The male phenotype in osteopathia striata congenita with cranial sclerosis

A Mosaic Variant in CTNNB1/β-catenin as a Novel Cause for Osteopathia Striata With Cranial Sclerosis

CONTEXT

Osteopathia striata with cranial sclerosis (OSCS) is a rare bone disorder with X-linked dominant inheritance, characterized by a generalized hyperostosis in the skull and long bones and typical metaphyseal striations in the long bones. So far, loss-of-function variants in AMER1 (also known as WTX or FAM123B), encoding the APC membrane recruitment protein 1 (AMER1), have been described as the only molecular cause for OSCS. AMER1 promotes the degradation of β-catenin via AXIN stabilization, acting as a negative regulator of the WNT/β-catenin signaling pathway, a central pathway in bone formation.

OBJECTIVE

In this study, we describe a Dutch adult woman with an OSCS-like phenotype, namely, generalized high bone mass and characteristic metaphyseal striations, but no genetic variant affecting AMER1.

RESULTS

Whole exome sequencing led to the identification of a mosaic missense variant (c.876A > C; p.Lys292Asn) in CTNNB1, coding for β-catenin. The variant disrupts an amino acid known to be crucial for interaction with AXIN, a key factor in the β-catenin destruction complex. Western blotting experiments demonstrate that the p.Lys292Asn variant does not significantly affect the β-catenin phosphorylation status, and hence stability in the cytoplasm. Additionally, luciferase reporter assays were performed to investigate the effect of p.Lys292Asn β-catenin on canonical WNT signaling. These studies indicate an average 70-fold increase in canonical WNT signaling activity by p.Lys292Asn β-catenin.

CONCLUSION

In conclusion, this study indicates that somatic variants in the CTNNB1 gene could explain the pathogenesis of unsolved cases of osteopathia striata.

Moyamoya disease/cerebral vasculopathy in osteopathia striata with cranial sclerosis: a rare but important complication

Osteopathia striata with cranial sclerosis (OSCS) is a rare X-linked dominant sclerosing osteodysplasia, due to AMER1 pathogenic variants. Characteristic features include craniofacial sclerosis and long-bone metaphyseal striations. Moyamoya disease (a type of progressive cerebral vasculopathy) and other types of cerebral vascular disease are not currently clearly associated with OSCS (except for two separate case reports), and can often first present with stroke. Through informal networks with UK-based bone experts and the UK skeletal dysplasia group, three cases from the UK and Ireland were identified. Medical literature was also reviewed to identify the known cases of OSCS with the described complications. We report four females, in whom OSCS and cerebral vasculopathy co-exist, with varying clinical outcomes. There appears to be an emerging association between OSCS and cerebral vasculopathy, which pre-disposes patients to stroke. Given this, screening OSCS patients for cerebral vasculopathy may be of value, especially pre-surgery. Further research regarding optimal screening and management is needed. The mechanism of cerebral vasculopathy and its progression remain unclear.

Osteopathia striata with cranial sclerosis causing a compressive optic neuropathy

BACKGROUND

Osteopathia striata combined with cranial sclerosis (OS-CS) is an inherited skeletal dysplasia that manifests with macrocephaly, orofacial abnormalities, thickened craniofacial bones, and vertically oriented radiodensities of the long bones.

CASE REPORT

Here, we present a severe case of OS-CS in a 4-year-old girl causing optic neuropathy as shown by radiographic evidence, ophthalmic findings, and histopathology. Previous genetic testing in this patient revealed a de novo heterozygous mutation in AMER1 (c.1057C>T, p.Arg353Ter). Although the patient had a pre-existing, appropriately functioning, ventriculoperitoneal (VP) shunt, a subsequent MRI of the brain and orbits showed narrowing of the bilateral optic nerve canals secondary to osseous thickening causing bilateral optic nerve atrophy, worse on the left. The patient underwent staged bilateral orbital osteotomies, optic canal decompression, and bilateral frontal craniotomy, and at 11 months postoperatively, her vision remained stable. Conclusions: While up to 50% of the patients with OS-CS may experience hearing loss due to cranial nerve compression, we present a case of severe visual loss secondary to OS-CS-associated optic nerve compression.

