WNT1 mutations in early-onset osteoporosis and osteogenesis imperfecta

This report identifies human skeletal diseases associated with mutations in WNT1. In 10 family members with dominantly inherited, early-onset osteoporosis, we identified a heterozygous missense mutation in WNT1, c.652T→G (p.Cys218Gly). In a separate family with 2 siblings affected by recessive osteogenesis imperfecta, we identified a homozygous nonsense mutation, c.884C→A, p.Ser295*. In vitro, aberrant forms of the WNT1 protein showed impaired capacity to induce canonical WNT signaling, their target genes, and mineralization. In mice, Wnt1 was clearly expressed in bone marrow, especially in B-cell lineage and hematopoietic progenitors; lineage tracing identified the expression of the gene in a subset of osteocytes, suggesting the presence of altered cross-talk in WNT signaling between the hematopoietic and osteoblastic lineage cells in these diseases.

Tracking motor units longitudinally across experimental sessions with high-density surface electromyography

KEY POINTS

Classic motor unit (MU) recording and analysis methods do not allow the same MUs to be tracked across different experimental sessions, and therefore, there is limited experimental evidence on the adjustments in MU properties following training or during the progression of neuromuscular disorders. We propose a new processing method to track the same MUs across experimental sessions (separated by weeks) by using high-density surface electromyography. The application of the proposed method in two experiments showed that individual MUs can be identified reliably in measurements separated by weeks and that changes in properties of the tracked MUs across experimental sessions can be identified with high sensitivity. These results indicate that the behaviour and properties of the same MUs can be monitored across multiple testing sessions. The proposed method opens new possibilities in the understanding of adjustments in motor unit properties due to training interventions or the progression of pathologies.

ABSTRACT

A new method is proposed for tracking individual motor units (MUs) across multiple experimental sessions on different days. The technique is based on a novel decomposition approach for high-density surface electromyography and was tested with two experimental studies for reliability and sensitivity. Experiment I (reliability): ten participants performed isometric knee extensions at 10, 30, 50 and 70% of their maximum voluntary contraction (MVC) force in three sessions, each separated by 1 week. Experiment II (sensitivity): seven participants performed 2 weeks of endurance training (cycling) and were tested pre-post intervention during isometric knee extensions at 10 and 30% MVC. The reliability (Experiment I) and sensitivity (Experiment II) of the measured MU properties were compared for the MUs tracked across sessions, with respect to all MUs identified in each session. In Experiment I, on average 38.3% and 40.1% of the identified MUs could be tracked across two sessions (1 and 2 weeks apart), for the vastus medialis and vastus lateralis, respectively. Moreover, the properties of the tracked MUs were more reliable across sessions than those of the full set of identified MUs (intra-class correlation coefficients ranged between 0.63-0.99 and 0.39-0.95, respectively). In Experiment II, ∼40% of the MUs could be tracked before and after the training intervention and training-induced changes in MU conduction velocity had an effect size of 2.1 (tracked MUs) and 1.5 (group of all identified motor units). These results show the possibility of monitoring MU properties longitudinally to document the effect of interventions or the progression of neuromuscular disorders.

A novel splice mutation in PLS3 causes X-linked early onset low-turnover osteoporosis

Genetic factors play an important role in the development of osteoporosis. Several monogenic forms of osteoporosis have been recognized, most recently an X-chromosomal form resulting from mutations in the gene encoding plastin 3 (PLS3). PLS3 is a protein involved in actin bundle formation in the cytoskeleton. We present a large family with early onset osteoporosis and X-linked inheritance. Phenotyping was performed on 19 family members and whole-exome sequencing on 7 family members (5 with a diagnosis of early onset osteoporosis and 2 with normal bone parameters). Osteoporosis had its onset in childhood and was characterized by recurrent peripheral fractures, low bone mineral density (BMD), vertebral compression fractures, and significant height loss in adulthood. Males were in general more severely affected than females. Bone histomorphometry findings in 4 males and 1 female showed severe trabecular osteoporosis, low amount of osteoid, and decreased mineral apposition rate, indicating impaired bone formation; resorption parameters were increased in some. All affected subjects shared a single base substitution (c.73-24T > A) in intron 2 of PLS3 on Xq23. The mutation, confirmed by Sanger sequencing, segregated according to the skeletal phenotype. The mutation introduces a new acceptor splice site with a predicted splice score of 0.99 and, thereby, as confirmed by cDNA sequencing, induces the insertion of 22 bases between exons 2 and 3, causing a frameshift and premature termination of mRNA translation (p.Asp25Alafs*17). The mutation affects the first N-terminal calcium-binding EF-hand domain and abolishes all calcium- and actin-binding domains of the protein. Our results confirm the role of PLS3 mutations in early onset osteoporosis. The mechanism whereby PLS3 affects bone health is unclear, but it may be linked to osteocyte dendrite function and skeletal mechanosensing. Future studies are needed to elucidate the role of PLS3 in osteoporosis and to define optimal treatment.

