Mutations in a novel gene Dymeclin (FLJ20071) are responsible for Dyggve-Melchior-Clausen syndrome

Further defining the molecular spectrum and long-term follow-up of 17 patients with Dyggve-Melchior-Clausen and Smith-McCort dysplasia type 2

Dyggve-Melchior-Clausen dysplasia (DMC) and Smith-McCort dysplasia (SMC types 1 and 2) are rare spondylo-epi-metaphyseal dysplasias with identical radiological and clinical findings. DMC and SMC type 1 are allelic disorders caused by homozygous or compound heterozygous variants in DYM, while biallelic causative variants in RAB33B lead to SMC type 2. The terminology "skeletal golgipathies" has been recently used to describe these conditions, highlighting the pivotal role of these two genes in the organization and intracellular trafficking of the Golgi apparatus. In this study, we investigated 17 affected individuals (8 males, 9 females) from 10 unrelated consanguineous families, 10 diagnosed with DMC and seven with SMC type 2. The mean age at diagnosis was 9.61 ± 9.72 years, ranging from 20 months to 34 years, and the average height at diagnosis was 92.85 ± 15.50 cm. All patients exhibited variable degrees of short trunk with a barrel chest, protruding abdomen, hyperlordosis, and decreased joint mobility. A total of nine different biallelic variants were identified, with six being located in the DYM gene and the remaining three detected in RAB33B. Notably, five variants were classified as novel, four in the DYM gene and one in the RAB33B gene. This study aims to comprehensively assess clinical, radiological, and molecular findings along with the long-term follow-up findings in 17 patients with DMC and SMC type 2. Our results suggest that clinical symptoms of the disorder typically appear from infancy to early childhood. The central notches of the vertebral bodies were identified as early as 20 months and tended to become rectangular, particularly around 15 years of age. Pseudoepiphysis was observed in five patients; we believe this finding should be taken into consideration when evaluating hand radiographs in clinical assessments. Furthermore, our research contributes to an enhanced understanding of clinical and molecular aspects in these rare "skeletal golgipathies," expanding the mutational spectrum and offering insights into long-term disease outcomes.

Surveying the landscape of RNA isoform diversity and expression across 9 GTEx tissues using long-read sequencing data

Even though alternative RNA splicing was discovered in 1977 (nearly 50 years ago), we still understand very little about most isoforms arising from a single gene, including in which tissues they are expressed and if their functions differ. Human gene annotations suggest remarkable transcriptional complexity, with approximately 252,798 distinct RNA isoform annotations from 62,710 gene bodies (Ensembl v109; 2023), emphasizing the need to understand their biological effects. For example, 256 gene bodies have ≥50 annotated isoforms and 30 have ≥100, where one protein-coding gene (MAPK10) even has 192 distinct RNA isoform annotations. Whether such isoform diversity results from biological noise (i.e., spurious alternative splicing) or whether it represents biological intent and specialized functions (even if subtle) remains a mystery. Recent studies by Aguzzoli-Heberle et al., Leung et al., and Glinos et al. demonstrate long-read RNAseq enables improved RNA isoform quantification for essentially any tissue, cell type, or biological condition (e.g., disease, development, aging, etc.) making it possible to better assess individual isoform expression and function. While each study provided important discoveries related to RNA isoform diversity, deeper exploration is needed. We sought, in part, to quantify real isoform usage across tissues (compared to annotations) and explore whether observed diversity is biological noise or intent. We used long-read RNAseq data from 58 GTEx samples across nine tissues (three brain, two heart, muscle, lung, liver, and cultured fibroblasts) generated by Glinos et al. and found considerable isoform diversity within and across tissues. Cerebellar hemisphere was the most transcriptionally complex tissue (22,522 distinct isoforms; 3,726 unique); liver was least diverse (12,435 isoforms; 1,039 unique). We highlight gene clusters exhibiting high tissue-specific isoform diversity per tissue (e.g., TPM1 expresses 19 in heart's atrial appendage), and specific genes (PAX6 and TPM1) that counterintuitively exhibit evidence that their expressed isoform diversity results from both biological noise and intent. We also validated 447 of the 700 new isoforms discovered by Aguzzoli-Heberle et al. and found that 88 were expressed in all nine tissues, while 58 were specific to a single tissue. This study represents a broad survey of the RNA isoform landscape, demonstrating isoform diversity across nine tissues and emphasizes the need to better understand how individual isoforms from a single gene body contribute to human health and disease.

A Rab33b missense mouse model for Smith-McCort dysplasia shows bone resorption defects and altered protein glycosylation

Smith McCort (SMC) dysplasia is a rare, autosomal recessive, osteochondrodysplasia that can be caused by pathogenic variants in either RAB33B or DYM genes. These genes codes for proteins that are located at the Golgi apparatus and have a role in intracellular vesicle trafficking. We generated mice that carry a Rab33b disease-causing variant, c.136A>C (p.Lys46Gln), which is identical to that of members from a consanguineous family diagnosed with SMC. In male mice at 4 months of age, the Rab33b variant caused a mild increase in trabecular bone thickness in the spine and femur and in femoral mid-shaft cortical thickness with a concomitant reduction of the femoral medullary area, suggesting a bone resorption defect. In spite of the increase in trabecular and cortical thickness, bone histomorphometry showed a 4-fold increase in osteoclast parameters in homozygous Rab33b mice suggesting a putative impairment in osteoclast function, while dynamic parameters of bone formation were similar in mutant versus control mice. Femur biomechanical tests showed an increased in yield load and a progressive elevation, from WT to heterozygote to homozygous mutants, of bone intrinsic properties. These findings suggest an overall impact on bone material properties which may be caused by disturbed protein glycosylation in cells contributing to skeletal formation, supported by the altered and variable pattern of lectin staining in murine and human tissue cultured cells and in liver and bone murine tissues. The mouse model only reproduced some of the features of the human disease and was sex-specific, manifesting in male but not female mice. Our data reveal a potential novel role of RAB33B in osteoclast function and protein glycosylation and their dysregulation in SMC and lay the foundation for future studies.

