Christine M. Hall

Nosology and classification of genetic skeletal disorders: 2010 revision

The objective of the paper is to provide the revision of the Nosology of Constitutional Disorders of Bone that incorporates newly recognized disorders and reflects new molecular and pathogenetic concepts. Criteria for inclusion of disorders were (1) significant skeletal involvement corresponding to the definition of skeletal dysplasias, metabolic bone disorders, dysostoses, and skeletal malformation and/or reduction syndromes, (2) publication and/or MIM listing, (3) genetic basis proven or very likely, and (4) nosologic autonomy confirmed by molecular or linkage analysis and/or distinctive diagnostic features and observation in multiple individuals or families. Three hundred seventy‐two different conditions were included and placed in 37 groups defined by molecular, biochemical and/or radiographic criteria. Of these conditions, 215 were associated with one or more of 140 different genes. Nosologic status was classified as final (mutations or locus identified), probable (pedigree evidence), or bona fide (multiple observations and clear diagnostic criteria, but no pedigree or locus evidence yet). The number of recognized genetic disorders with a significant skeletal component is growing and the distinction between dysplasias, metabolic bone disorders, dysostoses, and malformation syndromes is blurring. For classification purposes, pathogenetic and molecular criteria are integrating with morphological ones but disorders are still identified by clinical features and radiographic appearance. Molecular evidence leads to confirmation of individual entities and to the constitution of new groups, but also allows for delineation of related but distinct entities and indicates a previously unexpected heterogeneity of molecular mechanisms; thus, molecular evidence does not necessarily simplify the Nosology, and a further increase in the number of entities and growing complexity is expected. By providing an updated overview of recognized entities with skeletal involvement and of the underlying gene defects, the new Nosology can provide practical diagnostic help, facilitate the recognition of new entities, and foster and direct research in skeletal biology and genetic disorders.

A clinical and genetic study of campomelic dysplasia.

Campomelic dysplasia (CMD) is a rare skeletal disorder that is usually lethal. It is characterised by bowing of the lower limbs, severe respiratory distress, and many of the chromosomal (XY) males show sex reversal. Because of a number of reports of familial campomelic dysplasia it is considered to be inherited in an autosomal recessive manner. In this study, details of 36 patients with campomelic dysplasia were collected from genetic centres, radiologists, and pathologists in the United Kingdom. The chromosomal sex ratio was approximately 1:1. There was a preponderance of phenotypic females owing to sex reversal. Three quarters of the chromosomal males were sex reversed or had ambiguous genitalia. Three cases are still alive, two with chromosomal rearrangements involving chromosome 17q. The majority of the others died in the neonatal period. The 36 index cases had 41 sibs of whom only two were affected. Formal segregation analysis gave a segregation ratio of 0.05 (95% CI approximately 0.00 to 0.11). This excludes an autosomal recessive mode of inheritance. The data suggest a sporadic, autosomal dominant mode of inheritance. Patients with a chromosomal rearrangement involving 17q (q23.3-q25.1) show a milder phenotype. The molecular mechanism for the difference is still unknown.

α2-Chimaerin, Cyclin-Dependent Kinase 5/p35, and Its Target Collapsin Response Mediator Protein-2 Are Essential Components in Semaphorin 3A-Induced Growth-Cone Collapse

Neurite outgrowth is influenced by positive and negative signals that include the semaphorins, an important family of axonal outgrowth inhibitors. Here we report that the Rac GTPase activating protein (GAP)α2-chimaerin is involved in Semaphorin 3A (Sema 3A) signaling. In dorsal root ganglion neurons, Sema 3A-induced growth cone collapse was inhibited by α2-chimaerin mutated to eliminate GAP activity or interaction with phosphotyrosine. Activation of α2-chimaerin by phorbol ester caused growth cone collapse. Active α2-chimaerin interacts with collapsin response mediator protein-2 (CRMP-2) and cyclin-dependent kinase (Cdk) 5/p35 kinase through its SH2 and GAP domains, respectively. Cdk5 phosphorylates CRMP-2 at serine 522, possibly facilitating phosphorylation of serine 518 and threonine 514 by glycogen synthase kinase 3β (GSK3β), a kinase previously implicated in Sema 3A signaling. Phosphorylation of CRMP-2 serine 522 was essential for Sema 3A-induced growth cone collapse, which is dependent on Cdk5 but not Rho kinase activity. α2-chimaerin, like CRMP-2, can associate with the Sema 3A receptor. These results indicate that active α2-chimaerin Rac GAP, Cdk5/p35, and its substrate CRMP-2, are implicated in the dynamics of growth cone guidance initiated through Sema 3A signaling.

