Evaluation of Genetic and Nongenetic Risk Factors for Degenerative Cervical Myelopathy.

STUDY DESIGN: Cohort study. OBJECTIVE: We aimed to evaluate the associations of genetic and nongenetic factors with degenerative cervical myelopathy (DCM). SUMMARY OF BACKGROUND DATA: There is mounting evidence for an inherited predisposition for DCM, but uncertainty remains regarding specific genetic markers involved. Similarly, nongenetic factors are thought to play a role. MATERIALS AND METHODS: Using diagnosis codes from hospital records linked to the UK Biobank cohort, patients with cervical spondylosis were identified followed by the identification of a subset with DCM. Nongenetic variables evaluated included age, sex, race, Townsend deprivation index, body mass index, occupational demands, osteoporosis, and smoking. Genome-wide association analyses were conducted using logistic regression adjusted for age, sex, population principal components, and follow-up. RESULTS: A total of 851 DCM cases out of 2787 cervical spondylosis patients were identified. Several nongenetic factors were independently associated with DCM including age [odds ratio (OR)=1.11, 95% CI=1.01-1.21, P =0.024], male sex (OR=1.63, 95% CI=1.37-1.93, P <0.001), and relative socioeconomic deprivation (OR=1.03, 95% CI=1.00-1.06, P =0.030). Asian race was associated with lower DCM risk (OR=0.44, 95% CI=0.22-0.85, P =0.014). We did not identify genome-wide significant (≤5×10 -8 ) single-nucleotide polymorphisms (SNPs) associated with DCM. The strongest genome-wide signals were at SNP rs67256809 in the intergenic region of the genes LINC02582 and FBXO15 on chromosome 18 ( P =1.12×10 -7 ) and rs577081672 in the GTPBP1 gene on chromosome 22 ( P =2.9×10 -7 ). No SNPs reported in prior DCM studies were significant after adjusting for replication attempts. CONCLUSIONS: Increasing age, male sex, and relative socioeconomic deprivation were identified as independent risk factors for DCM, whereas Asian race was inversely associated. SNPs of potential interest were identified in GTPBP1 and an intergenic region on chromosome 18, but these associations did not reach genome-wide significance. Identification of genetic and nongenetic DCM susceptibility markers may guide understanding of DCM disease processes, inform risk, guide prevention and potentially inform surgical outcomes. LEVEL OF EVIDENCE: Prognostic level III.

Incidence and risk factors for acute compartment syndrome in pediatric tibia fractures.

Acute compartment syndrome (ACS) is a rare complication following traumatic injuries in pediatric patients, and tibia fractures represent the most common cause of ACS. To determine the incidence and risk factors of developing ACS, State Inpatient Databases, State Emergency Department Databases, and State Ambulatory Surgery and Services Databases from the Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality, were used to retrospectively identify patients 1-18 years of age with tibia fractures from 2006 to 2015 (quarter 3). The HCUP Nationwide Emergency Department Sample for nationwide data was also queried. Multivariable generalized estimating equations models were used to determine risk factors associated with development of ACS. A total of 50 640 patients with tibia fractures were studied, and 309 cases of ACS were identified. The incidence of ACS was 0.6 and 5.5% in the all tibia and open tibia fracture groups, respectively. Twenty-three cases of ACS (7.4% of all ACS) were diagnosed after discharge from the index admission, which was more common in teens treated nonoperatively. Predictors of increased ACS risk in the all tibia fracture group included age 13-18 [relative risk (RR): 4.04)], open fractures (RR: 3.83), and motor vehicle crash (MVC) mechanism (RR: 5.69). Nationwide, open and operatively treated fractures had an increased ACS rate (3.98 and 5.51%, respectively). Teenagers, open fractures, and MVC mechanisms were most strongly associated with ACS. ACS can present in a delayed fashion, as evidenced by postindex cases.

Does the Canadian Orthopaedic Foot and Ankle Society Postoperative COFAS End-Stage Ankle Arthritis Classification System Correlate With Pre- and Postoperative PROMIS Scores for Total Ankle Arthroplasty?