A Novel Homozygous Nonsense Variant in the DYM Underlies Dyggve-Melchior-Clausen Syndrome in Large Consanguineous Family

(1) Background: Dyggve-Melchior-Clausen Syndrome is a skeletal dysplasia caused by a defect in the DYM gene (OMIM number 607461). Pathogenic variants in the gene have been reported to cause Dyggve-Melchior-Clausen (DMC; OMIM 223800) dysplasia and Smith-McCort (SMC; OMIM 607326) dysplasia. (2) Methods: In the present study, large consanguineous families with five affected individuals with osteochondrodysplasia phenotypes were recruited. The family members were analyzed by polymerase chain reaction for homozygosity mapping using highly polymorphic microsatellite markers. Subsequent to linkage analysis, the coding exons and exon intron border of the DYM gene were amplified. The amplified products were then sent for Sanger sequencing. The structural effect of the pathogenic variant was analyzed by different bioinformatics tools. (3) Results: Homozygosity mapping revealed a 9 Mb homozygous region on chromosome 18q21.1 harboring DYM shared by all available affected individuals. Sanger sequencing of the coding exons and exon intron borders of the DYM gene revealed a novel homozygous nonsense variant [DYM (NM_017653.6):c.1205T>A, p.(Leu402Ter)] in affected individuals. All the available unaffected individuals were either heterozygous or wild type for the identified variant. The identified mutation results in loss of protein stability and weekend interactions with other proteins making them pathogenic (4) Conclusions: This is the second nonsense mutation reported in a Pakistani population causing DMC. The study presented would be helpful in prenatal screening, genetic counseling, and carrier testing of other members in the Pakistani community.

Case Report: Precision genetic diagnosis in a case of Dyggve-Melchior-Clausen syndrome reveals paternal isodisomy and heterodisomy of chromosome 18 with imprinting clinical implications

A twelve-year-old patient with a previous clinical diagnosis of spondylocostal skeletal dysplasia and moderate intellectual disability was genetically analyzed through next generation sequencing of a targeted gene panel of 179 genes associated to skeletal dysplasia and mucopolysaccharidosis in order to stablish a precision diagnosis. A homozygous nonsense [c.62C>G; p.(Ser21Ter)] mutation in DYM gene was identified in the patient. Null mutations in DYM have been associated to Dyggve-Melchior-Clausen syndrome, which is a rare autosomal-recessive disorder characterized by skeletal dysplasia and mental retardation, compatible with the patient´s phenotype. To confirm the pathogenicity of this mutation, a segregation analysis was carried out, revealing that the mutation p(Ser21Ter) was solely inherited from the father, who is a carrier of the mutation, while the mother does not carry the mutation. With the suspicion that a paternal disomy could be causing the disease, a series of microsatellite markers in chromosome 18, where the DYM gene is harbored, was analyzed in all the members of the family. Haplotype analysis provided strong evidence of paternal isodisomy and heterodisomy in that chromosome, confirming the pathological effect of this mutation. Furthermore, the patient may have a compromised expression of the ELOA3 gene due to modifications in the genomic imprinting that may potentially increase the risk of digestive cancer. All these results highlight the importance of obtaining a precision diagnosis in rare diseases.

Supply chain logistics - the role of the Golgi complex in extracellular matrix production and maintenance

The biomechanical and biochemical properties of connective tissues are determined by the composition and quality of their extracellular matrix. This, in turn, is highly dependent on the function and organisation of the secretory pathway. The Golgi complex plays a vital role in directing matrix output by co-ordinating the post-translational modification and proteolytic processing of matrix components prior to their secretion. These modifications have broad impacts on the secretion and subsequent assembly of matrix components, as well as their function in the extracellular environment. In this Review, we highlight the role of the Golgi in the formation of an adaptable, healthy matrix, with a focus on proteoglycan and procollagen secretion as example cargoes. We then discuss the impact of Golgi dysfunction on connective tissue in the context of human disease and ageing.

Mutations in HID1 Cause Syndromic Infantile Encephalopathy and Hypopituitarism

OBJECTIVE

Precursors of peptide hormones undergo posttranslational modifications within the trans-Golgi network (TGN). Dysfunction of proteins involved at different steps of this process cause several complex syndromes affecting the central nervous system (CNS). We aimed to clarify the genetic cause in a group of patients characterized by hypopituitarism in combination with brain atrophy, thin corpus callosum, severe developmental delay, visual impairment, and epilepsy.

METHODS

Whole exome sequencing was performed in seven individuals of six unrelated families with these features. Postmortem histopathological and HID1 expression analysis of brain tissue and pituitary gland were conducted in one patient. Functional consequences of the homozygous HID1 variant p.R433W were investigated by Seahorse XF Assay in fibroblasts of two patients.

RESULTS

Bi-allelic variants in the gene HID1 domain-containing protein 1 (HID1) were identified in all patients. Postmortem examination confirmed cerebral atrophy with enlarged lateral ventricles. Markedly reduced expression of pituitary hormones was found in pituitary gland tissue. Colocalization of HID1 protein with the TGN was not altered in fibroblasts of patients compared to controls, while the extracellular acidification rate upon stimulation with potassium chloride was significantly reduced in patient fibroblasts compared to controls.

INTERPRETATION

Our findings indicate that mutations in HID1 cause an early infantile encephalopathy with hypopituitarism as the leading presentation, and expand the list of syndromic CNS diseases caused by interference of TGN function. ANN NEUROL 2021;90:149-164.

A homozygous nonsense variant in DYM underlies Dyggve-Melchior-Clausen syndrome associated with ectodermal features

Dyggve melchior clausen syndrome (DMC, MIM 223800) is a very rare autosomal recessive form of skeletal dysplasia associated with various degrees of mental retardation. It is characterized by a progressive spondyloepimetaphyseal dysplasia (SEMD) with disproportionate short stature, generalized platyspondyly and lacy iliac crest. Here, we report characterization of large consanguineous family segregating DMC in autosomal recessive manner. Scanning SNP-based human genome identified a 5.3 Mb homozygous region on chromosome 18q21.1-q21.2. Sanger sequencing of the DYM gene, located in the homozygous region, revealed a novel homozygous nonsense variant [c.59 T > A; p.(Leu20*)] in affected members of the family. Analysis of the mRNA, extracted from hair follicles of an affected individual, suggested non-sense mediated decay (NMD) of the truncated transcript. This is the first nonsense and fourth loss of function variant in the DYM gene, causing DMC, reported in the Pakistani population. This study not only extended spectrum of the mutations in the DYM gene but will also facilitate diagnosis of similar other cases in Pakistani population.

