways.

LEVEL OF EVIDENCE

V.

Abnormal expression of TBX4 during anorectal development in rat embryos with ethylenethiourea-induced anorectal malformations

BACKGROUND

To assess the expression of T-box transcription factor 4 (TBX4) during the anorectal development in normal and ethylenethiourea (ETU)-induced anorectal malformations (ARM) rat embryos.

METHODS

Anorectal malformations was induced by ETU on the 10th gestational day (E10) in rat embryos. Spatio-temporal expression of TBX4 was evaluated in normal (n = 490) and ETU-induced ARM rat embryos (n = 455) from E13 to E16 by immunohistochemical staining, Western blot analysis and real-time RT-PCR.

RESULTS

In the normal embryos, immunohistochemical staining revealed that TBX4 expression was detected in the epithelium of hindgut and urorectal septum (URS) on E13. TBX4-immunopositive cells were increased significantly in the epithelium of hindgut and URS, the future anal orifice part of cloacal membrane on E14. On E15, abundant stained cells were observed in the rectum, URS and dorsal cloacal membrane and the expression of positive cells reached its peak. On E16, only sporadic positive cells were distributed in the epithelium of the distal rectum. In the ARM embryos, the hindgut/rectum, URS and dorsal cloacal membrane were faint for TBX4 immunohistochemical staining. In the normal group, TBX4 protein and mRNA expression showed time-dependent changes in the hindgut/rectum from E13 to E16 on Western blot and real-time RT-PCR. On E13 and E15, the expression level of TBX4 mRNA in the ARM group was significantly lower than that in the normal group (P < 0.05). On E15, the expression level of TBX4 protein in the ARM group was significantly lower than that in the normal group (P < 0.05).

CONCLUSIONS

The expression of TBX4 was downregulated in ETU-induced ARM embryos, which may play important roles in the pathogenesis of anorectal development.

Neonatal Lung Disease Associated with TBX4 Mutations

Variable lung disease was documented in 2 infants with heterozygous TBX4 mutations; their clinical presentations, pathology, and outcomes were distinct. These findings demonstrate that TBX4 gene mutations are associated with neonatal respiratory failure and highlight the wide spectrum of clinicopathological outcomes that have implications for patient diagnosis and management.

Epilepsy phenotype in patients with Xp22.31 microduplication

The clinical significance of Xp22.31 microduplication is still unclear. We describe a family in which a mother and two children have Xp22.31 microduplication associated with different forms of epilepsy and epileptiform EEG abnormalities. The proband had benign epilepsy with centrotemporal spikes with dysgraphia and dyscalculia (IQ 72), the sister had juvenile myoclonic epilepsy, and both had bilateral talipes anomalies. The mother, who was the carrier of the microduplication, was asymptomatic. The asymptomatic father did not possess the microduplication. These data contribute to delineate the phenotype associated with Xp22.31 microduplication and suggest a potential pathogenic role for an epilepsy phenotype.

•

Developmental disorders are commonly associated with Xp22.31 microduplication.

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Seizures may occur but specific epileptic syndromes are rare.

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Xp22.31 microduplication may have an additive role in epilepsy phenotype expression.

The etiology of idiopathic congenital talipes equinovarus: a systematic review

BACKGROUND

Also known as clubfoot, idiopathic congenital talipes equinovarus (ICTEV) is the most common pediatric deformity and occurs in 1 in every 1000 live births. Even though it has been widely researched, the etiology of ICTEV remains poorly understood and is often described as being based on a multifactorial genesis. Genetic and environmental factors seem to have a major role in the development of this disease. Thus, the aim of this review is to analyze the available literature to document the current evidence on ICTEV etiology.

METHODS

The literature on ICTEV etiology was systematically reviewed using the following inclusion criteria: studies of any level of evidence, reporting clinical or preclinical results, published in the last 20 years (1998-2018), and dealing with the etiology of ICTEV.

RESULTS

A total of 48 articles were included. ICTEV etiology is still controversial. Several hypotheses have been researched, but none of them are decisive. Emerging evidence suggests a role of several pathways and gene families associated with limb development (HOX family; PITX1-TBX4), the apoptotic pathway (caspases), and muscle contractile protein (troponin and tropomyosin), but a major candidate gene has still not been identified. Strong recent evidence emerging from twin studies confirmed major roles of genetics and the environment in the disease pathogenesis.