Background: Recently, the Canadian Orthopaedic Foot and Ankle Society (COFAS) proposed a classification system addressing adjunct procedures in the treatment for end-stage ankle arthritis. We reviewed Patient-Reported Outcome Measures Information System (PROMIS) data to determine if outcomes of total ankle arthroplasty (TAA) correlated with postoperative COFAS classification. We hypothesize that as COFAS classification increases, patients will demonstrate greater improvement in the change between pre- and postoperative PROMIS scores. Methods: From June 2015 to December 2018, a total of 127 patients underwent 132 TAA. Demographic factors and preoperative and most recent postoperative PROMIS scores were collected. Univariate, multivariate and post hoc analyses with a significance threshold of P <.05 were performed. Results: Eighty-seven patients with a mean follow-up of 13.6±7.3 months and complete PROMIS scores were classified into COFAS types 1-4. Significant differences were identified in the PROMIS Pain Interference domain comparing COFAS types 2 and 4 and COFAS types 3 and 4. These results demonstrate that more complex ankles with a higher COFAS score had worse interval improvement in PROMIS scores. Additionally, multivariate linear regression showed that age and BMI were associated with worse physical function and depression, whereas diabetes and a history of prior surgeries were associated with improved postoperative function. Conclusion: The COFAS postoperative classification system is useful for categorizing end-stage ankle arthritis. Further research into the ideal timing of surgery and higher-level studies to better determine TAA efficacy with different classification systems is warranted. This information can be helpful with preoperative counseling about treatment outcomes.Level of Evidence: Level IV, retrospective analysis of prospectively collected data.

Spine-specific skeletal related events and mortality in non-small cell lung cancer patients: a single-institution analysis.

OBJECTIVE: The population prevalence of non-small cell lung cancer (NSCLC) continues to increase; however, data are limited regarding the incidence rate of skeletal related events (SREs) (i.e., surgery to the spinal column, radiation to the spinal column, radiofrequency ablation, kyphoplasty/vertebroplasty, spinal cord compression, or pathological vertebral body fractures) and their impact on overall mortality. In this study, the authors sought to estimate the incidence rates of SREs in NSCLC patients and to quantify their impact on overall mortality. METHODS: This was a single-institution retrospective study of patients diagnosed with NSCLC between 2002 and 2014. The incidence rates for bone metastasis and subsequent SREs (per 1000 person-years) by time since lung cancer diagnosis were calculated and analyses were stratified separately for each histological type. Incidence rates for mortality at 1, 2, and 3 years from diagnosis stratified by the presence of SREs were also calculated. Kaplan-Meier survival curves were constructed to describe crude survival ratios in patients with spine metastasis and SREs and those with spine metastasis but without SREs. These curves were used to estimate the 1- and 2-year survival rates for each cohort. RESULTS: We identified 320 patients with incident NSCLC (median follow-up 9.5 months). The mean ± SD age was 60.65 ± 11.26 years; 94.48% of patients were smokers and 60.12% had a family history of cancer. The majority of first-time SREs were pathological vertebral body compression fractures (77.00%), followed by radiation (35%), surgery (14%), and spinal cord compression (13.04%). Mortality rates were highest in NSCLC patients with spine metastasis who had at least 1 SRE. Stratifying by histological subtype, the incidence rate of mortality in patients with SRE was highest in the large cell cohort, 7.42 per 1000 person-years (95% CI 3.09-17.84 per 1000 person-years); followed by the squamous cell cohort, 2.49 per 1000 person-years (95% CI 1.87-3.32 per 1000 person-years); and lowest in the adenocarcinoma cohort, 1.68 per 1000 person-years (95% CI 1.46-1.94 per 1000 person-years). Surgery for decompression of neural structures and stabilization of the spinal column was required in 6% of patients. CONCLUSIONS: SREs in NSCLC patients with bone metastasis are associated with an increased incidence rate of mortality.

Pediatric Orthopedics: Is One Fellowship Enough?

Dual-fellowship-trained surgeons specializing in both pediatric and sport medicine are treating an increasing number of pediatric orthopedic injuries, making pediatric orthopedic sports medicine a potential new emerging subspecialty. With fellowship training now being the norm rather than the exception across orthopedics, it is possible that dual-fellowship training may become a prerequisite for treatment of pediatric sports medicine patients. This may impact the practices of surgeons trained in either pediatric or sports medicine alone. As the trend toward dual-fellowship training is likely to continue, future studies are needed to characterize the impact it has on patient care and training patterns.

