A rare skeletal dysplasia in the etiology of severe scoliosis: Diaphanospondylodysostosis

Diaphanospondylodysostosis is a rare genetic skeletal disorder caused by biallelic variants in the BMPER gene. The term, diaphanospondylodysostosis, includes ischiospinal dysotosis, which was previously known as a distinct entity with milder clinical features. The clinical phenotype of diaphanospondylodysostosis is quite variable with mortality in early postnatal life in some patients. Main clinical and radiographic features are narrow thorax, vertebral segmentation defects, rib anomalies, ossification defects of vertebrae, ischium and sacrum, and renal cysts. In this study, we report on a 14-year-old girl patient with diaphanospondylodysostosis harbouring a novel BMPER mutation. The patient presented with severe scoliosis and severely hypoplastic/aplastic distal phalanges of the fingers and toes, findings yet hitherto not described in this syndrome.

Pseudohypoparathyroidism, acrodysostosis, progressive osseous heteroplasia: different names for the same spectrum of diseases?

Pseudohypoparathyroidism (PHP), the first known post-receptorial hormone resistance, derives from a partial deficiency of the α subunit of the stimulatory G protein (Gsα), a key component of the PTH/PTHrP signaling pathway. Since its first description, different studies unveiled, beside the molecular basis for PHP, the existence of different subtypes and of diseases in differential diagnosis associated with genetic alterations in other genes of the PTH/PTHrP pathway. The clinical and molecular overlap among PHP subtypes and with different but related disorders make both differential diagnosis and genetic counseling challenging. Recently, a proposal to group all these conditions under the novel term "inactivating PTH/PTHrP signaling disorders (iPPSD)" was promoted and, soon afterwards, the first international consensus statement on the diagnosis and management of these disorders has been published. This review will focus on the major and minor features characterizing PHP/iPPSDs as a group and on the specificities as well as the overlap associated with the most frequent subtypes.

A novel variant in the PDE4D gene is the cause of Acrodysostosis type 2 in a Lithuanian patient: a case report

BACKGROUND

Acrodysostosis is a rare hereditary disorder described as a primary bone dysplasia with or without hormonal resistance. Pathogenic variants in the PRKAR1A and PDE4D genes are known genetic causes of this condition. The latter gene variants are more frequently identified in patients with midfacial and nasal hypoplasia and neurological involvement. The aim of our study was to analyse and confirm a genetic cause of acrodysostosis in a male patient.

CASE PRESENTATION

We report on a 29-year-old Lithuanian man diagnosed with acrodysostosis type 2. The characteristic phenotype includes specific skeletal abnormalities, facial dysostosis, mild intellectual disability and metabolic syndrome. Using patient's DNA extracted from peripheral blood sample, the novel, likely pathogenic, heterozygous de novo variant NM_001104631.2:c.581G > C was identified in the gene PDE4D via Sanger sequencing. This variant causes amino acid change (NP_001098101.1:p.(Arg194Pro)) in the functionally relevant upstream conserved region 1 domain of PDE4D.

CONCLUSIONS

This report further expands the knowledge of the consequences of missense variants in PDE4D that affect the upstream conserved region 1 regulatory domain and indicates that pathogenic variants of the gene PDE4D play an important role in the pathogenesis mechanism of acrodysostosis type 2 without significant hormonal resistance.

Inactivating PTH/PTHrP signaling disorders (iPPSDs): evaluation of the new classification in a multicenter large series of 544 molecularly characterized patients

OBJECTIVE

Pseudohypoparathyroidism and related disorders belong to a group of heterogeneous rare diseases that share an impaired signaling downstream of Gsα-protein-coupled receptors. Affected patients may present with various combination of symptoms including resistance to PTH and/or to other hormones, ectopic ossifications, brachydactyly type E, early onset obesity, short stature and cognitive difficulties. Several years ago we proposed a novel nomenclature under the term of inactivating PTH/PTHrP signaling disorders (iPPSD). It is now of utmost importance to validate these criteria and/or improve the basis of this new classification.

DESIGN

Retrospective study of a large international series of 459 probands and 85 relatives molecularly characterized.

METHODS

Information on major and minor criteria associated with iPPSD and genetic results were retrieved from patient files. We compared the presence of each criteria according to the iPPSD subtype, age and gender of the patients.

RESULTS

More than 98% of the probands met the proposed criteria for iPPSD classification. Noteworthy, most patients (85%) presented a combination of symptoms rather than a single sign suggestive of iPPSD and the overlap among the different genetic forms of iPPSD was confirmed. The clinical and molecular characterization of relatives identified familial history as an additional important criterion predictive of the disease.

CONCLUSIONS

The phenotypic analysis of this large cohort confirmed the utility of the major and minor criteria and their combination to diagnose iPPSD. This report shows the importance of having simple and easily recognizable signs to diagnose with confidence these rare disorders and supports a better management of patients.

Novel progressive acrodysostosis-like skeletal dysplasia, cerebellar atrophy, and ichthyosis

Acrodysostosis refers to a rare heterogeneous group of bone dysplasias that share skeletal features, hormone resistance, and intellectual disability. Two genes have been associated with acrodysostosis with or without hormone resistance (PRKAR1A and PDE4D). Severe intellectual disability has been reported with acrodysostosis but brain malformations and ichthyosis have not been reported in these syndromes. Here we describe a female patient with acrodysostosis, intellectual disability, cerebellar hypoplasia, and lamellar ichthyosis. The patient has an evolving distinctive facial phenotype and childhood onset ataxia. X-rays showed generalized osteopenia, shortening of middle and distal phalanges, and abnormal distal epiphysis of the ulna and radius. Brain magnetic resonance imaging showed cerebellar atrophy without other brainstem abnormalities. Genetic workup included nondiagnostic chromosomal microarray and skeletal dysplasia molecular panels. These clinical findings are different from any recognized form of acrodysostosis syndrome. Whole exome sequencing did not identify rare or predicted pathogenic variants in genes associated with known acrodysostosis, lamellar ichthyosis, and other overlapping disorders. A broader search for rare alleles absent in healthy population databases and controls identified two heterozygous truncating alleles in FBNL7 and PPM1M genes, and one missense allele in the NPEPPS gene. Identification of additional patients is required to delineate the mechanism of this unique disorder.