CONCLUSIONS

The available literature on the etiology of ICTEV presents major limitations in terms of great heterogeneity and a lack of high-profile studies. Although many studies focus on the genetic background of the disease, there is lack of consensus on one or multiple targets. Genetics and smoking seem to be strongly associated with ICTEV etiology, but more studies are needed to understand the complex and multifactorial genesis of this common congenital lower-limb disease.

The developmental and genetic basis of 'clubfoot' in the peroneal muscular atrophy mutant mouse

Genetic factors underlying the human limb abnormality congenital talipes equinovarus ('clubfoot') remain incompletely understood. The spontaneous autosomal recessive mouse 'peroneal muscular atrophy' mutant (PMA) is a faithful morphological model of human clubfoot. In PMA mice, the dorsal (peroneal) branches of the sciatic nerves are absent. In this study, the primary developmental defect was identified as a reduced growth of sciatic nerve lateral motor column (LMC) neurons leading to failure to project to dorsal (peroneal) lower limb muscle blocks. The pma mutation was mapped and a candidate gene encoding LIM-domain kinase 1 (Limk1) identified, which is upregulated in mutant lateral LMC motor neurons. Genetic and molecular analyses showed that the mutation acts in the EphA4-Limk1-Cfl1/cofilin-actin pathway to modulate growth cone extension/collapse. In the chicken, both experimental upregulation of Limk1 by electroporation and pharmacological inhibition of actin turnover led to defects in hindlimb spinal motor neuron growth and pathfinding, and mimicked the clubfoot phenotype. The data support a neuromuscular aetiology for clubfoot and provide a mechanistic framework to understand clubfoot in humans.

17q23.2q23.3 de novo duplication in association with speech and language disorder, learning difficulties, incoordination, motor skill impairment, and behavioral disturbances: a case report

Background

Chromosomal rearrangements involving 17q23 have been described rarely. Deletions at 17q23.1q23.2 have been reported in individuals with developmental delay and growth retardation, whereas duplications at 17q23.1q23.2 appear to segregate with clubfoot. Dosage alterations in the TBX2 and TBX4 genes, located in 17q23.2, have been proposed to be responsible for the phenotypes observed in individuals with 17q23.1q23.2 deletions and duplications. In this report, we present the clinical phenotype of a child with a previously unreported de novo duplication at 17q23.2q23.3 located distal to the TBX2 and TBX4 region.

Case presentation

We report a 7.5-year-old boy with speech and language disorder, learning difficulties, incoordination, fine motor skill impairment, infrequent seizures with abnormal EEG, and behavior disturbances (mild self-inflicted injuries, hyperactivity-inattention, and stereotyped hand movements). Chromosomal microarray revealed a 2-Mb duplication of chromosome 17q23.2q23.3. Both parents did not have the duplication indicating that this duplication is de novo in the child.

Conclusions

The duplicated region encompasses 16 genes. It is possible that increased dosage of one or more genes in this region is responsible for the observed phenotype. The TANC2 gene is one of the genes in the duplicated region.It encodes a member of the TANC (tetratricopeptide repeat, ankyrin repeat and coiled-coil containing) family which includes TANC1 and TANC2. These proteins are highly expressed in brain and play major roles in synapsis regulation. Hence, it is suggestive that TANC2 is the likely candidate gene responsible for the observed phenotype as an increased TANC2 dosage can potentially alter synapsis, resulting in neuronal dysfunction and the neurobehavioral phenotype observed in this child with 17q23.2q23.3 duplication.