Improvements in Neck Pain and Disability Following C1-C2 Posterior Cervical Instrumentation and Fusion for Atlanto-Axial Osteoarthritis.

OBJECTIVE: Symptomatic Atlanto-axial (C1-2) osteoarthritis (AAOA) is a common phenomenon in elderly patients; however, there is a paucity of data on the effectiveness of posterior atlanto-axial fusion (PAAF) for this condition. To this end, here we assess changes in patient-reported outcomes and neck-related disability in adult patients undergoing PAAF for symptomatic C1-2 AAOA. METHODS: In this retrospective study, the clinical records of consecutive patients with symptomatic AAOA who underwent PAAF between 2004 and 2017 were reviewed. Patient demographics, comorbidities, intraoperative and postoperative variables, and complication rates were collected. Neck Disability Index (NDI) scores were recorded at baseline and 6 weeks, 6 months, 1 year, and 2 years postoperatively. RESULTS: Forty-two patients (average age, 72.04 ± 8.56 years; 26.19% males) met the study's inclusion criteria. In this cohort, 19.04% had previous subaxial cervical spine surgery, 35.71% had a history of smoking (all had stopped smoking before surgery), and 11.90% had type II diabetes. At baseline, the majority of patients had a normal neurologic exam. The average preoperative NDI score was 26.88 ± 24.85, which improved to 10.59 ± 14.88 at the 1-year follow-up and 13.20 ± 14.96 at the 2-year follow-up (P = 0.004). At baseline, 18% of the patients reported severe disability based on NDI score; this percentage decreased to 2% at 1 year and 0 at 2 years (P = 0.01). Importantly, a high percentage (11.90%) of patients had undergone previous subaxial cervical fusion for their pain due to a mistaken diagnosis for this condition, without symptom relief. CONCLUSIONS: In appropriately selected patients, PAAF may decrease neck pain and improve functional disability in patients with AAOA. Future prospective longitudinal studies are needed to corroborate these findings.

Optimal Surgical Management of Tarsal Coalitions.

Tarsal coalitions are common, but fortunately the majority of patients with coalitions are asymptomatic and do not require intervention. When symptomatic, preoperative radiographs and CT scans are useful to characterize the type and extent of coalition. If a trial of nonsurgical management fails, resection, deformity correction, and triple arthrodesis may be considered. Barring contraindications, resection has been shown to be an effective and reliable first line surgical option. Arthrodesis should be reserved for cases of failed resection or significant arthritis. Associated deformity should be factored into patient evaluation and surgical management.

Comparison of rod fracture rates in long spinal deformity constructs after transforaminal versus anterior lumbar interbody fusions: a single-institution analysis.

