Short-limbed Dwarfism Research Articles

Endocrinology & Metabolism News

Previous studies have suggested a regulatory relationship between serum phosphorus, vitamin D, and fibroblast growth factor 23 (FGF23), a hormone that promotes renal excretion of phosphate. Despite these associations, the identity of the primary regulator of serum FGF23 is unresolved. Jansen's metaphyseal chondrodysplasia is a rare autosomal dominant disorder associated with short-limbed dwarfism and other characteristic skeletal abnormalities. This condition is caused by mutations in the PTH/PTHrP receptor that result in ligand-independent cAMP accumulation, thus rendering the receptor constitutively active. These patients typically exhibit asymptomatic hypercalcemia and hypophosphatemia despite low or undetectable serum levels of PTH and PTHrP. A literature search revealed that serum FGF23 levels had not been studied in patients with Jansen's syndrome, a disorder in which the biochemical features present a unique opportunity to study the possible relationship between FGF23 and calcium-phosphorus-vitamin D metabolism. A case of Jansen's syndrome is presented in which serum FGF23 concentrations, along with serum phosphorus and 1,25(OH)(2) vitamin D levels, were measured and compared with those of age-matched controls. Serum FGF23 concentrations in the patient with Jansen's syndrome were found to be markedly and persistently elevated, compared with values in healthy, age-matched controls, despite hypophosphatemia and normal 1,25(OH)(2) vitamin D levels. Together, our findings indicate that serum FGF23 could be governed by factor(s) other than serum phosphorus, potentially by activation of the PTH/PTHrP receptor in bone.

Progressive joint limitations as the first alarming signs in a boy with short – limbed dwarfism: A case report

IntroductionContracture is a condition of abnormal shortening or shrinkage of a muscle, and or a tendon often with persistent flexion or distortion at a joint. Careful documentation of the kind of contractures encountered in different paediatric disorders is important in distinguishing a specific subtype. Achondroplasia has been considered as the most common short-limbed dwarfism syndrome, but there are a variety of other syndromes within this category, and other types of limb shortening.Case presentationWe report on a 5-year-old boy of Austrian origin who manifests progressive joint limitations in connection with a dysplastic form of short-limbed dwarfism namely chondrodysplasia punctata-tibial-metacarpal-type. Progressive joint limitations of maximal intensity over the hip, and the ankle joints were the main presenting features.ConclusionOsteochondrodysplasias involve abnormal bone or cartilage growth leading to skeletal maldevelopment, often short-limbed dwarfism. Diagnosis is by physical examination, radiographic documentation, and, in some cases, genetic testing. In patients with chondrodysplasia punctata, early life radiographic examination is fundamental, since resolution of the punctate calcifications leaving abnormal epiphyses and flared and irregular metaphyses after age one to three years seems to be characteristic.

Congenital Chloride-losing Diarrhea Causing Mutations in the STAS Domain Result in Misfolding and Mistrafficking of SLC26A3

Congenital chloride-losing diarrhea (CLD) is a genetic disorder causing watery stool and dehydration. Mutations in SLC26A3 (solute carrier 26 family member 3), which functions as a coupled Cl(-)/HCO(3)(-) exchanger, cause CLD. SLC26A3 is a membrane protein predicted to contain 12 transmembrane-spanning alpha-helices and a C-terminal STAS (sulfate transporters and anti-sigma-factor) domain homologous to the bacterial anti-sigma-factor antagonists. The STAS domain is required for SLC26A3 Cl(-)/HCO(3)(-) exchange function and for the activation of cystic fibrosis transmembrane conductance regulator by SLC26A3. Here we investigate the molecular mechanism(s) by which four CLD-causing mutations (DeltaY526/7, I544N, I675/6ins, and G702Tins) in the STAS domain lead to disease. In a heterologous mammalian expression system biochemical, immunohistochemical, and ion transport experiments suggest that the four CLD mutations cause SLC26A3 transporter misfolding and/or mistrafficking. Expression studies with the isolated STAS domain suggest that the I675/6ins and G702Tins mutations disrupt the STAS domain directly, whereas limited proteolysis experiments suggest that the DeltaY526/7 and I544N mutations affect a later step in the folding and/or trafficking pathway. The data suggest that these CLD-causing mutations cause disease by at least two distinct molecular mechanisms, both ultimately leading to loss of functional protein at the plasma membrane.

