Heterozygous NPR2 Mutations Cause Disproportionate Short Stature, Similar to Léri-Weill Dyschondrosteosis

CONTEXT

SHOX mutations have been detected in approximately 70% of Léri-Weill dyschondrosteosis (LWD) and approximately 2.5% of idiopathic short stature (ISS) cases, suggesting the implication of other genes or loci. The recent identification of NPR2 mutations in ISS suggested that NPR2 mutations may also be involved in disproportionate short stature.

OBJECTIVE

The objective of the study was to investigate whether NPR2 mutations can account for a proportion of the cases referred for LWD and ISS in whom no SHOX mutation was detected.

PATIENTS AND METHODS

We undertook NPR2 mutation screening in 173 individuals referred for suspected LWD and 95 for ISS, with no known defect in SHOX or its enhancers. Intracellular localization and natriuretic peptide precursor C-dependent guanylate cyclase activity were determined for the identified NPR2 variants.

RESULTS

Eight NPR2 variants were identified in nine individuals, seven referred for suspected LWD and two for ISS. Six were demonstrated to affect NPR-B cell trafficking and/or its ability to synthesize cyclic GMP (cGMP) under response to natriuretic peptide precursor C/brain natriuretic peptide stimulation. All pathogenic mutations were detected in the suspected LWD referral group (∼3%). Interestingly, one of these patients is currently being treated with recombinant human GH and in contrast to previous reports is showing a positive response to the treatment.

CONCLUSIONS

NPR2 mutations account for approximately 3% of patients with disproportionate short stature and/or clinical or radiographic indicators of SHOX deficiency and in whom no SHOX defect has been identified. However, no patient has yet presented with Madelung deformity. Thus, NPR2 should be screened in the SHOX-negative LWD referrals.

Effects of leukemia inhibitory receptor gene mutations on human hypothalamo-pituitary-adrenal function

BACKGROUND

Stuve-Wiedemann syndrome (STWS) (MIM #601559) is a rare autosomal recessive disorder caused by mutations in the leukemia inhibitory factor receptor (LIFR) gene. STWS has a diverse range of clinical features involving hematopoietic, skeletal, neuronal and immune systems. STWS manifests a high mortality due to increased risk of sudden death. Heterodimerization of the LIFR mediates leukemia inhibitory factor (LIF) signalling through the intracellular Janus kinase (JAK)/STAT3 signalling cascade. The LIF/LIFR system is highly expressed in and regulates the hypothalamo-pituitary-adrenal (HPA) axis.

OBJECTIVES

HPA function was investigated in three STWS patients to characterise consequences of impaired LIF/LIFR signalling on adrenal function.

DESIGN

Six genetically proven STWS patients from four unrelated Turkish families were included in the study. Sudden death occurred in three before 2 years of age. Basal adrenal function tests were performed by measurement of early morning serum cortisol and plasma ACTH concentrations on at least two different occasions. Low dose synacthen stimulation test and glucagon stimulation tests were performed to explore adrenal function in three patients who survived.

RESULTS

All patients carried the same LIFR (p.Arg692X) mutation. Our oldest patient had attenuated morning serum cortisol and plasma ACTH levels at repeated measurements. Two of three patients had attenuated cortisol response (<18 μg/dl) to glucagon, one of whom also had borderline cortisol response to low dose (1 μg) ACTH stimulation consistent with central adrenal insufficiency.

CONCLUSIONS

STWS patients may develop central adrenal insufficiency due to impaired LIF/LIFR signalling. LIF/LIFR system plays a role in human HPA axis regulation.

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly in a Finnish woman: first confirmation of a duplication in RUNX2 as pathogenic variant

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly (MDMHB) is an autosomal-dominant bone dysplasia that until now has only been reported in French Canadian individuals. We have recently identified an intragenic duplication in RUNX2, encompassing exons 3 to 5, as a cause of MDMHB in French Canadian families. Here we describe a 20-year-old Finnish woman who had typical clinical and radiological signs of MDMHB, the first reported individual with MDMHB who is not of French-Canadian origin. Copy number variant assays based on quantitative PCR of genomic DNA showed the presence of three copies within a part of RUNX2. Sequencing RUNX2 cDNA from the skin fibroblasts revealed a duplication of exons 3 to 5. The results demonstrated that the intronic breakpoints of the duplication differed from those previously found in the French Canadian family, but that the consequences on RUNX2 transcript were identical. These findings demonstrate that the MDMHB phenotype results from an intragenic duplication of RUNX2 exons 3 to 5 also outside of the community where the disorder was first identified.

Homozygosity for frameshift mutations in XYLT2 result in a spondylo-ocular syndrome with bone fragility, cataracts, and hearing defects

Heparan and chondroitin/dermatan sulfated proteoglycans have a wide range of roles in cellular and tissue homeostasis including growth factor function, morphogen gradient formation, and co-receptor activity. Proteoglycan assembly initiates with a xylose monosaccharide covalently attached by either xylosyltransferase I or II. Three individuals from two families were found that exhibited similar phenotypes. The index case subjects were two brothers, individuals 1 and 2, who presented with osteoporosis, cataracts, sensorineural hearing loss, and mild learning defects. Whole exome sequence analyses showed that both individuals had a homozygous c.692dup mutation (GenBank: NM_022167.3) in the xylosyltransferase II locus (XYLT2) (MIM: 608125), causing reduced XYLT2 mRNA and low circulating xylosyltransferase (XylT) activity. In an unrelated boy (individual 3) from the second family, we noted low serum XylT activity. Sanger sequencing of XYLT2 in this individual revealed a c.520del mutation in exon 2 that resulted in a frameshift and premature stop codon (p.Ala174Profs(∗)35). Fibroblasts from individuals 1 and 2 showed a range of defects including reduced XylT activity, GAG incorporation of (35)SO4, and heparan sulfate proteoglycan assembly. These studies demonstrate that human XylT2 deficiency results in vertebral compression fractures, sensorineural hearing loss, eye defects, and heart defects, a phenotype that is similar to the autosomal-recessive disorder spondylo-ocular syndrome of unknown cause. This phenotype is different from what has been reported in individuals with other linker enzyme deficiencies. These studies illustrate that the cells of the lens, retina, heart muscle, inner ear, and bone are dependent on XylT2 for proteoglycan assembly in humans.

Pericentrin: critical for spindle orientation

Mutations in the pericentrin (PCNT) gene cause Majewski osteodysplastic primordial dwarfism type II (MOPDII). Recent work reveals that a discrete set of centrosome proteins require PCNT for their robust localization to mitotic spindle poles. Critically, this complex is crucial for mitotic spindle orientation and involved in the pathogenesis of MOPDII.

Phenotypic variability of TRPV4 related neuropathies

Mutations in the transient receptor potential vanilloid 4 (TRPV4) gene have been associated with autosomal dominant skeletal dysplasias and peripheral nervous system syndromes (PNSS). PNSS include Charcot-Marie-Tooth disease (CMT) type 2C, congenital spinal muscular atrophy and arthrogryposis and scapuloperoneal spinal muscular atrophy. We report the clinical, electrophysiological and muscle biopsy findings in two unrelated patients with two novel heterozygous missense mutations in the TRPV4 gene. Whole exome sequencing was carried out on genomic DNA using Illumina Truseq(TM) 62Mb exome capture. Patient 1 harbours a de novo c.805C > T (p.Arg269Cys) mutation. Clinically, this patient shows signs of both scapuloperoneal spinal muscular atrophy and skeletal dysplasia. Patient 2 harbours a novel c.184G > A (p.Asp62Asn) mutation. While the clinical phenotype is compatible with CMT type 2C with the patient's muscle harbours basophilic inclusions. Mutations in the TRPV4 gene have a broad phenotypic variability and disease severity and may share a similar pathogenic mechanism with Heat Shock Protein related neuropathies.

