Table 1 Main findings of the included article

[12]

Kruse et al. (2008)

1093 individuals: 291 with clubfoot and 802 unaffected relatives

Polygenic threshold model with sex dimorphism

This study demonstrates the presence of the Carter effect in idiopathic clubfoot. A polygenic inheritance of clubfoot can explain this effect, with females requiring a greater genetic load to be affected.

[17]

Gurnett et al. (2008)

A five-generation family with asymmetric right-sided predominant idiopathic clubfoot

PITX1

A single missense mutation (c.388G → A) was identified in PITX1 through Genome-wide linkage analysis.

[18]

Poon (2009)

Primary cell culturefrom the medial aspect of the talonavicular joint and from the plantar surface of the calcaneocuboid joint (around 10 ft)

Beta-catenin

There was a more than twofold increase in the beta-catenin protein in the contracted tissues.

[19]

Pagnotta et al. (2011)

Three homozygous preterm triplets

Presence of Bilateral ICTEV

Such a presentation had not been previously described and supports a genetic etiology of congenital idiopathic talipes equinovarus deformity.

[20]

Sahin et al. (2013)

28 cases (infants with idiopathic CTEV) and 575 controls (healthy infants) were recruited

Case-control study

Significant risk factors for idiopathic CTEV were work status (employed), consanguineous marriage, sex (male), and gestational age (> 42 weeks).

[21]

Alvarado et al.(2013)

413 isolated talipes equinovarus patients

PITX1, TBX4, HOXC13, UTX, CHD1, and RIPPLY2

A genome-wide screening found 12 rare copy number variants segregated with talipes equinovarus in multiplex pedigrees, containing the developmentally expressed transcription factors and transcriptional regulators PITX1, TBX4, HOXC13, UTX, CHD (chromodomain protein)1, and RIPPLY2

[22]

Shyy et al. (2009)

CAND2 gene was sequenced in 256 clubfoot patients, and 75 control patients, while WNT7a was screened using 56 clubfoot patients and 50 control patients

CAND2 and WNT7

Polymorphism was found in each gene, but the single nucleotide change in CAND2 was a silent mutation that did not alter the amino acid product, and the single nucleotide change in WNT7a was in the upstream, non-coding or promoter region before the start codon.

[23]

Shyy et al. (2010)

24 bilateral congenital idiopathic clubfoot patients and 24 matched controls and screened an additional 76 patients in each discovered SNP

MYH 1, 2, 3, and 8

Many single-nucleotide polymorphisms were found; none proved to be significantly associated with the phenotype of congenital idiopathic clubfoot.

[24]

Herceg et al. (2006)

95 ft in 68 ICTEV patients yielded a total of 431 muscle specimens

Histological and histochemical muscle specimens analysis

This study does not support the theory that a neuromuscular abnormality may be significant in the etiology of idiopathic talipes equinovarus because of the absence of significant alteration.

[25]

Wang et al. (2008)

Rat embryo

HOXD13 – FHL1

The findings suggest that HOXD13 may regulate the expression of FHL1 in the development of ICTEV.

[26]

Ippolito et al. (2009)

MR of both legs was taken in three cohorts of patients with unilateral ICTEV: 8 untreated new-borns (age range 10 days to 2 weeks); 8 children who had been treated with the Ponseti method (age range 2–4 years); 8 adults whose deformity had been corrected (age range 19–23 years)

Muscular atrophy

The study shows that leg muscular atrophy is a primitive pathological component of CCF which is already present in the early stages of fetal CCF development.

[27]

Hecht et al. (2007)

56 multiplex ITEV families, 57 trios with a positive family history and 160 simplex trios with ITEV

NAT 1 and NAT 2

The result suggests that slow NAT2 acetylation may be a risk factor for ITEV.

[28]

Ošt’ádal et al. (2015)

13 relapsed ICTEV

Proteomic analysis of the extracellular matrix

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 beta.

[29]

Gurnett et al. (2009)

31 patients (five with familial vertical talus, 20 with familial clubfoot, and six with DA1

TNNT3, MYH3, TPM2

Although mutations in MYH3, TNNT3, and TPM2 are frequently associated with distal arthrogryposis syndromes, they were not present in patients with familial vertical talus or clubfoot.

