The Genomics of Arthrogryposis, a Complex Trait: Candidate Genes and Further Evidence for Oligogenic Inheritance

Arthrogryposis is a clinical finding that is present either as a feature of a neuromuscular condition or as part of a systemic disease in over 400 Mendelian conditions. The underlying molecular etiology remains largely unknown because of genetic and phenotypic heterogeneity. We applied exome sequencing (ES) in a cohort of 89 families with the clinical sign of arthrogryposis. Additional molecular techniques including array comparative genomic hybridization (aCGH) and Droplet Digital PCR (ddPCR) were performed on individuals who were found to have pathogenic copy number variants (CNVs) and mosaicism, respectively. A molecular diagnosis was established in 65.2% (58/89) of families. Eleven out of 58 families (19.0%) showed evidence for potential involvement of pathogenic variation at more than one locus, probably driven by absence of heterozygosity (AOH) burden due to identity-by-descent (IBD). RYR3, MYOM2, ERGIC1, SPTBN4, and ABCA7 represent genes, identified in two or more families, for which mutations are probably causative for arthrogryposis. We also provide evidence for the involvement of CNVs in the etiology of arthrogryposis and for the idea that both mono-allelic and bi-allelic variants in the same gene cause either similar or distinct syndromes. We were able to identify the molecular etiology in nine out of 20 families who underwent reanalysis. In summary, our data from family-based ES further delineate the molecular etiology of arthrogryposis, yielded several candidate disease-associated genes, and provide evidence for mutational burden in a biological pathway or network. Our study also highlights the importance of reanalysis of individuals with unsolved diagnoses in conjunction with sequencing extended family members.

Tibial tubercle-trochlear groove distance and angle are higher in children with patellar instability

PURPOSE

The purpose of this study was to assess the variations in tibial tubercle-trochlear groove distance and angle as a function of age and gender in a population of children without patellar instability (PI) compared with those with PI.

METHODS

A retrospective review of 869 children's knee MRIs, ages 5 to 15 years, were evaluated using a control group (792 children) without evidence of PI and a group with PI (77 children). Tibial tubercle-trochlear groove distance (TT-TGd) and angle (TT-TGa) were measured twice by two readers to assess intra- and inter-observer reliability and compared between PI and control groups. In both groups, functions of age and gender on TT-TGd and TT-TGa values were evaluated.

RESULTS

Both TT-TGd and TT-TGa measurements showed excellent intra- and inter-observer reliability. The mean TT-TGd for the PI group was 17.2 mm (SD 6.6) and significantly higher than the mean TT-TGd for the control group (10.4 SD 3.8 mm, P = 0.001). The mean TT-TGa for the PI was 20.8° (SD 8.3°), which was also significantly higher than the mean TT-TGa for the control group (12.5° SD 4.6°, P < 0.001). Control group revealed a positive correlation between age and TT-TGd measurements (r = 0.243, P < 0.001). The mean TT-TGa for girls (13.3° SD 4.7°) was higher than the mean TT-TGa for boys (11.9° SD 4.4°) in the control group (P < 0.001).

CONCLUSION

TT-TGa and TT-TGd are reliable and can be used for the evaluation of the extansor mechanism alignment in children with and without PI. However, it must be considered that TT-TGd is increasing in growing patients. Soft-tissue procedures may be prone to failure, since bony procedures for patellar alignment cannot be done until skeletal maturity.

LEVEL OF EVIDENCE

III.

The Effect of Previous Hip Surgery on the Outcome of Hip Arthroplasty in Young Patients

BACKGROUND

The incidence of total hip arthroplasty (THA) is increasing in all age groups, especially in young patients. The outcome of THA is believed to be affected by morphological deformities created by previous pelvic or femoral procedures performed in childhood. The aim of the present study was to assess whether previous hip surgery impaired the functional outcome in young patients who underwent THA.

METHODS

Data were collected from the records of patients aged less than 30 years who had undergone THA between 2002 and 2011. Thirty-five patients (44 hips) were included. The Western Ontario and McMaster Universities Osteoarthritis Index and Harris Hip Scores were collected as primary functional outcome measures. The secondary outcome measures were the major and minor complications. Patients were divided into 2 groups: those who had not undergone hip surgery before THA (group I, 17 patients, 24 hips) and those with a history of prior hip surgery (group II, 18 patients, 20 hips).