A Novel Homozygous Frameshift Variant in DYM Causing Dyggve-Melchior-Clausen Syndrome in Pakistani Patients

Background: Dyggve-Melchior-Clausen syndrome (DMC) is a skeletal dysplasia with associated defects of brain development and intelligence. The truncating pathogenic variants in DYM are the most frequent cause of DMC. Smith-McCort (SMC), another skeletal dysplasia, is also caused by non-synonymous DYM variants. Methods and Results: In the current study, we examined a Pakistani consanguineous family with three affected members. Clinical features like spondyloepimetaphyseal dysplasia, indicative of characteristic skeletal abnormalities, and intellectual disability were observed. Our male patients had microcephaly and coarse facial features while the female patient did not represent microcephaly or abnormal facies, which are significant features of DMC patients. Sanger sequencing identified a novel homozygous frameshift insertion (c.95_96insT, p.W33Lfs^*14) in DYM, which likely leads to nonsense-mediated decay (NMD). Conclusion: The novel frameshift change verifies the fact that pathogenic variants in DYM are the most frequent cause of DMC.

Molecular genetics and metabolism, special edition: Diagnosis, diagnosis and prognosis of Mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA, Morquio A syndrome) is an autosomal recessive disorder caused by the deficiency of N-acetylgalactosamine-6-sulfate sulfatase. Deficiency of this enzyme leads to the accumulation of specific glycosaminoglycans (GAGs), chondroitin-6-sulfate (C6S) and keratan sulfate (KS), which are mainly synthesized in the cartilage. Therefore, the substrates are stored primarily in the cartilage and its extracellular matrix (ECM), leading to a direct impact on bone development and successive systemic skeletal spondylepiphyseal dysplasia. The skeletal-related symptoms for MPS IVA include short stature with short neck and trunk, odontoid hypoplasia, spinal cord compression, tracheal obstruction, obstructive airway, pectus carinatum, restrictive lung, kyphoscoliosis, platyspondyly, coxa valga, genu valgum, waddling gait, and laxity of joints. The degree of imbalance of growth in bone and other organs and tissues largely contributes to unique skeletal dysplasia and clinical severity. Diagnosis of MPS IVA needs clinical, radiographic, and laboratory testing to make a complete conclusion. To diagnose MPS IVA, total urinary GAG analysis which has been used is problematic since the values overlap with those in age-matched controls. Currently, urinary and blood KS and C6S, the enzyme activity of GALNS, and GALNS molecular analysis are used for diagnosis and prognosis of clinical phenotype in MPS IVA. MPS IVA can be diagnosed with unique characters although this disorder relates closely to other disorders in some characteristics. In this review article, we comprehensively describe clinical, radiographic, biochemical, and molecular diagnosis and clinical assessment tests for MPS IVA. We also compare MPS IVA to other closely related disorders to differentiate MPS IVA. Overall, imbalance of growth in MPS IVA patients underlies unique skeletal manifestations leading to a critical indicator for diagnosis.

A novel iterative mixed model to remap three complex orthopedic traits in dogs

Hip dysplasia (HD), elbow dysplasia (ED), and rupture of the cranial (anterior) cruciate ligament (RCCL) are the most common complex orthopedic traits of dogs and all result in debilitating osteoarthritis. We reanalyzed previously reported data: the Norberg angle (a quantitative measure of HD) in 921 dogs, ED in 113 cases and 633 controls, and RCCL in 271 cases and 399 controls and their genotypes at ~185,000 single nucleotide polymorphisms. A novel fixed and random model with a circulating probability unification (FarmCPU) function, with marker-based principal components and a kinship matrix to correct for population stratification, was used. A Bonferroni correction at p<0.01 resulted in a P< 6.96 ×10-8. Six loci were identified; three for HD and three for RCCL. An associated locus at CFA28:34,369,342 for HD was described previously in the same dogs using a conventional mixed model. No loci were identified for RCCL in the previous report but the two loci for ED in the previous report did not reach genome-wide significance using the FarmCPU model. These results were supported by simulation which demonstrated that the FarmCPU held no power advantage over the linear mixed model for the ED sample but provided additional power for the HD and RCCL samples. Candidate genes for HD and RCCL are discussed. When using FarmCPU software, we recommend a resampling test, that a positive control be used to determine the optimum pseudo quantitative trait nucleotide-based covariate structure of the model, and a negative control be used consisting of permutation testing and the identical resampling test as for the non-permuted phenotypes.

Additional three patients with Smith-McCort dysplasia due to novel RAB33B mutations

Smith-McCort dysplasia (SMC OMIM 615222) and Dyggve-Melchior-Clausen dysplasia (DMC OMIM 223800) are allelic skeletal dysplasias caused by homozygous or compound heterozygous mutations in DYM (OMIM 607461). Both disorders share the same skeletal phenotypes characterized by spondylo-epi-metaphyseal dysplasia with distinctive lacy ilia. The difference rests on the presence or absence of intellectual disability, that is, intellectual disability in DMC and normal cognition in SMC. However, genetic heterogeneity was suspected in SMC. Recently, RAB33B (OMIM 605950) has been identified as the second gene for SMC. Nevertheless, only two affected families have been reported so far. Here we present three SMC patients with four novel pathogenic variants in RAB33B, including homozygosity for c.211C>T (p.R71*), homozygosity for c.365T>C (p.F122S), and compound heterozygosity for c.48delCGGGGCAG (p.G17Vfs*58) and c.490C>T (p.Q164*). We also summarize the clinical, radiological, and mutation profile of RAB33B after literature mining. This report ascertains the pathogenic relationship between RAB33B and SMC. © 2017 Wiley Periodicals, Inc.

Dymeclin deficiency causes postnatal microcephaly, hypomyelination and reticulum-to-Golgi trafficking defects in mice and humans

Dymeclin is a Golgi-associated protein whose deficiency causes Dyggve-Melchior-Clausen syndrome (DMC, MIM #223800), a rare recessively inherited spondyloepimetaphyseal dysplasia consistently associated with postnatal microcephaly and intellectual disability. While the skeletal phenotype of DMC patients has been extensively described, very little is known about their cerebral anomalies, which result in brain growth defects and cognitive dysfunction. We used Dymeclin-deficient mice to determine the cause of microcephaly and to identify defective mechanisms at the cellular level. Brain weight and volume were reduced in all mutant mice from postnatal day 5 onward. Mutant mice displayed a narrowing of the frontal cortex, although cortical layers were normally organized. Interestingly, the corpus callosum was markedly thinner, a characteristic we also identified in DMC patients. Consistent with this, the myelin sheath was thinner, less compact and not properly rolled, while the number of mature oligodendrocytes and their ability to produce myelin basic protein were significantly decreased. Finally, cortical neurons from mutant mice and primary fibroblasts from DMC patients displayed substantially delayed endoplasmic reticulum to Golgi trafficking, which could be fully rescued upon Dymeclin re-expression. These findings indicate that Dymeclin is crucial for proper myelination and anterograde neuronal trafficking, two processes that are highly active during postnatal brain maturation.

