Micro-magnetic resonance imaging and embryological analysis of wild-type and pma mutant mice with clubfoot

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.

First trimester physiological development of the fetal foot position using three-dimensional ultrasound in virtual reality

Aim

In anatomic studies of the embryo, it has been established that during the development of the lower limb, several changes in foot position can be observed defined as a temporary ‘physiological clubfoot’. The aim of this study was to develop and test a measurement tool for objective documentation of the first trimester foot position in vivo and made an attempt to create a chart for first trimester foot position.

Methods

We developed a virtual orthopedic protractor for measuring foot positioning using three‐dimensional virtual reality visualization. Three‐dimensional ultrasound volumes of 112 pregnancies of women examined during the first trimester were studied in a BARCO I‐Space. The frontal angle (plantar flexion) and the lateral angle (adduction) between the leg and foot were measured from 8 until 13 weeks gestational age.

Results

We observed that the frontal angle steadily decreases, whereas the lateral angle first increases, resulting in transient physiological clubfeet position at 10‐ to 11‐week gestation, followed by a decrease to a normal foot position.

Conclusion

A transient clubfoot position is present during the normal development of the lower limbs, and it has been measured in vivo for the first time. This study emphasizes that a diagnosis of congenital clubfoot should not be made in the first trimester of pregnancy.

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.

Anatomical Variation of the Tarsus in Common Inbred Mouse Strains

Rodent models are used for a variety of orthopedic research applications; however, anatomy references include mostly artistic representations. Advanced imaging techniques, including micro-computed tomography (microCT), can provide more accurate representations of subtle anatomical characteristics. A recent microCT atlas of laboratory mouse (Mus musculus) anatomy depicts the central and tarsal bone III (T3) as a single bone, differing from previous references. Fusion of tarsal bones is generally characterized as pathological secondary to mutations associated with growth factors, and normal variation has not been documented in the mouse tarsus. Therefore, it is unclear if this fusion is a normal or a pathological characteristic. The aim of this study is to characterize the tarsus of the laboratory mouse and compare it to the rat and selected outgroup species (i.e., white-footed mouse) via microCT and histology to determine if the central and T3 are separate or fused into a single bone. Laboratory mice (C57/Bl6 [n = 17] and BalbC [n = 2]) and rats (n = 5) were scanned with microCT. A representative laboratory mouse from each strain was evaluated histologically via serial sagittal sections through the mid-tarsus. General pedal anatomy was similar between all species; however, the central and T3 bones were fused in all laboratory mice but not the rat or white-footed mouse. A band of hyaline cartilage was identified within the fused bone of the laboratory mice. We conclude that the fusion found is a normal characteristic in laboratory mice, but timing of the fusion remains ambiguous. Anat Rec, 300:450-459, 2017. © 2016 Wiley Periodicals, Inc.

3D MRI analysis of the lower legs of treated idiopathic congenital talipes equinovarus (clubfoot)

Background

Idiopathic congenital talipes equinovarus (CTEV) is the commonest form of clubfoot. Its exact cause is unknown, although it is related to limb development. The aim of this study was to quantify the anatomy of the muscle, subcutaneous fat, tibia, fibula and arteries in the lower legs of teenagers and young adults with CTEV using 3D magnetic resonance imaging (MRI), and thus to investigate the anatomical differences between CTEV participants and controls.

Methodology/Principal Findings

The lower legs of six CTEV (2 bilateral, 4 unilateral) and five control young adults (age 12–28) were imaged using a 3T MRI Philips scanner. 5 of the CTEV participants had undergone soft-tissue and capsular release surgery. 3D T1-weighted and 3D magnetic resonance angiography (MRA) images were acquired. Segmentation software was used for volumetric, anatomical and image analysis. Kolmogorov-Smirnov tests were performed. The volumes of the lower affected leg, muscle, tibia and fibula in unilateral CTEV participants were consistently smaller compared to their contralateral unaffected leg, this was most pronounced in muscle. The proportion of muscle in affected CTEV legs was significantly reduced compared with control and unaffected CTEV legs, whilst proportion of muscular fat increased. No spatial abnormalities in the location or branching of arteries were detected, but hypoplastic anomalies were observed.