The phenotype of survivors of campomelic dysplasia

Five patients with campomelic dysplasia who have survived (age range 7 to 20 years) are described, all of whom have molecular or cytogenetic evidence of campomelic dysplasia. The phenotype and radiological features of these cases are consistent. Complications in this group include recurrent apnoea and upper respiratory infections, progressive kyphoscoliosis, mild to moderate learning difficulties, short stature, and dislocation of the hips. All five had very similar facial features. The radiological features include hypoplastic scapulae, defective ischiopubic ossification, absent or hypoplastic patellae, and spinal dysraphism. Campomelic dysplasia (CMD) is a rare skeletal dysplasia resulting from mutations in SOX9. It is usually lethal in the first year of life. Three-quarters of the cases with a male karyotype have complete or partial sex reversal.1 The skeletal changes in the neonatal period are well recognised and include hypoplastic scapulae, bowing of the long bones, vertical narrow iliac bones, and absence of ossification of the thoracic pedicles. The case histories of five children who share a number of clinical and radiological features are presented. ### Case 1 A mother was diagnosed at the age of 18 years after giving birth to a daughter with the classical features of campomelic dysplasia.2 The daughter had shortening of all four limbs, tibial bowing, with skin dimpling over the apex of each tibia. There was bilateral talipes equinovarus and relative macrocephaly (head circumference on the 50th centile, length <3rd centile). She had micrognathia and a depressed nasal bridge. The karyotype was normal female. She had the classical radiological features of campomelic dysplasia with hypoplastic scapulae and absent pedicles in the mid-thoracic region, 11 pairs of ribs, shortening of the long bones with bowing, narrow iliac bones with dislocation of the hips, short first metacarpals, and short phalanges in the hands and feet.2 She died of respiratory problems in …

Deletions in HOXD13 Segregate with an Identical, Novel Foot Malformation in Two Unrelated Families

Synpolydactyly (SPD) is a dominantly inherited congenital limb malformation consisting of 3/4 syndactyly in the hands and 4/5 syndactyly in the feet, with digit duplication in the syndactylous web. The condition recently has been found to result from different-sized expansions of an amino-terminal polyalanine tract in HOXD13. We report a novel type of mutation in HOXD13, associated in some cases with features of classic SPD and in all cases with a novel foot phenotype. In two unrelated families, each with a different intragenic deletion in HOXD13, all mutation carriers have a rudimentary extra digit between the first and second metatarsals and often between the fourth and fifth metatarsals as well. This phenotype has not been reported in any mice with genetic modifications of the HoxD gene cluster. The two different deletions affect the first exon and the homeobox, respectively, in each case producing frameshifts followed by a long stretch of novel sequence and a premature stop codon. Although the affected genes may encode proteins that exert a dominant negative or novel effect, they are most likely to act as null alleles. Either possibility has interesting implications for the role of HOXD13 in human autopod development.

Craniosynostosis associated with FGFR3 pro250arg mutation results in a range of clinical presentations including unisutural sporadic craniosynostosis.

Several mutations involving the fibroblast growth factor receptor (FGFR) gene family have been identified in association with phenotypically distinct forms of craniosynostosis. One such point mutation, resulting in the substitution of proline by arginine in a critical region of the linker region between the first and second immunoglobulin-like domains, is associated with highly specific phenotypic consequences in that mutation at this point in FGFR1 results in Pfeiffer syndrome and analogous mutation in FGFR2 results in Apert syndrome. We now show that a much more variable clinical presentation accompanies analogous mutation in the FGFR3 gene. Specifically, mental retardation, apparently unrelated to the management of the craniosynostosis, appears to be a variable clinical consequence of this FGFR3 mutation.