Genes predict long distance migration and large body size in a migratory fish, Pacific lamprey

Elucidation of genetic mechanisms underpinning migratory behavior could help predict how changes in genetic diversity may affect future spatiotemporal distribution of a migratory species. This ability would benefit conservation of one such declining species, anadromous Pacific lamprey (Entosphenus tridentatus). Nonphilopatric migration of adult Pacific lamprey has homogenized population-level neutral variation but has maintained adaptive variation that differentiates groups based on geography, run-timing and adult body form. To investigate causes for this adaptive divergence, we examined 647 adult lamprey sampled at a fixed location on the Columbia River and radiotracked during their subsequent upstream migration. We tested whether genetic variation [94 neutral and adaptive single nucleotide polymorphisms (SNPs) previously identified from a genomewide association study] was associated with phenotypes of migration distance, migration timing, or morphology. Three adaptive markers were strongly associated with morphology, and one marker also correlated with upstream migration distance and timing. Genes physically linked with these markers plausibly influence differences in body size, which is also consistently associated with migration distance in Pacific lamprey. Pacific lamprey conservation implications include the potential to predict an individual's upstream destination based on its genotype. More broadly, the results suggest a genetic basis for intrapopulation variation in migration distance in migratory species.

Unpredictability of hip behavior in Dyggve-Melchior-Clausen syndrome: a mid-term assessment of siblings

Dyggve-Melchior-Clausen syndrome is a rare spondylo-epiphyseal disease, which almost constantly leads to both bilateral hip degeneration and dislocation. Few authors have reported to date the surgical management of this orthopaedic disorder. We present two new cases affecting siblings. One brother was treated by unilateral triple pelvic osteotomy combined with varus osteotomy of the proximal femur; the other was treated by bilateral Pemberton osteotomies with varus osteotomy of the proximal femur. At a respective 5-year and 3-year follow-up delay, both cases had evolved towards progressive subluxation recurrence along with severe hip degeneration. Based on both our experience and literature review, it seems that one should avoid operating these hips unless pain renders surgery mandatory. Total hip arthroplasty seems the only reliable surgical solution at the adult age and paediatric surgeons should keep in mind that previous femoral osteotomies will make it more challenging for adult orthopaedic surgeons to implant on a remodeled anatomy.

Whole exome sequencing and functional studies identify an intronic mutation in TRAPPC2 that causes SEDT

Skeletal dysplasias are challenging to diagnose because of their phenotypic variability, genetic heterogeneity, and diverse inheritance patterns. We conducted whole exome sequencing of a Turkish male with a suspected X-linked skeletal dysplasia of unknown etiology as well as his unaffected mother and maternal uncle. Bioinformatic filtering of variants implicated in skeletal system development revealed a novel hemizygous mutation, c.341-(11_9)delAAT, in an intron of TRAPPC2, the causative locus of spondyloepiphyseal dysplasia tarda (SEDT). We show that this deletion leads to the loss of wild-type TRAPPC2 and the generation of two functionally impaired mRNAs in patient cells. These consequences are predicted to disrupt function of SEDLIN/TRAPPC2. The clinical and research data were returned, with appropriate caveats, to the patient and informed his disease status and reproductive choices. Our findings expand the allelic repertoire of SEDT and show how prior filtering of the morbid human genome informed by inheritance pattern and phenotype, when combined with appropriate functional tests in patient-derived cells, can expedite discovery, overcome issues of missing data and help interpret variants of unknown significance. Finally, this example shows how the return of a clinically confirmed mutational finding, supported by research allele pathogenicity data, can assist individuals with inherited disorders with life choices.

Diagnosing mucopolysaccharidosis IVA

Mucopolysaccharidosis IVA (MPS IVA; Morquio A syndrome) is an autosomal recessive lysosomal storage disorder resulting from a deficiency of N-acetylgalactosamine-6-sulfate sulfatase (GALNS) activity. Diagnosis can be challenging and requires agreement of clinical, radiographic, and laboratory findings. A group of biochemical genetics laboratory directors and clinicians involved in the diagnosis of MPS IVA, convened by BioMarin Pharmaceutical Inc., met to develop recommendations for diagnosis. The following conclusions were reached. Due to the wide variation and subtleties of radiographic findings, imaging of multiple body regions is recommended. Urinary glycosaminoglycan analysis is particularly problematic for MPS IVA and it is strongly recommended to proceed to enzyme activity testing even if urine appears normal when there is clinical suspicion of MPS IVA. Enzyme activity testing of GALNS is essential in diagnosing MPS IVA. Additional analyses to confirm sample integrity and rule out MPS IVB, multiple sulfatase deficiency, and mucolipidoses types II/III are critical as part of enzyme activity testing. Leukocytes or cultured dermal fibroblasts are strongly recommended for enzyme activity testing to confirm screening results. Molecular testing may also be used to confirm the diagnosis in many patients. However, two known or probable causative mutations may not be identified in all cases of MPS IVA. A diagnostic testing algorithm is presented which attempts to streamline this complex testing process.

A novel RAB33B mutation in Smith-McCort dysplasia

Smith-McCort dysplasia (SMC) is a rare autosomal recessive spondylo-epi-metaphyseal dysplasia with skeletal features identical to those of Dyggve-Melchior-Clausen syndrome (DMC) but with normal intelligence and no microcephaly. Although both syndromes were shown to result from mutations in the DYM gene, which encodes the Golgi protein DYMECLIN, a few SMC patients remained negative in DYM mutation screening. Recently, autozygosity mapping and exome sequencing in a large SMC family have allowed the identification of a missense mutation in RAB33B, another Golgi protein involved in retrograde transport of Golgi vesicles. Here, we report a novel RAB33B mutation in a second SMC case that leads to a marked reduction of the protein as shown by Western blot and immunofluorescence. These data confirm the genetic heterogeneity of SMC dysplasia and highlight the role of Golgi transport in the pathogenesis of SMC and DMC syndromes.