Spectrum of severe skeletal dysplasias in North India

Severe skeletal dysplasias are a group of bone growth disorders characterized by a lethal outcome in utero or infancy. We describe our experience of the severe skeletal dysplasias diagnosed amongst fetal autopsies done at a tertiary level centre over a five year period. We evaluated 15 cases with short limbed dwarfism, of which 13 fetuses were examined after termination of pregnancy and two were evaluated postnatally. Short rib dysplasia syndromes with or without polydactyly, osteogenesis imperfecta type II, thanatophoric dysplasia, campomelic dysplasia, chondrodysplasia punctata, rhizomelic type and achondrogenesis were the lethal skeletal dysplasias diagnosed. Precise identification of the tye of skeletal dysplasia is paramount for proper genetic counseling. Postnatal examination and detailed radiographic examination of the fetus especially of the pelvis, limbs, skull and spine are essential to identify the type of skeletal dysplasia.

Structural and Functional Characterization of Recombinant Matrilin-3 A-domain and Implications for Human Genetic Bone Diseases

Mutations in matrilin-3 result in multiple epiphyseal dysplasia, which is characterized by delayed and irregular bone growth and early onset osteoarthritis. The majority of disease-causing mutations are located within the beta-sheet of the single A-domain of matrilin-3, suggesting that they disrupt the structure and/or function of this important domain. Indeed, the expression of mutant matrilin-3 results in its intracellular retention within the rough endoplasmic reticulum of cells, where it elicits an unfolded protein response. To understand the folding characteristics of the matrilin-3 A-domain we determined its structure using CD, analytical ultracentrifugation, and dual polarization interferometry. This study defined novel structural features of the matrilin-3 A-domain and identified a conformational change induced by the presence or the absence of Zn(2+). In the presence of Zn(2+) the A-domain adopts a more stable "tighter" conformation. However, after the removal of Zn(2+) a potential structural rearrangement of the metal ion-dependent adhesion site motif occurs, which leads to a more "relaxed" conformation. Finally, to characterize the interactions of the matrilin-3 A-domain we performed binding studies on a BIAcore using type II and IX collagen and cartilage oligomeric matrix protein. We were able to demonstrate that it binds to type II and IX collagen and cartilage oligomeric matrix protein in a Zn(2+)-dependent manner. Furthermore, we have also determined that the matrilin-3 A-domain appears to bind exclusively to the COL3 domain of type IX collagen and that this binding is abolished in the presence of a disease causing mutation in type IX collagen.

Achondroplasia: From genotype to phenotype

This review focuses on the rheumatological features of achondroplasia, which is the most common skeletal dysplasia and the most frequent cause of short-limbed dwarfism. It is inherited in an autosomal dominant manner but results in the majority of cases of de novo mutations. The disease is related to a mutation in the fibroblast growth factor receptor-3 ( FGFR3) gene encoding one member of the FGFR subfamily of tyrosine kinase receptors, which results in constitutive activation of the receptor. Biochemical studies of FGFR3 combined with experiments in knock-out mice have demonstrated that FGFR3 is a negative regulator of chondrocytes proliferation and differentiation in growth plate. This mutation induces a disturbance of endochondral bone formation. The diagnosis of achondroplasia is based on typical clinical and radiological features including short stature, macrocephaly with frontal bossing, midface hypoplasia and rhizomelic shortening of the limbs. The most common rheumatological complications of achondroplasia are medullar and radicular compressions due to spinal stenosis and deformities of the lower limbs. Current treatment and future therapies are discussed.