Sclerostin and skeletal health

Sclerostin is a cysteine-knot glycoprotein product of the SOST gene, predominately expressed by osteocytes, that is a regulator of osteoblastic bone formation. When sclerostin binds to its low-density lipoprotein receptor-related proteins 5 and 6 on the cell membrane of osteoblasts, it inhibits canonical Wnt/β-catenin signaling and reduces osteoblastic bone formation. Sclerostin was first identified in the study of two rare autosomal recessive disorders, sclerosteosis and van Buchem disease, which are associated with absent or reduced levels of sclerostin. Although homozygote patients with these disorders have serious adverse clinical consequences due to excessive bone growth, heterozygote patients have a normal phenotype, high bone mass, and very low risk of fractures. This has led to the concept that downregulation of sclerostin might be effective in the treatment of osteoporosis. Several humanized monoclonal antibodies to sclerostin, including romosozumab and blosozumab, are now in clinical development. Preliminary data show that these agents result in a transient increase in bone formation markers, a sustained decrease in bone resorption markers, and a robust increase in bone mineral density. If any of these agents are found to reduce fracture risk with a favorable safety profile, it will expand the options for osteoanabolic therapy for patients at high risk for fractures.

Identification of a Novel Mutation in the COL2A1 Gene in a Chinese Family with Spondyloepiphyseal Dysplasia Congenita

Spondyloepiphyseal dysplasia congenita (SEDC) is an autosomal dominant chondrodysplasia characterized by disproportionate short-trunk dwarfism, skeletal and vertebral deformities. Exome sequencing and Sanger sequencing were performed in a Chinese Han family with typical SEDC, and a novel mutation, c.620G>A (p.Gly207Glu), in the collagen type II alpha-1 gene (COL2A1) was identified. The mutation may impair protein stability, and lead to dysfunction of type II collagen. Family-based study suggested that the mutation is a de novo mutation. Our study extends the mutation spectrum of SEDC and confirms genotype-phenotype relationship between mutations at glycine in the triple helix of the alpha-1(II) chains of the COL2A1 and clinical findings of SEDC, which may be helpful in the genetic counseling of patients with SEDC.

Clinical characteristics and molecular genetic analysis of 22 patients with neonatal diabetes from the South-Eastern region of Turkey: predominance of non-KATP channel mutations

BACKGROUND

Neonatal diabetes mellitus (NDM) is a rare form of monogenic diabetes and usually presents in the first 6 months of life. We aimed to describe the clinical characteristics and molecular genetics of a large Turkish cohort of NDM patients from a single centre and estimate an annual incidence rate of NDM in South-Eastern Anatolian region of Turkey.

DESIGN AND METHODS

NDM patients presenting to Diyarbakir Children State Hospital between 2010 and 2013, and patients under follow-up with presumed type 1 diabetes mellitus, with onset before 6 months of age were recruited. Molecular genetic analysis was performed.

RESULTS

Twenty-two patients (59% males) were diagnosed with NDM (TNDM-5; PNDM-17). Molecular genetic analysis identified a mutation in 20 (95%) patients who had undergone a mutation analysis. In transient neonatal diabetes (TNDM) patients, the genetic cause included chromosome 6q24 abnormalities (n=3), ABCC8 (n=1) and homozygous INS (n=1). In permanent neonatal diabetes (PNDM) patients, homozygous GCK (n=6), EIF2AK3 (n=3), PTF1A (n=3), and INS (n=1) and heterozygous KCNJ11 (n=2) mutations were identified. Pancreatic exocrine dysfunction was observed in patients with mutations in the distal PTF1A enhancer. Both patients with a KCNJ11 mutation responded to oral sulphonylurea. A variable phenotype was associated with the homozygous c.-331C>A INS mutation, which was identified in both a PNDM and TNDM patient. The annual incidence of PNDM in South-East Anatolian region of Turkey was one in 48 000 live births.

CONCLUSIONS

Homozygous mutations in GCK, EIF2AK3 and the distal enhancer region of PTF1A were the commonest causes of NDM in our cohort. The high rate of detection of a mutation likely reflects the contribution of new genetic techniques (targeted next-generation sequencing) and increased consanguinity within our cohort.

TREM2 sustains microglial expansion during aging and response to demyelination

Microglia contribute to development, homeostasis, and immunity of the CNS. Like other tissue-resident macrophage populations, microglia express the surface receptor triggering receptor expressed on myeloid cells 2 (TREM2), which binds polyanions, such as dextran sulphate and bacterial LPS, and activates downstream signaling cascades through the adapter DAP12. Individuals homozygous for inactivating mutations in TREM2 exhibit demyelination of subcortical white matter and a lethal early onset dementia known as Nasu-Hakola disease. How TREM2 deficiency mediates demyelination and disease is unknown. Here, we addressed the basis for this genetic association using Trem2(-/-) mice. In WT mice, microglia expanded in the corpus callosum with age, whereas aged Trem2(-/-) mice had fewer microglia with an abnormal morphology. In the cuprizone model of oligodendrocyte degeneration and demyelination, Trem2(-/-) microglia failed to amplify transcripts indicative of activation, phagocytosis, and lipid catabolism in response to myelin damage. As a result, Trem2(-/-) mice exhibited impaired myelin debris clearance, axonal dystrophy, oligodendrocyte reduction, and persistent demyelination after prolonged cuprizone treatment. Moreover, myelin-associated lipids robustly triggered TREM2 signaling in vitro, suggesting that TREM2 may directly sense lipid components exposed during myelin damage. We conclude that TREM2 is required for promoting microglial expansion during aging and microglial response to insults of the white matter.

[Marshall syndrome: Clinical, radiological and genetical features of a Tunisian family]

BACKGROUND

Marshall syndrome is a rare autosomal dominant skeletal dysplasia. It associates a particular facial dysmorphism with midface hypoplasia, ocular abnormalities and sensorineural hearing loss. It is caused by heterozygous mutations in COL11A1 gene coding the 1 chain of collagen XI. Stickler syndrome is the principal differential diagnosis of Marshall syndrome.

AIM

Clinical and radiological study of Marshall syndrome in a Tunisian family with a linkage study of the COL11A1 gene to this disease.

METHODS

We report the clinical and the radiological findings of a Tunisian family including 8 members affected by Marshall syndrome. The linkage of the COL11A1 gene to this disease was tested using the polymorphic microsatellite markers of DNA.

RESULTS

A variability of the clinical expression of Marshall syndrome was reported. Specific Marshall phenotype and an overlapping phenotype between the Marshall and Stickler syndromes were observed among the affected members of this family. The ocular manifestations were also heterogeneous. Marshall syndrome's specific radiological signs were found. The linkage study supports the linkage of the abnormal phenotype to the COL11A1 gene.

CONCLUSION

There is a variability of the clinical expression among the affected members of the study's family. We will continue searching the causative mutation to establish a clear genotype- phenotype correlation.

