Genetic spectrum of prenatally diagnosed skeletal dysplasias in a Finnish patient cohort.

OBJECTIVE: This retrospective cohort study aims to describe the genetic spectrum of fetal skeletal dysplasias detected in a Finnish patient cohort and the diagnostic yield of various analysis methods used. METHOD: A total of 121 pregnancies with prenatally suspected or diagnosed skeletal dysplasia were analyzed between 2013 and 2020. Clinical details and findings from genetic testing were collected. RESULTS: Abnormal ultrasound triggered further testing in most cases. However, there were several cases with increased nuchal translucency and/or abnormal risk ratio in the first trimester combined screening as the initial finding. Further genetic testing was performed in 84/121 (69.4%) cases. A genetic diagnosis was confirmed in 36/84 (42.9%) cases. Half of the identified cases could be attributed to a founder mutation specific to the Finnish Disease Heritage, whereas the other half consisted of a variety of other genetic defects. CONCLUSION: In our patient cohort, the overall genetic spectrum of prenatally diagnosed skeletal dysplasias was wide. However, the impact of Finnish founder mutations was considerable, suggesting that the genetic spectrum of skeletal dysplasias may differ significantly between populations. This should be taken into consideration during the diagnostic process especially as initial ultrasound findings may be unspecific and the interpretation of ultrasound features is usually difficult.

Oligogenic Inheritance of Monoallelic TRIP11, FKBP10, NEK1, TBX5, and NBAS Variants Leading to a Phenotype Similar to Odontochondrodysplasia.

Skeletal dysplasias are often well characterized, and only a minority of the cases remain unsolved after a thorough analysis of pathogenic variants in over 400 genes that are presently known to cause monogenic skeletal diseases. Here, we describe an 11-year-old Finnish girl, born to unrelated healthy parents, who had severe short stature and a phenotype similar to odontochondrodysplasia (ODCD), a monogenic skeletal dysplasia caused by biallelic TRIP11 variants. The family had previously lost a fetus due to severe skeletal dysplasia. Exome sequencing and bioinformatic analysis revealed an oligogenic inheritance of a heterozygous nonsense mutation in TRIP11 and four likely pathogenic missense variants in FKBP10, TBX5, NEK1, and NBAS in the index patient. Interestingly, all these genes except TBX5 are known to cause skeletal dysplasia in an autosomal recessive manner. In contrast, the fetus was found homozygous for the TRIP11 mutation, and achondrogenesis type IA diagnosis was, thus, molecularly confirmed, indicating two different skeletal dysplasia forms in the family. To the best of our knowledge, this is the first report of an oligogenic inheritance model of a skeletal dysplasia in a Finnish family. Our findings may have implications for genetic counseling and for understanding the yet unsolved cases of rare skeletal dysplasias.

Positive airway pressure therapy for obstructive sleep apnea in patients with Osteogenesis imperfecta: a prospective pilot study.

BACKGROUND: Obstructive sleep apnea (OSA) is prevalent in individuals with Osteogenesis imperfecta (OI). To date, no study has investigated treatment of OSA in adult individuals with OI using positive airway pressure (PAP). This observational pilot study examined the adherence of adults with OI to treatment of OSA with PAP therapy, and the evolution of self-experienced sleepiness and depression symptoms before and after treatment. METHODS: We included 20 patients, with a mean age of 51 years, who represented varying severity of OI and displayed an apnea and hypopnea index ≥ 5 /sleeping hour as recorded by an overnight polysomnography. PAP therapy was proposed to all patients. Epworth Sleepiness Scale (ESS) questionnaire to evaluate daytime sleepiness, and a validated self-rating depression questionnaire to identify possible depression, were completed prior to PAP therapy and repeated after a minimum of one year. The datasets supporting the conclusions of this article are included within the article. RESULTS: From the 20 patients, 15 initiated PAP therapy, and two patients later interrupted it. The mean PAP follow-up period was 1230 days. At baseline, an abnormally high ESS score was reported by 29% of the respondents, and an abnormally high number of symptoms suggesting depression by 29%. Follow-up questionnaires were completed by 60% of the patients, of whom 83% were adherent to PAP treatment. ESS score and depression symptoms did not decrease significantly with PAP therapy. CONCLUSIONS: Patients with OI accepted well PAP therapy and remained compliant. Sleepiness and depression persisted unaltered despite good PAP adherence. These unexpectedly poor improvements in symptoms by PAP therapy may be due to subjective depression symptoms and the complexity of factors underlying persisting sleepiness in OI. Further research is needed to confirm this novel finding.

Novel RPL13 Variants and Variable Clinical Expressivity in a Human Ribosomopathy With Spondyloepimetaphyseal Dysplasia.