Short-Limbed Dwarfism: slw Is a New Allele of Npr2 Causing Chondrodysplasia

Short-limbed dwarfism (SLW) is a new mutant mouse characterized by a dwarf phenotype with markedly short body, limbs, and tail. In the present study, we investigated the skeletal phenotypes of the SLW mouse and determined the chromosomal localization to identify the gene responsible for the phenotypes (slw). Skeletal preparations stained with alcian blue and alizarin red revealed that longitudinal growth of the extremities of the affected (slw/slw) mice was significantly reduced in comparison with that of normal mice, whereas the positions and numbers of skeletal elements were normal. Histological examination of tibial growth plates of the affected mice showed that the numbers of proliferating and hypertrophic chondrocytes were obviously diminished. These phenotypes resembled to those of human chondrodysplasias caused by defective chondrocyte proliferation and differentiation. We mapped the slw locus on an 11.7-cM interval of the proximal region of mouse chromosome 4 by linkage analysis. Furthermore, allelism test using Npr2(cn) locus, a mutant allele of Npr2 gene encoding a natriuretic peptide receptor B, revealed that slw locus is an allele of the Npr2 gene. These results suggest that the dwarf phenotype of the SLW mouse is caused by the disturbed endochondral ossification, and a mutation in the Npr2 gene is expected to be responsible for the phenotypes of the SLW mouse.

Reduced cell proliferation and increased apoptosis are significant pathological mechanisms in a murine model of mild pseudoachondroplasia resulting from a mutation in the C-terminal domain of COMP.

Pseudoachondroplasia (PSACH) is one of the more common skeletal dysplasias and results from mutations in cartilage oligomeric matrix protein (COMP). Most COMP mutations identified to date cluster in the TSP3 repeat region of COMP and the mutant protein is retained in the rough endoplasmic reticulum (rER) of chondrocytes and may result in increased cell death. In contrast, the pathomolecular mechanism of PSACH resulting from C-terminal domain COMP mutations remain largely unknown. This study describes the generation and analysis of a murine model of mild PSACH resulting from a p.Thr583Met mutation in the C-terminal globular domain (CTD) of COMP. Mutant animals are normal at birth, but grow slower than their wild-type littermates and by 9 weeks of age they have mild short-limb dwarfism. Furthermore, by 16 months of age mutant animals exhibit severe degeneration of articular cartilage, which is consistent with early onset osteoarthritis seen in PSACH patients. In the growth plates of mutant mice the chondrocyte columns are sparser and poorly organized. Mutant COMP is secreted into the extracellular matrix, but its localization is disrupted along with the distribution of several COMP-binding proteins. Although mutant COMP is not retained within the rER there is an unfolded protein/cell stress response and chondrocyte proliferation is significantly reduced, while apoptosis is both increased and spatially dysregulated. Overall, these data suggests a mutation in the CTD of COMP exerts a dominant-negative effect on both intra- and extracellular processes. This ultimately affects the morphology and proliferation of growth plate chondrocytes, eventually leading to chondrodysplasia and reduced long bone growth.

Preserved fertility in a non-mosaic Klinefelter patient with a mutation in the fibroblast growth factor receptor 3 gene: Case Report

Patients with Klinefelter syndrome (47,XXY) are characterized by eunuchoid body proportions, gynaecomastia, small firm testes and azoospermia. We describe a Klinefelter patient (non-mosaic 47,XXY karyotype) who was heterozygous for the classical 1138G>A mutation in the fibroblast growth factor receptor 3 (FGFR3) gene, which is a gain-of-function mutation resulting in achondroplasia. The patient had phenotypic characteristics of achondroplasia (e.g. short limbed dwarfism and frontal bossing). Testicular volume was 8 ml at 27 years of age and repeated semen samples showed sperm concentrations of 0.175 million/ml. Serum FSH levels were elevated (21.7 IU/l) compared to normal age-matched healthy male controls and patients with non-mosaic Klinefelter syndrome, and inhibin B levels were low-normal, in contrast to the usually undetectable inhibin B levels in adult Klinefelter patients. The patient fathered a child from a spontaneous pregnancy. The observed testicular size and function in our patient contrast the typical findings in classical Klinefelter syndrome. We speculate that the alteration of FGFR3 protein function in our Klinefelter patient alleviated the destruction of the seminiferous tubules and may suggest that the fibroblast growth factor family has a pleiotrophic function in human spermatogonia, which physiologically express FGFR3.