High-density surface electromyography provides reliable estimates of motor unit behavior

OBJECTIVE

To assess the intra- and inter-session reliability of estimates of motor unit behavior and muscle fiber properties derived from high-density surface electromyography (HDEMG).

METHODS

Ten healthy subjects performed submaximal isometric knee extensions during three recording sessions (separate days) at 10%, 30%, 50% and 70% of their maximum voluntary effort. The discharge timings of motor units of the vastus lateralis and medialis muscles were automatically identified from HDEMG by a decomposition algorithm. We characterized the number of detected motor units, their discharge rates, the coefficient of variation of their inter-spike intervals (CoVisi), the action potential conduction velocity and peak-to-peak amplitude. Reliability was assessed for each motor unit characteristics by intra-class correlation coefficient (ICC). Additionally, a pulse-to-noise ratio (PNR) was calculated, to verify the accuracy of the decomposition.

RESULTS

Good to excellent reliability within and between sessions was found for all motor unit characteristics at all force levels (ICCs>0.8), with the exception of CoVisi that presented poor reliability (ICC<0.6). PNR was high and similar for both muscles with values ranging between 45.1 and 47.6dB (accuracy>95%).

CONCLUSION

Motor unit features can be assessed non-invasively and reliably within and across sessions over a wide range of force levels.

SIGNIFICANCE

These results suggest that it is possible to characterize motor units in longitudinal intervention studies.

Skeletal Characteristics of WNT1 Osteoporosis in Children and Young Adults

WNT proteins comprise a 19-member glycoprotein family that act in several developmental and regenerative processes. In bone, WNT proteins regulate osteoblast differentiation and maintain bone health by activating the canonical WNT/β-catenin pathway. We reported a heterozygous missense mutation c.652T>G (p.C218G) in WNT1 exon 4 as the cause for severe early-onset, autosomal dominant osteoporosis. The initial study concerned a large Finnish family with 10 affected adults. Here we report clinical findings of the WNT1 osteoporosis in 8 children and young adults (median age 14 years; range 10 to 30 years) in two families, all with the p.C218G mutation in WNT1. Clinical assessments showed no apparent dysmorphia or features similar to typical osteogenesis imperfecta (OI). Biochemistry revealed no changes in parameters of calcium metabolism and bone turnover markers. Fracture frequencies varied, but all subjects had sustained at least one fracture and 4 had a pathological fracture history. Plain radiographs showed osteopenic appearance, loss in vertebral height, and thin diaphyses of the long bones. Bone densitometry showed the BMD to be below normal median in all subjects and the bone mass deficit seemed to be more severe in older participants. Bone histomorphometry revealed a low turnover osteoporosis in 2 subjects at ages 14 and 16 years. These findings are congruent with earlier findings in adult patients and indicate that WNT1 osteoporosis causes significant skeletal changes already in early childhood and impairs bone mass gain during pubertal years. Genetic testing of children or close relatives of affected individuals is recommended for appropriate preventive measures. © 2016 American Society for Bone and Mineral Research.

Normocalcaemic, vitamin D-sufficient hyperparathyroidism - high prevalence and low morbidity in the general population: A long-term follow-up study, the WHO MONICA project, Gothenburg, Sweden

OBJECTIVE

There is limited knowledge about the natural history of normocalcaemic, vitamin D-sufficient hyperparathyroidism (nHPT). The aim was to study the prevalence of nHPT and its relation to morbidity.

DESIGN

Cross-sectional and retrospective study at the Sahlgrenska University Hospital, Gothenburg, Sweden.