Genetics of clubfoot; recent progress and future perspectives

Clubfoot or talipes equinovarus (TEV) is an inborn three-dimensional deformity of leg, ankle and foot. It results from structural defects of several tissues of foot and lower leg leading to abnormal positioning of foot and ankle joints. TEV can lead to long-lasting functional disability, malformation and discomfort if left untreated. Substantial progress has been achieved in the management and diagnosis of limb defects; however, not much is known about the molecular players and signalling pathways underlying TEV disorder. The homeostasis and development of the limb depends on the complex interactions between the lateral plate mesoderm cells and outer ectoderm. These complex interactions include HOX signalling and PITX1-TBX4 pathways. The susceptibility to develop TEV is determined by a number of environmental and genetic factors, although the nature and level of interplay between them remains unclear. Familial occurrence and inter and intra phenotypic variability of TEV is well documented. Variants in genes that code for contractile proteins of skeletal myofibers might play a role in the aetiology of TEV but, to date, no strong candidate genes conferring increased risk have emerged, although variants in TBX4, PITX1, HOXA, HOXC and HOXD clusters genes, NAT2 and others have been shown to be associated with TEV. The mechanisms by which variants in these genes confer risk and the nature of the physical and genetic interaction between them remains to be determined. Elucidation of genetic players and cellular pathways underlying TEV will certainly increase our understanding of the pathophysiology of this deformity.

The 2017 ABJS Nicolas Andry Award: Advancing Personalized Medicine for Clubfoot Through Translational Research

BACKGROUND

Clubfoot is one of the most common pediatric orthopaedic disorders. While the Ponseti method has revolutionized clubfoot treatment, it is not effective for all patients. When the Ponseti method does not correct the foot, patients are at risk for lifelong disability and may require more-extensive surgery.

QUESTIONS/PURPOSES

(1) What genetic and morphologic abnormalities contribute to the development of clubfoot? (2) How can this information be used to devise personalized treatment paradigms for patients with clubfoot?

METHODS

Human gene sequencing, molecular genetic engineering of mouse models of clubfoot, MRI of clubfoot, and development of new treatment methods all have been used by our group to understand the biological basis and improve therapy for this group of disorders.

RESULTS

We gained new insight into clubfoot pathogenesis from our discovery that mutations in the PITX1-TBX4-HOXC transcriptional pathway cause familial clubfoot and vertical talus in a small number of families, with the unique lower limb expression of these genes providing an explanation for the lack of upper extremity involvement in these disorders. MRI studies revealed corresponding morphologic abnormalities, including hypomorphic muscle, bone, and vasculature, that are not only associated with these gene mutations, but also are biomarkers for treatment-resistant clubfoot.

CONCLUSIONS

Based on an understanding of the underlying biology, we improved treatment methods for neglected and syndromic clubfoot, developed new treatment for congenital vertical talus based on the principles of the Ponseti method, and designed a new dynamic clubfoot brace to improve strength and compliance.

Design and descriptive data of the randomized Clubfoot Foot Abduction Brace Length of Treatment Study (FAB24)

The aim of this study was to describe the design and baseline characteristics of participants enrolled in the prospective randomized-controlled Clubfoot Foot Abduction Brace Length of Treatment Study (FAB24). Foot abduction bracing is currently the standard of care for preventing clubfoot relapse. Current recommendations include full-time bracing for the first 3 months and then 8-12 h a day for 4 years; however, the optimal length of bracing is not known. The FAB24 trial is a clinical randomized study to determine the effectiveness of 2- versus 4-year foot abduction bracing. Participant enrollment for FAB24 was conducted at eight sites in North America and included enrollment and randomization of 139 participants with isolated clubfoot. This clinical trial will generate evidence-based data that will inform and improve patient care.

T-Box Genes in Human Development and Disease

T-box genes are important development regulators in vertebrates with specific patterns of expression and precise roles during embryogenesis. They encode transcription factors that regulate gene transcription, often in the early stages of development. The hallmark of this family of proteins is the presence of a conserved DNA binding motif, the "T-domain." Mutations in T-box genes can cause developmental disorders in humans, mostly due to functional deficiency of the relevant proteins. Recent studies have also highlighted the role of some T-box genes in cancer and in cardiomyopathy, extending their role in human disease. In this review, we focus on ten T-box genes with a special emphasis on their roles in human disease.

A systematic review of association studies of common variants associated with idiopathic congenital talipes equinovarus (ICTEV) in humans in the past 30 years

The genetic cause of idiopathic congenital talipes equinovarus (ICTEV) is largely unknown. We performed a systematic review to describe the findings from 21 studies that have examined the genetic variants related to ICTEV, and to evaluate the quality of reporting. We found that ICTEV was positively associated with Hox family genes, collagen family genes, GLI3, N-acetylation genes, T-box family genes, apoptotic pathway genes, and muscle contractile family genes. Negative and controversial results were also discussed, and several genes associated with ICTEV were identified. Due to the limitation of the included studies, rare coding variants should be further investigated, sample size should be enlarged, and candidate genes should be replicated in larger ICTEV populations. Epigenetic study, pathways, chromosome capture, and detailed gene-environment interaction will also allow further elucidation of factors involved in ICTEV pathogenesis and may shed light on diagnosis and timely and accurate interventions.