Characterization of RhoA-binding kinase ROK-alpha-implication of the PH domain in ROK-alpha function using region-specific antibodies

Rho-binding kinase α (ROKα) is a serine/threonine kinase with multiple functional domains involved in actomyosin assembly. It has previously been documented that the C terminus part of ROKα interacts with the N-terminal kinase domain and thereby regulates its catalytic activity. Here we used antibodies against different domains of ROKα and were able to reveal some structural aspects that are essential for the specific functions of ROKα. Antibodies against the kinase domain revealed that this part of the protein is highly complex and inaccessible. Further experiments confirmed that this domain could undergo inter- and intramolecular interactions in a complex manner, which regulates the kinase catalytic activity. Other antibodies that raised against the coiled-coil domain, Rho binding domain, and the pleckstrin homology (PH) domain were all effective in recognizing the native proteins in an immunoprecipitation assay. Only the anti-Rho binding domain antibodies could activate the kinase independent of RhoA. The PH antibodies had no apparent effects on the catalytic activity but were effective in blocking actomyosin assembly and cell contractility. Likewise, mutations of the PH domains can abrogate its dominant negative effects on actin morphology. The subsequent disruption of endogenous ROK localization to the actomyosin network by overexpressing the PH domain is supportive of a role of the PH domain of ROK in targeting the kinase to these structures.

Spectrum of craniosynostosis phenotypes associated with novel mutations at the fibroblast growth factor receptor 2 locus.

The causative relationship between several of the syndromic forms of craniosynostosis and mutations in the fibroblast growth factor receptor (FGFR) loci is now well established. However, within the group of patients with craniosynostosis, there are several families and sporadic cases whose clinical features differ in variable degrees from the classically described syndromes of craniosynostosis. In this communication we present novel FGFR2 mutations associated with a spectrum of craniosynostosis phenotypes in 4 sporadic cases and in one family in which craniosynostosis segregates. The mutation and phenotype data presented emphasise the clinical variability of mutations at this locus and underline the plasticity of the phenotype-genotype relationship in this important group of congenital malformation syndromes. Mutations found were tyrosine 105 to cysteine, glycine 338 to glutamic acid, serine 351 to cysteine and glycine 384 to arginine. These are the first reported mutations in the first immunoglobulin-like loop (tyrosine 105 to cysteine) and the transmembrane domain (glycine 384 to arginine) of FGFR2, providing further insights into the mechanism of abnormal receptor function in FGFR2 mutations.

Neurone‐Specific Enolase and Creatine Phosphokinase Are Protein Components of Rat Brain Synaptic Plasma Membranes

Abstract: Neuron‐specific enolase and creatine phosphokinase were found, by 2‐dimensional gel analysis, in rat brain synaptic plasma membranes (SPM). The identity of these enzymes was confirmed by comigration with purified rat brain NSE and CPK and by peptide analysis. The specific enzymatic activities of enolase and creatine phosphokinase, as well as of pyruvate kinase, also present on the membranes, were comparable to those in the homogenates when these three enzymes were fully activated. In the SPM all three enzymes, particularly enolase, were partially cryptic in that enzymatic activities were very low unless the membranes were treated with Triton X‐100. They were resistant to both low‐salt and high‐salt extraction and to trypsin, except when Triton X‐100 was present. These results suggest that the enzymes are tightly bound protein components of the membrane and that they may constitute an assembly capable of generating ATP.

Pseudoachondroplasia and multiple epiphyseal dysplasia: A 7‐year comprehensive analysis of the known disease genes identify novel and recurrent mutations and provides an accurate assessment of their relative contribution

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are relatively common skeletal dysplasias resulting in short‐limbed dwarfism, joint pain, and stiffness. PSACH and the largest proportion of autosomal dominant MED (AD‐MED) results from mutations in cartilage oligomeric matrix protein (COMP); however, AD‐MED is genetically heterogenous and can also result from mutations in matrilin‐3 (MATN3) and type IX collagen (COL9A1, COL9A2, and COL9A3). In contrast, autosomal recessive MED (rMED) appears to result exclusively from mutations in sulphate transporter solute carrier family 26 (SLC26A2). The diagnosis of PSACH and MED can be difficult for the nonexpert due to various complications and similarities with other related diseases and often mutation analysis is requested to either confirm or exclude the diagnosis. Since 2003, the European Skeletal Dysplasia Network (ESDN) has used an on‐line review system to efficiently diagnose cases referred to the network prior to mutation analysis. In this study, we present the molecular findings in 130 patients referred to ESDN, which includes the identification of novel and recurrent mutations in over 100 patients. Furthermore, this study provides the first indication of the relative contribution of each gene and confirms that they account for the majority of PSACH and MED. Hum Mutat 33:144–157, 2012.