Parathyroid hormone resistance syndromes - Inactivating PTH/PTHrP signaling disorders (iPPSDs)

Metabolic disorders caused by impairments of the Gsα/cAMP/PKA pathway affecting the signaling of PTH/PTHrP lead to features caused by non-responsiveness of target organs, in turn leading to manifestations similar to the deficiency of the hormone itself. Pseudohypoparathyroidism (PHP) and related disorders derive from a defect of the α subunit of the stimulatory G protein (Gsα) or of downstream effectors of the same pathway, such as the PKA regulatory subunit 1A and the phosphodiesterase type 4D. The increasing knowledge on these diseases made the actual classification of PHP outdated as it does not include related conditions such as acrodysostosis (ACRDYS) or progressive osseous heteroplasia (POH), so that a new nomenclature and classification has been recently proposed grouping these disorders under the term "inactivating PTH/PTHrP signaling disorder" (iPPSD). This review will focus on the pathophysiology, clinical and molecular aspects of these rare, heterogeneous but closely related diseases.

Pseudohypoparathyroidism and Gsα-cAMP-linked disorders: current view and open issues

Pseudohypoparathyroidism exemplifies an unusual form of hormone resistance as the underlying molecular defect is a partial deficiency of the α subunit of the stimulatory G protein (Gsα), a key regulator of the cAMP signalling pathway, rather than of the parathyroid hormone (PTH) receptor itself. Despite the first description of this disorder dating back to 1942, later findings have unveiled complex epigenetic alterations in addition to classic mutations in GNAS underpining the molecular basis of the main subtypes of pseudohypoparathyroidism. Moreover, mutations in PRKAR1A and PDE4D, which encode proteins crucial for Gsα-cAMP-mediated signalling, have been found in patients with acrodysostosis. As acrodysostosis, a disease characterized by skeletal malformations and endocrine disturbances, shares clinical and molecular characteristics with pseudohypoparathyroidism, making a differential diagnosis and providing genetic counselling to patients and families is a challenge for endocrinologists. Accumulating data on the genetic and clinical aspects of this group of diseases highlight the limitation of the current classification system and prompt the need for a new definition as well as for new diagnostic and/or therapeutic algorithms. This Review discusses both the current understanding and future challenges for the clinical and molecular diagnosis, classification and treatment of pseudohypoparathyroidism.

Functional Characterization of PRKAR1A Mutations Reveals a Unique Molecular Mechanism Causing Acrodysostosis but Multiple Mechanisms Causing Carney Complex

The main target of cAMP is PKA, the main regulatory subunit of which (PRKAR1A) presents mutations in two genetic disorders: acrodysostosis and Carney complex. In addition to the initial recurrent mutation (R368X) of the PRKAR1A gene, several missense and nonsense mutations have been observed recently in acrodysostosis with hormonal resistance. These mutations are located in one of the two cAMP-binding domains of the protein, and their functional characterization is presented here. Expression of each of the PRKAR1A mutants results in a reduction of forskolin-induced PKA activation (measured by a reporter assay) and an impaired ability of cAMP to dissociate PRKAR1A from the catalytic PKA subunits by BRET assay. Modeling studies and sensitivity to cAMP analogs specific for domain A (8-piperidinoadenosine 3',5'-cyclic monophosphate) or domain B (8-(6-aminohexyl)aminoadenosine-3',5'-cyclic monophosphate) indicate that the mutations impair cAMP binding locally in the domain containing the mutation. Interestingly, two of these mutations affect amino acids for which alternative amino acid substitutions have been reported to cause the Carney complex phenotype. To decipher the molecular mechanism through which homologous substitutions can produce such strikingly different clinical phenotypes, we studied these mutations using the same approaches. Interestingly, the Carney mutants also demonstrated resistance to cAMP, but they expressed additional functional defects, including accelerated PRKAR1A protein degradation. These data demonstrate that a cAMP binding defect is the common molecular mechanism for resistance of PKA activation in acrodysosotosis and that several distinct mechanisms lead to constitutive PKA activation in Carney complex.

Canine disorder mirrors human disease: exonic deletion in HES7 causes autosomal recessive spondylocostal dysostosis in miniature Schnauzer dogs

Spondylocostal dysostosis is a congenital disorder of the axial skeleton documented in human families from diverse racial backgrounds. The condition is characterised by truncal shortening, extensive hemivertebrae and rib anomalies including malalignment, fusion and reduction in number. Mutations in the Notch signalling pathway genes DLL3, MESP2, LFNG, HES7 and TBX6 have been associated with this defect. In this study, spondylocostal dysostosis in an outbred family of miniature schnauzer dogs is described. Computed tomography demonstrated that the condition mirrors the skeletal defects observed in human cases, but unlike most human cases, the affected dogs were stillborn or died shortly after birth. Through gene mapping and whole genome sequencing, we identified a single-base deletion in the coding region of HES7. The frameshift mutation causes loss of functional domains essential for the oscillatory transcriptional autorepression of HES7 during somitogenesis. A restriction fragment length polymorphism test was applied within the immediate family and supported a highly penetrant autosomal recessive mode of inheritance. The mutation was not observed in wider testing of 117 randomly sampled adult miniature schnauzer and six adult standard schnauzer dogs; providing a significance of association of P_raw = 4.759e^-36 (genome-wide significant). Despite this apparently low frequency in the Australian population, the allele may be globally distributed based on its presence in two unrelated sires from geographically distant locations. While isolated hemivertebrae have been observed in a small number of other dog breeds, this is the first clinical and genetic diagnosis of spontaneously occurring spondylocostal dysostosis in a non-human mammal and offers an excellent model in which to study this devastating human disorder. The genetic test can be utilized by dog breeders to select away from the disease and avoid unnecessary neonatal losses.