SUBJECTS

A random population of 608 men and women, age 25-64 years, was studied in 1995 as part of the WHO MONICA study and reinvestigated in 2008 (n = 410, of whom 277 were vitamin D sufficient).

MEASUREMENTS

A serum intact parathyroid hormone (S-PTH) ≥60 ng/l was considered as HPT, S-calcium 2·15-2·49 mmol/l as normocalcaemia and S-25(OH)D ≥ 50 nmol/l as vitamin D sufficiency. Data on fractures, stroke and myocardial infarction were retrieved until 2013, that is a 17-year follow-up.

RESULTS

The prevalence of nHPT was 2·0% in 1995 (age 25-64) and 11·0% in 2008 (age 38-79). S-PTH was positively correlated with age and BMI. After adjustment for these variables, a high S-PTH level (≥60 ng/l) at follow-up was associated with previously low S-25(OH)D, high osteocalcin, S-PTH and both past and presently treated hypertension. No relation was seen with creatinine, cystatin C, malabsorption markers, thyroid function, glucose, insulin, lipids, calcaneal quantitative ultrasound, fractures, myocardial infarction, stroke or death at follow-up.

CONCLUSIONS

This small random population study showed that nHPT was common, 11% at follow-up. Only one individual developed mild hypercalcaemia in 13 years. Previous S-PTH was predictive of nHPT and hypertension was prevalent, but no increase in hard end-points was seen over a 17-year period.

Osteoporosis-pseudoglioma syndrome: three novel mutations in the LRP5 gene and response to bisphosphonate treatment

BACKGROUND/AIMS

Osteoporosis-pseudoglioma (OPPG) syndrome is a rare disorder characterized by congenital or infancy-onset visual loss and severe juvenile osteoporosis. OPPG is caused by homozygous mutations in the low-density lipoprotein receptor-related protein 5 (LRP5) gene. We present three novel homozygous LRP5 mutations found in 3 unrelated Turkish children with consanguineous parents, along with clinical phenotypes and response to treatment with bisphosphonates (bisP).

METHODS/RESULTS

The LRP5 gene was analyzed by direct sequencing after PCR amplification. Mutation screening for LRP5 revealed homozygous nonsense R1002X mutation in the first patient and homozygous missense mutations V336M and G507S in the second and third patient, respectively. The parents were heterozygous for these mutations. The patients' eye symptoms began during the first months of life but the OPPG diagnoses were made based on skeletal deformities and osteopenia after 4 years of age. The patients' bone mineral density Z scores were very low and consistent with osteopenia. All patients were treated with bisP for 3.5-7 years.

CONCLUSION

We report three novel LRP5 mutations in 3 Turkish patients with OPPG. We show that the response of bisP therapy has improved the lumbar spinal bone mineral density Z scores and the patients' quality of life as the bone pains decreased.

Osteocyte Protein Expression Is Altered in Low-Turnover Osteoporosis Caused by Mutations in WNT1 and PLS3

CONTEXT

Osteocytes express proteins that regulate bone remodeling and mineralization.

OBJECTIVE

To evaluate the relationship between osteocyte-specific protein expression and bone histology in patients with monogenic osteoporosis due to wingless integration site 1 (WNT1) or plastin 3 (PLS3) mutations.

DESIGN AND SETTING

Cross-sectional cohort study at a university hospital.

PARTICIPANTS

Six patients (four males; ages: 14 to 72 years) with a heterozygous WNT1 mutation and five patients (four males; ages: 9 to 70 years) with a heterozygous/hemizygous PLS3 mutation.

METHODS AND MAIN OUTCOME MEASURES

Immunohistochemistry was performed for fibroblast growth factor 23 (FGF23), dentin matrix protein 1 (DMP1), sclerostin, and phosphorylated (phospho-)β-catenin in iliac crest samples and compared with bone histomorphometry.

RESULTS

FGF23 expression in WNT1 patients was 243% that observed in PLS3 patients (P < 0.01). DMP1, sclerostin, and phospho-β-catenin expression did not differ between groups. Serum phosphate correlated inversely with FGF23 expression (r = -0.79, P = 0.01) and serum ionized calcium correlated inversely with sclerostin expression (r = -0.60, P = 0.05). Phospho-β-catenin expression correlated inversely with DMP1 expression (r = -0.88, P < 0.001), osteoid volume/bone volume (r = -0.68, P = 0.02), and bone formation rate (r = -0.78, P < 0.01). FGF23 expression did not correlate with DMP1 expression, sclerostin expression, or bone histomorphometry. Marrow adiposity was higher in WNT1 than in PLS3 patients (P = 0.04).