Decreased chondrocyte proliferation and dysregulated apoptosis in the cartilage growth plate are key features of a murine model of epiphyseal dysplasia caused by a matn3 mutation

Disruption to endochondral ossification leads to delayed and irregular bone formation and can result in a heterogeneous group of genetic disorders known as the chondrodysplasias. One such disorder, multiple epiphyseal dysplasia (MED), is characterized by mild dwarfism and early-onset osteoarthritis and can result from mutations in the gene encoding matrilin-3 (MATN3). To determine the disease mechanisms that underpin the pathophysiology of MED we generated a murine model of epiphyseal dysplasia by knocking-in a matn3 mutation. Mice that are homozygous for the mutation develop a progressive dysplasia and have short-limbed dwarfism that is consistent in severity with the relevant human phenotype. Mutant matrilin-3 is retained within the rough endoplasmic reticulum of chondrocytes and is associated with an unfolded protein response. Eventually, there is reduced proliferation and spatially dysregulated apoptosis of chondrocytes in the cartilage growth plate, which is likely to be the cause of disrupted linear bone growth and the resulting short-limbed dwarfism in the mutant mice.

Specific osseous spurs in a lethal form of hypophosphatasia correlated with 3D prenatal ultrasonographic images

Hypophosphatasia is an osseous dysplasia with highly variable clinical expression, ranging from a recessive lethal prenatal type to late onset dominant short stature with premature shedding of teeth. Lethal forms of hypophosphatasia include short limb dwarfism with lack of ossification, especially on the vertebral bodies, very slender ribs and clavicles, and bowed, short lower extremities, with a bifid aspect of the diaphyses. Alkaline phosphatase is abnormally low in liver, bone, kidney and plasma. We present here the prenatal images of a lethal form of hypophosphatasia, diagnosed precociously because of specific osseous spurs in a context of recurrent short limb dwarfism. Prenatal 3D ultrasonography has shown these spurs as early as 18 weeks. Molecular biology found compound heterozygous mutations in the gene TNSALP. In a context of short limb dwarfism, the search for these specific osseous spurs orient strongly toward the diagnosis of lethal hypophosphatasia.

Non‐invasive prenatal detection of achondroplasia in size‐fractionated cell‐free DNA by MALDI‐TOF MS assay

Achondroplasia is the most common form of short-limbed dwarfism in humans and is caused by mutations in the FGFR3 gene. Currently, prenatal diagnosis of this disorder relies on invasive procedures. Recent studies have shown that fetal single gene point mutations could be detected in cell-free DNA (cf-DNA) from maternal plasma by either the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) assay with single allele base extension reaction (SABER) approach or the size fractionation of cf-DNA in maternal plasma. Here, we combined the two approaches to non-invasively examine the fetal G1138A mutation in maternal plasma. cf-DNA was extracted from maternal plasma samples obtained from two pregnant women at risk for achondroplasia. The fetal G1138A mutation was determined by the analysis of size-fractionated cf-DNA in maternal plasma using MALDI-TOF MS with SABER approach and homogenous MassEXTEND (hME) assay, respectively. The fetal G1138A mutation was detectable in the two achondroplasia-affected pregnancies by the analysis of cf-DNA in maternal plasma using MALDI-TOF MS. However, the size-fractionation approach led to a more precise detection of the fetal mutation in both analyses. This analysis would be suitable for non-invasive prenatal diagnosis of diseases caused by fetal single gene point mutations.

Novel FGFR3 mutations creating cysteine residues in the extracellular domain of the receptor cause achondroplasia or severe forms of hypochondroplasia

Achondroplasia (ACH) and hypochondroplasia (HCH) are two autosomal-dominant skeletal disorders caused by recurrent missense FGFR3 mutations in the transmembrane (TM) and tyrosine kinase 1 (TK1) domains of the receptor. Although 98% of ACH cases are accounted for by a single G380R substitution in the TM, a common mutation (N540K) in the TK1 region is detected in only 60-65% of HCH cases. The aim of this study was to determine whether the frequency of mutations in patients with HCH was the result of incomplete mutation screening or genetic heterogeneity. Eighteen exons of the FGFR3 gene were entirely sequenced in a cohort of 25 HCH and one ACH patients in whom common mutations had been excluded. Seven novel missense FGFR3 mutations were identified, one causing ACH and six resulting in HCH. Six of these substitutions were located in the extracellular region and four of them creating additional cysteine residues, were associated with severe phenotypes. No mutations were detected in 19 clinically diagnosed HCH patients. Our results demonstrate that the spectrum of FGFR3 mutations causing short-limb dwarfism is wider than originally recognised and emphasise the requirement for complete screening of the FGFR3 gene if appropriate genetic counselling is to be offered to patients with HCH or ACH lacking the most common mutations and their families.