X-Linked intellectual disability update 2022

Genes that are involved in the transcription process, mitochondrial function, glycoprotein metabolism, and ubiquitination dominate the list of 21 new genes associated with X-linked intellectual disability since the last update in 2017. The new genes were identified by sequencing of candidate genes (2), the entire X-chromosome (2), the whole exome (15), or the whole genome (2). With these additions, 42 (21%) of the 199 named XLID syndromes and 27 (25%) of the 108 numbered nonsyndromic XLID families remain to be resolved at the molecular level. Although the pace of discovery of new XLID genes has slowed during the past 5 years, the density of genes on the X chromosome that cause intellectual disability still appears to be twice the density of intellectual disability genes on the autosomes.

Mosaic deletions of known genes explain skeletal dysplasias with high and low bone mass

Mosaicism, a state in which an individual has two or more genetically distinct populations of cells in the body, can be difficult to detect because of either mild or atypical clinical presentation and limitations in the commonly used detection methods. Knowledge of the role of mosaicism is limited in many skeletal disorders, including osteopathia striata with cranial sclerosis (OSCS) and cleidocranial dysplasia (CCD). We used whole‐genome sequencing (WGS) with coverage >40× to identify the genetic causes of disease in two clinically diagnosed patients. In a female patient with OSCS, we identified a mosaic 7‐nucleotide frameshift deletion in exon 2 of AMER1, NM_152424.4:c.855_861del:p.(His285Glnfs*7), affecting 8.3% of the WGS reads. In a male patient with CCD, approximately 34% of the WGS reads harbored a 3710‐basepair mosaic deletion, NC_000006.11:g.45514471_45518181del, starting in intron 8 of RUNX2 and terminating in the 3′ untranslated region. Droplet digital polymerase chain reaction was used to validate these deletions and quantify the absolute level of mosaicism in each patient. Although constitutional variants in AMER1 and RUNX2 are a known cause of OSCS and CCD, respectively, the mosaic changes here reported have not been described previously. Our study indicates that mosaicism should be considered in unsolved cases of skeletal dysplasia and should be investigated with comprehensive and sensitive detection methods. © 2022 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The phenotypic spectrum of AMER1-related osteopathia striata with cranial sclerosis: The first Canadian cohort

Osteopathia striata with cranial sclerosis (OSCS; OMIM# 300373) is a rare X-linked disorder caused by mutations of the AMER1 gene. OSCS is traditionally considered a skeletal dysplasia, characterized by cranial sclerosis and longitudinal striations in the long bone metaphyses. However, OSCS affects many body systems and varies significantly in phenotypic severity between individuals. This case series focuses on the phenotypic presentation and development of individuals with OSCS. We provide an account of 12 patients with OSCS, ranging from 5 months to 38 years of age. These patients were diagnosed with OSCS after genetic testing confirmed pathogenic mutations in AMER1. Patient consent was obtained for photos and participation. Data were collected regarding perinatal history, dysmorphic features, and review of systems. This case series documents common facial dysmorphology, as well as rare extraskeletal features of OSCS, including two patients with intestinal malrotation and two patients with pyloric stenosis. We share four apparently nonmosaic males with OSCS (one de novo and three maternal variants). We also provide a clinical update on a patient who was previously published by Chénier et al. (2012). American Journal of Medical Genetics Part A, 158, 2946-2952. More research is needed to investigate the links between genotype and phenotype and assess the long-term comorbidities and overall quality of life of individuals with OSCS.

Deletion of Exon 1 in AMER1 in Osteopathia Striata with Cranial Sclerosis

Osteopathia striata with cranial sclerosis (OSCS) is an X-linked dominant condition characterised by metaphyseal striations, macrocephaly, cleft palate, and developmental delay in affected females. Males have a more severe phenotype with multi-organ malformations, and rarely survive. To date, only frameshift and nonsense variants in exon 2, the single coding exon of AMER1, or whole gene deletions have been reported to cause OSCS. In this study, we describe two families with phenotypic features typical of OSCS. Exome sequencing and multiplex ligation-dependent probe amplification (MLPA) did not identify pathogenic variants in AMER1. Therefore, genome sequencing was employed which identified two deletions containing the non-coding exon 1 of AMER1 in the families. These families highlight the importance of considering variants or deletions of upstream non-coding exons in conditions such as OSCS, noting that often such exons are not captured on probe or enrichment-based platforms because of their high G/C content.

