A genetic approach to fracture epidemiology in childhood

Standardizing genetic and metabolic consults for non-accidental trauma at a large pediatric academic center

BACKGROUND

Evaluations of suspected non-accidental trauma (NAT) often include consultation with genetic and metabolic teams to assess patients for rare genetic conditions that can mimic or exacerbate child abuse. Diagnoses that may be questioned during court proceedings include osteogenesis imperfecta (OI) and glutaric aciduria type 1 (GA1). Currently there are no official society guidelines for the genetic or metabolic workup of suspected NAT.

OBJECTIVE

To standardize consult recommendations for suspected NAT through collaboration between the Genetics and Genomics Division and the Child Protection Team (CPT).

PARTICIPANTS AND SETTINGS

Children evaluated for suspected NAT at a single pediatric referral center.

METHODS

A year of inpatient consult requests for suspected NAT to the genetics division were reviewed. The most common indications for consult were fractures and subdural hematoma. Consult recommendations for similar indications varied between providers. A standard operating procedure (SOP) with specific recommendations for suspected NAT consults for fractures, intracranial hemorrhage, and other indications was created based on expert reviews and other relevant literature. A questionnaire assessing division practice patterns for these consults was distributed both pre (n = 17) and post-introduction of the SOP (n = 11).

RESULTS

Adherence to the SOP and impact on suspected NAT consult recommendations were assessed at 18 months after SOP introduction. Consult recommendations were in line with the SOP for 7/11 consults pre-intervention and 6/7 consults post-intervention. Providers were more likely to report feeling extremely or very confident they were using evidence-based medicine for NAT consults post-intervention.

The Polygenic and Monogenic Basis of Paediatric Fractures

PURPOSE OF REVIEW

Fractures are frequently encountered in paediatric practice. Although recurrent fractures in children usually unveil a monogenic syndrome, paediatric fracture risk could be shaped by the individual genetic background influencing the acquisition of bone mineral density, and therefore, the skeletal fragility as shown in adults. Here, we examine paediatric fractures from the perspective of monogenic and complex trait genetics.

RECENT FINDINGS

Large-scale genome-wide studies in children have identified ~44 genetic loci associated with fracture or bone traits whereas ~35 monogenic diseases characterized by paediatric fractures have been described. Genetic variation can predispose to paediatric fractures through monogenic risk variants with a large effect and polygenic risk involving many variants of small effects. Studying genetic factors influencing peak bone attainment might help in identifying individuals at higher risk of developing early-onset osteoporosis and discovering drug targets to be used as bone restorative pharmacotherapies to prevent, or even reverse, bone loss later in life.

Fracture Patterns Differ Between Osteogenesis Imperfecta and Routine Pediatric Fractures

BACKGROUND

It is important to estimate the likelihood that a pediatric fracture is caused by osteogenesis imperfecta (OI), especially the least severe type of OI (type 1).

METHODS

We reviewed records of 29,101 pediatric patients with fractures from 2003 through 2015. We included patients with closed fractures not resulting from motor vehicle accidents, gunshot wounds, nonaccidental trauma, or bone lesions. Patients with OI of any type were identified through International Classification of Diseases-9 code. We randomly sampled 500 pediatric patients in whom OI was not diagnosed to obtain a control (non-OI) group. We reviewed age at time of fracture, sex, fracture type, laterality, and bone and bone region fractured. Bisphosphonate use and OI type were documented for OI patients. Subanalysis of patients with type-1 OI was performed. The Fisher exact and χ tests were used to compare fracture rates between groups. P<0.05 was considered significant. Positive likelihood ratios for OI were calculated by fracture pattern.

RESULTS

The non-OI group consisted of 500 patients with 652 fractures. The OI group consisted of 52 patients with 209 fractures. Non-OI patients were older at the time of fracture (mean, 9.0±5.0 y) than OI patients (mean, 5.5±4.4 y) (P<0.001). OI patients had more oblique, transverse, diaphyseal, and bilateral long-bone fractures than non-OI patients (all P<0.001). Non-OI patients had more buckle (P=0.013), metaphyseal (P<0.001), and physeal (P<0.001) fractures than OI patients. For patients with type-1 OI and long-bone fractures (n=18), rates of transverse and buckle fractures were similar compared with controls. Transverse humerus (15.2), olecranon (13.8), and diaphyseal humerus (13.0) fractures had the highest positive likelihood ratios for OI, and physeal (0.09) and supracondylar humerus (0.1) fractures had the lowest.