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.

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.

PRKAR1A mutation affecting cAMP-mediated G protein-coupled receptor signaling in a patient with acrodysostosis and hormone resistance

CONTEXT

Acrodysostosis is a rare autosomal dominant disorder characterized by short stature, peculiar facial appearance with nasal hypoplasia, and short metacarpotarsals and phalanges with cone-shaped epiphyses. Recently, mutations of PRKAR1A and PDE4D downstream of GNAS on the cAMP-mediated G protein-coupled receptor (GPCR) signaling cascade have been identified in acrodysostosis with and without hormone resistance, although functional studies have been performed only for p.R368X of PRKAR1A.

OBJECTIVE

Our objective was to report a novel PRKAR1A mutation and its functional consequence in a Japanese female patient with acrodysostosis and hormone resistance.

PATIENT

This patient had acrodysostosis-compatible clinical features such as short stature and brachydactyly and mildly elevated serum PTH and TSH values.

RESULTS

Although no abnormality was detected in GNAS and PDE4D, a novel de novo heterozygous missense mutation (p.T239A) was identified at the cAMP-binding domain A of PRKAR1A. Western blot analysis using primary antibodies for the phosphorylated cAMP-responsive element (CRE)-binding protein showed markedly reduced CRE-binding protein phosphorylation in the forskolin-stimulated lymphoblastoid cell lines of this patient. CRE-luciferase reporter assays indicated significantly impaired response of protein kinase A to cAMP in the HEK293 cells expressing the mutant p.T239A protein.

CONCLUSIONS

The results indicate that acrodysostosis with hormone resistance is caused by a heterozygous mutation at the cAMP-binding domain A of PRKAR1A because of impaired cAMP-mediated GPCR signaling. Because GNAS, PRKAR1A, and PDE4D are involved in the GPCR signal transduction cascade and have some different characters, this would explain the phenotypic similarity and difference in patients with GNAS, PRKAR1A, and PDE4D mutations.

Acrodysostosis

Acrodysostosis refers to a group of rare skeletal dysplasias that share in common characteristic clinical and radiological features including brachydactyly, facial dysostosis, and nasal hypoplasia. In the past, the term acrodysostosis has been used to describe patients with heterogeneous phenotypes, including, in some cases, patients that today would be given alternative diagnoses. The recent finding that mutations impairing the cAMP binding to PRKAR1A are associated with "typical" acrodysostosis and hormonal resistance initiates the era where this group of disorders can be categorized on a genetic basis. In this review, we will first discuss the clinical, radiologic, and metabolic features of acrodysostosis, emphasizing evidence that several forms of the disease are likely to exist. Second, we will describe recent results explaining the pathogenesis of acrodysostosis with hormonal resistance (ADOHR). Finally, we will discuss the similarities and differences observed comparing patients with ADOHR and other diseases resulting from defects in the PTHR1 signaling pathway, in particular, pseudohypoparathyroidism type 1a and pseudopseudohypoparathyroidism.

Recurrent PRKAR1A mutation in acrodysostosis with hormone resistance

The skeletal dysplasia characteristic of acrodysostosis resembles the Albright's hereditary osteodystrophy seen in patients with pseudohypoparathyroidism type 1a, but defects in the α-stimulatory subunit of the G-protein (GNAS), the cause of pseudohypoparathyroidism type 1a, are not present in patients with acrodysostosis. We report a germ-line mutation in the gene encoding PRKAR1A, the cyclic AMP (cAMP)-dependent regulatory subunit of protein kinase A, in three unrelated patients with acrodysostosis and resistance to multiple hormones. The mutated subunit impairs the protein kinase A response to stimulation by cAMP; this explains our patients' hormone resistance and the similarities of their skeletal abnormalities with those observed in patients with pseudohypoparathyroidism type 1a.

Skeletal phenotype of mandibuloacral dysplasia associated with mutations in ZMPSTE24

Mandibuloacral dysplasia (MAD) is a rare recessively inherited premature aging disease characterized by skeletal and metabolic anomalies. It is part of the spectrum of diseases called laminopathies and results from mutations in genes regulating the synthesis of the nuclear laminar protein, lamin A. Homozygous or compound heterozygous mutations in the LMNA gene, which encodes both the precursor protein prelamin A and lamin C, are the commonest cause of MAD type A. In a few cases of MAD type B, mutations have been identified in the ZMPSTE24 gene encoding a zinc metalloproteinase important in the post-translational modification of lamin A. Here we describe a new case of MAD resulting from compound heterozygote mutations in ZMPSTE24 (p.N256S/p.Y70fs). The patient had typical skeletal changes of MAD, but in addition a number of unusual skeletal features including neonatal tooth eruption, amorphous calcific deposits, submetaphyseal erosions, vertebral beaking, severe cortical osteoporosis and delayed fracture healing. Treatment with conventional doses of pamidronate improved estimated volumetric bone density in the spine but did not arrest cortical bone loss. We reviewed the literature on cases of MAD associated with proven LMNA and ZMPSTE24 mutations and found that the unusual features described above were all substantially more prevalent in patients with mutations in ZMPSTE24 than in those with LMNA mutations. We conclude that MAD associated with ZMPSTE24 mutations has a more severe phenotype than that associated with LMNA mutations--probably reflecting the greater retention of unprocessed farnesylated prelamin A in the nucleus, which is toxic to cells.