OBJECTIVE: Pseudarthrosis is a common complication of long-segment fusions after surgery for correction of adult spinal deformity (ASD). Interbody fusions are frequently used at the caudal levels of long-segment spinal deformity constructs as adjuncts for anterior column support. There is a paucity of literature comparing rod fracture rates (proxy for pseudarthrosis) in patients undergoing transforaminal lumbar interbody fusion (TLIF) versus anterior lumbar interbody fusion (ALIF) at the caudal levels of the long spinal deformity construct. In this study the authors sought to compare rod fracture rates in patients undergoing surgery for correction of ASD with TLIF versus ALIF at the caudal levels of long spinal deformity constructs. METHODS: We reviewed clinical records of patients who underwent surgery for correction of ASD between 2008 and 2014 at a single institution. Data including demographics, comorbidities, and indications for surgery, as well as postoperative variables, were collected for each patient. All patients had a minimum 2-year follow-up. Patients were dichotomized into two groups for comparison on the basis of undergoing a TLIF versus an ALIF procedure at the caudal levels of long spinal deformity constructs. The primary outcome of interest was the rate of rod fractures. RESULTS: A total of 198 patients (TLIF 133 patients; ALIF 65 patients) underwent a long-segment fusion to the sacrum with iliac fixation. The mean ± standard deviation follow-up period was 62.23 ± 29.26 months. Baseline demographic variables were similar in both patient groups. There were no significant differences between groups in the severity of the baseline sagittal plane deformity (i.e., baseline lumbar-pelvic parameters) or the final deformity correction achieved. Mean total recombinant human bone morphogenetic protein 2 (rhBMP-2) dose for L1-sacrum fusion was significantly higher in the ALIF (100 mg) than in the TLIF (62 mg) group. The overall rod failure rate (cases with rod fracture/total cases) within this case series was 19.19% (38/198); 10.60% (21/198) were unilateral rod fractures and 8.58% (17/198) were bilateral rod fractures. At last clinical follow-up, there were no statistically significant differences in bilateral rod fracture rates between the group of patients who had a TLIF procedure and the group who had an ALIF procedure at the caudal levels of the long spinal deformity constructs (TLIF 10.52% vs ALIF 4.61%, p = 0.11). However, the incidence rate (cases per patient follow-up years) for bilateral rod fractures was significantly higher in the TLIF than in the ALIF cohort (TLIF 2.20% vs ALIF 0.70%, p < 0.0001). The reoperation rate for rod fractures was similar between the patient groups (p = 0.40). CONCLUSIONS: Although both ALIF and TLIF procedures at the caudal levels of long spinal deformity constructs achieved similar and satisfactory deformity correction, ALIFs were associated with a lower rod fracture incidence rate. There were no differences between groups in the prevalence of rod fracture or revision surgery, however, and both groups had low bilateral rod fracture prevalence and incidence rates. One technique is not clearly superior to the other.

Pediatric Orthopedic Workforce: A Review of Recent Trends.

Pediatric orthopedic surgery has changed in many ways over the past 2 decades. Member surveys and recent literature confirm that there has been a sustained balance of interest and opportunity in growth of applicant numbers and fellowship spots. Pediatric orthopedics is leading the way in gender diversity in orthopedics. Concerns of competition are valid and appear to be rising; however, case load data suggest that with increased training of pediatric orthopedists, there seems to be an adequate increase in cases. Periodic workforce analysis should continue to gauge any changes in attitudes or monitor concerns of competition.

Displaced Radial Neck Fractures: What Are My Options?

Pediatric radial head and neck fractures are uncommon injuries. Fractures are classified using the Judet system based on fracture angulation and displacement. Judet type I and II fractures can be managed nonsurgically with a short course of immobilization in a cast or splint without closed reduction. Most of these patients have an excellent prognosis and functional outcomes. Judet type III and IV injuries, as well as injuries that demonstrate a mechanical block to motion, should be closed reduced with the patient under conscious sedation or general anesthesia. Patients who undergo an unsuccessful closed reduction require closed or open reduction in the operating room. Closed reduction methods include the push and lever techniques with the use of Kirschner wires or Steinmann pins or intramedullary nails. Percutaneous fixation with wires or pins is needed only if the fracture fragment is determined to be unstable, whereas nails are left in place and require a second surgery for removal. Both methods have similar outcomes and an overall positive prognosis for patients. Open reduction and internal fixation should be avoided if at all possible given the higher incidence of wide-ranging complications.

Fractures Around the Knee in Children.

Knee injuries are common in children, but epiphyseal and physeal injuries involving the distal femur and proximal tibia are relatively rare. This can make diagnosis and evaluation of pediatric knee injuries challenging. Pediatric knee physeal injuries can also be complicated by vascular injuries with potentially devastating consequences, and thus, a heightened suspicion for these injuries is indicated. Distal femoral and proximal tibial physeal injuries can be diagnosed with plain radiographs or with advanced imaging if the initial findings are equivocal. Physeal fractures of the distal femur and proximal tibia can be managed nonsurgically if nondisplaced or surgically with cannulated screw fixation or smooth, percutaneous pin fixation. Tibial tubercle injuries can have point tenderness or an extensor lag, are diagnosed with plain radiographs, and are often managed with physeal-sparing cannulated screw fixation. These injuries have an increased risk of compartment syndrome. Tibial eminence fractures are epiphyseal avulsion injuries caused by traction from the anterior cruciate ligament. Arthroscopic and open techniques for reduction and stable fixation yield good outcomes. Patellar sleeve injuries are often misdiagnosed and may require advanced imaging for diagnosis. They represent pediatric extensor mechanism injuries that often necessitate open reduction and fixation or patellar tendon advancement. Understanding the relevant anatomy, diagnosis, and management options can help guide the treating physician in the management of the fractures of the pediatric knee.