RESULTS

The mean age at the time of surgery was 25 ± 4 years in group I and 23 ± 4 years in group II. The mean Harris Hip Score was slightly higher in group I (90 ± 7) than in group II (87 ± 7) (P = .2). The mean Western Ontario and McMaster Universities Osteoarthritis Index scores were similar in both groups (in group I 14 ± 7 and in group II 14 ± 6, P = .9). Complication rates were also similar in both groups (P = .7).

CONCLUSIONS

It is often difficult to decide whether to perform THA in young patients. One potential risk factor for complications is hip surgery before THA. Our study revealed that young patients with or without a history of previous hip surgery achieved satisfactory functional outcomes with similar complication rates after THA.

Results of one-stage surgical treatment in children with Tönnis grade 4 developmental dysplasia of the hip: is it worse when it is bilateral?

This retrospective study compared the results of one-stage surgery of unilateral and bilateral Tönnis grade 4 hips (high dislocation in developmental hip dysplasia, DDH) : 41 hips, 30 patients. Mean follow-up was 56 months. Pelvic radiographs were evaluated at three time points. Acetabular inclination angle improved significantly in both groups. Results were satisfactory (Severin classes I-II) in 13 hips (68.5%) (unilateral group) and 21 hips (89.5%) (bilateral group). Functional evaluation (McKay classification) at final follow-up revealed satisfactory results in 94.8% (unilateral group) and 63.6% (bilateral group). One-stage surgery is a reliable method for treating children with unilateral or bilateral DDH.

Angular deformity development after the distal tibial physeal fractures

Several clinical and radiological factors can be prognostic in the development of angular deformity following physeal injuries of the distal tibia. One of the radiological parameters, premature physeal closure (PPC), can be detected during postoperative follow-ups. Aim of our study was to identify the prognostic factors in development of angular deformity and its relationship with PPC. One hundred and four patients treated due to physeal injuries of the distal tibia were included in our study. Patients were divided into three groups based on Salter-Harris (SH) classification. The intergroup relationships between sex, age, the amount of energy sustained during injury, premature physeal closure, the amount of residual gap, and deformity were analyzed. Angular deformity developed in 25% (3/12) of SH Type 2, in 60% (9/15) of Type 3 and 30% (3/10) of Type 4 patients with PPC. A residual displacement of more than 2 mm, age and premature physeal closure were specified as significant risk factors for development of angular deformity. 2 mm limit for residual displacement and findings of premature physeal closure in the radiological evaluations during follow-ups are prognostic factors in avoiding malalignment of the distal tibia.

LEVEL OF EVIDENCE

Level 3.

Correction of Pelvic Obliquity After Spinopelvic Fixation in Children With Cerebral Palsy: A Comparison Study With Minimum Two-Year Follow-up

STUDY DESIGN

Single institution cohort data were collected prospectively and reviewed retrospectively.

OBJECTIVES

This study aims to compare outcomes among three different instrumentation types: unit rod, iliac screws, and sacral alar iliac (SAI) screws in terms of pelvic obliquity correction in children with cerebral palsy (CP).

SUMMARY OF BACKGROUND DATA

The optimal choice for spinopelvic fixation in CP scoliosis with pelvic obliquity is controversial.

METHODS

Patients with minimum 2 years' follow-up were divided into three groups according to instrumentation type and matched based on preoperative pelvic obliquity and coronal major curve magnitude. Radiographic measurements included horizontal pelvic obliquity angle (PO), spinopelvic angle (SPA), coronal and sagittal Cobb angles, and T1 pelvic angle. Procedures were performed in one pediatric institution between 2004 and 2012. All measurements were performed by a single independent reviewer who was not involved in the procedures.

RESULTS

Seventy-seven patients (42 unit rod, 14 iliac screw, and 21 SAI screw) were included. Gender and age distribution was similar across all groups (56% males, 44% females, mean age 13.5 years). Mean follow-up was 3.6 years. Comparing pre- and postoperative measurements, there was a significant decrease (p < .05) in PO, SPA, and coronal major cob angle in all groups. No significant loss of correction occurred during follow-up. Postoperatively, TPA improved in all groups. Nonsymptomatic loosening was noted in 59% of unit rods, 57% of iliac screws, and 52% of SAI screws. One prominent iliac screw needed removal. One nonsymptomatic rod fracture, one infected pseudarthrosis, and one rod malposition occurred in unit rod group.

CONCLUSIONS

This study suggests that for correction of pelvic obliquity in cerebral palsy scoliosis, iliac and SAI screws were similar to the unit rod in comparative effectiveness and implant safety profile.