[Genetic basis for skeletal disease. Molecular advances in sclerosing bone disorders]

Sclerosing bone disorders are caused by impaired osteoclastic bone resorption or increased bone formation. Osteopetrosis, a representative disease caused by impaired bone resorption, is a heterogeneous disease, and various molecules have been recently identified to be responsible. In infantile malignant osteopetrosis, there are osteoclast-rich and osteoclast-poor forms, which are caused by dysfunction of osteoclasts and impaired osteoclastogenesis, respectively. As to the sclerosing bone diseases related to the increased bone formation, molecular analyses of these disorders uncovered the involvement of TGF-beta and Wnt signaling in the regulation of bone mass.

[Genetic basis for skeletal disease. Radiological approach for genetic skeletal disorders]

Genetic skeletal disorders comprise two broad categories, including bone dysplasia and dysostosis. Bone dysplasia refers to disorders in which the entire skeleton is more or less affected, while dysostosis to disorders in which individual bones are affected singly or in combination. The former occurs as a result of impaired genes (proteins) that play a pivotal role in both organogenesis and maintenance of bone and cartilage, while the latter as a result of impaired genes (proteins) that are important only in the organogenesis. In this review, the author focuses on radiological signs and their pathogenic mechanism commonly seen in bone dysplasias. However, it is important to realize that a radiological diagnosis of bone dysplasias depends on an overall pattern of skeletal abnormalities rather than single radiological signs, alone or in combination.

Near normalization of adult height and body proportions by growth hormone in pycnodysostosis

CONTEXT

Mutations in the cathepsin K gene (CTSK) cause a very rare form of short-limb dwarfism called pyknodysostosis (online inheritance in man 265800) that reduces adult height to 130-150 cm.

OBJECTIVE

To study the effects of GH in children with pyknodysostosis.

DESIGN AND METHODS

This was a pilot open study of three children with pyknodysostosis (P1, P2, P3) and 16 age-matched children with idiopathic short stature (ISS) treated with a similar IGF-I-based dosing of GH therapy. P1, P2, and P3 received a mean GH dose of 29, 67, and 120 microg/kg x d, respectively, during 12, 6.5, and 5 yr, whereas the ISS group received a mean dose of 62 +/- 21 microg/kg x d during 5.4 +/- 2 yr.

RESULTS

P1, P2, and P3 had the typical clinical and radiological features of pyknodysostosis. They were shown to carry three different homozygous missense mutations of the CTSK gene. After onset of GH at 4.5, 5.4, and 10.9 yr of age, respectively, height increased from -2, -4.2, and -3 SD score to -1, -0.5, and -1 SD score after a 12, 6.5, and 5 yr GH treatment. Remarkably, body disproportion was largely corrected by GH treatment. IGF-I levels in P1, P2, and P3 were within the range of the ISS group.

CONCLUSIONS

Pyknodysostotic patients can reach near-normal stature and skeletal proportions with a personalized GH treatment targeted at appropriate IGF-I levels. Given the severity of this rare dwarfism, we propose that GH should be offered to affected children.

[Four cases of Jarcho-Levin's syndrome in the province of Antioquia, Colombia]

Four cases of Jarcho-Levin's syndrome in the province of Antioquia, Colombia Jarcho-Levin's syndrome is a skeletal dysplasia with changes in the morphogenesis and costal vertebrae segmentation. It is manifested by hemivertebrae, fused vertebral bodies, absent vertebrae or fused ribs. This entity has also been called spondylo-costal or spondylo-thoracic dysplasia-dysostosis. This paper presents four cases evaluated at the Hospital University San Vicente de Paúl, Medellín, Colombia. Three had family origins in southwestern Antioquia and one in Medellin, indicating the possibility of a predisposing genetic allele with elevated frequency in this population. The clinical and radiological manifestations were described, a well as the most notable complications, such as restrictive lung disease with permanent oxygen requirement (all 4 patients) and portal hypertension etiology (1 patient). The latter has not been reported previously as a manifestation of this syndrome.

Defective somitogenesis and abnormal vertebral segmentation in man

In recent years molecular genetics has revolutionized the study of somitogenesis in developmental biology and advances that have taken place in animal models have been applied successfully to human disease. Abnormal segmentation in man is a relatively common birth defect and advances in understanding have come through the study of cases clustered in families using DNA linkage analysis and candidate gene approaches, the latter stemming directly from knowledge gained through the study of animal models. Only a minority of abnormal segmentation phenotypes appear to follow Mendelian inheritance but three genes--DLL3, MESP2 and LNFG--have now been identified for spondylocostal dysostosis (SCD), a spinal malformation characterized by extensive hemivertebrae, trunkal shortening and abnormally aligned ribs with points of fusion. In affected families autosomal recessive inheritance is followed. These genes are all important components of the Notch signaling pathway. Other genes within the pathway cause diverse phenotypes such as Alagille syndrome (AGS) and CADASIL, conditions that may have their origin in defective vasculogenesis. This review deals mainly with SCD, with some consideration of AGS. Significant future challenges lie in identifying causes of the many abnormal segmentation phenotypes in man but it is hoped that combined approaches in collaboration with developmental biologists will reap rewards.

Congenital joint dislocations caused by carbohydrate sulfotransferase 3 deficiency in recessive Larsen syndrome and humero-spinal dysostosis

Deficiency of carbohydrate sulfotransferase 3 (CHST3; also known as chondroitin-6-sulfotransferase) has been reported in a single kindred so far and in association with a phenotype of severe chondrodysplasia with progressive spinal involvement. We report eight CHST3 mutations in six unrelated individuals who presented at birth with congenital joint dislocations. These patients had been given a diagnosis of either Larsen syndrome (three individuals) or humero-spinal dysostosis (three individuals), and their clinical features included congenital dislocation of the knees, elbow joint dysplasia with subluxation and limited extension, hip dysplasia or dislocation, clubfoot, short stature, and kyphoscoliosis developing in late childhood. Analysis of chondroitin sulfate proteoglycans in dermal fibroblasts showed markedly decreased 6-O-sulfation but enhanced 4-O-sulfation, confirming functional impairment of CHST3 and distinguishing them from diastrophic dysplasia sulphate transporter (DTDST)-deficient cells. These observations provide a molecular basis for recessive Larsen syndrome and indicate that recessive Larsen syndrome, humero-spinal dysostosis, and spondyloepiphyseal dysplasia Omani type form a phenotypic spectrum.