Length of Stay Beyond Medical Readiness in Neurosurgical Patients: A Prospective Analysis.

BACKGROUND: In an era of growing healthcare costs, there is increased pressure on medical care providers to discharge patients once they are medically fit. However, it is not uncommon for patients to stay beyond medical readiness (BMR). OBJECTIVE: To analyze the frequency with which patients remain in the hospital BMR. METHODS: A prospective cohort analysis utilizing a database maintained between 2014 and 2015 included 718 adults admitted to the neurosurgical service. The attending for admitted patients was asked on a daily basis as to whether the patient was medically cleared for discharge. Standard statistical analyses were performed. RESULTS: Of the 718 patients, 105 (14.6%) remained in the hospital BMR. Of the patients who presented with a spinal pathology, 17.8% had a length of stay (LOS)-BMR compared to 13.9% who presented with cerebrovascular pathologies and 14.8% who presented with a brain tumor. The average LOS-BMR was 1.8 d. Only 7.7% of patients who were discharged home had an LOS-BMR compared to 30.7% of patients who were discharged to a skilled nursing facility or rehabilitation center (P < .001). In logistic regression, a physical therapy consultation and discharge to a specialized nursing facility were both associated with a longer LOS (average 2.4 d longer, P < .001, and 6.2 d longer, P = .028, respectively). However, neither was associated with an LOS-BMR. CONCLUSION: LOS-BMR is an important process engineering concept within neurosurgery that represents a potential area for improvement to maximize limited healthcare resources. A sizeable portion of neurosurgical patients remained in the hospital BMR.

Weight Gain After Vertical Expandable Prosthetic Titanium Rib Surgery May Be From Nutritional Optimization Rather Than Improvement in Pulmonary Function.

STUDY DESIGN: Prospective comparative study. OBJECTIVE: To evaluate whether weight percentile (WP) increases after vertical expandable prosthetic titanium rib (VEPTR) insertion, and whether WP correlates with nutrition laboratories and pulmonary function. SUMMARY OF BACKGROUND DATA: Children with thoracic insufficiency syndrome often have "failure to thrive" (WP ≤5). Previous authors have reported an increase in WP after VEPTR surgery. Weight gain was hypothesized to be secondary to improved pulmonary function. The presence of a correlation between WP and nutrition laboratories and pulmonary function tests (PFT) after VEPTR insertion has not been studied. METHODS: Demographic, nutrition, radiographic, and PFT data were collected on 35 VEPTR patients with a minimum follow-up of 2 years. The relationship between WP and nutrition laboratories and pulmonary function was analyzed. RESULTS: Preoperative WP was ≤5 (PREOP≤5) in 13 patients (37%) and >5 (PREOP>5) in 22 patients (63%). Although all children gained weight, the PREOP≤5 group was more likely to have an increase in WP (P = 0.014). Sixty-eight percent of the PREOP>5 group had a decrease in WP and 32% of the PREOP>5 patients met the criteria for failure to thrive at final follow-up. Overall, there was no change in the number of children with a WP ≤5 (13 vs. 15). Forty-two percent of the children who maintained or increased their WP had a gastrostomy tube, compared to 19% of those who decreased their WP. Seventy-three percent of the patients with failure to thrive at final follow-up did not have a gastrostomy tube. No significant correlations were found between WP and nutrition laboratories, radiographic measures, or PFTs. CONCLUSION: We did not find an overall change in WP after VEPTR insertion. We did not find any correlation between WP and nutrition laboratories or pulmonary function. Weight gain after VEPTR surgery may be secondary to nutritional optimization in high-risk patients. Children who do not have failure to thrive at presentation also require attention. LEVEL OF EVIDENCE: 2.

Characterization of the Tetraspan Junctional Complex (4JC) superfamily.

