A Rab33b missense mouse model for Smith-McCort dysplasia shows bone resorption defects and altered protein glycosylation

Smith McCort (SMC) dysplasia is a rare, autosomal recessive, osteochondrodysplasia that can be caused by pathogenic variants in either RAB33B or DYM genes. These genes codes for proteins that are located at the Golgi apparatus and have a role in intracellular vesicle trafficking. We generated mice that carry a Rab33b disease-causing variant, c.136A>C (p.Lys46Gln), which is identical to that of members from a consanguineous family diagnosed with SMC. In male mice at 4 months of age, the Rab33b variant caused a mild increase in trabecular bone thickness in the spine and femur and in femoral mid-shaft cortical thickness with a concomitant reduction of the femoral medullary area, suggesting a bone resorption defect. In spite of the increase in trabecular and cortical thickness, bone histomorphometry showed a 4-fold increase in osteoclast parameters in homozygous Rab33b mice suggesting a putative impairment in osteoclast function, while dynamic parameters of bone formation were similar in mutant versus control mice. Femur biomechanical tests showed an increased in yield load and a progressive elevation, from WT to heterozygote to homozygous mutants, of bone intrinsic properties. These findings suggest an overall impact on bone material properties which may be caused by disturbed protein glycosylation in cells contributing to skeletal formation, supported by the altered and variable pattern of lectin staining in murine and human tissue cultured cells and in liver and bone murine tissues. The mouse model only reproduced some of the features of the human disease and was sex-specific, manifesting in male but not female mice. Our data reveal a potential novel role of RAB33B in osteoclast function and protein glycosylation and their dysregulation in SMC and lay the foundation for future studies.

Discovery of small molecule agonists of the Relaxin Family Peptide Receptor 2

The relaxin/insulin-like family peptide receptor 2 (RXFP2) belongs to the family of class A G-protein coupled receptors (GPCRs) and it is the only known target for the insulin-like factor 3 peptide (INSL3). The importance of this ligand-receptor pair in the development of the gubernacular ligament during the transabdominal phase of testicular descent is well established. More recently, RXFP2 has been implicated in maintaining healthy bone formation. In this report, we describe the discovery of a small molecule series of RXFP2 agonists. These compounds are highly potent, efficacious, and selective RXFP2 allosteric agonists that induce gubernacular invagination in mouse embryos, increase mineralization activity in human osteoblasts in vitro, and improve bone trabecular parameters in adult mice. The described RXFP2 agonists are orally bioavailable and display favorable pharmacokinetic properties, which allow for future evaluation of the therapeutic benefits of modulating RXFP2 activation in disease models.

Specific small molecule RXFP2 agonists with favorable pharmacokinetic properties induce gubernacular invagination in mouse embryos, increase mineralization activity in human osteoblasts in vitro, and improve bone trabecular parameters in adult mice.

Mechanical Analysis of 3 Posterior Fusion Assemblies Intended to Cross the Cervicothoracic Junction

STUDY DESIGN

This was a biomechanical comparison study.

OBJECTIVE

The objective of this study is to evaluate the mechanical properties of 3 posterior spinal fusion assemblies commonly used to cross the cervicothoracic junction.

SUMMARY OF BACKGROUND

When posterior cervical fusions are extended into the thoracic spine, an instrumentation transition is often utilized. The cervical rod (3.5 mm) can continue using thoracic screws designed to accept the cervical rods. Alternatively, traditional thoracic screws may be used to accept thoracic rods (5.5 mm). This requires the use of a 3.5-5.5 mm transition rod or a separate 5.5 mm rod and a connector to fix the 3.5 and 5.5 mm rod together. Fusion success depends on the immobilization of vertebrae, yet the mechanics provided by these different assemblies are unknown.

MATERIALS AND METHODS

Three titanium alloy posterior fusion assemblies intended to cross the cervicothoracic junction underwent static compressive bending, tensile bending, and torsion as described in ASTM F1717 to a torque of 2.5 Nm. Five samples of each assembly were attached to ultrahigh molecular weight polyethylene blocks via multiaxial screws for testing. Force and displacement were recorded, and the stiffness of each construct was calculated.

RESULTS

The 2 assemblies that included a 5.5 mm rod were found to be stiffer and have less range of motion than the assembly that used only 3.5 mm rods.

CONCLUSIONS

The results of this study indicate that incorporating a 5.5 mm rod in a fusion assembly adds significant stiffness to the construct. When the stability of a fusion is of heightened concern, as demonstrated by the ASTM F1717 vertebrectomy (worst-case scenario) model, including 5.5 mm rods may increase fusion success rates.

LEVEL OF EVIDENCE

Level V.