CODAS syndrome is associated with mutations of LONP1, encoding mitochondrial AAA+ Lon protease

CODAS syndrome is a multi-system developmental disorder characterized by cerebral, ocular, dental, auricular, and skeletal anomalies. Using whole-exome and Sanger sequencing, we identified four LONP1 mutations inherited as homozygous or compound-heterozygous combinations among ten individuals with CODAS syndrome. The individuals come from three different ancestral backgrounds (Amish-Swiss from United States, n = 8; Mennonite-German from Canada, n = 1; mixed European from Canada, n = 1). LONP1 encodes Lon protease, a homohexameric enzyme that mediates protein quality control, respiratory-complex assembly, gene expression, and stress responses in mitochondria. All four pathogenic amino acid substitutions cluster within the AAA(+) domain at residues near the ATP-binding pocket. In biochemical assays, pathogenic Lon proteins show substrate-specific defects in ATP-dependent proteolysis. When expressed recombinantly in cells, all altered Lon proteins localize to mitochondria. The Old Order Amish Lon variant (LONP1 c.2161C>G[p.Arg721Gly]) homo-oligomerizes poorly in vitro. Lymphoblastoid cell lines generated from affected children have (1) swollen mitochondria with electron-dense inclusions and abnormal inner-membrane morphology; (2) aggregated MT-CO2, the mtDNA-encoded subunit II of cytochrome c oxidase; and (3) reduced spare respiratory capacity, leading to impaired mitochondrial proteostasis and function. CODAS syndrome is a distinct, autosomal-recessive, developmental disorder associated with dysfunction of the mitochondrial Lon protease.

Miscellaneous Bone Disorders

This chapter deals with a few of the important childhood bone disorders associated with high bone mass as well as conditions associated with fragility fractures and limb deformities that have not been addressed in previous chapters. A couple of skeletal dysplasias that can sometimes be confused with rickets are also dealt with in this chapter.

Inborn errors of metabolism in the biosynthesis and remodelling of phospholipids

Since the proposal to define a separate subgroup of inborn errors of metabolism involved in the biosynthesis and remodelling of phospholipids, sphingolipids and long chain fatty acids in 2013, this group is rapidly expanding. This review focuses on the disorders involved in the biosynthesis of phospholipids. Phospholipids are involved in uncountable cellular processes, e.g. as structural components of membranes, by taking part in vesicle and mitochondrial fusion and fission or signal transduction. Here we provide an overview on both pathophysiology and the extremely heterogeneous clinical presentations of the disorders reported so far (Sengers syndrome (due to mutations in AGK), MEGDEL syndrome (or SERAC defect, SERAC1), Barth syndrome (or TAZ defect, TAZ), congenital muscular dystrophy due to CHKB deficiency (CHKB). Boucher-Neuhäuser/Gordon Holmes syndrome (PNPLA6), PHARC syndrome (ABHD12), hereditary spastic paraplegia type 28, 54 and 56 (HSP28, DDHD1; HSP54, DDHD2; HSP56, CYP2U1), Lenz Majewski syndrome (PTDSS1), spondylometaphyseal dysplasia with cone-rod dystrophy (PCYT1A), atypical haemolytic-uremic syndrome due to DGKE deficiency (DGKE).

[SMARCAL1 gene analysis of 2 Chinese Schimke immuno-osseous dysplasia children]

OBJECTIVE

Schimke immuno-osseous dysplasia (SIOD), is an autosomal recessive inherited disease caused by SMARCAL1 (MIM:20606622) mutations, while in about half of the patients no any mutation in SMARCAL1 could be found. This disease involves multiple systems and is characterized by short and dissymmetric stature with spondyloepiphyseal dysplasia, progressive renal failure, lymphopenia with recurrent infections, and hyperpigmented macules. This study aimed to analyze SMARCAL1 gene of 2 unrelated suspected SIOD children, to make definite diagnosis, and find more SMARCAL1 mutation types of Chinese SIOD.

METHOD

Two suspected Chinese Han male SIOD children who visited our hospital from 2008 to 2014, aged 3 y 6 m and 7 y 8 m, both were short and had spondyloepiphyseal dysplasia, progressive renal failure, lymphopenia with recurrent infections. After informed consent, they and their parents's DNA were extracted from blood. PCRs for all 16 exons of SMARCAL1 were performed and PCR products were purified by 2% gel electrophoresis and sequenced directly. Pathogenicity of missense variations was confirmed by SIFT and sequencing SMARCAL1 of fifty normal controls.

RESULT

(1) Four gene variations were found in the two children: Two reported missense mutations c.1129G>C, p.Glu377Gln and c.1933C>T, p. Arg645Cys. Two splicing mutations c.1334+1G>A and c.2142-1 G>A were detected. (2) c.1129G>C, p.Glu377Gln were reported as a disease-causing mutations before, but it was an single nucleotide polymorphism (SNP) which was found in 15 of 50 normal controls. (3) Two novel splicing mutations were found in this study: c.1334+1G>A and c.2142-1 G>A.

CONCLUSION

(1) We detected 3 disease-causing mutations in 2 SIOD children by SMARCAL1 gene analysis, while 2 splicing mutations were novel mutations. (2) c.1129G>C, p.Glu377Gln was a SNP but not a disease-causing mutation at least in Chinese population.

An anadysplasia-like, spontaneously remitting spondylometaphyseal dysplasia secondary to lamin B receptor (LBR) gene mutations: further definition of the phenotypic heterogeneity of LBR-bone dysplasias

We describe a boy who has an anadysplasia-like spondylometaphyseal dysplasia. By whole exome sequencing he was shown to have compound heterozygous mutations of LBR that codes for the lamin B receptor. He shares many similarities with a case previously described, but in whom the early natural history could not be established [Borovik et al., 2013]. Thus, in addition to Greenberg dysplasia (a perinatal lethal disorder), homozygosity or compound heterozygosity of mutations in LBR can result in a mild, spontaneously regressing bone dysplasia.

Primary hypothyroidism: an unusual manifestation of Wolcott-Rallison syndrome

Wolcott-Rallison syndrome has been reported to be associated with early-onset diabetes, epiphyseal dysplasia, hepatic and renal dysfunction, mental retardation, severe growth retardation, neutropenia, exocrine pancreatic dysfunction, and central hypothyroidism. We report on primary hypothyroidism, which has not been previously described, of a patient with Wolcott-Rallison syndrome due to novel mutation (W521X), who showed improved growth after thyroid hormone treatment.

Exome sequencing reveals a mutation in DMP1 in a family with familial sclerosing bone dysplasia

INTRODUCTION

Hypophosphatemic rickets (HR) comprises a rare group of inherited diseases. Very recently, mutations in the dentin matrix protein 1 (DMP1) gene were identified in patients with an extremely rare autosomal recessive form of HR (ARHR). To date, very few cases of these mutations were reported.

MATERIALS AND METHODS

A Lebanese consanguineous family with 2 affected sisters was studied. Patients aged 45 and 47years old presented with short stature, severe genu varum, cranial hyperostosis and a very high bone density that led to a diagnosis of a familial sclerosing bone dysplasia. Molecular analysis of known genes involved in osteopetrosis showed normal results. A combination of genotyping and exome sequencing was performed in order to elucidate the genetic basis of this pathology.

RESULTS

Biochemical analysis was consistent with normal serum calcium and 1-25(OH)2D levels, low to normal serum phosphorus and elevated PTH values. Serum c-terminal FGF-23 was elevated in one of the two patients. A homozygous mutation disrupting the initiation codon of the DMP1 gene (OMIM 600980), NM_001079911.2: c.1A>G, p.Met1Val, was identified by exome sequencing and confirmed by Sanger sequencing.

CONCLUSION

We report here a family of ARHR secondary to a DMP1 mutation located in the first coding exon of the gene. Our cases show that some ARHR cases may develop with age an unaccountable increase in bone density and bone overgrowth.

A novel variant in CDKN1C is associated with intrauterine growth restriction, short stature, and early-adulthood-onset diabetes

CONTEXT

CDKN1C, a cyclin-dependent kinase inhibitor and negative regulator of cellular proliferation, is paternally imprinted and has been shown to regulate β-cell proliferation. CDKN1C mutations are associated with growth disorders, including Beckwith-Wiedemann syndrome and IMAGe syndrome.

OBJECTIVE

To investigate the genetic basis for a familial disorder characterized by intrauterine growth restriction, short stature, and early-adulthood-onset diabetes.