[30]

Wang et al. (2013)

Abductor hallucis muscle samples were obtained from 15 ICTEV patients. Peripheral blood samples were obtained from 84 ICTEV patients

SOX 9

mRNA and protein expression levels of SOX9 were detected through real-time polymerase chain reaction and western blot analysis, respectively and were found to be significantly higher in ICTEV muscle samples compared with those in control samples

[31]

Cao et al. (2009)

Rat ICTEV model

HOXD13 – Gli3

Findings suggest that HoxD13 directly interacts with the promoter of Gli3. The increase of Gli3 expression in the ICTEV model animal might result from the low expression of HoxD13.

[32]

Engell et al. (2014)

46,418 twin individuals

Twin study

The study found an overall self-reported prevalence of congenital clubfoot of 0.0027. They concluded that non-genetic factors must play a role, and a genetic factor might contribute, in the etiology of congenital clubfoot.

[33]

Parker et al. (2009)

6139 cases of clubfoot from 2001 through 2005 plus 10 controls per case.

Risk factors and prevalence

The overall prevalence of clubfoot was 1.29 per 1000 in live births. Maternal smoking and diabetes showed significant associations.

[34]

Hackshaw et al. (2011)

15,673 clubfoot cases

Smoking

Significant positive associations with maternal smoking were found for clubfoot (OR 1.28, 95% CI 1.10–1.47)

[35]

Dickinson et al (2008)

443 cases of clubfoot and 4492 randomly sampled controls

Smoking

This study is consistent with the hypothesis that smoking during pregnancy is associated with a slightly increased risk of an infant being born with clubfoot.

[36]

Honein (2000)

346 infants with isolated clubfoot and 3029 infants without defects

Smoking

This study confirms the importance of familial factors and smoking in the etiology of clubfoot and identifies a potentially important interaction.

[37]

Wang et al. (2005)

84 idiopathic congenital talipes equinovarus nuclear pedigrees

HOXD10, HOXD12 and HOXD13

HOXD12 andHOXD13 are important susceptible genes of idiopathic congenital talipes equinovarus.

[38]

Ester et al. (2009)

179 extended families and 331 simplex families and 88 trios with a positive family history. The validation population consisted of 144 NHW simplex trios

HOXA and HOXD gene clusters

These results suggest a biologic model for clubfoot in which perturbation of HOX and apoptotic genes together affect muscle and limb development, which may cause the downstream failure of limb rotation into a plantar grade position.

[39]

Alvarado et al. (2016)

1178 probands with clubfoot or verticaltalus and 1775 controls

HOXC

Since HOXD10 has been implicated in the etiology of congenital vertical talus, variation in its expression may contribute to the lower limb phenotypes occurring with 5’ HOXC microdeletions.

[40]

Weymouth et al. (2016)

Nuclear extracts isolated from undifferentiated and differentiated C2C12 mouse muscle cells

HOXA9, TPM1, and TPM2

Results show that associated promoter variants in HOXA9, TPM1, and TPM2, alter promoter expression suggesting that they have a functional role.

[41]

Liu et al. (2011)

25 children with ICTEV and 5 normal controls

COL9A1

COL9A1 protein is highly expressed in patients with ICTEV and rs1135056, which is located in the coding region of COL9A1 gene, may be associated with the pathogenesis of ICTEV.

[42]

Zhao et al. (2016)

87 children with congenital talipes equinovarus and 174 control subjects

COL9A1

In conclusion, our results indicate that the COL9A1 rs35470562 variant may contribute to congenital talipes equinovarus susceptibility in the Chinese population examined.

[43]

Zhang et al. (2006)

84 idiopathic congenital talipes equinovarus nuclear pedigree

GLI3

There is an association between GLI3 gene and ICTEV, and exons 9,10,11,12 are not its mutation hot spots.

[44]

Lu et al. (2012)

605 probands (from 148 multiplex and 457 simplex families) with non-syndromic clubfoot

TBX4 and chromosome 17q23.1q23.2

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 non-syndromic clubfoot-associated region.

[45]

Peterson et al. (2014)

One family: mother, daughter, and two sons

TBX4

Although TBX4 remains the candidate gene for congenital clubfoot involving 17q23.1–q23.2 duplications, the explanation for variable expressivity and penetrance remains unknown.