Conclusions/Significance

Combining 3D MRI and MRA is effective for quantitatively characterizing CTEV anatomy. Reduction in leg muscle volume appears to be a sensitive marker. Since 5/6 CTEV cases had soft-tissue surgery, further work is required to confirm that the treatment did not affect the MRI features observed. We propose that the proportion of muscle and intra-muscular fat within the lower leg could provide a valuable addition to current clinical CTEV classification. These measures could be useful for clinical care and guiding treatment pathways, as well as treatment research and clinical audit.

Pitx1 haploinsufficiency causes clubfoot in humans and a clubfoot-like phenotype in mice

Clubfoot affects 1 in 1000 live births, although little is known about its genetic or developmental basis. We recently identified a missense mutation in the PITX1 bicoid homeodomain transcription factor in a family with a spectrum of lower extremity abnormalities, including clubfoot. Because the E130K mutation reduced PITX1 activity, we hypothesized that PITX1 haploinsufficiency could also cause clubfoot. Using copy number analysis, we identified a 241 kb chromosome 5q31 microdeletion involving PITX1 in a patient with isolated familial clubfoot. The PITX1 deletion segregated with autosomal dominant clubfoot over three generations. To study the role of PITX1 haploinsufficiency in clubfoot pathogenesis, we began to breed Pitx1 knockout mice. Although Pitx1(+/-) mice were previously reported to be normal, clubfoot was observed in 20 of 225 Pitx1(+/-) mice, resulting in an 8.9% penetrance. Clubfoot was unilateral in 16 of the 20 affected Pitx1(+/-) mice, with the right and left limbs equally affected, in contrast to right-sided predominant hindlimb abnormalities previously noted with complete loss of Pitx1. Peroneal artery hypoplasia occurred in the clubfoot limb and corresponded spatially with small lateral muscle compartments. Tibial and fibular bone volumes were also reduced. Skeletal muscle gene expression was significantly reduced in Pitx1(-/-) E12.5 hindlimb buds compared with the wild-type, suggesting that muscle hypoplasia was due to abnormal early muscle development and not disuse atrophy. Our morphological data suggest that PITX1 haploinsufficiency may cause a developmental field defect preferentially affecting the lateral lower leg, a theory that accounts for similar findings in human clubfoot.

Is there evidence for aetiologically distinct subgroups of idiopathic congenital talipes equinovarus? A case-only study and pedigree analysis

BACKGROUND

Idiopathic congenital talipes equinovarus (CTEV) is a common developmental foot disorder, the aetiology of which remains largely unknown. Some aspects of the epidemiology suggest the possibility of aetiologically distinct subgroups. Previous studies consider CTEV as a homogenous entity which may conceal risk factors in particular subgroups. We investigate evidence for aetiologically distinct subgroups of CTEV.

METHODS

Parents of 785 probands completed a postal questionnaire. Family pedigrees were compiled by telephone. Case-only analysis was used to investigate interactions between risk factors and sex of the proband, CTEV laterality and CTEV family history.

RESULTS

The male:female ratio was 2.3:1, 58% of probands were affected bilaterally and 11% had a first-second degree family history. There were modest interactions between family history and twin births (multivariate case - only odds ratio [ORca] = 3.87, 95%CI 1.19-12.62) and family history and maternal use of folic acid supplements in early pregnancy (ORca = 0.62, 95%CI 0.38-1.01); and between sex of the proband and maternal alcohol consumption during pregnancy (female, positive history and alcohol consumed: ORca = 0.33, 95%CI 0.12-0.89). Previous reports of an interaction between maternal smoking and family history were not confirmed. Relatives of female probands were affected more often than relatives of male probands.

CONCLUSIONS

These results provide tentative evidence for aetiologically distinct CTEV subgroups. They support the 'Carter effect', suggesting CTEV develops though a multifactorial threshold model with females requiring a higher risk factor 'load', and suggest areas where future aetiological investigation might focus. Large multi-centre studies are needed to further advance understanding of this common condition.