A recurrent mutation in Moroccan patients with Dyggve-Melchior-Clausen syndrome: Report of a new case and review

Dyggve-Melchior-Clausen (DMC) syndrome is a rare autosomal recessive disorder. It is a spondyloepimetaphyseal dysplasia associated with mental retardation. Clinical manifestations include coarse facies, microcephaly, short trunk dwarfism, and mental retardation. Mutations in Dymeclin gene (DYM), mapped to chromosome 18q21.1, is responsible for DMC. We report here the observation of a consanguineous Moroccan patient having DMC syndrome. The molecular studies showed a previously reported homozygous mutation at c.1878delA of DYM gene. We discuss this recurrent mutation in Moroccan patients with DMC syndrome with a review.

Management of progressive genu varum in a patient with Dyggve-Melchior-Clausen syndrome

We describe the orthopaedic management of progressive genu varum in a child who manifested the full phenotypic characterization of Dyggve-Melchior-Clausen syndrome.

Common structural features characterize interstitial intrachromosomal Xp and 18q triplications

Rare intrachromosomal triplications producing partial tetrasomies have been reported for a number of chromosomes. A detailed molecular characterization, necessary to define the mechanism of their formation, has so far been lacking. We report on the detailed clinical, cytogenetic, and molecular characterization of two triplications, one de novo involving chromosome 18q, the other familial on chromosome Xp. The clinical phenotype of the patient with 18q triplication, very likely due to overexpression of one or more of the genes in the region, consists mainly of facial dysmorphisms and developmental delay. The familial Xp triplication does not cause an increase in the number of copies of any gene and is almost certainly a polymorphism. The rearrangements are actually complex duplications/triplications. In both patients, their proximal breakpoints are located within complex segmental duplications, one containing the VCX gene cluster on chromosome Xp, the other the TCEB3 genes on chromosome 18q. A proximal duplicated region is also present in both patients. All junctions we analyzed were formed by non-homologous end joining (NHEJ). The structural features shared between our patients suggest the involvement of a common mechanism in the genesis of interstitial intrachromosomal triplications.

Dyggve melchior clausen syndrome

Dyggve Melchior Clausen syndrome is a rare autosomal recessive disorder, characterized by progressive spondylo epi metaphyseal dysplasia associated with mental retardation. The clinical and radiological findings resembles Morquio disease at the onset of condition, which may hinder its diagnosis. Two siblings with chatacteristic clinical (progressive postnatal dwarfism and mental retardation) and radiological features (irregular lace-like appearance of the iliac crests) are reported.

Dymeclin, the gene underlying Dyggve-Melchior-Clausen syndrome, encodes a protein integral to extracellular matrix and golgi organization and is associated with protein secretion pathways critical in bone development

Dyggve-Melchior-Clausen syndrome (DMC), a severe autosomal recessive skeletal disorder with mental retardation, is caused by mutation of the gene encoding Dymeclin (DYM). Employing patient fibroblasts with mutations characterized at the genomic and, for the first time, transcript level, we identified profound disruption of Golgi organization as a pathogenic feature, resolved by transfection of heterologous wild-type Dymeclin. Collagen targeting appeared defective in DMC cells leading to near complete absence of cell surface collagen fibers. DMC cells have an elevated apoptotic index (P< 0.01) likely due to a stress response contingent upon Golgi-related trafficking defects. We performed spatiotemporal mapping of Dymeclin expression in zebrafish embryos and identified high levels of transcript in brain and cartilage during early development. Finally, in a chondrocyte cDNA library, we identified two novel secretion pathway proteins as Dymeclin interacting partners: GOLM1 and PPIB. Together these data identify the role of Dymeclin in secretory pathways essential to endochondral bone formation during early development.

Rare and frequent promoter methylation, respectively, of TSHZ2 and 3 genes that are both downregulated in expression in breast and prostate cancers

Background

Neoplastic cells harbor both hypomethylated and hypermethylated regions of DNA. Whereas hypomethylation is found mainly in repeat sequences, regional hypermethylation has been linked to the transcriptional silencing of certain tumor suppressor genes. We attempted to search for candidate genes involved in breast/prostate carcinogenesis, using the criteria that they should be expressed in primary cultures of normal breast/prostate epithelial cells but are frequently downregulated in breast/prostate cancer cell lines and that their promoters are hypermethylated.

Methodology/Principal Findings

We identified several dozens of candidates among 194 homeobox and related genes using Systematic Multiplex RT-PCR and among 23,000 known genes and 23,000 other expressed sequences in the human genome by DNA microarray hybridization. An additional examination, by real-time qRT-PCR of clinical specimens of breast cancer, further narrowed the list of the candidates. Among them, the most frequently downregulated genes in tumors were NP_775756 and ZNF537, from the homeobox gene search and the genome-wide search, respectively. To our surprise, we later discovered that these genes belong to the same gene family, the 3-member Teashirt family, bearing the new names of TSHZ2 and TSHZ3. We subsequently determined the methylation status of their gene promoters. The TSHZ3 gene promoter was found to be methylated in all the breast/prostate cancer cell lines and some of the breast cancer clinical specimens analyzed. The TSHZ2 gene promoter, on the other hand, was unmethylated except for the MDA-MB-231 breast cancer cell line. The TSHZ1 gene was always expressed, and its promoter was unmethylated in all cases.

Conclusions/Significance

TSHZ2 and TSHZ3 genes turned out to be the most interesting candidates for novel tumor suppressor genes. Expression of both genes is downregulated. However, differential promoter methylation suggests the existence of distinctive mechanisms of transcriptional inactivation for these genes.

HID-1 is a peripheral membrane protein primarily associated with the medial- and trans- Golgi apparatus

Caenorhabditis elegans hid-1 gene was first identified in a screen for mutants with a high-temperature-induced dauer formation (Hid) phenotype. Despite the fact that the hid-1 gene encodes a novel protein (HID-1) which is highly conserved from Caenorhabditis elegans to mammals, the domain structure, subcellular localization, and exact function of HID-1 remain unknown. Previous studies and various bioinformatic softwares predicted that HID-1 contained many transmembrane domains but no known functional domain. In this study, we revealed that mammalian HID-1 localized to the medial- and trans- Golgi apparatus as well as the cytosol, and the localization was sensitive to brefeldin A treatment. Next, we demonstrated that HID-1 was a peripheral membrane protein and dynamically shuttled between the Golgi apparatus and the cytosol. Finally, we verified that a conserved N-terminal myristoylation site was required for HID-1 binding to the Golgi apparatus. We propose that HID-1 is probably involved in the intracellular trafficking within the Golgi region.