Genetic basis of hindlimb loss in a naturally occurring vertebrate model

Here we genetically characterise pelvic finless, a naturally occurring model of hindlimb loss in zebrafish that lacks pelvic fin structures, which are homologous to tetrapod hindlimbs, but displays no other abnormalities. Using a hybrid positional cloning and next generation sequencing approach, we identified mutations in the nuclear localisation signal (NLS) of T-box transcription factor 4 (Tbx4) that impair nuclear localisation of the protein, resulting in altered gene expression patterns during pelvic fin development and the failure of pelvic fin development. Using a TALEN-induced tbx4 knockout allele we confirm that mutations within the Tbx4 NLS (A78V; G79A) are sufficient to disrupt pelvic fin development. By combining histological, genetic, and cellular approaches we show that the hindlimb initiation gene tbx4 has an evolutionarily conserved, essential role in pelvic fin development. In addition, our novel viable model of hindlimb deficiency is likely to facilitate the elucidation of the detailed molecular mechanisms through which Tbx4 functions during pelvic fin and hindlimb development.

Summary: Here we genetically characterise mutations in tbx4 which underlie pelvic finless, a naturally occurring model of hindlimb loss in zebrafish that lacks pelvic fin structures.

Deletions of 5' HOXC genes are associated with lower extremity malformations, including clubfoot and vertical talus

BACKGROUND

Deletions of the HOXC gene cluster result in variable phenotypes in mice, but have been rarely described in humans.

OBJECTIVE

To report chromosome 12q13.13 microdeletions ranging from 13 to 175 kb and involving the 5' HOXC genes in four families, segregating congenital lower limb malformations, including clubfoot, vertical talus and hip dysplasia.

METHODS

Probands (N=253) with clubfoot or vertical talus were screened for point mutations and copy number variants using multiplexed direct genomic selection, a pooled BAC targeted capture approach. SNP genotyping included 1178 probands with clubfoot or vertical talus and 1775 controls.

RESULTS

The microdeletions share a minimal non-coding region overlap upstream of HOXC13, with variable phenotypes depending upon HOXC13, HOXC12 or the HOTAIR lncRNA inclusion. SNP analysis revealed HOXC11 p.Ser191Phe segregating with clubfoot in a small family and enrichment of HOXC12 p.Asn176Lys in patients with clubfoot or vertical talus (rs189468720, p=0.0057, OR=3.8). Defects in limb morphogenesis include shortened and overlapping toes, as well as peroneus muscle hypoplasia. Finally, HOXC and HOXD gene expression is reduced in fibroblasts from a patient with a 5' HOXC deletion, consistent with previous studies demonstrating that dosage of lncRNAs alters expression of HOXD genes in trans.

CONCLUSIONS

Because HOXD10 has been implicated in the aetiology of congenital vertical talus, variation in its expression may contribute to the lower limb phenotypes occurring with 5' HOXC microdeletions. Identification of 5' HOXC microdeletions highlights the importance of transcriptional regulators in the aetiology of severe lower limb malformations and will improve their diagnosis and management.