Augmentation of core decompression with synthetic bone graft does not improve mechanical properties of the proximal femur

Core decompression is a minimally invasive surgical technique used to treat patients with avascular necrosis of the femoral head. The procedure requires an entry hole in the lateral cortex of the femur which potentially leaves patients susceptible to subtrochanteric fractures. The purpose of this study was to determine if filling the core decompression tract with synthetic bone-graft mechanically strengthens the proximal femur. Twenty composite synthetic femurs underwent a core decompression procedure; ten were augmented with synthetic bone-graft (PRO-DENSE™, Wright Medical) and ten femurs were left unfilled as a control group. Compressive testing to failure was performed using a mechanical testing machine. Stiffness, fracture load, and toughness did not significantly differ between groups. More subtrochanteric fractures were seen in the control group (6 of 10 specimens) compared to the bone-graft augmented group (2 of 10 specimens). In conclusion, augmentation of a core decompression tract does not improve mechanical properties in a synthetic bone model but may be protective of subtrochanteric fracture.

Validation of a custom spine biomechanics simulator: A case for standardization

Mechanical testing machines used in cadaveric spine biomechanics research vary between labs. It is a necessary first step to understand the capabilities and limitations in any testing machine prior to publishing experimental data. In this study, a reproducible protocol that uses a synthetic spine was developed and used to quantify the inherent rotation error and the ability to apply loads in a single physiologic plane (pure-moment) of a custom spine biomechanics simulator. Rotation error was evaluated by comparing data collected by the test machine and the data collected by an optical motion capture system. Pure-moment loading was assessed by comparing the out-of-plane loads to the primary plane load. Using synthetic functional spine units previously shown to have mechanics similar to the cadaveric human spine, the simulator was evaluated using a dynamic test protocol reflective of its future use in the study of cadaveric spine specimens. Rotation errors inherent in the test machine were <0.25° compared to motion capture. Out of plane loads were <4.0% of the primary plane load, which confirmed pure-moment loading. The authors suggest that a standard validation protocol for biomechanical spine testing machines is needed for transparency and accurate field-wide data interpretation and comparison. We offer recommendations based on the reproducible use of a synthetic spinal specimen for consideration.

Stressful life events, bipolar disorder, and the "kindling model"

A common misconception is that bipolar disorder is an endogenous process. However, previous research suggests a role for life events in the onset of and recovery from bipolar episodes. Yet, there remains some question as to whether the relationship between life events and onset changes over the course of the disorder as a result of the number of episodes an individual has experienced. Using a rigorous interview measure of stressful life events, the current study tested the kindling model (R. M. Post, 1992), which theorizes that major life events play a diminishing role over the course of illness in bipolar patients. Analyses revealed that the number of episodes experienced does not appear to have a significant effect on bipolar 1 patients' reactivity to external stressors. In addition, the results suggest that a more complex relationship exists among age, stress, and onset of new episodes than can be adequately explained by the kindling model.

Stressful life events, bipolar disorder, and the "kindling model"

A common misconception is that bipolar disorder is an endogenous process. However, previous research suggests a role for life events in the onset of and recovery from bipolar episodes. Yet, there remains some question as to whether the relationship between life events and onset changes over the course of the disorder as a result of the number of episodes an individual has experienced. Using a rigorous interview measure of stressful life events, the current study tested the kindling model (R. M. Post, 1992), which theorizes that major life events play a diminishing role over the course of illness in bipolar patients. Analyses revealed that the number of episodes experienced does not appear to have a significant effect on bipolar 1 patients' reactivity to external stressors. In addition, the results suggest that a more complex relationship exists among age, stress, and onset of new episodes than can be adequately explained by the kindling model.

Social rhythm disruption and stressful life events in the onset of bipolar and unipolar episodes

BACKGROUND

An association between social rhythm disruption (SRD) and onset of manic episodes has recently been observed. Whether other types of bipolar (depressive and cycling) or unipolar depressive episodes are similarly related to SRD is unclear, as is the association between severely threatening life events and onset of bipolar manic, depressed and cycling episodes.

METHODS

Bipolar patients with purely manic (N= 21), purely depressed (N = 21) and cycling (N = 24) episodes, and 44 patients with recurrent unipolar depression, were interviewed with the Bedford College Life Events and Difficulties Schedule. The presence of severe and SRD events during the year prior to index episode onset was then determined.

RESULTS

More manic than cycling and unipolar subjects experienced SRD events during 8- and 20-week pre-onset periods, and severe events during 20-week pre-onset periods. Controlling for age and prior number of episodes left most findings unchanged. An earlier finding of more manic subjects with SRD events in an 8-week pre-onset versus control period was also replicated.

CONCLUSIONS

It appears that manic onsets are influenced by stressful life events, especially those involving SRD, in a unique manner compared to onsets of other types of bipolar and unipolar episodes. Onset of bipolar cycling episodes, in contrast, seems to be relatively unaffected by SRD or severe life events. These findings refine the hypothesis that SRD may precipitate onset of affective episodes to be specific to manic onsets.

Is life stress more likely to provoke depressive episodes in women than in men?