A case of Shwachman-Diamond syndrome confirmed with genetic analysis in a Korean child

Shwachman-Diamond syndrome (SDS) is an autosomal recessive genetic disorder, consisting of exocrine pancreatic insufficiency, chronic neutropenia, neutrophil chemotaxis defects, metaphyseal dysostosis, short stature, dental caries, and multiple organ involvements. Although SDS is the second most common hereditary abnormality of exocrine pancreas following cystic fibrosis in the Western countries, it has rarely been reported in Asia. We diagnosed a case of SDS in a 42-month-old girl, and genetic analysis including the relatives of the patient confirmed the diagnosis for the first time in Korea. She had short stature, steatorrhea, dental caries, and recurrent prulent otitis media and pneumonias. Laboratory studies revealed cyclic neutropenia, and serum levels of trypsin, amylase, and lipase were decreased. Simple radiography revealed metaphyseal sclerotic changes at the distal femur. A CT scan demonstrated a fatty infiltration and atrophy of the pancreas. On direct sequencing analysis of Shwachman-Bodian-Diamond Syndrome gene exon 2 region, the patient was homozygous for the c.258+2T>C mutation and heterozygous for the c.183_184TA>CT mutation and c.201A>G single nucleotide polymorphism. Treatment with pancreatic enzyme replacement, multivitamin supplementation, and regular to high fat diet improved her weight gain and steatorrhea.

Acrodysostosis with unusual iridal color changing with age

Acrodysostosis is a rare congenital anomaly syndrome characterized by peculiar facial appearance with a small nose and an open mouth, short stature, short metacarpotarsal, and phalangeal bones with cone-shaped epiphyses, advanced bone-age, and variable degrees of mental retardation. It is most likely that the disease is inherited in an autosomal dominant mode, its pathogenesis has remained unknown. We report a 4-year-old Japanese girl who suffered from acrodysostosis with unusual iridal color. The color of patient's irides was gray-bluish in her infancy but became light-brownish by age 4 years. Of eight Japanese patients reported, four had abnormal eye color: a 7-month-old boy with blue irides and his 2-year-old elder sister with light-blue eyes a 6-year-old girl with gray-brownish irides, and a 4-year-old girl (present case) with blue-brownish irides. The degree of iris pigmentation in acrodysostosis patients may change with age. It is likely that the putative gene for acrodysostosis might play a role not only in remodeling of bones but also in iris pigmentation.

Molecular analysis and characterization of nine novel CTSK mutations in twelve patients affected by pycnodysostosis

Molecular characterization of twelve unrelated patients affected by the autosomal recessive osteosclerotic skeletal dysplasia, Pycnodysostosis (cathepsin k deficiency), revealed 11 different genotypes. The mutational profile consisted of 12 different mutations, including nine previously unreported ones, spread throughout the whole gene. One mutation occurred in regions coding predomain, two affected the prodomain and nine others occurred in the mature domain. The novel lesions consisted in six missense mutations c.20T>C (p.L7P), c.494A>G (p.Q165R), c.580G>A (p.G194S), c.746T>C (p.I249T), c.749A>G (p.D250G), c.955G>T (p.G319C), two frameshifts c.60_61dupGA (p.I21RfsX29), c.282dupA (p.S95VfsX9) and a splicing mutation c.890G>A (r.785_890del). The six new missense mutations were examined by western blots of COS-7 cells transfected with mutant CTSK genes. The L7P, occurring within the predicted hydrophobic domain of signal peptide, showed a significantly reduced expression level compared to the wild type control. These findings suggested that the mutation affected targeting and translocation of the nascent lysosomal protein across the endoplasmatic reticulum membrane. The novel amino acid changes were also modeled into the three-dimensional structure that predicted incorrect protein folding for all of them. Molecular characterization of the patients is of particular value for genetic counseling of patients and their families as diagnosis of Pycnodysostosis based on enzyme assay is unpractical and thus not offered routinely.

[Shwachman-Diamond syndrome: clinical manifestations and molecular genetics]

The Shwachman-Diamond syndrome is a rare, autosomal recessive primary immunodeficiency disorder characterized by exocrine pancreatic insufficiency, metaphyseal dysostosis, short stature, bone marrow dysfunction and recurrent infections. The authors summarize current knowledge on molecular pathomechanisms, diagnostic criteria, therapy, and clinical manifestations of the syndrome. They present the first Hungarian patient with Shwachman-Diamond syndrome, in whom mutation analysis was performed. The patient had neutropenia, exocrine pancreatic failure, severe growth retardation, and recurrent skin and respiratory tract infections. Two previously undescribed mutations in the Shwachman-Diamond syndrome gene (c.362A > C, p.N121T and c.523C > T, p.R175W) were found. Recently, the mother became pregnant again and requested prenatal diagnosis, which revealed a carrier status of the c.523C > T, (p.R175W) mutation only, so the mother decided to complete the pregnancy.

Spondylocostal dysostosis, anal and genitourinary malformations in a fetal case: A new case of Casamassima–Morton–Nance syndrome?

Casamassima-Morton-Nance syndrome belongs to the heterogeneous group of spondylocostal dysostoses (SCD) represented by a large heterogeneous group in which diverse diagnoses, associations and modes of inheritance are found. Common features include segmentation abnormalities of the vertebrae and ribs. Here, we report on a fetal case with spondylocostal dysostosis, anal and genitourinary malformations and discuss Casamassima-Morton-Nance syndrome.