Use of Targeted Exome Sequencing for Molecular Diagnosis of Skeletal Disorders

Genetic disorders of the skeleton comprise a large group of more than 450 clinically distinct and genetically heterogeneous diseases associated with mutations in more than 300 genes. Achieving a definitive diagnosis is complicated due to the genetic heterogeneity of these disorders, their individual rarity and their diverse radiographic presentations. We used targeted exome sequencing and designed a 1.4Mb panel for simultaneous testing of more than 4,800 exons in 309 genes involved in skeletal disorders. DNA from 69 individuals from 66 families with a known or suspected clinical diagnosis of a skeletal disorder was analyzed. Of 36 cases with a specific clinical hypothesis with a known genetic basis, mutations were identified for eight cases (22%). Of 20 cases with a suspected skeletal disorder but without a specific diagnosis, four causative mutations were identified. Also included were 11 cases with a specific skeletal disorder but for which there was at the time no known associated gene. For these cases, one mutation was identified in a known skeletal disease genes, and re-evaluation of the clinical phenotype in this case changed the diagnoses from osteodysplasia syndrome to Apert syndrome. These results suggest that the NGS panel provides a fast, accurate and cost-effective molecular diagnostic tool for identifying mutations in a highly genetically heterogeneous set of disorders such as genetic skeletal disorders. The data also stress the importance of a thorough clinical evaluation before DNA sequencing. The strategy should be applicable to other groups of disorders in which the molecular basis is largely known.

Proteomic analysis of the extracellular matrix in idiopathic pes equinovarus

Idiopathic pes equinovarus is a congenital deformity of the foot and lower leg defined as a fixation of the foot in adduction, supination, and varus. Although the pathogenesis of clubfoot remains unclear, it has been suggested that fibroblasts and growth factors are involved. To directly analyze the protein composition of the extracellular matrix in contracted tissue of patients with clubfoot. A total of 13 infants with idiopathic clubfoot treated with the Ponseti method were included in the present study. Tissue samples were obtained from patients undergoing surgery for relapsed clubfeet. Contracted tissues were obtained from the medial aspect of the talonavicular joint. Protein was extracted after digestion and delipidation using zip-tip C18. Individual collagenous fractions were detected using a chemiluminescent assay. Amino acid analysis of tissue samples revealed a predominance of collagens, namely collagen types I, III, and VI. The high content of glycine and h-proline suggests a predominance of collagens I and III. A total of 19 extracellular matrix proteins were identified. The major result of the present study was the observation that the extracellular matrix in clubfoot is composed of an additional 16 proteins, including collagens V, VI, and XII, as well as the previously described collagen types I and III and transforming growth factor β. The characterization of the general protein composition of the extracellular matrix in various regions of clubfoot may help in understanding the pathogenesis of this anomaly and, thus, contribute to the development of more efficacious therapeutic approaches.

Are copy number variants associated with adolescent idiopathic scoliosis?

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is a complex genetic disorder that causes spinal deformity in approximately 3% of the population. Candidate gene, linkage, and genome-wide association studies have sought to identify genetic variation that predisposes individuals to AIS, but the genetic basis remains unclear. Copy number variants are associated with several isolated skeletal phenotypes, but their role in AIS, to our knowledge, has not been assessed.

QUESTIONS/PURPOSES

We determined the frequency of recurrent copy number rearrangements, chromosome aneuploidy, and rare copy number variants in patients with AIS.

METHODS

Between January 2010 and August 2014, we evaluated 150 patients with isolated AIS and spinal curvatures measuring 10° or greater, and 148 agreed to participate. Genomic copy number analysis was performed on patients and 1079 control subjects using the Affymetrix(®) Genome-wide Human SNP Array 6.0. After removing poor quality samples, 143 (97%) patients with AIS were evaluated for copy number variation.

RESULTS

We identified a duplication of chromosome 1q21.1 in 2.1% (N = 3/143) of patients with AIS, which was enriched compared with 0.09% (N = 1/1079) of control subjects (p = 0.0057) and 0.07% (N = 6/8329) of a large published control cohort (p = 0.0004). Other notable findings include trisomy X, which was identified in 1.8% (N = 2/114) of female patients with AIS, and rearrangements of chromosome 15q11.2 and 16p11.2 that previously have been associated with spinal phenotypes. Finally, we report rare copy number variants that will be useful in future studies investigating candidate genes for AIS.

CONCLUSIONS

Copy number variation and chromosomal aneuploidy may contribute to the pathogenesis of adolescent idiopathic scoliosis.

CLINICAL RELEVANCE

Chromosomal microarray may reveal clinically useful abnormalities in some patients with AIS.

Soft-Tissue Abnormalities Associated with Treatment-Resistant and Treatment-Responsive Clubfoot: Findings of MRI Analysis

BACKGROUND

Clubfoot treatment commonly fails and often results in impaired quality of life. An understanding of the soft-tissue abnormalities associated with both treatment-responsive and treatment-resistant clubfoot is important to improving the diagnosis of clubfoot, the prognosis for patients, and treatment.