DESIGN, SETTING, AND PARTICIPANTS

Genomic DNA samples (15 affected and 26 unaffected from a six-generation pedigree) were analyzed by genome-wide single nucleotide polymorphism arrays, whole exome and Sanger sequencing, and multiplex ligation-dependent probe amplification.

MAIN OUTCOME MEASURE(S)

Subjects were assessed for height, weight, adrenal gland size, ACTH, diabetes status, and testis volume. Linkage and sequence analyses were performed, and the identified genetic variant was functionally evaluated in reconstitution studies.

RESULTS

The pedigree followed a paternally imprinted pattern of inheritance, and genetic linkage analysis identified a single significant 2.6-megabase locus on chromosome 11p15, within the imprinting center region 2. Multiplex ligation-dependent probe amplification did not detect copy number variants or methylation abnormalities. Whole exome sequencing revealed a single novel variant in the proliferating cell nuclear antigen-binding region of CDKN1C (c.842G>T, p.R281I) that co-segregated with affected status and, unlike variants found in IMAGe, did not entirely abrogate proliferating cell nuclear antigen binding. Clinical assessments revealed that affected individuals had low testicular volume but normal adrenal function.

CONCLUSIONS

We report a novel CDKN1C mutation associated with features of IMAGe syndrome, but without adrenal insufficiency or metaphyseal dysplasia, and characterized by early-adulthood-onset diabetes. Our data expand the range of phenotypes observed with CDKN1C defects and suggest that CDKN1C mutations may represent a novel monogenic form of diabetes.

Radiological and clinical analysis of Madelung's deformity in children

INTRODUCTION

Madelung's deformity is a bone dysplasia that occurs predominantly in adolescent females, characterized by early epiphyseal growth arrest in the medial part of the distal radius. This leads to an upward and medial displacement of the radial joint surface, restricting range of motion.

OBJECTIVES

The objective of this study was to determine whether there was a link between clinical and radiological data in children with Madelung's deformity and to test the hypothesis of a relation between the deformity and a genetic mutation.

METHODS

A retrospective study recruited 13 patients with Madelung's deformity, with a mean age of 13.2 years (range, 8-18 years). Assessment comprised level of pain, range of motion and grip force, with standard AP and lateral wrist X-rays. Every patient except one underwent molecular genetic screening, adhering to current recommendations.

RESULTS

Pronation-supination, radial inclination and grip force were significantly impaired compared to normal results. All X-ray measurements were significantly abnormal, except for the lunate-covering ratio. Genetic mutation (SHOX) was systematic in the 12 patients screened.

DISCUSSION

Radiological deformity did not correlate with functional disturbance or pain. Non-acquired Madelung's deformity requires molecular screening for SHOX or XO mutation, which definitively diagnoses Léri-Weill dyschondrosteosis or Turner syndrome.

CONCLUSION

A larger series is necessary to confirm these preliminary results, which nevertheless suggest that non-acquired Madelung's deformity is not isolated but syndromic. Early detection of Léri-Weill or Turner syndrome is essential, due to their therapeutic specificities. LEVEL: IV.

CDKN1C mutations: two sides of the same coin

Cyclin-dependent kinase (CDK)-inhibitor 1C (CDKN1C) negatively regulates cellular proliferation and it has been shown that loss-of-function mutations in the imprinted CDKN1C gene (11p15.5) are associated with the overgrowth disorder Beckwith-Wiedemann syndrome (BWS). With recent reports of gain-of-function mutations of the PCNA domain of CDKN1C in growth-retarded patients with IMAGe syndrome or Silver-Russell syndrome (SRS), its key role for growth has been confirmed. Thereby, the last gap in the spectrum of molecular alterations in 11p15.5 in growth-retardation and overgrowth syndromes could be closed. Recent functional studies explain the strict association of CDKN1C mutations with clinically opposite phenotypes and thereby contribute to our understanding of the function and regulation of the gene in particular and epigenetic regulation in general.

Microcephalic osteodysplastic primordial dwarfism type II (MOPD II) with multiple vascular complications misdiagnosed as Dubowitz syndrome

To date, the genetic basis of Dubowitz syndrome (short stature, microcephaly, facial abnormalities, eczema) is unknown and vascular complications are not known to be associated with this syndrome. In microcephalic osteodysplastic primordial dwarfism type II (MOPD II; disproportionate short statue, microcephaly, facial abnormalities), however, cerebral aneurysms and other vascular abnormalities are frequent complications. MOPD II is a genetic disorder caused by mutations in the pericentrin (PCNT) gene (21q22). We report on a patient who came to our attention as a 22-year-old with subarachnoid bleeding due to a ruptured cranial aneurysm. Until then, the patient was thought and published to have Dubowitz syndrome; previously, he was treated with coronary bypass surgery for extensive coronary angiopathy. Consecutive genetic testing revealed MOPD II. After clinical stabilization, the patient was discharged to a specialized rehabilitation center where he died due to re-rupture of a cranial aneurysm.

CONCLUSION

In patients with short stature-especially when clinical features are accompanied by vascular complications-MOPD II should be considered as a differential diagnosis leading to consecutive genetic testing. After detection of mutations in the PCNT gene, a full vascular status including cerebral imaging and cardiac evaluation needs to be determined in order to analyze vascular abnormalities and initiate prophylactic treatment.

Sclerosing bone dysplasias: leads toward novel osteoporosis treatments

Sclerosing bone dysplasias are a group of rare, monogenic disorders characterized by increased bone density resulting from the disturbance in the fragile equilibrium between bone formation and resorption. Over the last decade, major contributions have been made toward better understanding of the pathogenesis of these conditions. These studies provided us with important insights into the bone biology and yielded the identification of numerous drug targets for the prevention and treatment of osteoporosis. Here, we review this heterogeneous group of disorders focusing on their utility in the development of novel osteoporosis therapies.

Mutations in CENPE define a novel kinetochore-centromeric mechanism for microcephalic primordial dwarfism

Defects in centrosome, centrosomal-associated and spindle-associated proteins are the most frequent cause of primary microcephaly (PM) and microcephalic primordial dwarfism (MPD) syndromes in humans. Mitotic progression and segregation defects, microtubule spindle abnormalities and impaired DNA damage-induced G2-M cell cycle checkpoint proficiency have been documented in cell lines from these patients. This suggests that impaired mitotic entry, progression and exit strongly contribute to PM and MPD. Considering the vast protein networks involved in coordinating this cell cycle stage, the list of potential target genes that could underlie novel developmental disorders is large. One such complex network, with a direct microtubule-mediated physical connection to the centrosome, is the kinetochore. This centromeric-associated structure nucleates microtubule attachments onto mitotic chromosomes. Here, we described novel compound heterozygous variants in CENPE in two siblings who exhibit a profound MPD associated with developmental delay, simplified gyri and other isolated abnormalities. CENPE encodes centromere-associated protein E (CENP-E), a core kinetochore component functioning to mediate chromosome congression initially of misaligned chromosomes and in subsequent spindle microtubule capture during mitosis. Firstly, we present a comprehensive clinical description of these patients. Then, using patient cells we document abnormalities in spindle microtubule organization, mitotic progression and segregation, before modeling the cellular pathogenicity of these variants in an independent cell system. Our cellular analysis shows that a pathogenic defect in CENP-E, a kinetochore-core protein, largely phenocopies PCNT-mutated microcephalic osteodysplastic primordial dwarfism-type II patient cells. PCNT encodes a centrosome-associated protein. These results highlight a common underlying pathomechanism. Our findings provide the first evidence for a kinetochore-based route to MPD in humans.

Elevated circulating Sclerostin concentrations in individuals with high bone mass, with and without LRP5 mutations

CONTEXT

The role and importance of circulating sclerostin is poorly understood. High bone mass (HBM) caused by activating LRP5 mutations has been reported to be associated with increased plasma sclerostin concentrations; whether the same applies to HBM due to other causes is unknown.