Dyggve-Melchior-Clausen syndrome: novel splice mutation with atlanto-axial subluxation

Dyggve-Melchior-Clausen (DMC) syndrome is a rare autosomal recessive disorder characterized by the association of a progressive spondyloepimetaphyseal dysplasia and mental retardation ranging from mild to severe. The disorder results from mutations in the dymeclin (DYM) gene in the 18q12-12.1 chromosomal region. We report two siblings with classical clinical and radiological features of DMC and asymptomatic atlanto-axial dislocation. A novel homozygous splice-site mutation (IVS15+3G>T) was detected. Reverse transcriptase polymerase chain reaction (RT-PCR) confirmed that this mutation affects normal splicing. To the best of our knowledge, this is the first report of DMC from Saudi Arabia. The splice mutation noted in our patients was compared to the previously reported cases and supports the hypothesis that loss of DYM function is the likely mechanism of disease pathogenesis. In conclusion, distinction between this type of skeletal dysplasia and Morquio disease (MPS IV) is important for paediatricians and clinical geneticist in providing standard patient care and genetic counselling.

HID-1, a new component of the peptidergic signaling pathway

hid-1 was originally identified as a Caenorhabditis elegans gene encoding a novel conserved protein that regulates the decision to enter into the enduring dauer larval stage. We isolated a novel allele of hid-1 in a forward genetic screen for mutants mislocalizing RBF-1 rabphilin, a RAB-27 effector. Here we demonstrate that HID-1 functions in the nervous system to regulate neuromuscular signaling and in the intestine to regulate the defecation motor program. We further show that a conserved N-terminal myristoylated motif of both invertebrate and vertebrate HID-1 is essential for its association with intracellular membranes in nematodes and PC12 cells. C. elegans neuronal HID-1 resides on intracellular membranes in neuronal cell somas; however, the kinesin UNC-104 also transports HID-1 to synaptic regions. HID-1 accumulates in the axons of unc-13 and unc-31 mutants, suggesting it is associated with neurosecretory vesicles. Consistent with this, genetic studies place HID-1 in a peptidergic signaling pathway. Finally, a hid-1 null mutation reduces the levels of endogenous neuropeptides and alters the secretion of fluorescent-tagged cargos derived from neuronal and intestinal dense core vesicles (DCVs). Taken together, our findings indicate that HID-1 is a novel component of a DCV-based neurosecretory pathway and that it regulates one or more aspects of the biogenesis, maturation, or trafficking of DCVs.

Association of linear growth impairment in pediatric Crohn's disease and a known height locus: a pilot study

The etiology of growth impairment in Crohn's disease (CD) has been inadequately explained by nutritional, hormonal, and/or disease-related factors, suggesting that genetics may be an additional contributor. The aim of this cross-sectional study was to investigate genetic variants associated with linear growth in pediatric-onset CD. We genotyped 951 subjects (317 CD patient-parent trios) for 64 polymorphisms within 14 CD-susceptibility and 23 stature-associated loci. Patient height-for-age Z-score < -1.64 was used to dichotomize probands into growth-impaired and nongrowth-impaired groups. The transmission disequilibrium test (TDT) was used to study association to growth impairment. There was a significant association between growth impairment in CD (height-for-age Z-score < -1.64) and a stature-related polymorphism in the dymeclin gene DYM (rs8099594) (OR = 3.2, CI [1.57-6.51], p = 0.0007). In addition, there was nominal over-transmission of two CD-susceptibility alleles, 10q21.1 intergenic region (rs10761659) and ATG16L1 (rs10210302), in growth-impaired CD children (OR = 2.36, CI [1.26-4.41] p = 0.0056 and OR = 2.45, CI [1.22-4.95] p = 0.0094, respectively). Our data indicate that genetic influences due to stature-associated and possibly CD risk alleles may predispose CD patients to alterations in linear growth. This is the first report of a link between a stature-associated locus and growth impairment in CD.

Spondylo-epiphyseal dysplasia, Maroteaux type (pseudo-Morquio syndrome type 2), and parastremmatic dysplasia are caused by TRPV4 mutations

Recent discoveries have established the existence of a family of skeletal dysplasias caused by dominant mutations in TRPV4. This family comprises, in order of increasing severity, dominant brachyolmia, spondylo-metaphyseal dysplasia Kozlowski type, and metatropic dysplasia. We tested the hypothesis that a further condition, Spondylo-epiphyseal dysplasia (SED), Maroteaux type (MIM 184095; also known as pseudo-Morquio syndrome type 2), could be caused by TRPV4 mutations. We analyzed six individuals with Maroteaux type SED, including three who had previously been reported. All six patients were found to have heterozygous TRPV4 mutations; three patients had unreported mutations, while three patients had mutations previously described in association with metatropic dysplasia. In addition, we tested one individual with a distinct rare disorder, parastremmatic dysplasia (MIM 168400). This patient had a common, recurrent mutation seen in several patients with Kozlowski type spondylo-metaphyseal dysplasia. We conclude that SED Maroteaux type and parastremmatic dysplasia are part of the TRPV4 dysplasia family and that TRPV4 mutations show considerable variability in phenotypic expression resulting in distinct clinical-radiographic phenotypes.

Mutations of a country: a mutation review of single gene disorders in the United Arab Emirates (UAE)

The United Arab Emirates inhabitants are ethnically diverse, with ancestries from Arabia, Persia, Baluchistan, and Africa. However, the majority of the current five million inhabitants are expatriates from the Asian subcontinent, Middle Eastern, African, and European countries. Consanguineous marriages within most UAE subpopulations are still the norm, leading to the formation of isolates and higher frequencies of recessive conditions. The UAE is ranked sixth in terms of prevalence of birth defects, with more than 270 genetic disorders reported in the national population. The UAE has high frequencies of blood disorders including thalassemias, sickle cell disease, and G6PD. In addition, certain genetic conditions are relatively common including cystic fibrosis, Joubert, and Meckel syndromes. Furthermore, numerous rare congenital malformations and metabolic disorders have been reported. We review the single gene disorders that have been studied at the molecular level in the UAE (which currently stand at 76) and compile the mutations found. Several novel (p.S2439fs) mutations have been reported including c.7317delA in NF1, c.5C>T (p.A2V) in DKC1, c.1766T>A (p.I589N) in TP63, and c.2117G>T (p.R706L) in VLDLR. We hope that this review will form the basis to establish a UAE mutations database and serve as a model for the collection of mutations of a country.