METHODS

Twenty patients with clubfoot treated with the Ponseti method were recruited for magnetic resonance imaging (MRI) of their lower extremities. Among these were seven patients (six unilateral cases) with treatment-responsive clubfoot and thirteen patients (five unilateral cases) with treatment-resistant clubfoot. Demographic information and physical examination findings were recorded. A descriptive analysis of the soft-tissue abnormalities was performed for both patient cohorts. For the patients with unilateral clubfoot, we calculated the percentage difference in cross-sectional area between the affected limb and the unaffected limb in terms of muscle, subcutaneous fat, intracompartment fat, and total area. With use of the Wilcoxon signed-rank test, we compared inter-leg differences in cross-sectional areas and the intracompartment adiposity index (IAI) between treatment-responsive and treatment-resistant groups. The IAI characterizes the cross-sectional area of fat within a muscle compartment.

RESULTS

Extensive soft-tissue abnormalities were more present in patients with treatment-resistant clubfoot than in patients with treatment-responsive clubfoot. Treatment-resistant clubfoot abnormalities included excess epimysial fat and intramuscular fat replacement as well as unique patterns of hypoplasia in specific muscle groups that were present within a subset of patients. Among the unilateral cases, treatment-resistant clubfoot was associated with a significantly greater difference in muscle area between the affected and unaffected limb (-47.8%) compared with treatment-responsive clubfoot (-26.6%) (p = 0.02), a significantly greater difference in intracompartment fat area between the affected and unaffected limb (402.6%) compared with treatment-responsive clubfoot (9%) (p = 0.01), and a corresponding higher inter-leg IAI ratio (8.7) compared with treatment-responsive clubfoot (1.5) (p = 0.01).

CONCLUSIONS

MRI demonstrated a range of soft-tissue abnormalities in patients, including unique patterns of specific muscle-compartment aplasia/hypoplasia that were present in patients with treatment-resistant clubfoot and not present in patients with treatment-responsive clubfoot. Correlations between MRI, physical examination, and treatment responsiveness may aid in the development of a prognostic classification system for clubfoot.

LEVEL OF EVIDENCE

Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The contralateral foot in children with unilateral clubfoot, is the unaffected side normal?

The unilateral unaffected clubfoot has previously been used as a control in longitudinal studies of clubfoot outcomes. However, we have observed that the unaffected clubfoot does not necessarily exhibit the same pedobarographic measurements as seen in normal control subjects. The purpose of this study was to evaluate whether the unaffected foot is indeed normal or if there are differences in the pedobarographic measurements of the unaffected foot compared to healthy normal controls.The Tekscan HR Mat™ was used to dynamically test the walking pattern of 103 subjects with unilateral clubfeet and compare the results to our previously published series of normal controls. Patients were divided into three groups: Group 1 (< 2 years), Group 2 (2-5 years) and Group 3 (>5 years). An unpaired t-test (p < 0.05) was used to compare percentage of stance at initiation of force, the percentage of stance at maximum force, the percentage of stance at termination of force, the maximum percentage force and the average force/time integral between a group of normal age matched controls and the unaffected foot in patients with unilateral clubfoot. Significant differences were identified between the unaffected side and normal controls for the pressure distribution, order of initial contact and foot contact time. These differences evolved and changed with age. The pedobarographic measurements of patients with clubfoot are not normal for the unaffected foot. As such the unaffected foot should not be referred to as normal, nor should it be used as a control.

Etiopathogenesis of equinovarus foot malformations

Congenital talipes equinovarus (CTEV) is the most common musculoskeletal birth defect affecting approximately 1/700-1/1000 of liveborns. Even though extensive epidemiological and genetic studies have been carried out to address its causes, the precise mechanisms leading to this common birth defect remain elusive. CTEV is a multifactorial disorder, hence the combination of genetic and environmental factors are known contributors to this developmental abnormality. So far a handful of genes involved in limb patterning like PITX1, HOXA, HOXD, TBX4, and RBM10, as well as genes involved in muscle contraction, have been identified as possible players. Among many environmental factors investigated, maternal smoking seems to hold the strongest consistent association with this disorder. This article will review and discuss some of the most common genetic and environmental factors associated with the etiopathogenesis of CTEV.