[46]

Alvarado et al. (2011)

Mice model

Pitx1

Morphological data suggest that PITX1 haplo insufficiency may cause a developmental field defect preferentially affecting the lateral lower leg, a theory that accounts for similar findings in human clubfoot.

[47]

Alvarado et al. (2010)

66 isolated idiopathic clubfoot probands with at least one affected first-degree relative

TBX4

Our result suggests that this chromosome 17q23.1q23.2 microduplication is a relatively common cause of familial isolated clubfoot and provides strong evidence linking clubfoot etiology to abnormal early limb development.

[48]

Dobbs et al. (2006)

21 affected individuals and 17 unaffected individuals

HOXD10

This mutation was recently described in a family of Italian descent with congenital vertical talus (CVT) and Charcot-Marie-Tooth deformity HOXD10 gene mutations were not identified in any of the other families or sporadic patients with CVT, suggesting that genetic heterogeneity underlies this disorder.

[49]

Shrimpton et al. (2004)

36 members of a single family

HOXD10

In the study family, this mutation was fully penetrant and exhibited significant evidence of linkage (LOD 6.33; θ = 0), and it very likely accounts for congenital vertical talus in heterozygotes.

[50]

Heck et al. (2005)

57 multiplex ITEV families and 83 simplex trios

CASP8, CASP10

Genotyping of SNPs throughout the genes in this sample of ITEV families has revealed positive linkage with association to the major allele of a variant in CASP10 in simplex ITEV white and Hispanic trios.

[51]

Duce et al. (2013)

The lower legs of six CTEV (2 bilateral, 4 unilateral) and five control young adults (ages 12–28)

3D MRI and MRA

The proportion of muscle in affected CTEV legs was significantly reduced compared with control and unaffected CTEV legs, while proportion of muscular fat increased. No spatial abnormalities in the location or branching of arteries were detected, but hypoplastic anomalies were observed.

[52]

Zhang et al. (2016)

29 individuals of the same family

ANXA3 and MTHFR

Following whole genome sequencing and comparative analysis, several differential gene variants were identified to enable a further distinction from clubfoot.

[53]

Lochmiller et al. (1998)

A total of 285 propositi were ascertained, with detailed family history information available in 173 cases and medical records on the remaining 112 propositi

Genetic and environmental risk factor

A family history of ITEV was noted in 24.4% of all propositi studied. These findings, in addition to the detailed analysis of 53 pedigrees with ITEV history, suggest that the potential role of a gene or genes operating in high-risk families produces this foot deformity.

[54]

Yang et al. (2016)

three-generation pedigree and 53 sporadic patients with CTEV

FLNB

The results provide evidence for the involvement of FLNB in the pathogenesis of isolated CTEV and have expanded the clinical spectrum of FLNB mutations.

[55]

Zhang et al. (2014)

96 isolated clubfoot patients and 1000 controls

NCOR2, ZNF664 FOXN3, SORCS1, and MMP7/TMEM123

The study suggests a potential role for common genetic variation in several genes that have not previously been implicated in clubfoot pathogenesis.

[56]

Weymouth et al. (2011)

The discovery dataset was comprised of 224 multiplex families, which include 137 non Hispanic white (NHW) and 87 Hispanic families, and 357 simplex families, which includes 139 NHW and 218 Hispanic families

TNNC2 and TPM1

The results reported suggest that variation in genes that encode contractile proteins of skeletal myofibers may play a role in the etiology of clubfoot.

[57]

Gilbert et al. (2001)

Two normal feet from a 40-week-old stillborn fetus, and samples from six calcanei from children with relapsed CTEV, aged 2, 3, 4, and 5 years, were studied

Histological analysis of the calcaneum

The process of ossification in CTEV was retarded. The talipes cartilage matrix contained fewer cartilage canals and chondrocytes

[58]

Ester et al. (2007)

210 simplex trios and 139 multiplex families

SNPs spanning seven apoptotic genes-Casp3, Casp8, Casp9, Casp10, Bid, Bcl-2, and Apaf1

One SNP in each of the genes provided impressive evidence of association with idiopathic talipes equinovarus

[60]

Sharp et al (2006).

375 case-parent triads

C677T polymorphism in MTHFR

DNA synthesis may be relevant in clubfoot development

[61]

Bonafe et al. (2002)

125 ITEV probands and their parents

DTDST

The R279W mutation is no more frequent in this population of ITEV probands than in controls.