Connexins or innexins form gap junctions, while claudins and occludins form tight junctions. In this study, statistical data, derived using novel software, indicate that these four junctional protein families and eleven other families of channel and channel auxiliary proteins are related by common descent and comprise the Tetraspan (4 TMS) Junctional Complex (4JC) Superfamily. These proteins all share similar 4 transmembrane α-helical (TMS) topologies. Evidence is presented that they arose via an intragenic duplication event, whereby a 2 TMS-encoding genetic element duplicated tandemly to give 4 TMS proteins. In cases where high resolution structural data were available, the conclusion of homology was supported by conducting structural comparisons. Phylogenetic trees reveal the probable relationships of these 15 families to each other. Long homologues containing fusions to other recognizable domains as well as internally duplicated or fused domains are reported. Large "fusion" proteins containing 4JC domains proved to fall predominantly into family-specific patterns as follows: (1) the 4JC domain was N-terminal; (2) the 4JC domain was C-terminal; (3) the 4JC domain was duplicated or occasionally triplicated and (4) mixed fusion types were present. Our observations provide insight into the evolutionary origins and subfunctions of these proteins as well as guides concerning their structural and functional relationships.

'Myxoedema madness' with Capgras syndrome and catatonic features responsive to combination olanzapine and levothyroxine.

We present the case of an elderly woman with hypothyroidism and no psychiatric history who presented with new onset of psychosis, paranoia, catatonic features and Capgras syndrome (CS). This case illustrates the spectrum of neuropsychiatric symptoms that may accompany hypothyroidism and the importance of considering thyroid dysfunction as a primary contributor to severe psychiatric symptoms, especially in previously stable patients. We demonstrate the effectiveness of combination levothyroxine and olanzapine, with its favourable cardiac profile, in the treatment of myxoedema madness. Antipsychotics can be weaned once psychiatric symptoms resolve and hormone levels are stabilised.

Morphometric analysis of abdominal organs and rib cage: Implication for risk of solid organ injuries in children.

BACKGROUND: Motor vehicle crashes are the leading cause of injury-related mortality in children, with a higher rate of multiorgan injuries than in adults. This may be related to increased solid organ volume relative to abdominal cavity and decreased protection of an underdeveloped cartilaginous rib cage in young children. To date, these anatomic relationships have not been fully described. Our study used analytic morphomics to obtain precise measures of the pediatric liver, spleen, kidneys, and ribs. METHODS: This pilot study included 215 trauma patients (aged 0-18 years) with anonymized computed tomography (CT) scans. Liver, spleen, and kidney volumes were modeled using semiautomatic algorithms (MATLAB 2013a, MathWorks Inc., Natick, MA). Thirty-one scans were adequate to model the rib cage. Pearson's r was used to correlate absolute organ volume, fractional organ volume, and organ exposure with age and weight. RESULTS: Spleen, right and left kidney, and liver volumes increased with age and weight (p < 0.01). Right/left kidney and liver fractional volumes decreased with age (p < 0.01), whereas spleen fractional volume remained relatively constant. Exposed surface area of the liver only significantly decreased with age in the anterior (p < 0.01), right (p < 0.01), and posterior views (p = 0.02). DISCUSSION: With this study, we have demonstrated the ability to model solid organ and rib cage anatomy of children using cross-sectional imaging. In younger children, there may be a decrease in fractional organ volume and increase in liver surface exposure, although analysis of a larger sample size is warranted. In the future, this information may be used to improve the design of safety restraints in motor vehicles.

The transporter-opsin-G protein-coupled receptor (TOG) superfamily.

Visual rhodopsins are recognized members of the large and diverse family of G protein-coupled receptors (GPCRs), but their evolutionary origin and relationships to other proteins are not known. In a previous paper [Shlykov MA, Zheng WH, Chen JS & Saier MH Jr (2012) Biochim Biophys Acta 1818, 703-717], we characterized the 4-toluene sulfonate uptake permease (TSUP) family of transmembrane proteins, and showed that these 7-transmembrane segment (TMS) or 8-TMS proteins arose by intragenic duplication of a gene encoding a 4-TMS protein, sometimes followed by loss of a terminal TMS. In this study, we show that the TSUP, GPCR and microbial rhodopsin families are related to each other and to six other currently recognized transport protein families. We designate this superfamily the transporter/opsin/G protein-coupled receptor (TOG) superfamily. Despite their 8-TMS origins, the members of most constituent families exhibit 7-TMS topologies that are well conserved, and these arose by loss of either the N-terminal TMS (more frequent) or the C-terminal TMS (less frequent), depending on the family. Phylogenetic analyses revealed familial relationships within the superfamily and protein relationships within each of the nine families. The results of the statistical analyses leading to the conclusion of homology were confirmed using hidden Markov models, Pfam and 3D superimpositions. Proteins functioning by dissimilar mechanisms (channels, primary active transporters, secondary active transporters, group translocators and receptors) are interspersed on a phylogenetic tree of the TOG superfamily, suggesting that changes in the transport and energy-coupling mechanisms occurred multiple times during evolution of this superfamily.