Multiplexed direct genomic selection (MDiGS): a pooled BAC capture approach for highly accurate CNV and SNP/INDEL detection

Despite declining sequencing costs, few methods are available for cost-effective single-nucleotide polymorphism (SNP), insertion/deletion (INDEL) and copy number variation (CNV) discovery in a single assay. Commercially available methods require a high investment to a specific region and are only cost-effective for large samples. Here, we introduce a novel, flexible approach for multiplexed targeted sequencing and CNV analysis of large genomic regions called multiplexed direct genomic selection (MDiGS). MDiGS combines biotinylated bacterial artificial chromosome (BAC) capture and multiplexed pooled capture for SNP/INDEL and CNV detection of 96 multiplexed samples on a single MiSeq run. MDiGS is advantageous over other methods for CNV detection because pooled sample capture and hybridization to large contiguous BAC baits reduces sample and probe hybridization variability inherent in other methods. We performed MDiGS capture for three chromosomal regions consisting of ∼550 kb of coding and non-coding sequence with DNA from 253 patients with congenital lower limb disorders. PITX1 nonsense and HOXC11 S191F missense mutations were identified that segregate in clubfoot families. Using a novel pooled-capture reference strategy, we identified recurrent chromosome chr17q23.1q23.2 duplications and small HOXC 5′ cluster deletions (51 kb and 12 kb). Given the current interest in coding and non-coding variants in human disease, MDiGS fulfills a niche for comprehensive and low-cost evaluation of CNVs, coding, and non-coding variants across candidate regions of interest.

Heritability of clubfoot: a twin study

INTRODUCTION

The aetiology of congenital clubfoot is unclear. Although studies on populations, families, and twins suggest a genetic component to the aetiology, other studies have identified environmental factors. The purpose of this study was to calculate heritability in order to determine to what extent genetic and/or environmental factors contribute to the aetiology of congenital clubfoot and to asses whether there was a change in the prevalence over time.

MATERIALS AND METHODS

The Odense based Danish Twin Registry is unique as it contains data on all the approximately 85,000 twin pairs born in Denmark over the last 140 years. All 46,418 twin individuals born from 1931 through 1982, who had earlier consented to contact, received a 17-page Omnibus questionnaire in the spring of 2002. Data were analysed with structural equation models to identify the best fitting aetiological model based on a balance of goodness-of-fit and parsimony and to estimate heritability.

RESULTS

We found an overall self-reported prevalence of congenital clubfoot of 0.0027 (95 % confidence interval 0.0022-0.0034). Fifty-five complete (both twins answered the question) twin pairs were identified representing 12 monozygotic, 22 same-sex dizygotic, 18 opposite-sex dizygotic, and 3 with unclassified zygosity. The model with only environmental factors (CE) was best fitting based on AIC, and the model with an additive genetic factor (ACE) came in second. Due to the small statistical power, we hypothesise that the model with both genetic and environmental effects (ACE) was the better model. Choosing the ACE-model we found a heritability of clubfoot of 30 %. Regression coefficient for age was -0.002 (-0.011 to 0.005), indicating that there has been no change in prevalence of clubfoot over the 50-year age span we examined.

DISCUSSION

We conclude that non-genetic factors must play a role, and a genetic factor might contribute, in the aetiology of congenital clubfoot.

Update on clubfoot

Congental talipes equinovarus, or clubfoot, remains one of the commonest congenital limb deformities. The genetics of this condition are not yet fully understood. It is increasingly being diagnosed on prenatal ultrasound with implications for prenatal counselling. With the widespread acceptance of the Ponseti method of clubfoot treatment major surgical interventions are needed much less frequently and long-term outcomes are improved.

TBX4 mutations (small patella syndrome) are associated with childhood-onset pulmonary arterial hypertension

Background

Childhood-onset pulmonary arterial hypertension (PAH) is rare and differs from adult-onset disease in clinical presentation, with often unexplained mental retardation and dysmorphic features (MR/DF). Mutations in the major PAH gene, BMPR2, were reported to cause PAH in only 10–16% of childhood-onset patients. We aimed to identify more genes associated with childhood-onset PAH.