Spondyloepimetaphyseal dysplasias (SEMDs) are a heterogeneous group of disorders with variable growth failure and skeletal impairments affecting the spine and long bone epiphyses and metaphyses. Here we report on four unrelated families with SEMD in which we identified two monoallelic missense variants and one monoallelic splice site variant in RPL13, encoding the ribosomal protein eL13. In two out of four families, we observed autosomal dominant inheritance with incomplete penetrance and variable clinical expressivity; the phenotypes of the mutation-positive subjects ranged from normal height with or without hip dysplasia to severe SEMD with severe short stature and marked skeletal dysplasia. In vitro studies on patient-derived dermal fibroblasts harboring RPL13 missense mutations demonstrated normal eL13 expression, with proper subcellular localization but reduced colocalization with eL28 (p < 0.001). Cellular functional defects in fibroblasts from mutation-positive subjects indicated a significant increase in the ratio of 60S subunits to 80S ribosomes (p = 0.007) and attenuated global translation (p = 0.017). In line with the human phenotype, our rpl13 mutant zebrafish model, generated by CRISPR-Cas9 editing, showed cartilage deformities at embryonic and juvenile stages. These findings extend the genetic spectrum of RPL13 mutations causing this novel human ribosomopathy with variable skeletal features. Our study underscores for the first time incomplete penetrance and broad phenotypic variability in SEMD-RPL13 type and confirms impaired ribosomal function. Furthermore, the newly generated rpl13 mutant zebrafish model corroborates the role of eL13 in skeletogenesis. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR)..

Hypomorphic Mutations in TONSL Cause SPONASTRIME Dysplasia.

SPONASTRIME dysplasia is a rare, recessive skeletal dysplasia characterized by short stature, facial dysmorphism, and aberrant radiographic findings of the spine and long bone metaphysis. No causative genetic alterations for SPONASTRIME dysplasia have yet been determined. Using whole-exome sequencing (WES), we identified bi-allelic TONSL mutations in 10 of 13 individuals with SPONASTRIME dysplasia. TONSL is a multi-domain scaffold protein that interacts with DNA replication and repair factors and which plays critical roles in resistance to replication stress and the maintenance of genome integrity. We show here that cellular defects in dermal fibroblasts from affected individuals are complemented by the expression of wild-type TONSL. In addition, in vitro cell-based assays and in silico analyses of TONSL structure support the pathogenicity of those TONSL variants. Intriguingly, a knock-in (KI) Tonsl mouse model leads to embryonic lethality, implying the physiological importance of TONSL. Overall, these findings indicate that genetic variants resulting in reduced function of TONSL cause SPONASTRIME dysplasia and highlight the importance of TONSL in embryonic development and postnatal growth.

Novel fibronectin mutations and expansion of the phenotype in spondylometaphyseal dysplasia with "corner fractures".

Heterozygous pathogenic variants in the FN1 gene, encoding fibronectin (FN), have recently been shown to be associated with a skeletal disorder in some individuals affected by spondylometaphyseal dysplasia with "corner fractures" (SMD-CF). The most striking feature characterizing SMD-CF is irregularly shaped metaphyses giving the appearance of "corner fractures". An array of secondary features, including developmental coxa vara, ovoid vertebral bodies and severe scoliosis, may also be present. FN is an important extracellular matrix component for bone and cartilage development. Here we report five patients affected by this subtype of SMD-CF caused by five novel FN1 missense mutations: p.Cys123Tyr, p.Cys169Tyr, p.Cys213Tyr, p.Cys231Trp and p.Cys258Tyr. All individuals shared a substitution of a cysteine residue, disrupting disulfide bonds in the FN type-I assembly domains located in the N-terminal assembly region. The abnormal metaphyseal ossification and "corner fracture" appearances were the most remarkable clinical feature in these patients. In addition, generalized skeletal fragility with low-trauma bilateral femoral fractures was identified in one patient. Interestingly, the distal femoral changes in this patient healed with skeletal maturation. Our report expands the phenotypic and genetic spectrum of the FN1-related SMD-CF and emphasizes the importance of FN in bone formation and possibly also in the maintenance of bone strength.

Novel variants in natriuretic peptide receptor 2 in unrelated patients with acromesomelic dysplasia type Maroteaux.

Acromesomelic dysplasia are a heterogeneous group of disorders with variable spectrum and severity of skeletal anomalies in the affected individuals. Acromesomelic dysplasia type Maroteaux (AMDM) is characterized by extreme shortening of the forelimbs and disproportionate short stature. Several homozygous inactivating mutations in NPR2 have been identified in different AMDM patients. We report five novel variants in affected individuals in four different families. These include two nonsense and three missense variants. This study broadens the genotypic spectrum of NPR2 mutations in individuals with AMDM and also describes the intra- and inter-familial phenotypic variability due to NPR2 variants.