An association study between the dymeclin gene and schizophrenia in the Japanese population

Many gene variants are involved in the susceptibility to schizophrenia and some of them are expected to be associated with other human characters. Recently reported meta-analysis of genetic associations revealed nucleotide variants in synaptic vesicular transport/Golgi apparatus genes with schizophrenia. In this study, we selected the dymeclin gene (DYM) as a candidate gene for schizophrenia. The DYM gene encodes dymeclin that has been identified to be associated with the Golgi apparatus and with transitional vesicles of the reticulum-Golgi interface. A three-step case-control study of total of 2105 Japanese cases of schizophrenia and 2087 Japanese control subjects was carried out for tag single-nucleotide polymorphisms (SNPs) in the DYM gene and an association between an SNP, rs833497, and schizophrenia was identified (allelic P=2 × 10(-5), in the total sample). DYM is the causal gene for Dyggve-Melchior-Clausen syndrome and this study shows the second neuropsychiatric disorder in which the DYM gene is involved. The present data support the involvement of Golgi function and vesicular transport in the presynapse in schizophrenia.

Dyggve-Melchior-Clausen syndrome: clinical, genetic, and radiological study of 15 Egyptian patients from nine unrelated families

INTRODUCTION

Dyggve-Melchior-Clausen (DMC) syndrome is a rare autosomal recessive type of skeletal dysplasia. It is characterized by the association of progressive spondyloepimetaphyseal dysplasia (SEMD), microcephaly, mental retardation (MR), and coarse facies. The radiographic appearance of generalized platyspondyly with double-humped end plates and the lace-like appearance of iliac crests are pathognomonic and distinctive of DMC syndrome. The disorder results from mutations in the DYM gene mapped in the 18q12-12.1 chromosomal region.

MATERIALS AND METHODS

In this report, we studied 15 Egyptian cases with DMC syndrome from nine unrelated families. We aimed to emphasize the characteristic clinical and radiological features in order to differentiate the condition from other SEMDs and mucopolysaccharidosis (MPS). Patients were subjected to detailed history taking, three-generation family pedigree analysis, complete physical examination, anthropometric measurements, quantitative estimation, and two-dimensional electrophoresis of glycosaminoglycans in the urine and measurement of α-l-iduronidase and galactose-6-sulfatase enzyme activities to exclude Hurler and Morquio diseases (MPS type I and MPS type IVA), respectively. Other investigations were carried out whenever indicated. All patients were the offspring of consanguineous apparently normal parents. Positive family history and similarly affected sibs were noted, confirming the autosomal recessive inheritance pattern of the syndrome. Short stature, microcephaly, variable degree of MR, and coarse facies were constant features. The frequency of characteristic orthopedic and radiological findings was reported. Orthopedic surgical intervention was carried out for two patients.

CONCLUSIONS

The study concluded that DMC syndrome may be more frequent in Egypt than previously thought, especially due to misdiagnosis. Characteristic facial dysmorphism, body habitus, and pathognomonic radiological signs suggest the diagnosis and differentiate it from other types of SEMDs and MPS for proper genetic counseling and management.

The gene responsible for Dyggve-Melchior-Clausen syndrome encodes a novel peripheral membrane protein dynamically associated with the Golgi apparatus

Dyggve-Melchior-Clausen dysplasia (DMC) is a rare inherited dwarfism with severe mental retardation due to mutations in the DYM gene which encodes Dymeclin, a 669-amino acid protein of yet unknown function. Despite a high conservation across species and several predicted transmembrane domains, Dymeclin could not be ascribed to any family of proteins. Here we show, using in situ hybridization, that DYM is widely expressed in human embryos, especially in the cortex, the hippocampus and the cerebellum. Both the endogenous and the recombinant protein fused to green fluorescent protein co-localized with Golgi apparatus markers. Electron microscopy revealed that Dymeclin associates with the Golgi apparatus and with transitional vesicles of the reticulum-Golgi interface. Moreover, permeabilization assays revealed that Dymeclin is not a transmembrane but a peripheral protein of the Golgi apparatus as it can be completely released from the Golgi after permeabilization of the plasma membrane. Time lapse confocal microscopy experiments on living cells further showed that the protein shuttles between the cytosol and the Golgi apparatus in a highly dynamic manner and recognizes specifically a subset of mature Golgi membranes. Finally, we found that DYM mutations associated with DMC result in mis-localization and subsequent degradation of Dymeclin. These data indicate that DMC results from a loss-of-function of Dymeclin, a novel peripheral membrane protein which shuttles rapidly between the cytosol and mature Golgi membranes and point out a role of Dymeclin in cellular trafficking.

Dyggve-Melchior-Clausen syndrome: chondrodysplasia resulting from defects in intracellular vesicle traffic

Dyggve-Melchior-Clausen syndrome and Smith-McCort dysplasia are recessive spondyloepimetaphyseal dysplasias caused by loss-of-function mutations in dymeclin (Dym), a gene with previously unknown function. Here we report that Dym-deficient mice display defects in endochondral bone formation similar to that of Dyggve-Melchior-Clausen syndrome and Smith-McCort dysplasia, demonstrating functional conservation between the two species. Dym-mutant cells display multiple defects in vesicle traffic, as evidenced by enhanced dispersal of Golgi markers in interphase cells, delayed Golgi reassembly after brefeldin A treatment, delayed retrograde traffic of an endoplasmic reticulum-targeted Shiga toxin B subunit, and altered furin trafficking; and the Dym protein associates with multiple cellular proteins involved in vesicular traffic. These results establish dymeclin as a novel protein involved in Golgi organization and intracellular vesicle traffic and clarify the molecular basis for chondrodysplasia in mice and men.

Spondylo-epi-metaphyseal dysplasia

The spondylo-epi-metaphyseal dysplasias (SEMD) are a heterogeneous group of disorders comprising more than 20 distinct entities with differing modes of inheritance, all defined by the combination of vertebral, epiphyseal and metaphyseal abnormalities. The presenting symptom of SEMD patients is usually disproportionate short stature. The diagnosis is either based on the specificity of the skeletal manifestations or on the presence of characteristic extraskeletal features which may appear during the course of the disease, highlighting the importance of follow-up of SEMD patients. The complications are variable but epiphyseal dysplasia is often a predominant feature, and the course of the disease is marked by premature osteoarthritis. A systematic survey of odontoid hypoplasia responsible for atlantoaxial instability with a risk of spinal cord is also required.