CONCLUSIONS

Transverse and diaphyseal humerus and olecranon fractures were most likely to indicate OI. Physeal and supracondylar humerus fractures were least likely to indicate OI. Radiographic fracture pattern is useful for estimating likelihood of OI.

LEVEL OF EVIDENCE

Level III.

Current Practices and the Provider Perspectives on Inconclusive Genetic Test Results for Osteogenesis Imperfecta in Children with Unexplained Fractures: ELSI Implications

Genetic testing can be used to determine if unexplained fractures in children could have resulted from a predisposition to bone fractures, e.g., osteogenesis imperfecta. However, uncertainty is introduced if a variant of unknown significance (VUS) is identified. Proper interpretation of VUS in these situations is critical because of its influence on clinical care and in court rulings. This study sought to understand how VUS are interpreted and used by practitioners when there is a differential diagnosis including both osteogenesis imperfecta and non-accidental injury.A 15-question survey was emailed to physicians who requested analysis of two genes, COL1A1 and COL1A2, from the University of Washington from 2005-2013 for patient cases involving suspicion of child abuse.Among the 89 participants, responses differed about when genetic testing should be ordered for osteogenesis imperfecta, who should be consulted about utilization of VUS test results, follow-up procedures, and who should receive the VUS results.There are no clear guidelines for how to interpret and follow up on VUS. In the legal setting, misinterpreted VUS could lead to unintended consequences and deleterious ramifications for family members. The need for better practice guidelines to help promote more equitable handling of these sensitive legal cases is clear.

The Child with Multiple Fractures, What Next?

Fractures are common during childhood; however, they can also be the presenting symptom of primary or secondary causes of bone fragility. The challenge is to identify those children who warrant further investigation. In children who present with multiple fractures that are not commonly associated with mild to moderate trauma or whose fracture count is greater than what is typically seen for their age, an initial evaluation, including history, physical examination, biochemistry, and spinal radiography, should be performed. In children with bone pain or evidence of more significant bone fragility, referral for specialist evaluation and consideration of pharmacologic treatment may be warranted.

Bone structure at the distal radius during adolescent growth

The incidence of distal forearm fractures peaks during the adolescent growth spurt, but the structural basis for this is unclear. Thus, we studied healthy 6- to 21-yr-old girls (n = 66) and boys (n = 61) using high-resolution pQCT (voxel size, 82 microm) at the distal radius. Subjects were classified into five groups by bone-age: group I (prepuberty, 6-8 yr), group II (early puberty, 9-11 yr), group III (midpuberty, 12-14 yr), group IV (late puberty, 15-17 yr), and group V (postpuberty, 18-21 yr). Compared with group I, trabecular parameters (bone volume fraction, trabecular number, and thickness) did not change in girls but increased in boys from late puberty onward. Cortical thickness and density decreased from pre- to midpuberty in girls but were unchanged in boys, before rising to higher levels at the end of puberty in both sexes. Total bone strength, assessed using microfinite element models, increased linearly across bone age groups in both sexes, with boys showing greater bone strength than girls after midpuberty. The proportion of load borne by cortical bone, and the ratio of cortical to trabecular bone volume, decreased transiently during mid- to late puberty in both sexes, with apparent cortical porosity peaking during this time. This mirrors the incidence of distal forearm fractures in prior studies. We conclude that regional deficits in cortical bone may underlie the adolescent peak in forearm fractures. Whether these deficits are more severe in children who sustain forearm fractures or persist into later life warrants further study.