CONCLUSIONS

Mutations that disrupt WNT signaling and osteocytic mechanosensing affect osteocyte protein expression. Abnormal osteocyte function may play a role in the pathogenesis of monogenetic forms of osteoporosis.

FGF23 gene variation and its association with phosphate homeostasis and bone mineral density in Finnish children and adolescents

Fibroblast growth factor 23 (FGF23), a bone-derived hormone, participates in the hormonal bone-parathyroid-kidney axis, which is modulated by PTH, 1,25-dihydroxyvitamin D, plasma phosphate (Pi), and diet. Inappropriately high serum FGF23, seen in certain genetic and acquired disorders, results in urinary phosphate wasting and impaired bone mineralization. This study investigated the impact of FGF23 gene variation on phosphate homeostasis and bone health. The study included 183 children and adolescents (110 girls) aged 7-19 years (median 13.2years). Urine and blood parameters of calcium and phosphate homeostasis were analyzed. Bone characteristics were quantified by DXA and peripheral quantitative computed tomography (pQCT). Genetic FGF23 variation was assessed by direct sequencing of coding exons and flanking intronic regions. Nine FGF23 polymorphisms were detected; three of them were common: rs3832879 (c.212-37insC), rs7955866 (c.716C>T, p.T239M) and rs11063112 (c.2185A>T). Four different haplotypes and six different diplotypes were observed among these three polymorphisms. The variations in FGF23 significantly associated with plasma PTH and urinary Pi excretion, even after adjusting for relevant covariates. FGF23 variations independently associated with total hip BMD Z-score, but not with other bone outcomes. In instrument analysis, genetic variance in FGF23 was considered a weak instrument as it only induced small variations in circulating FGF23, PTH and Pi concentrations (F statistic less than 10). The observed associations between FGF23 variations and circulating PTH, and Pi excretion and total hip BMD Z-scores suggest that FGF23 polymorphisms may play a role in mineral homeostasis and bone metabolism.

Primary osteoporosis without features of OI in children and adolescents: clinical and genetic characteristics

Our aim was to characterize clinical findings and familial associations, and to examine candidate genes for disease-causing mutations in a cohort of children suffering from primary osteoporosis without features of osteogenesis imperfecta. Patients with osteoporosis and their nuclear families were studied. Medical history was reviewed. Calcium homeostasis parameters were measured and spinal radiographs obtained. BMD was determined by DXA for patients, parents and siblings. LRP5, LRP6, and PTHLH genes were sequenced. Twenty-seven patients (14 males) from 24 families were recruited. Median age at presentation was 10.1 years (range 3.3-15.6 years). One-third of the children had at least one parent with a BMD below the expected range for age. LRP5, LRP6, and PTHLH showed no causative mutations. Four polymorphisms in LRP5 were overrepresented in patients; the minor allele frequency of Q89R, V667M, N740N, and A1330V was significantly higher than in controls. Age of onset, clinical severity, and inheritance patterns are variable in children with primary osteoporosis. Several patients had evidence suggestive of familial transmission. The underlying genetic factors remain to be elucidated.

Bone material properties and response to teriparatide in osteoporosis due to WNT1 and PLS3 mutations

CONTEXT

Patients with osteoporosis-associated WNT1 or PLS3 mutations have unique bone histomorphometric features and osteocyte-specific hormone expression patterns.

OBJECTIVE

To investigate the effects of WNT1 and PLS3 mutations on bone material properties.

DESIGN

Transiliac bone biopsies were evaluated by quantitative backscattered electron imaging, immunohistochemistry, and bone histomorphometry.

SETTING

Ambulatory patients.

PATIENTS

Three pediatric and eight adult patients with WNT1 or PLS3 mutations.

INTERVENTION

Bone mineralization density distribution and osteocyte protein expression was evaluated in 11 patients and repeated in six patients who underwent repeat biopsy after 24 months of teriparatide treatment.