One of the most consistent findings in psychiatric research is that rates of major depression are at least twofold higher among women than among men. Although there is considerable agreement in the literature that life events play a role in producing, triggering, or maintaining episodes of depression, less is known about the relationship among gender, life events, and depression. In the present study, we compared the rates, focus ("interpersonal" vs. "non-interpersonal"), and timing of stressful life experiences reported in rigorous interviews of male and female patients with unipolar recurrent depression and nondepressed contrast subjects. Consistent with hypotheses, female patients were more likely to experience stressful life experiences than their male counterparts; rates of stressful life experiences did not differ between female and male controls. Unexpectedly, rates of interpersonal stress did not differ among males and females regardless of patient or control status. We also found no significant differences in the timing of pre-onset events: stressful events were generally concentrated in the period immediately preceding onset for both men and women. Thus, although these data suggest that life stress may play a larger role in the provocation of recurrent episodes of depression for women than for men, there do not seem to be sex differences in the extent to which interpersonal vs. noninterpersonal events and difficulties are associated with depression onset or in the temporal distribution of events. Implications of these results are discussed in the context of research on other putative factors contributing to gender differences in rates of depression.

Interview schedule for children and adolescents (ISCA)

OBJECTIVE

To describe the development, use, and psychometric properties of the semistructured, symptom-oriented Interview Schedule for Children and Adolescents (ISCA) and its versions suitable for reevaluation.

METHOD

Data are summarized on the reliability, construct validity, and predictive validity of symptom ratings and resultant diagnoses, and information regarding the feasibility of a version of the ISCA for young adult subjects is presented.

RESULTS

The evidence suggests that these instruments yield reliable symptom ratings and diagnoses relevant to a wide range of syndromes and diagnoses over time and that the ISCA is useful with psychiatric and pediatric medical populations.

CONCLUSIONS

The ISCA and its follow-up versions are useful clinical tools in research focusing on developmental psychopathology.

Stressful life events and social rhythm disruption in the onset of manic and depressive bipolar episodes: a preliminary investigation

BACKGROUND

The association between stressful life events and onset of bipolar episodes is unclear. The association between bipolar episode onset and types of life events that disrupt social routines, and potentially sleep, has not yet been investigated.

METHODS

Thirty-nine bipolar patients with primarily manic (n = 20) or depressed (n = 19) index episodes were interviewed with the Bedford College Life Event and Difficulty Schedule to determine the presence of severe events during 8-week pre-onset and control periods. All life events were also rated for degree of social rhythm disruption (SRD).

RESULTS

More bipolar subjects experienced at least 1 SRD event and severe event in the pre-onset vs control periods. When subjects were divided into those with manic or depressive onsets, the only significant pre-onset vs control difference was for manic patients with SRD events. Additionally, the proportion of subjects with a pre-onset SRD event was greater for manic than for depressed patients.

CONCLUSIONS

We found evidence that life events characterized by SRDs routines are associated with the onset of manic, but not depressive, episodes. Severe events seem to be related to onset of bipolar episodes, although it remains unclear whether severe events relate differentially to depressive and manic onsets.

Psychoeducational workshops for elderly patients with recurrent major depression and their families

OBJECTIVE

This report details an extension of the use of psychoeducational workshops with psychiatric patients and their families to families of elderly patients with recurrent unipolar late-life depression.

METHODS

Subjects were 132 participants in a study of maintenance therapies for late-life depression and their 182 family members and significant others who accepted invitations to single-session family workshops. Participants provided feedback on their satisfaction with the content and quality of the workshops. Associations between workshop attendance, preworkshop demographic and clinical characteristics, treatment adherence, and outcome were explored through comparisons between 108 patients who attended workshops and 24 patients who declined the workshop invitation.

RESULTS

Favorable feedback from participants suggested that the extension of the workshops to families of elderly patients with depression was successful. Workshop attendance was associated with a lower rate of dropout during continuation treatment.

CONCLUSIONS

Results associating workshop refusal and treatment dropout, as well as the overall treatment compliance and retention rates in this randomized clinical trial involving geriatric patients, support the need for further study of factors relating to elderly patients' willingness to engage in family-centered interventions.

When reprimand consistency may and may not matter

The present study examined the importance of discipline consistency by varying not only the probability of punishment but also the nature of the discipline agent's response to nonpunished transgressions. Eighteen first through third graders attending a remedial summer school were assigned to one of four feedback conditions in a 2 (Low vs. High Reprimand Consistency) x 2 (Ignore vs. Attend) design. An analysis of the simple effects of reprimand consistency indicated that consistency was important only when the teacher's alternative response was attending. Thus the nature of the adult's response to nonpunished transgressions is important for understanding how discipline consistency affects children's behavior. The importance of conceptualizing discipline consistency as a multivariate construct and of understanding the variables and parameters that may interact with the probability of punishment are discussed.