A Wide Spectrum of Autoimmune Manifestations and Other Symptoms Suggesting Immune Dysregulation in Patients With Cartilage-Hair Hypoplasia.

Background: Mutations in RMRP, encoding a non-coding RNA molecule, underlie cartilage-hair hypoplasia (CHH), a syndromic immunodeficiency with multiple pathogenetic mechanisms and variable phenotype. Allergy and asthma have been reported in the CHH population and some patients suffer from autoimmune (AI) diseases. Objective: We explored AI and allergic manifestations in a large cohort of Finnish patients with CHH and correlated clinical features with laboratory parameters and autoantibodies. Methods: We collected clinical and laboratory data from patient interviews and hospital records. Serum samples were tested for a range of autoantibodies including celiac, anti-cytokine, and anti-21-hydroxylase antibodies. Nasal cytology samples were analyzed with microscopy. Results: The study cohort included 104 patients with genetically confirmed CHH; their median age was 39.2 years (range 0.6-73.6). Clinical autoimmunity was common (11/104, 10.6%) and included conditions previously undescribed in subjects with CHH (narcolepsy, psoriasis, idiopathic thrombocytopenic purpura, and multifocal motor axonal neuropathy). Patients with autoimmunity more often had recurrent pneumonia, sepsis, high immunoglobulin (Ig) E and/or undetectable IgA levels. The mortality rates were higher in subjects with AI diseases ( χ(2)2 = 14.056, p = 0.0002). Several patients demonstrated serum autoantibody positivity without compatible symptoms. We confirmed the high prevalence of asthma (23%) and allergic rhinoconjunctivitis (39%). Gastrointestinal complaints, mostly persistent diarrhea, were also frequently reported (32/104, 31%). Despite the history of allergic rhinitis, no eosinophils were observed in nasal cytology in five tested patients. Conclusions: AI diseases are common in Finnish patients with CHH and are associated with higher mortality, recurrent pneumonia, sepsis, high IgE and/or undetectable IgA levels. Serum positivity for some autoantibodies was not associated with clinical autoimmunity. The high prevalence of persistent diarrhea, asthma, and symptoms of inflammation of nasal mucosa may indicate common pathways of immune dysregulation.

Polyostotic Fibrous Dysplasia With and Without McCune-Albright Syndrome-Clinical Features in a Nordic Pediatric Cohort.

OBJECTIVE: Fibrous dysplasia (FD) presents as skeletal lesions in which normal bone is replaced by abnormal fibrous tissue due to mosaic GNAS mutation. McCune-Albright syndrome (MAS) refers to FD combined with skin (café-au-lait) and endocrine manifestations. This study describes the clinical childhood manifestations of polyostotic FD and MAS in a Nordic cohort. PATIENTS AND DESIGN: We retrospectively reviewed a cohort of pediatric patients (n = 16) with polyostotic FD with or without MAS diagnosed and followed in two Nordic Pediatric tertiary clinics between 1996 and 2017. RESULTS: Half of the 16 patients with polyostotic FD presented with MAS. All patients with MAS (n = 8) had café-au-lait spots, and either gonadotropin-independent precocious puberty (PP) (girls; n = 5) or abnormal testicle structure (boys, n = 3). None manifested hyperthyroidism or growth hormone excess. Mild hypophosphatemia was common (11/16), but none had signs of hypophosphatemic rickets. Craniofacial bone involvement was found in 12 patients (75%); in 5 of these, skeletal lesions were limited to craniofacial area. One child with craniofacial disease had lost vision due to optic nerve damage. Eleven (69%) patients had sustained a fracture at FD lesion, over half of them requiring surgical fixation of the fracture, most commonly in the proximal femur. The first symptoms leading to FD/MAS diagnosis included skull/facial asymmetry (n = 4), PP (n = 3), abnormal gait (n = 3), pathologic fracture (n = 3), wide-spread café-au-lait spots (n = 1), headache (n = 1), and vision loss (n = 1). CONCLUSION: Polyostotic FD and MAS remain diagnostic and therapeutic challenges because of the broad clinical spectrum. Recurrent fractures, pain, and even vision loss may impair the quality of life in children with FD.

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/ß-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.

Compromised peak bone mass in patients with inflammatory bowel disease--a prospective study.