Temporal and spatial expression of collagens during murine atrioventricular heart valve development and maintenance

Heart valve function is achieved by organization of matrix components including collagens, yet the distribution of collagens in valvular structures is not well defined. Therefore, we examined the temporal and spatial expression of select fibril-, network-, beaded filament-forming, and FACIT collagens in endocardial cushions, remodeling, maturing, and adult murine atrioventricular heart valves. Of the genes examined, col1a1, col2a1, and col3a1 transcripts are most highly expressed in endocardial cushions. Expression of col1a1, col1a2, col2a1, and col3a1 remain high, along with col12a1 in remodeling valves. Maturing neonate valves predominantly express col1a1, col1a2, col3a1, col5a2, col11a1, and col12a1 within defined proximal and distal regions. In adult valves, collagen protein distribution is highly compartmentalized, with ColI and ColXII observed on the ventricular surface and ColIII and ColVa1 detected throughout the leaflets. Together, these expression data identify patterning of collagen types in developing and maintained heart valves, which likely relate to valve structure and function.

Autosomal dominant gigantiform cementoma associated with bone fractures

Here, we report a family with gigantiform cementomas, bone fractures, and autosomal dominant inheritance. Lesions are composed of benign, lobulated, calcified masses resembling cementum. Identification of a COL1A2 mutation in one patient was a polymorphism of no pathological significance. The subject of gigantiform cementomas and the associated bone disorder is both confusing and complex. Reported familial instances indicate genetic heterogeneity with (1) osteopenia and bone fractures, (2) one form of osteogenesis imperfecta, and (3) a polyostotic diaphyseal bone disorder.

Bone mineral density in children and adolescents with neurofibromatosis type 1

OBJECTIVE

To assess whether children and adolescents with neurofibromatosis type 1 (NF1) have decreased bone mineral density (BMD).

STUDY DESIGN

Bone densitometry of the whole body, hip, and lumbar spine was used in a case-to-control design (84 individuals with NF1: 293 healthy individuals without NF1). Subjects were 5 to 18 years old. Subjects with NF1 were compared with control subjects by using an analysis-of-covariance with a fixed set of covariates (age, weight, height, Tanner stage, and sex).

RESULTS

Subjects with NF1 had decreased areal BMD (aBMD) of the hip (P <.0001), femoral neck (P <.0001), lumbar spine (P = .0025), and whole body subtotal (P <.0001). When subjects with NF1 were separated in groups with and without a skeletal abnormality, those who did not have a skeletal abnormality still had statistically significant decreases in aBMD compared with control subjects (P <.0001 for whole body subtotal aBMD), although they were less pronounced than in those with osseous abnormalities.

CONCLUSIONS

These data suggest that individuals with NF1 have a unique generalized skeletal dysplasia, predisposing them to localized osseous defects. Dual energy x-ray absorptiometry may prove useful in identifying individuals with NF1 who are at risk for clinical osseous complications and monitoring therapeutic trials.

The new bone biology: Pathologic, molecular, and clinical correlates

Bone and cartilage and their disorders are addressed under the following headings: functions of bone; normal and abnormal bone remodeling; osteopetrosis and osteoporosis; epithelial-mesenchymal interaction, condensation and differentiation; osteoblasts, markers of bone formation, osteoclasts, components of bone, and pathology of bone; chondroblasts, markers of cartilage formation, secondary cartilage, components of cartilage, and pathology of cartilage; intramembranous and endochondral bone formation; RUNX genes and cleidocranial dysplasia (CCD); osterix; histone deacetylase 4 and Runx2; Ligand to receptor activator of NFkappaB (RANKL), RANK, osteoprotegerin, and osteoimmunology; WNT signaling, LRP5 mutations, and beta-catenin; the role of leptin in bone remodeling; collagens, collagenopathies, and osteogenesis imperfecta; FGFs/FGFRs, FGFR3 skeletal dysplasias, craniosynostosis, and other disorders; short limb chondrodysplasias; molecular control of the growth plate in endochondral bone formation and genetic disorders of IHH and PTHR1; ANKH, craniometaphyseal dysplasia, and chondrocalcinosis; transforming growth factor beta, Camurati-Engelmann disease (CED), and Marfan syndrome, types I and II; an ACVR1 mutation and fibrodysplasia ossificans progressiva; MSX1 and MSX2: biology, mutations, and associated disorders; G protein, activation of adenylyl cyclase, GNAS1 mutations, McCune-Albright syndrome, fibrous dysplasia, and Albright hereditary osteodystrophy; FLNA and associated disorders; and morphological development of teeth and their genetic mutations.