Insulin-Like Growth Factor-I Is Essential for Embryonic Bone Development

Although IGF-I has been identified as an important growth factor for the skeleton, the role of IGF-I on embryonic bone development remains unknown. Here we show that, in IGF-I-deficient (IGF-I(-/-)) mice, skeletal malformations, including short-limbed dwarfism, were evident at days post coitus (dpc) 14.5 to 18.5, accompanied by delays of mineralization in the spinal column, sternum, and fore paws. Reduced chondrocyte proliferation and increased chondrocyte apoptosis were identified in both the spinal ossification center and the growth plate of long bones. Abnormal chondrocyte differentiation and delayed initiation of mineralization was characterized by small size and fewer numbers of type X collagen expressing hypertrophic chondrocytes and lower osteocalcin expression. The Indian hedgehog-PTHrP feedback loop was altered; expression of Indian hedgehog was reduced in IGF-I(-/-) mice in long bones and in the spine, whereas expression of PTHrP was increased. Our results indicate that IGF-I plays an important role in skeletal development by promoting chondrocyte proliferation and maturation while inhibiting apoptosis to form bones of appropriate size and strength.

A Unique Presentation of Immuno‐Osseous Dysplasia

The immuno-osseous dysplasias are a rare group of conditions in which short-limbed dwarfism is associated with an immune defect. The best known of these is cartilage hair hypoplasia. However, several reports of other distinct conditions exist, which have been arbitrarily classified on the basis of the immune defect. We present a child with a previously unreported combination of immune and skeletal abnormalities in whom there was an unusual and distinctive skin appearance associated with defective cutaneous elastic fibers. These cutaneous features suggest a unifying link with other immuno-osseous dysplasia but the combination of immune and skeletal defects exposes weaknesses in the current method of classification.

Ellis—van Creveld Syndrome

Ellis—van Creveld syndrome is a rare, singlegene genetic congenital skeletal disorder. It is an autosomal recessive inherited disorder, which means that both parents must carry the gene for the child to be affected. It involves abnormalities of multiple body systems, including teeth, nails, hair, lungs, and liver, and approximately 50% of affected patients will have major heart defects. There is short-limbed dwarfism, with the extremities being disproportionate with the trunk, this being more apparent in the lower limbs. Postaxial polydactyly, or extra digits in the hands, is seen in virtually 100% of those individuals affected with Ellis—van Creveld. Despite the advances in sonography, the prenatal diagnosis of a specific skeletal dysplasia remains very difficult and often can only be made after birth or termination of the pregnancy.

Aspects of achondroplasia in the skulls of dwarf transgenic mice: A cephalometric study

Achondroplasia, the most common short-limbed dwarfism in humans, results from a single nucleotide substitution in the gene for fibroblast growth factor receptor 3 (FGFR3). FGFR3 regulates bone growth in part via the mitogen-activated protein kinase pathway (MAPK). To examine the role of this pathway in chondrocyte differentiation, a transgenic mouse was generated that expresses a constitutively active mutant of MEK1 in chondrocytes and exhibits dwarfing characteristics typical of human achondroplasia, i.e., shortened axial and appendicular skeletons, mid-facial hypoplasia, and dome-shaped cranium. In this study, cephalometrics of the MEK1 mutant skulls were assessed to determine if the MEK1 mice are a good model of achondroplasia. Skull length, arc of the cranial vault, and area, maximum and minimum diameters of the brain case were measured on digitized radiographs of skulls of MEK1 and control mice. Cranial base and nasal bone length and foramen magnum diameter were measured on midsagittal micro-CT sections. Data were normalized by dividing by the cube root of each animal's weight. Transgenic mice exhibited a domed skull, deficient midface, and (relatively) prognathic mandible and had a shorter cranial base and nasal bone than the wild-type. Skull length was significantly less in transgenic mice, but cranial arc was significantly greater. The brain case was larger and more circular and minimum diameter of the brain case was significantly greater in transgenic mice. The foramen magnum was displaced anteriorly but not narrowed. MEK1 mouse cephalometrics confirm these mice as a model for achondroplasia, demonstrating that the MAP kinase signaling pathway is involved in FGF signaling in skeletal development.