OBJECTIVE

Our objective was to determine circulating sclerostin concentrations in HBM.

DESIGN AND PARTICIPANTS

In this case-control study, 406 HBM index cases were identified by screening dual-energy x-ray absorptiometry (DXA) databases from 4 United Kingdom centers (n = 219 088), excluding significant osteoarthritis/artifact. Controls comprised unaffected relatives and spouses.

MAIN MEASURES

Plasma sclerostin; lumbar spine L1, total hip, and total body DXA; and radial and tibial peripheral quantitative computed tomography (subgroup only) were evaluated.

RESULTS

Sclerostin concentrations were significantly higher in both LRP5 HBM and non-LRP5 HBM cases compared with controls: mean (SD) 130.1 (61.7) and 88.0 (39.3) vs 66.4 (32.3) pmol/L (both P < .001, which persisted after adjustment for a priori confounders). In combined adjusted analyses of cases and controls, sclerostin concentrations were positively related to all bone parameters found to be increased in HBM cases (ie, L1, total hip, and total body DXA bone mineral density and radial/tibial cortical area, cortical bone mineral density, and trabecular density). Although these relationships were broadly equivalent in HBM cases and controls, there was some evidence that associations between sclerostin and trabecular phenotypes were stronger in HBM cases, particularly for radial trabecular density (interaction P < .01).

CONCLUSIONS

Circulating plasma sclerostin concentrations are increased in both LRP5 and non-LRP5 HBM compared with controls. In addition to the general positive relationship between sclerostin and DXA/peripheral quantitative computed tomography parameters, genetic factors predisposing to HBM may contribute to increased sclerostin levels.

Biochemical defects in minor spliceosome function in the developmental disorder MOPD I

Biallelic mutations of the human RNU4ATAC gene, which codes for the minor spliceosomal U4atac snRNA, cause the developmental disorder, MOPD I/TALS. To date, nine separate mutations in RNU4ATAC have been identified in MOPD I patients. Evidence suggests that all of these mutations lead to abrogation of U4atac snRNA function and impaired minor intron splicing. However, the molecular basis of these effects is unknown. Here, we use a variety of in vitro and in vivo assays to address this question. We find that only one mutation, 124G>A, leads to significantly reduced expression of U4atac snRNA, whereas four mutations, 30G>A, 50G>A, 50G>C and 51G>A, show impaired binding of essential protein components of the U4atac/U6atac di-snRNP in vitro and in vivo. Analysis of MOPD I patient fibroblasts and iPS cells homozygous for the most common mutation, 51G>A, shows reduced levels of the U4atac/U6atac.U5 tri-snRNP complex as determined by glycerol gradient sedimentation and immunoprecipitation. In this report, we establish a mechanistic basis for MOPD I disease and show that the inefficient splicing of genes containing U12-dependent introns in patient cells is due to defects in minor tri-snRNP formation, and the MOPD I-associated RNU4ATAC mutations can affect multiple facets of minor snRNA function.

IMAGe syndrome: clinical and genetic implications based on investigations in three Japanese patients

OBJECTIVE

Arboleda et al. have recently shown that IMAGe (intra-uterine growth restriction, metaphyseal dysplasia, adrenal hypoplasia congenita and genital abnormalities) syndrome is caused by gain-of-function mutations of maternally expressed gene CDKN1C on chromosome 11p15.5. However, there is no other report describing clinical findings in patients with molecularly studied IMAGe syndrome. Here, we report clinical and molecular findings in Japanese patients.

PATIENTS

We studied a 46,XX patient aged 8·5 years (case 1) and two 46,XY patients aged 16·5 and 15·0 years (cases 2 and 3).

RESULTS

Clinical studies revealed not only IMAGe syndrome-compatible phenotypes in cases 1-3, but also hitherto undescribed findings including relative macrocephaly and apparently normal pituitary-gonadal endocrine function in cases 1-3, familial glucocorticoid deficiency (FGD)-like adrenal phenotype and the history of oligohydramnios in case 2, and arachnodactyly in case 3. Sequence analysis of CDKN1C, pyrosequencing-based methylation analysis of KvDMR1 and high-density oligonucleotide array comparative genome hybridization analysis for chromosome 11p15.5 were performed, showing an identical de novo and maternally inherited CDKN1C gain-of-function mutation (p.Asp274Asn) in cases 1 and 2, respectively, and no demonstrable abnormality in case 3.

CONCLUSIONS

The results of cases 1 and 2 with CDKN1C mutation would argue the following: [1] relative macrocephaly is consistent with maternal expression of CDKN1C in most tissues and biparental expression of CDKN1C in the foetal brain; [2] FGD-like phenotype can result from CDKN1C mutation; and [3] genital abnormalities may primarily be ascribed to placental dysfunction. Furthermore, lack of CDKN1C mutation in case 3 implies genetic heterogeneity in IMAGe syndrome.

Unexpected high frequency of skeletal dysplasia in idiopathic short stature and small for gestational age patients

OBJECTIVE

To assess the prevalence of skeletal dysplasias (SDs) in patients with idiopathic short stature (ISS) or small for gestational age (SGA) status.

SETTING

Rare Endocrine/Growth Diseases Center in Paris, France.

DESIGN

A prospective study on consecutive patients with ISS and SGA enrolled from 2004 to 2009.

METHOD

We used a standardized workup to classify patients into well-established diagnostic categories. Of 713 patients with ISS (n=417) or SGA status (n=296), 50.9% underwent a skeletal survey. We chose patients labeled normal or with a prepubertal slowdown of growth as a comparison group.

RESULTS

Diagnoses were ISS (16.9%), SGA (13.5%), normal growth (24.5%), transient growth rate slowing (17.3%), endocrine dysfunction (12%), genetic syndrome (8.9%), chronic disease (5.1%), and known SD (1.8%). SD was found in 20.9% of SGA and 21.8% ISS patients and in only 13.2% in our comparison group. SD prevalence was significantly higher in the ISS group than in the comparison group, especially (50%) for patients having at least one parent whose height was <-2 SDS. Dyschondrosteosis and hypochondroplasia were the most frequently identified SD, and genetic anomaly was found in 61.5 and 30% respectively. Subtle SD was found equally in the three groups and require long-term growth follow-up to evaluate the impact on final height.

CONCLUSION

SD may explain more than 20% of cases of growth retardation ascribed to ISS or SGA, and this proportion is higher when parental height is <-2 SDS. A skeletal survey should be obtained in patients with delayed growth in a context of ISS or SGA.

Endoplasmic reticulum stress-unfolding protein response-apoptosis cascade causes chondrodysplasia in a col2a1 p.Gly1170Ser mutated mouse model

The collagen type II alpha 1 (COL2A1) mutation causes severe skeletal malformations, but the pathogenic mechanisms of how this occurs are unclear. To understand how this may happen, a col2a1 p.Gly1170Ser mutated mouse model was constructed and in homozygotes, the chondrodysplasia phenotype was observed. Misfolded procollagen was largely synthesized and retained in dilated endoplasmic reticulum and the endoplasmic reticulum stress (ERS)-unfolded protein response (UPR)-apoptosis cascade was activated. Apoptosis occurred prior to hypertrophy, prevented the formation of a hypertrophic zone, disrupted normal chondrogenic signaling pathways, and eventually caused chondrodysplasia. Heterozygotes had normal phenotypes and endoplasmic reticulum stress intensity was limited with no abnormal apoptosis detected. Our results suggest that earlier chondrocyte death was related to the ERS-UPR-apoptosis cascade and that this was the chief cause of chondrodysplaia. The col2a1 p.Gly1170Ser mutated mouse model offered a novel connection between misfolded collagen and skeletal malformation. Further investigation of this mouse mutant model can help us understand mechanisms of type II collagenopathies.