Mutation of the LUNATIC FRINGE gene in humans causes spondylocostal dysostosis with a severe vertebral phenotype

The spondylocostal dysostoses (SCDs) are a heterogeneous group of vertebral malsegmentation disorders that arise during embryonic development by a disruption of somitogenesis. Previously, we had identified two genes that cause a subset of autosomal recessive forms of this disease: DLL3 (SCD1) and MESP2 (SCD2). These genes are important components of the Notch signaling pathway, which has multiple roles in development and disease. Here, we have used a candidate-gene approach to identify a mutation in a third Notch pathway gene, LUNATIC FRINGE (LFNG), in a family with autosomal recessive SCD. LFNG encodes a glycosyltransferase that modifies the Notch family of cell-surface receptors, a key step in the regulation of this signaling pathway. A missense mutation was identified in a highly conserved phenylalanine close to the active site of the enzyme. Functional analysis revealed that the mutant LFNG was not localized to the correct compartment of the cell, was unable to modulate Notch signaling in a cell-based assay, and was enzymatically inactive. This represents the first known mutation in the human LFNG gene and reinforces the hypothesis that proper regulation of the Notch signaling pathway is an absolute requirement for the correct patterning of the axial skeleton.

Shwachman-Diamond syndrome

Shwachman-Diamond syndrome (SDS) is an inherited marrow failure disorder with varying cytopenia, pancreatic dysfunction, and metaphyseal dysostosis. SDS is also characterized by a risk of myelodysplasia and leukemia in up to one third of the patients. Over the last 5 years, major advances have been made in understanding the bone marrow phenotype. The gene associated with the disease, SBDS, has recently been identified. Herein we provide an update on the clinical features, the hematopoietic defects, and the genetics of the disease as they are currently understood. We also review the diagnostic and therapeutic approaches to the hematological complications in the syndrome.

Acrodysostosis: autosomal dominant transmission

We describe a two and half year old male child with acrodysostosis, presenting with nasal hypoplasia, peripheral dysostosis (gross shortening of hands and feet), cone-shaped epiphysis, advanced bone age, and mental retardation. He and his mother also had bilateral first ray hyperplasia of the feet thereby expressing the autosomal dominant inheritance pattern.

Thoracic three-dimensional spiral CT findings of an infant with spondylothoracic dysostosis

Spondylocostal dysostoses are a group of rare inherited disease with a heterogeneous disorder of vertebral segmentation defects and rib anomalies, which lead to respiratory problems predicting the clinical outcome. Spiral CT with three-dimensional (3D) imaging provides exact measurement of the bony rib cage. We report a case of an infant with spondylothoracic dysostosis, a phenotype of spondylocostal dysostoses, and 3D spiral CT findings of his rib cage since it may contribute to the surgical planning.

[Spondylocostal dysostosis: a rare genetic disease]

Spondylocostal dysostoses represent a group of very rare genetic disorders, characterised by vertebral and costal segmentation defects, sometimes accompanied by visceral malformations. The major gene involved is DLL3, on chromosome 19. A mutation may lead to a somitogenesis defect, with segmentation defect of axial skeleton and deformations. Depending on the nature of the mutation of DLL3, spondylocostal dysostosis is transmitted as an autosomal dominant (less severe) or autosomal recessive trait (often more severe, but non lethal). Spondylocostal dysostoses must not to be confused with the Jarcho-Levin spondylothoracic dysostosis, a severe, autosomal recessive syndrome. Its most typical aspect is the crab-like appearance of the rib cage leading to major respiratory disorders. Death, due to respiratory insufficiency, usually occurs before the age of two, most often during the first few months. At this time, guidelines for treatment do not exist. We report a case of spondylocostal dysosotosis in a patient born to consanguineous turkish parents, and review the clinical and genetic data on that group of skeletal disorders.

Spondylocostal dysostosis: thirteen new cases treated by conservative and surgical means

STUDY DESIGN

Prospective assessment of a cohort of patients affected by spondylocostal dysostosis.

OBJECTIVE

To report on the results of conservative and operative management of spondylocostal dysostosis and, based on this, to propose an assessment and treatment protocol for the condition.

SUMMARY OF BACKGROUND DATA

Spondylocostal dysostosis and spondylothoracic dysostosis are subtypes of Jarcho-Levin syndrome, a hereditary condition manifested by vertebral body and related rib malformations. Mortality prevails in spondylothoracic dysostosis because of more severe respiratory compromise.

METHODS

Details of prenatal and postnatal diagnosis, history, and management of 13 patients with spondylocostal dysostosis are presented. All patients were treated postnatally with repeated chest physiotherapy. Two patients refractory to conservative treatment underwent surgical intervention: the first had a chest wall reconstruction via a latissimus dorsi flap, the second a posterior spinal instrumented fusion for progressive scoliosis.

RESULTS

Prenatal ultrasound in 4 of 13 cases showed full details of vertebral and rib anomalies. Thoracic and lumbar hemivertebrae were most common, leading to congenital scoliosis in 10 of 13 cases. A number of extraskeletal abnormalities were also identified. At an average follow-up of 4.5 years, the survival rate was 100% with a remarkable decrease of the rate of respiratory complications. Surgical treatment in selected cases led to satisfactory results.

CONCLUSIONS

Prenatal diagnosis of spondylocostal dysostosis allows exclusion of spondylothoracic dysostosis and aids genetic counseling in quantifying the risk to siblings. Postnatally, prompt management of these patients with physiotherapy leads to prolonged survival. Surgical intervention may then be indicated to stabilize chest wall or spine deformities, with promising results.