Methods

We studied 20 consecutive cases with idiopathic or heritable PAH. In patients with accompanying MR/DF (n=6) array-comparative genomic hybridisation analysis was performed, with the aim of finding common deletion regions containing candidate genes for PAH. Three patients had overlapping deletions of 17q23.2. TBX2 and TBX4 were selected from this area as candidate genes and sequenced in all 20 children. After identifying TBX4 mutations in these children, we subsequently sequenced TBX4 in a cohort of 49 adults with PAH. Because TBX4 mutations are known to cause small patella syndrome (SPS), all patients with newly detected TBX4 mutations were screened for features of SPS. We also screened a third cohort of 23 patients with SPS for PAH.

Results

TBX4 mutations (n=3) or TBX4-containing deletions (n=3) were detected in 6 out of 20 children with PAH (30%). All living patients and two parents with TBX4 mutations appeared to have previously unrecognised SPS. In the adult PAH-cohort, one TBX4 mutation (2%) was detected. Screening in the cohort of (predominantly adult) SPS patients revealed no PAH.

Conclusions

These data indicate that TBX4 mutations are associated with childhood-onset PAH, but that the prevalence of PAH in adult TBX4 mutation carriers is low.

Copy number analysis of 413 isolated talipes equinovarus patients suggests role for transcriptional regulators of early limb development

Talipes equinovarus is one of the most common congenital musculoskeletal anomalies and has a worldwide incidence of 1 in 1000 births. A genetic predisposition to talipes equinovarus is evidenced by the high concordance rate in twin studies and the increased risk to first-degree relatives. Despite the frequency of isolated talipes equinovarus and the strong evidence of a genetic basis for the disorder, few causative genes have been identified. To identify rare and/or recurrent copy number variants, we performed a genome-wide screen for deletions and duplications in 413 isolated talipes equinovarus patients using the Affymetrix 6.0 array. Segregation analysis within families and gene expression in mouse E12.5 limb buds were used to determine the significance of copy number variants. We identified 74 rare, gene-containing copy number variants that were present in talipes equinovarus probands and not present in 759 controls or in the Database of Genomic Variants. The overall frequency of copy number variants was similar between talipes equinovarus patients compared with controls. Twelve rare copy number variants segregate with talipes equinovarus in multiplex pedigrees, and contain the developmentally expressed transcription factors and transcriptional regulators PITX1, TBX4, HOXC13, UTX, CHD (chromodomain protein)1, and RIPPLY2. Although our results do not support a major role for recurrent copy number variations in the etiology of isolated talipes equinovarus, they do suggest a role for genes involved in early embryonic patterning in some families that can now be tested with large-scale sequencing methods.

Studies of TBX4 and chromosome 17q23.1q23.2: an uncommon cause of nonsyndromic clubfoot

Clubfoot is a common birth defect characterized by inward posturing and rigid downward displacement of one or both feet. The etiology of syndromic forms of clubfoot is varied and the causes of isolated clubfoot are not well understood. A microduplication of 2.2 Mb on chromosome 17q23.1q23.2 which includes T-box 4 (TBX4), a hindlimb-specific gene, and 16 other genes was recently identified in 3 of 66 families reported as nonsyndromic clubfoot, but additional non-foot malformations place them in the syndromic clubfoot category. Our study assesses whether variation in or around TBX4 contributes to nonsyndromic clubfoot. To determine whether this microduplication was a common cause of nonsyndromic clubfoot, 605 probands (from 148 multiplex and 457 simplex families) with nonsyndromic clubfoot were evaluated by copy number and oligonucleotide array CGH testing modalities. Only one multiplex family (0.68%) that had 16 with clubfoot and 9 with other foot anomalies, had a 350 kb microduplication, which included the complete duplication of TBX4 and NACA2 and partial duplication of BRIP1. The microduplication was transmitted in an autosomal dominant pattern and all with the microduplication had a range of phenotypes from short wide feet and toes to bilateral clubfoot. Minimal evidence was found for an association between TBX4 and clubfoot and no pathogenic sequence variants were identified in the two known TBX4 hindlimb enhancer elements. Altogether, these results demonstrate that variation in and around the TBX4 gene and the 17q23.1q23.2 microduplication are not a frequent cause of this common orthopedic birth defect and narrows the 17q23.1q23.2 nonsyndromic clubfoot-associated region.