Whole Exome Sequencing Provides the Correct Diagnosis in a Case of Osteopathia Striata with Cranial Sclerosis: Case Report of a Novel Frameshift Mutation in AMER1

The diagnosis of rare diseases with multisystem manifestations can constitute a difficult process that delays the determination of the underlying cause. Whole exome sequencing (WES) provides a suitable option to examine multiple target genes associated with several disorders that display common features. In this study, we report the case of a female patient suspected of having Sotos syndrome. Screening for the initially selected genes, considering Sotos syndrome and Sotos-like disorders, did not identify any pathogenic variants that could explain the phenotype. The extended analysis, which considered all genes in the exome associated with features consistent with those shown by the studied patient, revealed a novel frameshift variant in the AMER1 gene, responsible for osteopathia striata with cranial sclerosis. WES analysis and an updated revision of previously reported disease-causing mutations, proved useful to reach an accurate diagnosis and guide further examination to identify critical abnormalities.

Zebrafish Wtx is a negative regulator of Wnt signaling but is dispensable for embryonic development and organ homeostasis

BACKGROUND

The X-chromosomally linked gene WTX is a human disease gene and a member of the AMER family. Mutations in WTX are found in Wilms tumor, a form of pediatric kidney cancer and in patients suffering from OSCS (Osteopathia striata with cranial sclerosis), a sclerosing bone disorder. Functional data suggest WTX to be an inhibitor of the Wnt/β-catenin signaling pathway. Deletion of Wtx in mouse leads to perinatal death, impeding the analysis of its physiological role.

RESULTS

To gain insights into the function of Wtx in development and homeostasis we have used zebrafish as a model and performed both knockdown and knockout studies using morpholinos and transcription activator-like effector nucleases (TALENs), respectively. Wtx knockdown led to increased Wnt activity and embryonic dorsalization. Also, wtx mutants showed a transient upregulation of Wnt target genes in the context of caudal fin regeneration. Surprisingly, however, wtx as well as wtx/amer2/amer3 triple mutants developed normally, were fertile and did not show any anomalies in organ maintenance.

CONCLUSIONS

Our data show that members of the zebrafish wtx/amer gene family, while sharing a partially overlapping expression pattern do not compensate for each other. This observation demonstrates a remarkable robustness during development and regeneration in zebrafish.

Genetic and Molecular Insights Into Genotype-Phenotype Relationships in Osteopathia Striata With Cranial Sclerosis (OSCS) Through the Analysis of Novel Mouse Wtx Mutant Alleles

The X-linked WTX/AMER1 protein constitutes an important component of the β-catenin destruction complex that can both enhance and suppress canonical β-catenin signaling. Somatic mutations in WTX/AMER1 have been found in a proportion of the pediatric kidney cancer Wilms' tumor. By contrast, germline mutations cause the severe sclerosing bone dysplasia osteopathia striata congenita with cranial sclerosis (OSCS), a condition usually associated with fetal or perinatal lethality in male patients. Here we address the developmental and molecular function of WTX by generating two novel mouse alleles. We show that in addition to the previously reported skeletal abnormalities, loss of Wtx causes severe midline fusion defects including cleft palate and ectopic synostosis at the base of the skull. By contrast, deletion of the C-terminal part of the protein results in only mild developmental abnormalities permitting survival beyond birth. Adult analysis, however, revealed skeletal defects including changed skull morphology and an increased whole-body bone density, resembling a subgroup of male patients carrying a milder, survivable phenotype. Molecular analysis in vitro showed that while β-catenin fails to co-immunoprecipitate with the truncated protein, partial recruitment appears to be achieved in an indirect manner using AXIN/AXIN2 as a molecular bridge. Taken together our analysis provides a novel model for WTX-caused bone diseases and explains on the molecular level how truncation mutations in this gene may retain some of WTX-protein functions. © 2018 American Society for Bone and Mineral Research.