Mutated MESP2 causes spondylocostal dysostosis in humans

Spondylocostal dysostosis (SCD) is a term given to a heterogeneous group of disorders characterized by abnormal vertebral segmentation (AVS). We have previously identified mutations in the Delta-like 3 (DLL3) gene as a major cause of autosomal recessive spondylocostal dysostosis. DLL3 encodes a ligand for the Notch receptor and, when mutated, defective somitogenesis occurs resulting in a consistent and distinctive pattern of AVS affecting the entire spine. From our study cohort of cases of AVS, we have identified individuals and families with abnormal segmentation of the entire spine but no mutations in DLL3, and, in some of these, linkage to the DLL3 locus at 19q13.1 has been excluded. Within this group, the radiological phenotype differs mildly from that of DLL3 mutation-positive SCD and is variable, suggesting further heterogeneity. Using a genomewide scanning strategy in one consanguineous family with two affected children, we demonstrated linkage to 15q21.3-15q26.1 and furthermore identified a 4-bp duplication mutation in the human MESP2 gene that codes for a basic helix-loop-helix transcription factor. No MESP2 mutations were found in a further 7 patients with related radiological phenotypes in whom abnormal segmentation affected all vertebrae, nor in a further 12 patients with diverse phenotypes.

Pseudodominant inheritance of spondylocostal dysostosis type 1 caused by two familial delta-like 3 mutations

Spondylocostal dysostoses (SCD) are a heterogeneous group of disorders of axial skeletal malformation characterized by multiple vertebral segmentation defects and rib anomalies. Sporadic cases with diverse phenotypes, sometimes including multiple organ abnormalities, are relatively common, and monogenic forms demonstrating autosomal recessive (AR) and, more rarely, autosomal dominant (AD) inheritance have been reported. We previously showed that mutations in delta-like 3 (DLL3), a somitogenesis gene that encodes a ligand for the notch signaling pathway, cause AR SCD with a consistent pattern of abnormal segmentation. We studied an SCD family previously reported to show AD inheritance, in which the phenotype is similar to that in AR cases. Direct DLL3 sequencing of individuals in two generations identified the affected father as homozygous for a novel frameshift mutation, 1440delG. His two affected children were compound heterozygotes for this mutation and a novel missense mutation, G504D, the first putative missense mutation reported in the transmembrane domain of DLL3. Their two unaffected siblings were heterozygotes for the 1440delG mutation. Pseudodominant inheritance has been confirmed, and the findings raise potential consequences for genetic counseling in relation to the SCD disorders.

Decreased bone turnover and deterioration of bone structure in two cases of pycnodysostosis

Pycnodysostosis is an uncommon human genetic disorder characterized by osteosclerosis of the skeleton, short stature, and bone fragility. The disease results from mutations in the cathepsin K gene, a lysosomal cysteine protease highly expressed in osteoclasts and crucial for the degradation of organic matrix from mineralized bone. Recently, interest has focused on a pharmaceutical inhibition of cathepsin K to prevent bone loss. However, little is known about the cellular activity or material quality of bone in pycnodysostosis. In the present study, transiliac bone biopsies from two affected individuals, aged 5 and 21 yr, were investigated using light microscopy, quantitative backscattered electron imaging, and small angle x-ray scattering. Results were compared with published age-matched reference data. The mutations in the cathepsin K gene of both patients were identified, including one novel defect. Both individuals had severe osteosclerosis, and their biopsies displayed multinucleated osteoclasts apposed to areas of demineralized matrix as well as bone-lining cells adjacent to this undigested collagen left over by osteoclasts. The homogeneity of the mineralized matrix was markedly disturbed due to large inclusions of mineralized cartilage residues. Histomorphometric evaluation showed a quantitative decrease in static parameters of bone formation. In contrast and despite deficient cathepsin K activity, osteoclastic parameters were close to normal range. At the nanostructural level, there was a marked increase in the mean thickness of the mineral particles, reflecting decreased bone remodeling. Examination of the trabecular structure revealed that the lamellae were highly disordered, which was also apparent from a poor alignment of mineral crystals oriented along the longitudinal axis of collagen fibrils. Taken together, these results strongly suggest that functional cathepsin K is important for balanced bone turnover, and enzyme deficiency results in a profound deterioration of bone quality with respect to trabecular architecture and lamellar arrangement, which is presumably the reason for bone fragility in pycnodysostosis.

Aberrant Pax1 and Pax9 expression in Jarcho-Levin syndrome: report of two Caucasian siblings and literature review

We report two consecutive Caucasian male siblings of nonconsanguineous parents autopsied at 22 and 13 weeks gestational age both with prenatal diagnosis of Jarcho-Levin syndrome (JLS). Segmentation anomalies of the vertebrae and ribs encompass a spectrum of syndromes with or without associated anomalies of other developmental fields, and include spondylothoracic dysostosis (STD), JLS, Casamassima-Morton-Nance (CMN) syndrome, and spondylocostal dysostosis (SCD), among others. In both these new JLS cases the autopsies confirmed that there were severe developmental alterations in the thoracic and vertebral skeleton (including "crab-like" thorax), accompanied in the older fetus by renal defects. Because vertebral development is controlled by a limited number of master genes including Pax1 and Pax9, we analyzed protein expression from these genes in these two cases compared to age-matched controls. Immunochemical analysis showed a significant reduction in levels of Pax1 and Pax9 protein expression in chondrocytes of the vertebral column. Implications for the etiology and pathogenesis of JLS and related disorders are discussed.