Evolutionary relationships of ATP-Binding Cassette (ABC) uptake porters.

BACKGROUND: The ATP-Binding Cassette (ABC) functional superfamily includes integral transmembrane exporters that have evolved three times independently, forming three families termed ABC1, ABC2 and ABC3, upon which monophyletic ATPases have been superimposed for energy-coupling purposes [e.g., J Membr Biol 231(1):1-10, 2009]. The goal of the work reported in this communication was to understand how the integral membrane constituents of ABC uptake transporters with different numbers of predicted or established transmembrane segments (TMSs) evolved. In a few cases, high resolution 3-dimensional structures were available, and in these cases, their structures plus primary sequence analyses allowed us to predict evolutionary pathways of origin. RESULTS: All of the 35 currently recognized families of ABC uptake proteins except for one (family 21) were shown to be homologous using quantitative statistical methods. These methods involved using established programs that compare native protein sequences with each other, after having compared each sequence with thousands of its own shuffled sequences, to gain evidence for homology. Topological analyses suggested that these porters contain numbers of TMSs ranging from four or five to twenty. Intragenic duplication events occurred multiple times during the evolution of these porters. They originated from a simple primordial protein containing 3 TMSs which duplicated to 6 TMSs, and then produced porters of the various topologies via insertions, deletions and further duplications. Except for family 21 which proved to be related to ABC1 exporters, they are all related to members of the previously identified ABC2 exporter family. Duplications that occurred in addition to the primordial 3 → 6 duplication included 5 → 10, 6 → 12 and 10 → 20 TMSs. In one case, protein topologies were uncertain as different programs gave discrepant predictions. It could not be concluded with certainty whether a 4 TMS ancestral protein or a 5 TMS ancestral protein duplicated to give an 8 or a 10 TMS protein. Evidence is presented suggesting but not proving that the 2TMS repeat unit in ABC1 porters derived from the two central TMSs of ABC2 porters. These results provide structural information and plausible evolutionary pathways for the appearance of most integral membrane constituents of ABC uptake transport systems. CONCLUSIONS: Almost all integral membrane uptake porters of the ABC superfamily belong to the ABC2 family, previously established for exporters. Most of these proteins can have 5, 6, 10, 12 or 20 TMSs per polypeptide chain. Evolutionary pathways for their appearance are proposed.

The amino acid-polyamine-organocation superfamily.

The amino acid-polyamine-organocation (APC) superfamily has been shown to include five recognized families, four of which are specific for amino acids and their derivatives. Recent high-resolution X-ray crystallographic data have shown that four additional transporter families (BCCT, TC No. 2.A.15; SSS, 2.A.21; NSS, 2.A.22; and NCS1, 2.A.39), transporting a wide range of solutes, exhibit sufficiently similar folds to suggest a common evolutionary origin. We have used established statistical methods, based on sequence similarity, to show that these families are, in fact, members of the APC superfamily. We also identify two additional families (NCS2, 2.A.40; SulP, 2.A.53) as being members of this superfamily. Repeat sequences, each having five transmembrane α-helical segments and arising via ancient intragenic duplications, are demonstrated for all of these families, further strengthening the conclusion of homology. The APC superfamily appears to be the second largest superfamily of secondary carriers, the largest being the major facilitator superfamily (MFS). Although the topology of the members of the APC superfamily differs from that of the MFS, both families appear to have arisen from a common ancestral 2 TMS hairpin structure that underwent intragenic triplication followed by loss of a TMS in the APC family, to give the repeat units that are characteristic of these two superfamilies.