High bone mass in adults

A finding of high bone mineral density (BMD) from routine dual-energy X-ray absorptiometry (DXA) screening is not uncommon. No consensus exists about the definition of high BMD, and T-score and/or Z-score cutoffs of ≥+2.5 or ≥+4 have been suggested. The many disorders that can result in high BMD are usually classified based on whether the BMD changes are focal vs. generalized or acquired vs. constitutional. In over half the cases, careful interpretation of the DXA report and images identifies the cause as an artefact (e.g., degenerative spinal disease, vascular calcifications, or syndesmophytes) or focal lesion (e.g., sclerotic bone metastasis or Paget's disease). Generalized acquired high BMD may be secondary to a diverse range of disorders such as fluorosis, diffuse bone sclerosis related to renal osteodystrophy, hematological diseases, and hepatitis C. Identification of the cause may require additional investigations such as imaging studies, serum tryptase assay, or serological tests for the hepatitis C virus. Finally, high BMD is a feature of many genetic diseases, most notably osteopetrosis and the disorders caused by mutations in the sclerostin gene SOST (sclerosing bone dysplasia and van Buchem disease) or in the LRP5 gene encoding the low-density lipoprotein receptor-related protein 5 (which is the Wnt co-receptor).

Male child with somatic mosaic Osteopathia Striata with Cranial Sclerosis caused by a novel pathogenic AMER1 frameshift mutation

Osteopathia striata with cranial sclerosis (OSCS; OMIM #300373) is a rare X-linked dominant condition caused by mutations in the AMER1 gene (also known as WTX or FAM123B). It is a condition which usually affects females in whom the clinical phenotype can be extremely variable. Conversely affected males typically die in utero or during the neonatal period [Perdu et al. (); Clinical Genetics 80: 383-388; Vasiljevic et al. (); Prenatal Diagnosis 35: 302-304]. There have been a small number of reported cases of surviving males, including three patients who are somatic mosaic for the condition [Chénier, Noor, Dupuis, Stavropoulos, & Mendoza-Londono, (); American Journal of Medical Genetics Part A 158A: 2946-2952; Holman et al. (); American Journal of Medical Genetics Part A 155A: 2397-2408; Joseph, Shoji, & Econs, (); The Journal of Clinical Endocrinology and Metabolism 95: 1506-1507]. We report a case of a male child who has proven somatic mosaicism for OSCS associated with a novel pathogenic frameshift mutation, c.607_611delAGGCC (p.Arg203 fs) in AMER1. We describe the multisystemic clinical features which include macrocephaly with ventriculomegaly and requirement for ventriculoperitoneal shunt, cleft palate, and respiratory difficulties after birth requiring tracheostomy insertion, persistent patent ductus arteriosus, failure to thrive and gastrostomy insertion, growth retardation, ophthalmoplegia, kidney malformation, cryptorchidism, and developmental delay. The use of new technologies with next generation sequencing (NGS) may improve the detection rate of mosaicism in rare conditions.

Germline mosaicism in osteopathia striata with cranial sclerosis--recurrence in siblings

We report recurrence of osteopathia striata with cranial sclerosis (OSCS) in two full siblings conceived by unaffected parents. Molecular confirmation of OSCS in both siblings was achieved by identification of a novel heterozygous mutation in the WTX gene. Neither parent had clinical features of OSCS nor was the pathogenic mutation demonstrable in DNA extracted from both peripheral blood leucocytes and buccal cells. This case demonstrates germline mosaicism in OSCS and represents the third report of mosaicism affecting the germline in families with OSCS. Previous reports were of parental gonadosomal mosaicism, with one showing recurrence in multiple children. Our observation adds to a body of evidence that suggests that germline mosaicism in OSCS may occur more frequently than believed previously and may have implications for counselling families with OSCS.