NPPB and ACAN, two novel SHOX2 transcription targets implicated in skeletal development

SHOX and SHOX2 transcription factors are highly homologous, with even identical homeodomains. Genetic alterations in SHOX result in two skeletal dysplasias; Léri-Weill dyschondrosteosis (LWD) and Langer mesomelic dysplasia (LMD), while no human genetic disease has been linked to date with SHOX2. SHOX2 is, though, involved in skeletal development, as shown by different knockout mice models. Due to the high homology between SHOX and SHOX2, and their functional redundancy during heart development, we postulated that SHOX2 might have the same transcriptional targets and cofactors as SHOX in limb development. We selected two SHOX transcription targets regulated by different mechanisms: 1) the natriuretic peptide precursor B gene (NPPB) involved in the endochondral ossification signalling and directly activated by SHOX; and 2) Aggrecan (ACAN), a major component of cartilage extracellular matrix, regulated by the cooperation of SHOX with the SOX trio (SOX5, SOX6 and SOX9) via the protein interaction between SOX5/SOX6 and SHOX. Using the luciferase assay we have demonstrated that SHOX2, like SHOX, regulates NPPB directly whilst activates ACAN via its cooperation with the SOX trio. Subsequently, we have identified and characterized the protein domains implicated in the SHOX2 dimerization and also its protein interaction with SOX5/SOX6 and SHOX using the yeast-two hybrid and co-immunoprecipitation assays. Immunohistochemistry of human fetal growth plates from different time points demonstrated that SHOX2 is coexpressed with SHOX and the members of the SOX trio. Despite these findings, no mutation was identified in SHOX2 in a cohort of 83 LWD patients with no known molecular defect, suggesting that SHOX2 alterations do not cause LWD. In conclusion, our work has identified the first cofactors and two new transcription targets of SHOX2 in limb development, and we hypothesize a time- and tissue-specific functional redundancy between SHOX and SHOX2.

Homozygosity for a DTDST mutation in a child with multiple epiphyseal dysplasia

BACKGROUND

Multiple epiphyseal dysplasia (MED) is one of the common hereditary osteochondrodysplasias. Mutations in diastrophic dysplasia sulfate transporter gene (DTDST) result in recessive MED.

OBJECTIVE

To investigate the possible gene mutation in a recessive MED patient.

SUBJECTS

A boy with typical clinical features of recessive MED and his parents.

METHODS

Clinical and radiological evaluations, DTDST gene sequence analysis, and sulfate uptake assay were performed on the patient and his parents.

RESULTS

The patient showed typical symptoms of recessive MED. The radiological evaluation confirmed dysplasia in multiple epiphysis of the patient, while his parents did not show the similar clinical and radiological features. Gene sequence showed the patient was homozygous of A2092T (T689S) mutation, while his parents were both of heterozygous of the same mutation. No such mutation in DTDST gene was found in 81 normal control individuals. The patient showed reduced sulfate uptake ability in dermal fibroblast compared with his parents and normal controls.

CONCLUSION

The homozygous A2092T (T689S) mutation could be one of the mutations in the DTDST gene causing MED.

[Multiple epiphyseal dysplasia: skeletal dysplasia presenting as neuromuscular disease]

BACKGROUND

Multiple epiphyseal dysplasia (MED) is a clinically and genetically heterogeneous skeletal dysplasia. MED is usually inherited as a dominant trait, however, in a quarter of patients it is a recessive trait. Common symptoms of MED are pain and stiffness of joints. However, MED also can present as a neuromuscular disorder with hypotonia and muscle weakness, particularly in childhood.

CASE DESCRIPTION

We saw a 7-year-old boy with abnormal gait and slight weakness of the upper legs at our outpatient clinic. Because of his short stature and other skeletal anomalies, skeletal dysplasia was considered. The diagnosis of MED was confirmed by DNA analysis. A mutation in the cartilage oligomeric matrix protein (COMP) gene was found.

CONCLUSION

Skeletal dysplasia should be included in the differential diagnosis of children with unexplained neuromuscular symptoms.

Mutation of KCNJ8 in a patient with Cantú syndrome with unique vascular abnormalities - support for the role of K(ATP) channels in this condition

KCNJ8 (NM_004982) encodes the pore forming subunit of one of the ATP-sensitive inwardly rectifying potassium (KATP) channels. KCNJ8 sequence variations are traditionally associated with J-wave syndromes, involving ventricular fibrillation and sudden cardiac death. Recently, the KATP gene ABCC9 (SUR2, NM_020297) has been associated with the multi-organ disorder Cantú syndrome or hypertrichotic osteochondrodysplasia (MIM 239850) (hypertrichosis, macrosomia, osteochondrodysplasia, and cardiomegaly). Here, we report on a patient with a de novo nonsynonymous KCNJ8 SNV (p.V65M) and Cantú syndrome, who tested negative for mutations in ABCC9. The genotype and multi-organ abnormalities of this patient are reviewed. A careful screening of the KATP genes should be performed in all individuals diagnosed with Cantú syndrome and no mutation in ABCC9.

Two Somali half-siblings with CHST3-related chondrodysplasia illustrating the phenotypic spectrum and intrafamilial variability

Deficiency of carbohydrate sulfotransferase 3 (CHST3; also known as chondroitin-6-sulfotranferase) has been associated with a phenotype of severe chondrodysplasia and progressive spinal involvement. Recent reports indicate that affected individuals initially present with neonatal multiple joint dislocations. We describe a 14-year-old Somali patient and her 3-year-old maternal half-brother with novel homozygous CHST3 mutations. The proband presented at the age 5½ years with short stature and genua valga. Her clinical course was characterized by rapid progression of spinal deformities and large joint contractures. Her half-brother presented at birth with bilateral knee dislocation and talipes equinovarus. This report of a Somali family with CHST3-related chondrodysplasia illustrates the intrafamilial variability in phenotypic expression of this rare disorder. © 2013 Wiley Periodicals, Inc.

Identification of six novel PTH1R mutations in families with a history of primary failure of tooth eruption

Primary Failure of tooth Eruption (PFE) is a non-syndromic disorder which can be caused by mutations in the parathyroid hormone receptor 1 gene (PTH1R). Traditionally, the disorder has been identified clinically based on post-emergent failure of eruption of permanent molars. However, patients with PTH1R mutations will not benefit from surgical and/or orthodontic treatment and it is therefore clinically important to establish whether a given failure of tooth eruption is caused by a PTH1R defect or not. We analyzed the PTH1R gene in six patients clinically diagnosed with PFE, all of which had undergone surgical and/or orthodontic interventions, and identified novel PTH1R mutations in all. Four of the six mutations were predicted to abolish correct mRNA maturation either through introduction of premature stop codons (c.947C>A and c.1082G>A), or by altering correct mRNA splicing (c.544-26_544-23del and c.989G>T). The latter was validated by transfection of minigenes. The six novel mutations expand the mutation spectrum for PFE from eight to 14 pathogenic mutations. Loss-of-function mutations in PTH1R are also associated with recessively inherited Blomstrand chondrodysplasia. We compiled all published PTH1R mutations and identified a mutational overlap between Blomstrand chondrodysplasia and PFE. The results suggest that a genetic approach to preclinical diagnosis will have important implication for surgical and orthodontic treatment of patients with failure of tooth eruption.

Large-scale pooled next-generation sequencing of 1077 genes to identify genetic causes of short stature

CONTEXT

The majority of patients presenting with short stature do not receive a definitive diagnosis. Advances in genetic sequencing allow for large-scale screening of candidate genes, potentially leading to genetic diagnoses.