LEVEL OF EVIDENCE

Therapeutic study, Level III.

Molecular etiology of arthrogryposis in multiple families of mostly Turkish origin

BACKGROUND

Arthrogryposis, defined as congenital joint contractures in 2 or more body areas, is a clinical sign rather than a specific disease diagnosis. To date, more than 400 different disorders have been described that present with arthrogryposis, and variants of more than 220 genes have been associated with these disorders; however, the underlying molecular etiology remains unknown in the considerable majority of these cases.

METHODS

We performed whole exome sequencing (WES) of 52 patients with clinical presentation of arthrogryposis from 48 different families.

RESULTS

Affected individuals from 17 families (35.4%) had variants in known arthrogryposis-associated genes, including homozygous variants of cholinergic γ nicotinic receptor (CHRNG, 6 subjects) and endothelin converting enzyme-like 1 (ECEL1, 4 subjects). Deleterious variants in candidate arthrogryposis-causing genes (fibrillin 3 [FBN3], myosin IXA [MYO9A], and pleckstrin and Sec7 domain containing 3 [PSD3]) were identified in 3 families (6.2%). Moreover, in 8 families with a homozygous mutation in an arthrogryposis-associated gene, we identified a second locus with either a homozygous or compound heterozygous variant in a candidate gene (myosin binding protein C, fast type [MYBPC2] and vacuolar protein sorting 8 [VPS8], 2 families, 4.2%) or in another disease-associated genes (6 families, 12.5%), indicating a potential mutational burden contributing to disease expression.

CONCLUSION

In 58.3% of families, the arthrogryposis manifestation could be explained by a molecular diagnosis; however, the molecular etiology in subjects from 20 families remained unsolved by WES. Only 5 of these 20 unrelated subjects had a clinical presentation consistent with amyoplasia; a phenotype not thought to be of genetic origin. Our results indicate that increased use of genome-wide technologies will provide opportunities to better understand genetic models for diseases and molecular mechanisms of genetically heterogeneous disorders, such as arthrogryposis.

FUNDING

This work was supported in part by US National Human Genome Research Institute (NHGRI)/National Heart, Lung, and Blood Institute (NHLBI) grant U54HG006542 to the Baylor-Hopkins Center for Mendelian Genomics, and US National Institute of Neurological Disorders and Stroke (NINDS) grant R01NS058529 to J.R. Lupski.

Medial malleolar screw hemiepiphysiodesis for ankle valgus in children with spina bifida

Medial malleolar screw hemiepiphysiodesis has been shown to be an effective procedure for the treatment of ankle valgus in children with spina bifida. The purpose of this study was to highlight the guided growth technique and discuss its efficacy. We retrospectively reviewed 10 spina bifida patients with 18 ankle valgus deformities treated with medial malleolar screw hemiepiphysiodesis. Medical reports were obtained to document age at surgery, gender, concurrent operative procedures and postoperative early and late complications. Anteroposterior and lateral weight bearing radiographs of both ankles were evaluated using the tibiotalar angle, pre and postoperatively. The average age at operation was 10.05 years. Average follow up was 15.33 months (11-21 months). During follow-up, the average preoperative distal tibiotalar angle of 16.27 degrees improved to an average of 2.88 degrees with statistical significance (p < 0.05). No major complications were detected. In conclusion, hemiepiphysiodesis is a safe and sufficient method to correct ankle valgus deformity in children with spina bifida, with a low incidence.

Clinical and radiological outcomes are correlated with the age of the child in single-stage surgical treatment of developmental dysplasia of the hip

The principles of treatment of developmental dislocation of the hip (DDH) in an older child are different from those in a newborn. In the older child retraction of the muscles around the hip, associated with a marked acetabular dysplasia and elongation of the joint capsule explain the difficulty and instability of reduction and the frequency of complications. The aim of this study is to evaluate the effect of age on the results of a one-stage open reduction in developmental dislocation of the hip. We present the results of 21 children (27 hips) with a mean age of 6 years and 10 months at time of operation, consisting of one- stage open reduction, femoral shortening and Salter or triple pelvic osteotomy. Two groups were formed : one older and one younger than 8 years of age. We evaluated the patients according to the Severin and Mc Kay classifications. After an average follow-up of 49 months (24-84 months) 74% of patients showed a very good or good result according to Severin's radiological classification and 63% according to Mc Kay's clinical classification. When analyzed with regard to age, we found important differences in the clinical and radiological results between the children younger and older than 8 years.