MAIN OUTCOME MEASURE

Bone mineralization density distribution and protein expression.

RESULTS

Children with WNT1 or PLS3 mutations had heterogeneous bone matrix mineralization, consistent with bone modeling during growth. Bone matrix mineralization was homogenous in adults and increased throughout the age spectrum. Teriparatide had very little effect on matrix mineralization or bone formation in patients with WNT1 or PLS3 mutations. However, teriparatide decreased trabecular osteocyte lacunae size and increased trabecular bone FGF23 expression.

CONCLUSION

The contrast between preserved bone formation with heterogeneous mineralization in children and low bone turnover with homogenous bone mineral content in adults suggests that WNT1 and PLS3 have differential effects on bone modeling and remodeling. The lack of change in matrix mineralization in response to teriparatide, despite clear changes in osteocyte lacunae size and protein expression, suggests that altered WNT1 and PLS3 expression may interfere with coupling of osteocyte, osteoblast, and osteoclast function. Further studies are warranted to determine the mechanism of these changes.

Diagnosis of Osteoporosis in Children and Adolescents

Osteoporosis is traditionally regarded as a disease of elderly women. However, this bone disorder occurs in patients of both sexes and of all ages and is also increasingly recognised in the paediatric setting. In particular, patients, including young children, with other chronic diseases are at risk of developing bone fragility. There are also several forms of hereditary osteoporosis, which should be identified at an early stage to ensure adequate treatment. The diagnosis of osteoporosis in children is challenging, since their bone mineral density (BMD) is affected by growth and pubertal development. In addition to low BMD, a child must also exhibit a significant proneness to fractures before the osteoporosis diagnosis can be made. Through early diagnosis and treatment for paediatric bone fragility, we can also ameliorate bone health in adulthood. In this article we review the aetiology, known risk factors and the diagnostic criteria of osteoporosis in the young.

COL1A1 mutation in an Indian child with Caffey disease

Caffey disease or infantile cortical hyperostosis is a rare skeletal disorder with both sporadic and familial occurrence. The autosomal dominant familial form has been found to be a collagenopathy. The case being reported is a 7- month-old Indian boy with Caffey disease who was found to have the R1014C heterozygous mutation in the COL1A1 gene. This is the first mutation report of an Indian case with Caffey disease.

Low health-related quality of life in hypoparathyroidism and need for PTH analog

OBJECTIVE

Hypoparathyroidism (HypoPT) is a rare endocrine disorder in which insufficient levels of parathyroid hormone (PTH) lead to low serum calcium (S-Ca) levels and muscular cramps. The aim was to study the health-related quality of life (HRQoL) and comorbidities in patients with HypoPT compared with the general population and to estimate the need of treatment with PTH analog.

DESIGN

Patients with HypoPT were identified and compared with a population sample. Short Form-36 (SF-36) and EuroQol-5 Dimensions Visual Analogue Scale questionnaires were used. All patients were followed up at the Sahlgrenska University Hospital outpatient clinic.

METHODS

From the medical records between 2007 and 2020, 203 patients with HypoPT were identified and compared with a population sample (n = 414) from the World Health Organization's (WHO) MONICA project, Gothenburg, Sweden. Of the 203 patients who met the diagnostic criteria, 164 were alive and 65% answered the HRQoL questionnaires.

RESULTS

Patients with HypoPT, 80% postsurgical, and controls had similar age (60 years) and sex distribution (80% women). Patients had lower SF-36 summary component scores for physical (40.0 (interquartile range (IQR): 21) vs 51.2 (IQR: 14.6); P < 0.001) and mental (43.1 (IQR:17.4) vs 56.1(IQR:13.3); P < 0.001) well-being, irrespective of etiology or calcium levels. Individuals with HypoPT had more medications and lower renal function but not higher mortality than controls. Low HRQoL together with low calcium was present in 23% of individuals with HypoPT.

CONCLUSION

HRQoL was markedly lower in patients with HypoPT than in controls and independent of S-Ca levels. Treatment with PTH analog could be considered at least among patients with both low HRQoL and low calcium levels.