OBJECTIVES

The purpose of this study was to discover genetic variants that contribute to short stature in a cohort of children with no known genetic etiology.

DESIGN

This was a prospective cohort study of subjects with short stature.

SETTING

The setting was a pediatric endocrinology and genetics clinics at an academic center.

PATIENTS

A total of 192 children with short stature with no defined genetic etiology and 192 individuals of normal stature from the Framingham Heart Study were studied.

INTERVENTION

Pooled targeted sequencing using next-generation DNA sequencing technology of the exons of 1077 candidate genes was performed.

MAIN OUTCOME MEASURES

The numbers of rare nonsynonymous genetic variants found in case patients but not in control subjects, known pathogenic variants in case patients, and potentially pathogenic variants in IGF1R were determined.

RESULTS

We identified 4928 genetic variants in 1077 genes that were present in case patients but not in control subjects. Of those, 1349 variants were novel (898 nonsynonymous). False-positive rates from pooled sequencing were 4% to 5%, and the false-negative rate was 0.1% in regions covered well by sequencing. We identified 3 individuals with known pathogenic variants in PTPN11 causing undiagnosed Noonan syndrome. There were 9 rare potentially nonsynonymous variants in IGF1R, one of which is a novel, probably pathogenic, frameshift mutation. A previously reported pathogenic variant in IGF1R was present in a control subject.

CONCLUSIONS

Large-scale sequencing efforts have the potential to rapidly identify genetic etiologies of short stature, but data interpretation is complex. Noonan syndrome may be an underdiagnosed cause of short stature.

Frequency and spectrum of Wolcott-Rallison syndrome in Saudi Arabia: a systematic review

BACKGROUND

Wolcott-Rallison syndrome (WRS) is caused by recessive EIF2AK3 gene mutations and characterized by permanent neonatal diabetes (PNDM), skeletal dysplasia, and recurrent hepatitis. The frequency of this rare syndrome is largely unknown.

OBJECTIVES

To define the frequency and spectrum of WRS in the Kingdom of Saudi Arabia (KSA) based on published data.

METHODS

The Medline database was searched for published articles on WRS. The number of reported cases from KSA was compared to the total number of WRS cases reported worldwide. The genotype and phenotype of WRS patients from KSA were reviewed.

RESULTS

Ten articles describing 23 WRS patients from 12 Saudi families from 1995 to 2012 were identified. This figure accounts for 27.7% (23/83) of the patients and 22.2% (12/54) of the families with WRS reported worldwide until January 2013. All Saudi patients with WRS presented with PNDM, and they represent 59% of all PNDM cases from WRS. At reporting, 73% of patients experienced recurrent hepatitis, 56.5% had skeletal abnormalities, and 39.1% of them were dead. There was a variation in the phenotype even between affected siblings. Genetic diagnosis was confirmed in all 12 families with no correlation between the genotype and phenotype. Eight of the nine EIF2AK3 mutations were only reported in these families, and one was shared with a patient from Qatar, a neighboring Arab state.

CONCLUSIONS

No study on the frequency of WRS has been published. However, the available data indicate that KSA has the largest collection of patients with WRS worldwide, and nine of the identifiable EIF2AK3 mutations appear to be confined to Arabs. Establishing a national or international registry for WRS would provide more reliable data on this rare condition.

[A novel mutation of cartilage oligomeric matrix protein gene underlies multiple epiphyseal dysplasia]

OBJECTIVE

To perform mutation analysis for a female with multiple epiphyseal dysplasia (MED) and provide pre-symptomatic and prenatal diagnosis.

METHODS

Mutation screening of cartilage oligomeric matrix protein (COMP) gene was carried out through targeted next-generation DNA sequencing and Sanger sequencing.

RESULTS

A novel c.956 A>T resulting in substitution of Aspartic acid 319 for Valine (p.Asp319Val) has been identified in exon 9 of the COMP gene in the patient. As predicted by a SIFT software, above mutation can cause damage to the structure of COMP protein.

CONCLUSION

A novel c.956 A>T substitution mutation has been identified in a patient featuring MED.

Spatiotemporal disorder in the axial skeleton development of the Mesp2-null mouse: a model of spondylocostal dysostosis and spondylothoracic dysostosis

Spondylocostal dysostosis (SCDO) is a genetic disorder characterized by severe malformation of the axial skeleton. Mesp2 encodes a basic helix-loop-helix type transcription factor that is required for somite formation. Its human homologue, Mesp2, is a gene affected in patients with SCDO and a related vertebral disorder, spondylothoracic dysostosis (STDO). This work investigated how the loss of Mesp2 affects axial skeleton development and causes the clinical features of SCDO and STDO. We first confirmed, by three-dimensional computed tomography scanning, that Mesp2-null mice exhibited mineralized tissue patterning resembling the radiological features of SCDO and STDO. Histological observations and in situ hybridization probing for extracellular matrix molecules demonstrated that the developing vertebral bodies in Mesp2-null mice were extensively fused with rare insertions of intervertebral tissue. Unexpectedly, the intervertebral tissues were mostly fused longitudinally in the vertebral column, instead of exhibiting extended formation, as was expected based on the caudalized properties of Mesp2-null somite derivatives. Furthermore, the differentiation of vertebral body chondrocytes in Mesp2-null mice was spatially disordered and largely delayed, with an increased cell proliferation rate. The quantitative three-dimensional immunofluorescence image analyses of phospho-Smad2 and -Smad1/5/8 revealed that these chondrogenic phenotypes were associated with spatially disordered inputs of TGF-β and BMP signaling in the Mesp2-null chondrocytes, and also demonstrated an amorphous arrangement of cells with distinct properties. Furthermore, a significant delay in ossification in Mesp2-null vertebrae was observed by peripheral quantitative computed tomography. The current observations of the spatiotemporal disorder of vertebral organogenesis in the Mesp2-null mice provide further insight into the pathogenesis of SCDO and STDO, and the physiological development of the axial skeleton.

EDM1: a novel point mutation in cartilage oligomeric matrix protein gene in a Chinese family with multiple epiphyseal dysplasia

BACKGROUND

Multiple epiphysis dysplasia (MED) is a common skeletal dysplasia with a significant locus heterogeneity. In the majority of clinically defined cases, mutations have been identified in the gene encoding cartilage algometric matrix protein (COMP).

METHODS

Five patients were included in the study. Linkage analysis and mutation analysis of the COMP gene were conducted in the patients and their family members.

RESULTS

We have identified a novel mutation in axon 14 of COMP gene in the family.

CONCLUSIONS

This mutation produced a severe MED phenotype with marked short stature, early onset osteoarthritis, and remarkable radiographic changes. Our results extended the range of disease-causing mutations in COMP gene and contributed more information about relationship between mutations and phenotype.

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly is caused by a duplication in RUNX2

Metaphyseal dysplasia with maxillary hypoplasia and brachydactyly (MDMHB) is an autosomal-dominant bone dysplasia characterized by metaphyseal flaring of long bones, enlargement of the medial halves of the clavicles, maxillary hypoplasia, variable brachydactyly, and dystrophic teeth. We performed genome-wide SNP genotyping in five affected and four unaffected members of an extended family with MDMHB. Analysis for copy-number variations revealed that a 105 kb duplication within RUNX2 segregated with the MDMHB phenotype in a region with maximum linkage. Real-time PCR for copy-number variation in genomic DNA in eight samples, as well as sequence analysis of fibroblast cDNA from one subject with MDMHB confirmed that affected family members were heterozygous for the presence of an intragenic duplication encompassing exons 3 to 5 of RUNX2. These three exons code for the Q/A domain and the functionally essential DNA-binding runt domain of RUNX2. Transfection studies with murine Runx2 cDNA showed that cellular levels of mutated RUNX2 were markedly higher than those of wild-type RUNX2, suggesting that the RUNX2 duplication found in individuals with MDMHB leads to a gain of function. Until now, only loss-of-function mutations have been detected in RUNX2; the present report associates an apparent gain-of-function alteration of RUNX2 function with a distinct rare disease.