Sclerosteosis (craniotubular hyperostosis-syndactyly) with complex hyperphalangy of the index finger

We report a 4-year-old boy with sclerosteosis associated with severe digital dysostosis. The initial medical consultation was prompted by bilateral, asymmetrical syndactyly of the index and middle fingers. The left index finger had complicated phalangeal anomalies: hyperphalangy (supernumerary phalanx distal to the middle phalanx) and hypoplasia with bracket epiphyses of the proximal and middle phalanges. Development of facial nerve palsy, hearing impairment and generalized osteosclerosis had occurred between 3 years and 4 years of age, with the subsequent identification of a homozygous SOST mutation. Bilateral second and third fingers syndactyly associated with abnormal patterning of the same fingers should be considered prodromal signs of sclerosteosis.

Clinical utility of the X-chromosome array

Previous studies have limited the use of specific X-chromosome array designed platforms to the evaluation of patients with intellectual disability. In this retrospective analysis, we reviewed the clinical utility of an X-chromosome array in a variety of scenarios. We divided patients according to the indication for the test into four defined categories: (1) autism spectrum disorders and/or developmental delay and/or intellectual disability (ASDs/DD/ID) with known family history of neurocognitive disorders; (2) ASDs/DD/ID without known family history of neurocognitive disorders; (3) breakpoint definition of an abnormality detected by a different cytogenetic test; and (4) evaluation of suspected or known X-linked conditions. A total of 59 studies were ordered with 27 copy number variants detected in 25 patients (25/59 = 42%). The findings were deemed pathogenic/likely pathogenic (16/59 = 27%), benign (4/59 = 7%) or uncertain (7/59 = 12%). We place particular emphasis on the utility of this test for the diagnostic evaluation of families affected with X-linked conditions and how it compares to whole genome arrays in this setting. In conclusion, the X-chromosome array frequently detects genomic alterations of the X chromosome and it has advantages when evaluating some specific X-linked conditions. However, careful interpretation and correlation with clinical findings is needed to determine the significance of such changes. When the X-chromosome array was used to confirm a suspected X-linked condition, it had a yield of 63% (12/19) and was useful in the evaluation and risk assessment of patients and families.

Osteopathia striata with cranial sclerosis and developmental delay in a male with a mosaic deletion in chromosome region Xq11.2

Osteopathia striata with cranial sclerosis (OSCS) is an X-linked disease caused by mutations involving WTX (FAM123B), a tumor suppressor protein with dual functions. OSCS typically affects females whereas males generally have fetal or neonatal lethality. Surviving affected males have characteristic facial dysmorphisms, skeletal features such as macrocephaly and short stature, neurodevelopmental disabilities and a high prevalence of neuromuscular anomalies. On imaging, hemizygous males display marked cranial and peripheral skeletal sclerosis without the metaphyseal striations that are seen in women with OSCS. Observations of striation in males may be indicative of a somatic mosaic mutation in WTX. To date only two cases of surviving males haves been confirmed with mosaic point mutations in WTX. We report on the first case of a male with a mosaic deletion of the entire WTX gene. We show that a mosaic deletion in a hemizygous male patient can cause a mild phenotype of OSCS, including facial and skull base bone striations, nasal stenosis, conductive hearing loss, global developmental delay, and mild facial dysmorphology without short stature or macrocephaly.

WTX R353X mutation in a family with osteopathia striata and cranial sclerosis (OS-CS): case report and literature review of the disease clinical, genetic and radiological features

Osteopathia striata with cranial sclerosis (OS-CS) or Horan-Beighton syndrome is a rare X-linked dominant inherited bone dysplasia, characterized by longitudinal striations of long bones and cranial sclerosis. Patients can be asymptomatic or present with typical facial dysmorphism, sensory defects, internal organs anomalies, growth and mental retardation, depending on the severity of the disease. WTX gene (Xq11) has been recently identified as the disease causing gene. Aim of this article is to present the case of a 6 year old girl initially evaluated for bilateral hearing loss. Patient's head CT scan pointed out sclerosis of skull base and mastoid cells, and abnormal middle-ear ossification. Clinical examination of the patient and her mother were suspicious for OS-CS. The diagnosis was confirmed by X-rays examination showing typical longitudinal striation. Genetic analysis allowed the identification of maternally transmitted heterozygous nonsense c.1057C>T (p.R353X) WTX gene mutation. We also provide a systematic review of currently available knowledge about clinical, radiologic and genetic features typical of the OS-CS.