Hyperparathyroidism in men - morbidity and mortality during 21 years' follow-up

Hyperparathyroidism (HPT), including normocalcaemic, vitamin D sufficient (Serum (S)-25(OH)D ≥ 50 nmol/L) hyperparathyroidism (nHPT), has increasingly been diagnosed in the last few decades due to the more common use of the serum parathyroid hormone (S-PTH) assay. We investigated if men with HPT had higher morbidity and mortality than men without HPT during 21 years' follow-up.A random population sample of 750 men, all 50 years of age, was examined in 1993. Endpoints were retrieved 21 years later at 71 years of age.Albumin-corrected serum (S) calcium, S-25-hydroxyvitamin D and S-PTH were assessed along with data on cardiovascular risk factors and medication. Outcome data on fractures, stroke, myocardial infarction, cancer and death were retrieved in 2014; 21 years after primary assessment. The prevalence of HPT at 50 years of age was 9.3%; nHPT 2.8%, primary HPT 0.4%, secondary HPT 0.4%, and HPT with vitamin D insufficiency 6%. Fracture rate, myocardial infarction, stroke, cancer and death occurred similarly in men with or without HPT, as well as in men with nHPT as compared with men without calcium/PTH aberrations during 21 years' follow-up. S-PTH was evenly distributed in the univariable analyses for each outcome. Cox regression analyses showed no increase in serious morbidity or in mortality in men with HPT, irrespective of cause, compared with men with normal S-PTH over a 21-year period. None had HPT at a S-25(OH)D level of 100 nmol/L.

Aortic size predicts aortic dissection in Turner syndrome - A 25-year prospective cohort study

BACKGROUND

Women with Turner syndrome (TS) have an increased risk of aortic dissection. The current recommended cutoff to prevent aortic dissection in TS is an aortic size index (ASI) of ≥2.5 cm/m². This study estimated which aortic size had the best predictive value for the risk of aortic dissection, and whether adjusting for body size improved risk prediction.

METHODS

A prospective, observational study in Sweden, of women with TS, n = 400, all evaluated with echocardiography of the aorta and data on medical history for up to 25 years. Receiver operating characteristic (ROC) curves, sensitivity and specificity were calculated for the absolute ascending aortic diameter (AAD), ascending ASI and TS specific z-score.

RESULTS

There were 12 patients (3%) with aortic dissection. ROC curves demonstrated that absolute AAD and TS specific z-score were superior to ascending ASI in predicting aortic dissection. The best cutoff for absolute AAD was 3.3 cm and 2.12 for the TS specific z-score, respectively, with a sensitivity of 92% for both. The ascending ASI cutoff of 2.5 cm/m² had a sensitivity of 17% only. Subgroup analyses in women with an aortic diameter ≥ 3.3 cm could not demonstrate any association between karyotype, aortic coarctation, bicuspid aortic valve, BMI, antihypertensive medication, previous growth hormone therapy or ongoing estrogen replacement treatment and aortic dissection. All models failed to predict a dissection in a pregnant woman.

CONCLUSIONS

In Turner syndrome, absolute AAD and TS-specific z-score were more reliable predictors for aortic dissection than ASI. Care should be taken before and during pregnancy.

Case report: fast reversal of severe osteoporosis after correction of excessive levothyroxine treatment and long-term follow-up

This case report describes a 38-year-old woman, who presented with bilateral femoral stress fractures and osteoporosis after years of excessive levothyroxine treatment. Her bone health was restored rapidly and long-lasting with the reduction of levothyroxine dosage. No bone-active treatment was warranted.

INTRODUCTION

Hyperthyroidism is a known risk factor for osteoporosis and fractures. Recent studies on patients with serum thyrotropin-suppressive therapy have not, however, indicated adverse effects on bone during long-term follow-up.

METHODS

This case report describes long-term follow-up data of a clinically euthyreoid patient, who developed symptomatic osteoporosis due to excessive levothyroxine treatment.

RESULTS

After correction of levothyroxine dosage, her bone mineral density (BMD) and previously elevated serum osteocalcin levels normalized rapidly and she remained free from fractures during 23 years of follow-up over menopause.

CONCLUSION

Excessive TSH suppression contributed to the secondary osteoporosis in this patient; BMD normalized after dose reduction of levothyroxine and no fractures occurred during 23 years' follow-up. Some patients develop severe osteoporosis if they are over-substituted with levothyroxine, and decent follow-up of patients with levothyroxine supplementation is mandatory.