Molecular genetic prenatal diagnosis for a case of autosomal recessive spondylocostal dysostosis

Autosomal recessive spondylocostal dysostosis type 1 (ARSCD1) is a member of the heterogeneous group of disorders termed the spondylocostal dysostoses that are characterized by multiple vertebral segmentation defects and rib anomalies. In these patients, the entire vertebral column is malformed and is replaced by multiple hemivertebrae giving rise to truncal shortening, abdominal protrusion and non-progressive spinal curvature. Genetic studies have shown that some cases of ARSCD are due to mutations in the somitogenesis gene, Delta-like 3 (DLL3), that encodes a ligand for the Notch signalling pathway-ARSCD type 1. To date, 17 different DLL3 gene mutations have been reported. A consanguineous family of Turkish origin with ARSCD type 1 due to a homozygous DLL3 mutation requested genetic prenatal diagnosis. Using DNA from a chorionic villus sample, both linkage analysis of the DLL3/19q region and direct sequencing for the familial mutation demonstrated that the unborn fetus was an unaffected carrier. This is the first case of molecular genetic prenatal diagnosis in any form of SCD.

A cluster of autosomal recessive spondylocostal dysostosis caused by three newly identified DLL3 mutations segregating in a small village

In 1982, one of us reported a cluster of eight individuals affected by spondylocostal dysostosis (SD, MIM 277300) in four nuclear families indigenous to a village from eastern Switzerland. We tested the hypothesis that the molecular basis for this cluster was segregation of a single mutation in the DLL3 gene, recently linked to SD. Marker haplotypes around the DLL3 locus contradicted this hypothesis as three different haplotypes were seen in affected individuals, but sequence analysis showed that three unreported DLL3 mutations were segregating: a duplication of 17 bp in exon 8 (c.1285-1301dup), a single-nucleotide deletion in exon 5 (c.615delC), and a R238X nonsense mutation in exon 6. Contrary to our initial assumption of a single allele segregating in this small community, three different pathogenic alleles were observed, with a putative founder mutation occurring at the homozygous state but also compounding with, and thus revealing, two other independent mutations. As all three mutations predict truncation of the DLL3 protein and loss of the membrane-attaching domain, the results confirm that autosomal recessive spondylocostal dysostosis represents the null phenotype of DLL3, with remarkable phenotypic consistency across families.

Novel mutations in DLL3, a somitogenesis gene encoding a ligand for the Notch signalling pathway, cause a consistent pattern of abnormal vertebral segmentation in spondylocostal dysostosis

The spondylocostal dysostoses (SCD) are a group of disorders characterised by multiple vertebral segmentation defects and rib anomalies. SCD can either be sporadic or familial, and can be inherited in either autosomal dominant or recessive modes. We have previously shown that recessive forms of SCD can be caused by mutations in the delta-like 3 gene, DLL3. Here, we have sequenced DLL3 in a series of SCD cases and identified 12 mutations in a further 10 families. These include 10 novel mutations in exons 4-8, comprising nonsense, missense, frameshift, splicing, and in frame insertion mutations that are predicted to result in either the truncation of the mature protein in the extracellular domain, or affect highly conserved amino acid residues in the epidermal growth factor-like repeats of the protein. The affected cases represent diverse ethnic backgrounds and six come from traditionally consanguineous communities. In all affected subjects, the radiological phenotype is abnormal segmentation throughout the entire vertebral column with smooth outlines to the vertebral bodies in childhood, for which we suggest the term "pebble beach sign". This is a very consistent phenotype-genotype correlation and we suggest the designation SCD type 1 for the AR form caused by mutations in the DLL3 gene.

Notch signaling and inherited disease syndromes

The Notch signaling pathway is an evolutionarily conserved, intercellular signaling mechanism essential for proper embryonic development in organisms as diverse as insects, nematodes, echinoderms and mammals. Disruptions in conserved developmental pathways frequently result in inherited congenital anomalies in humans. Mutations in genes encoding Notch pathway components underlie three inherited human diseases: Alagille syndrome, spondylocostal dysostosis, and cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy. Mouse models for these three diseases have been developed, and are leading to novel insights into the pathology of these diseases in humans.

A new mutation in the skeletal ryanodine receptor gene (RYR1) is potentially causative of malignant hyperthermia, central core disease, and severe skeletal malformation

Malignant hyperthermia susceptibility (MHS) and central core disease (CCD) have been shown to result from missense mutations in the ryanodine receptor gene of the skeletal muscle (RYR1). A 15-year-old patient who had spondylocostal dysostosis (SCD) developed an MH crisis during general anesthesia. The patient was characterized phenotypically by block vertebrae, vertebral fusion, short neck and thorax, fused ribs, craniofacial abnormalities, spina bifida occulta, and a diaphragmatic defect closed surgically in early infancy. The diagnosis MH susceptible (MHS) was confirmed by the in vitro contracture test (IVCT) on a muscle biopsy. Surprisingly, the histopathological investigation revealed the presence of CCD too. Molecular genetic investigation of the RYR1 gene was performed to search for known MH-related mutations. Cluster regions of the RYR1 gene, in which mutations have already been found, were examined by direct automated sequencing. In addition to the diagnosis MHS and CCD we were able to identify a novel RYR1 mutation in exon 46: 7358ATC > ACC, resulting in an Ile2453Thr substitution. This mutation was also present in the mother, in whom MH disposition and CCD were determined by muscle investigations. We suggest that the newly identified RYR1 mutation is closely associated with MH and CCD. A probable causative role of the RYR1 gene in SCD patients should be assessed by further genetic investigations.

[Pycnodysostosis--common ancestor of some Danish patients. Examination and diagnosis based on molecular genetics]

Eight patients with pycnodysostosis from six Danish families were examined for mutations in the cathepsin K gene. Three different mutations are the cause of pycnodysostosis in the six families--five of whom come from Ringkøbing County and one from Vejle County. One mutation has a high frequency in the families from Ringkoebing County. The five families are related through a common ancestor, who introduced the mutation around the year 1100. The disease is described with respect to aetiology, symptoms, prognosis, diagnosis, and symptomatic treatment. Research in pycnodysostosis may bring important knowledge to the understanding of related diseases, such as osteoporosis.