Variable phenotype in five patients with Wolcott-Rallison syndrome due to the same EIF2AK3 (c.1259delA) mutation

Wolcott-Rallison syndrome (WRS) is a rare condition characterized by permanent neonatal diabetes (PND), skeletal dysplasia, and recurrent hepatitis. Other features, including central hypothyroidism, have been reported. We compared the phenotype of five patients from two families with WRS caused by the same EIF2AK3 mutation who have been followed up since diagnosis. Direct sequencing of the EIF2AK3 gene identified a homozygous frameshift mutation (c.1259delA) in all patients that has been reported only in these families. All patients presented with PND and four experienced recurrent hepatitis. A 3.5-year-old girl has isolated PND, whereas her younger sister has typical WRS features. Two children developed skeletal abnormalities and two had transient central hypothyroidism. Other reported features of WRS were not detected. The EIF2AK3 c.1259delA mutation results in a variable phenotype, ranging from isolated PND to typical WRS. Thyroid dysfunction in WRS is a transient phenomenon reflecting euthyroid sickness.

Clinical and molecular characterization of Chilean patients with Léri-Weill dyschondrosteosis

AIM

Léri-Weill dyschondrosteosis (LWD) is a mesomelic dysplasia with disproportionate short stature associated with short stature homeobox-containing gene (SHOX) haploinsufficiency. The objective of this study was to improve the diagnosis of patients with suspected LWD through molecular analysis.

METHODS

Twelve patients from 11 families with a clinical diagnosis of LWD were analyzed with multiplex ligation-dependent probe amplification to detect deletions and duplications of SHOX and its enhancer regions. High resolution melting and sequencing was employed to screen for mutations in SHOX coding exons.

RESULTS

The molecular-based screening strategy applied in these patients allowed detection of five SHOX deletions and two previously unreported SHOX missense mutations.

CONCLUSION

Molecular studies confirmed the clinical diagnosis of LWD in seven out of 12 patients, which provided support for therapeutic decisions and improved genetic counseling in their families.

Human skeletal dysplasia caused by a constitutive activated transient receptor potential vanilloid 4 (TRPV4) cation channel mutation

The transient receptor potential vanilloid 4 (TRPV4) cation channel, a member of the TRP vanilloid subfamily, is expressed in a broad range of tissues where it participates in the generation of Ca²⁺ signals and/or depolarization of the membrane potential. Regulation of TRPV4 abundance at the cell surface is critical for osmo- and mechanotransduction. Defects in TRPV4 are the cause of several human diseases, including brachyolmia type 3 (MIM:113500) (also known as brachyrachia or spondylometaphyseal dysplasia Kozlowski type [MIM:118452]), and metatropic dysplasia (MIM:156530) (also called metatropic dwarfism or parastremmatic dwarfism [MIM:168400]). These bone dysplasia mutants are characterized by severe dwarfism, kyphoscoliosis, distortion and bowing of the extremities, and contractures of the large joints. These diseases are characterized by a combination of decreased bone density, bowing of the long bones, platyspondyly, and striking irregularities of endochondral ossification with areas of calcific stippling and streaking in radiolucent epiphyses, metaphyses, and apophyses. In this review, we discuss the potential effect of the mutation on the regulation of TRPV4 functions, which are related to human diseases through deviated function. In particular, we emphasize how the constitutive active TRPV4 mutant affects endochondral ossification with a reduced number of hypertrophic chondrocytes and the presence of cartilage islands within the zone of primary mineralization. In addition, we summarize current knowledge about the role of TRPV4 in the pathogenesis of several diseases.

PRKAR1A and PDE4D mutations cause acrodysostosis but two distinct syndromes with or without GPCR-signaling hormone resistance

CONTEXT

Acrodysostosis is a rare skeletal dysplasia that is associated with multiple resistance to G protein-coupled receptor (GPCR) signaling hormones in a subset of patients. Acrodysostosis is genetically heterogeneous because it results from heterozygous mutations in PRKAR1A or PDE4D, two key actors in the GPCR-cAMP-protein kinase A pathway.

OBJECTIVE

Our objective was to identify the phenotypic features that distinguish the two genotypes causing acrodysostosis.

PATIENTS AND METHODS

Sixteen unrelated patients with acrodysostosis underwent a candidate-gene approach and were investigated for phenotypic features.

RESULTS

All patients had heterozygous de novo mutations. Fourteen patients carried a PRKAR1A mutation (PRKAR1A patients), five each a novel PRKAR1A mutation (p.Q285R, p.G289E, p.A328V, p.R335L, or p.Q372X), nine the reported PRKAR1A p.R368X mutation; two patients harbored a mutation in PDE4D (PDE4D patients) (one novel mutation, p.A227S; one reported, p.E590A). All PRKAR1A, but none of the PDE4D mutated patients were resistant to PTH and TSH. Two PRKAR1A patients each with a novel mutation presented a specific pattern of brachydactyly. One PDE4D patient presented with acroskyphodysplasia. Additional phenotypic differences included mental retardation in PDE4D patients. In addition, we report the presence of pigmented skin lesions in PRKAR1A and PDE4D patients, a feature not yet described in the acrodysostosis entity.

CONCLUSIONS

All PRKAR1A and PDE4D patients present similar bone dysplasia characterizing acrodysostosis. Phenotypic differences, including the presence of resistance to GPCR-cAMP signaling hormones in PRKAR1A but not PDE4D patients, indicate phenotype-genotype correlations and highlight the specific contributions of PRKAR1A and PDE4D in cAMP signaling in different tissues.

Identification of the first ATRIP-deficient patient and novel mutations in ATR define a clinical spectrum for ATR-ATRIP Seckel Syndrome

A homozygous mutational change in the Ataxia-Telangiectasia and RAD3 related (ATR) gene was previously reported in two related families displaying Seckel Syndrome (SS). Here, we provide the first identification of a Seckel Syndrome patient with mutations in ATRIP, the gene encoding ATR-Interacting Protein (ATRIP), the partner protein of ATR required for ATR stability and recruitment to the site of DNA damage. The patient has compound heterozygous mutations in ATRIP resulting in reduced ATRIP and ATR expression. A nonsense mutational change in one ATRIP allele results in a C-terminal truncated protein, which impairs ATR-ATRIP interaction; the other allele is abnormally spliced. We additionally describe two further unrelated patients native to the UK with the same novel, heterozygous mutations in ATR, which cause dramatically reduced ATR expression. All patient-derived cells showed defective DNA damage responses that can be attributed to impaired ATR-ATRIP function. Seckel Syndrome is characterised by microcephaly and growth delay, features also displayed by several related disorders including Majewski (microcephalic) osteodysplastic primordial dwarfism (MOPD) type II and Meier-Gorlin Syndrome (MGS). The identification of an ATRIP-deficient patient provides a novel genetic defect for Seckel Syndrome. Coupled with the identification of further ATR-deficient patients, our findings allow a spectrum of clinical features that can be ascribed to the ATR-ATRIP deficient sub-class of Seckel Syndrome. ATR-ATRIP patients are characterised by extremely severe microcephaly and growth delay, microtia (small ears), micrognathia (small and receding chin), and dental crowding. While aberrant bone development was mild in the original ATR-SS patient, some of the patients described here display skeletal abnormalities including, in one patient, small patellae, a feature characteristically observed in Meier-Gorlin Syndrome. Collectively, our analysis exposes an overlapping clinical manifestation between the disorders but allows an expanded spectrum of clinical features for ATR-ATRIP Seckel Syndrome to be defined.