Congenital Hypothyroidism in Peters Plus Syndrome

Peters plus syndrome is a multiple malformation syndrome characterized by a combination of Peters anomaly of the eye and other extraocular defects, including short-limb dwarfism, a thin upper lip, hypoplastic columella, and a round face. Two unrelated children with the typical features of Peters plus syndrome and hypothyroidism have been previously reported in medical literature. Herein, we report a male patient who exhibited the Peters plus syndrome phenotype as well as hypothyroidism and provide further evidence that hypothyroidism may represent an under-recognized feature of Peters plus syndrome. The consanguinity of the parents in the present case supports, but does not confirm, the notion that a homozygous defect in a single autosomal recessive gene might be responsible for the normal morphogenesis of both the anterior chamber and the thyroid gland.

Natriuretic Peptides, Their Receptors, and Cyclic Guanosine Monophosphate-Dependent Signaling Functions

Natriuretic peptides are a family of structurally related but genetically distinct hormones/paracrine factors that regulate blood volume, blood pressure, ventricular hypertrophy, pulmonary hypertension, fat metabolism, and long bone growth. The mammalian members are atrial natriuretic peptide, B-type natriuretic peptide, C-type natriuretic peptide, and possibly osteocrin/musclin. Three single membrane-spanning natriuretic peptide receptors (NPRs) have been identified. Two, NPR-A/GC-A/NPR1 and NPR-B/GC-B/NPR2, are transmembrane guanylyl cyclases, enzymes that catalyze the synthesis of cGMP. One, NPR-C/NPR3, lacks intrinsic enzymatic activity and controls the local concentrations of natriuretic peptides through constitutive receptor-mediated internalization and degradation. Single allele-inactivating mutations in the promoter of human NPR-A are associated with hypertension and heart failure, whereas homozygous inactivating mutations in human NPR-B cause a form of short-limbed dwarfism known as acromesomelic dysplasia type Maroteaux. The physiological effects of natriuretic peptides are elicited through three classes of cGMP binding proteins: cGMP-dependent protein kinases, cGMP-regulated phosphodiesterases, and cyclic nucleotide-gated ion channels. In this comprehensive review, the structure, function, regulation, and biological consequences of natriuretic peptides and their associated signaling proteins are described.

FGF upregulates osteopontin in epiphyseal growth plate chondrocytes: Implications for endochondral ossification

Fibroblast growth factor receptor 3 (FGFR3) signaling pathways are essential for normal longitudinal bone growth. Mutations in this receptor lead to various human growth disorders, including Achondroplasia, disproportionately short-limbed dwarfism, characterized by narrowing of the hypertrophic region of the epiphyseal growth plates. Here we find that FGF9, a preferred ligand for FGFR3 rapidly induces the upregulation and secretion of the matrix resident phosphoprotein, osteopontin (OPN) in cultured chicken chondrocytes. This effect was observed as early as two hours post stimulation and at FGF9 concentrations as low as 1.25 ng/ml at both mRNA and protein levels. OPN expression is known to be associated with chondrocyte and osteoblast differentiation and osteoclast activation. Unexpectedly, FGF9 induced OPN was accompanied by inhibition of differentiation and increased proliferation of the treated chondrocytes. Moreover, FGF9 stimulated OPN expression irrespective of the differentiation stage of the cells or culture conditions. In situ hybridization analysis of epiphyseal growth plates from chicken or mice homozygous for the Achondroplasia, G369C/mFGFR3 mutation demonstrated co-localization of OPN expression and osteoclast activity, as evidenced by tartarate resistant acid phosphatase positive cells in the osteochondral junction. We propose that FGF signaling directly activates OPN expression independent of chondrocytes differentiation. This may enhance the recruitment and activation of osteoclasts, and increase in cartilage resorption and remodeling in the chondro-osseus border.