OBJECTIVE: To evaluate peak bone mass attainment in children and adolescents with inflammatory bowel disease and to identify risk factors for suboptimal bone mass attainment. STUDY DESIGN: We conducted a prospective follow-up study of 47 children and adolescents (24 males) with ulcerative colitis (n = 30) or Crohn's disease (n = 17). They were assessed for lumbar spine areal bone mineral density (aBMD) and for height-adjusted whole body less head bone mineral content (BMC); the values were corrected for bone age. RESULTS: Altogether, 73% of the patients had completed pubertal development after the median follow-up time of over 5 years. Despite clinical inactivity of the disease in 70% of the patients at the follow-up visit, BMD or BMC Z-scores improved in none of the measurement sites. Lumbar spine aBMD Z-scores (mean difference [95% CI], -0.47 [-0.92 to -0.03]; P = .04) and whole body less head BMC height- and bone age-adjusted Z-scores (-0.52 [-1.01 to -0.02]; P = .04) decreased in patients who were pubertal at baseline and completed their pubertal development during the follow-up. Postpubertal patients had lower aBMD and BMC Z-scores in comparison with prepubertal and pubertal patients. Low lumbar spine aBMD (Z-score < -1.0) was associated with completed pubertal development, underweight, and greater lifetime cumulative weight-adjusted prednisolone dose. Vertebral fractures were detected in 3 patients (6%). One-fourth of the patients had insufficient serum 25-hydroxyvitamin D concentrations (<50 nmol/L). CONCLUSIONS: The longitudinal follow-up over the pubertal years shows that inflammatory bowel disease poses a significant threat for bone health. The suboptimal peak bone mass attainment may have life-long consequences.

Pediatric solid organ transplantation and osteoporosis: a descriptive study on bone histomorphometric findings.

BACKGROUND: Organ transplantation may lead to secondary osteoporosis in children. This study characterized bone histomorphometric findings in pediatric solid organ transplant recipients who were assessed for suspected secondary osteoporosis. METHODS: Iliac crest biopsies were obtained from 19 children (7.6-18.8 years, 11 male) who had undergone kidney (n = 6), liver (n = 9), or heart (n = 4) transplantation a median 4.6 years (range 0.6-16.3 years) earlier. All patients had received oral glucocorticoids at the time of the biopsy. RESULTS: Of the 19 patients, 21 % had sustained peripheral fractures and 58 % vertebral compression fractures. Nine children (47 %) had a lumbar spine BMD Z-score below -2.0. Histomorphometric analyses showed low trabecular bone volume (< -1.0 SD) in 6 children (32 %) and decreased trabecular thickness in 14 children (74 %). Seven children (37 %) had high bone turnover at biopsy, and low turnover was found in 6 children (32 %), 1 of whom had adynamic bone disease. CONCLUSIONS: There was a great heterogeneity in the histological findings in different transplant groups, and the results were unpredictable using non-invasive methods. The observed changes in bone quality (i.e. abnormal turnover rate, thin trabeculae) rather than the actual loss of trabecular bone, might explain the increased fracture risk in pediatric solid organ transplant recipients.

Different mutations in PDE4D associated with developmental disorders with mirror phenotypes.

BACKGROUND: Point mutations in PDE4D have been recently linked to acrodysostosis, an autosomal dominant disorder with skeletal dysplasia, severe brachydactyly, midfacial hypoplasia and intellectual disability. The purpose of the present study was to investigate clinical and cellular implications of different types of mutations in the PDE4D gene. METHODS: We studied five acrodysostosis patients and three patients with gene dose imbalances involving PDE4D clinically and by whole exome sequencing, Sanger sequencing and array comparative hybridisation. To evaluate the functional consequences of the PDE4D changes, we used overexpression of mutated human PDE4D message and morpholino-based suppression of pde4d in zebrafish. RESULTS: We identified three novel and two previously described PDE4D point mutations in the acrodysostosis patients and two deletions and one duplication involving PDE4D in three patients suffering from an intellectual disability syndrome with low body mass index, long fingers, toes and arms, prominent nose and small chin. When comparing symptoms in patients with missense mutations and gene dose imbalances involving PDE4D, a mirror phenotype was observed. By comparing overexpression of human mutated transcripts with pde4d knockdown in zebrafish embryos, we could successfully assay the pathogenicity of the mutations. CONCLUSIONS: Our findings indicate that haploinsufficiency of PDE4D results in a novel intellectual disability syndrome, the 5q12.1-haploinsufficiency syndrome, with several opposing features compared with acrodysostosis that is caused by dominant negative mutations. In addition, our results expand the spectrum of PDE4D mutations underlying acrodysostosis and indicate that, in contrast to previous reports, patients with PDE4D mutations may have significant hormone resistance with consequent endocrine abnormalities.