Scanning copy number and gene expression on the 18q21-qter chromosomal region by the systematic multiplex PCR and reverse transcription-PCR methods

We examined differences in copy number and expression of 127 genes located on the 18q21-qter chromosomal region of the breast and prostate cancer cell lines, using the systematic multiplex PCR and reverse transcription-PCR (SM PCR and SM RT-PCR) methods that we developed. Semi-quantitative data were obtained that were comparable in quality, but not in quantity, to data from DNA microarray hybridization analysis. In the chromosomal region where losses are frequent in breast, prostate, and other cancers, we detected a homozygous deletion of the SMAD4 gene in the MDA-MB-468 breast cancer cell line. We also observed partial or entire loss of expression in genes such as CCBE1, CCDC11, CD226, NP_115536.1, NP_689683.2, RNF152, SERPINB8, and TCF4 in certain breast and/or prostate cancer cell lines. An increase in gene expression was rare, but found with the transcription factor ONECUT2 gene in all of the cancer cell lines examined. Real-time qRT-PCR experiments confirmed these SM RT-PCR results. Further analysis of clinical specimens of breast cancer by real-time qRT-PCR demonstrated that the gene expression of CCBE1, TCF4, NP_115536.1, and NP_689683.2 was downregulated in the majority of clinical cases of breast cancer.

[Dyggve-Melchior-Clausen syndrome: presentation of a case with a mutation of possible Spanish origin]

BACKGROUND AND OBJECTIVE

The Dyggve-Melchior-Clausen syndrome is a progressive spondyloepimetaphyseal dysplasia characterized by a short trunk dwarfism, barrel chest, sternal protrusion, kyphoscoliosis, severe platyspondyly, with a central constriction, irregular iliac wings with a lacy appearance, rhizomelic shortening of the limbs, microcephaly, coarse face, and variable mental retardation. This condition is extremely rare and the diagnosis is difficult without any previous experience on it. It is inherited as an autosomal recessive condition, its gene (DYM) having been mapped in the 18q12-21.1 chromosomal region. At least 21 different mutations of this gene have been reported.

MATERIAL AND METHODS

We describe an affected Spanish child and include his molecular analysis. We also review the current knowledge on this syndrome.

RESULTS

The diagnosis of this patient, based on his clinical and radiological features, was later confirmed by analysis of the DYM gene mutations. The patient had two different mutations, one inherited from the mother and the other inherited from the father.

CONCLUSIONS

One of the mutations of this patient (exon 8) is extremely rare and has mostly been reported in patients with Spanish ancestors (from Chile, Argentina, Guam islands and a French patient with Spanish ancestors). These observations, together with that of the patient described here, led us to consider this mutation as having a possible Spanish/Portuguese origin. This condition may be more frequent in Spain than previously thought, especially due to misdiagnosis. This is important in order to undertake quaternary prevention, which is quite necessary for rare syndromes with polysystemic affectation.

Neurocutaneous syndrome with mental delay, autism, blockage in intracellular vescicular trafficking and melanosome defects

We evaluated a 11-year-old male patient with mental delay, autism and brownish and whitish skin spots. The former resembled those of neurofibromatosis, the latter those of tuberous sclerosis. The patient received a complete clinical work-up to exclude neurofibromatosis, tuberous sclerosis, or any other known neurocutaneous disease, with biochemistry, chromosome analysis and analysis of skin specimens. Being all the other tests not significant, two main ultrastructural defects were observed. The first was a blockage in intracellular vescicular trafficking with sparing of the mitochondria; the second an aberrant presence of melanosomes in vacuoles of several cell lines and abnormal transfer of these organelles to keratinocytes. This patient presented with a unique clinical picture distinct from neurofibromatosis or tuberous sclerosis or any other known neurocutaneous disease. The ultrastructural abnormalities suggested a defect in cell trafficking involving several cell lines and compartments.

Searching WormBase for information about Caenorhabditis elegans

WormBase is the major public biological database for the nematode Caenorhabditis elegans. It is meant to be useful to any biologist who wants to use C. elegans, whatever his or her specialty. WormBase contains information about the genomic sequence of C. elegans, its genes and their products, and its higher-level traits such as gene expression patterns and neuronal connectivity. WormBase also contains genomic sequences and gene structures of C. briggsae and C. remanei, two closely related worms. These data are interconnected, so that a search beginning with one object (such as a gene) can be directed to related objects of a different type (e.g., the DNA sequence of the gene or the cells in which the gene is active). One can also perform searches for complex data sets. The WormBase developers group actively invites suggestions for improvements from the database users. WormBase's source code and underlying database are freely available for local installation and modification.

Dyggve-Melchior-Clausen syndrome and Smith-McCort dysplasia: clinical and molecular findings in three families supporting genetic heterogeneity in Smith-McCort dysplasia

Dyggve-Melchior-Clausen syndrome (DMC) (MIM 223800) and Smith-McCort dysplasia (SMC) (MIM 607326) are rare allelic autosomal recessive spondylo-epi-metaphyseal dysplasias (SEMDs) characterized by similar skeletal manifestations. Both phenotypes have been mapped to chromosome 18q21.1 and mutations in the DYM (dymeclin) gene were identified in 13 families with DMC and in two families with SMC. Most mutations identified in DMC predict a loss of function, while those identified in SMC are mainly missense mutations, presumably associated with residual DYM activity and a less severe phenotype. We studied three consanguineous families from Turkey, Lebanon, and Georgia, one with SMC and two with DMC and identified different homozygous DYM mutations (IVS3 194-1G > A, 938_942delTGTCT) in the DMC families. No mutation was identified in the SMC family, possibly suggesting genetic heterogeneity of this disorder.

Identification of Proteins from a Cell Wall Fraction of the Diatom Thalassiosira pseudonana

Diatoms are unicellular eucaryotic algae with cell walls containing silica, intricately and ornately structured on the nanometer scale. Overall silica structure is formed by expansion and molding of the membrane-bound silica deposition vesicle. Although molecular details of silica polymerization are being clarified, we have limited insight into molecular components of the silica deposition vesicle, particularly of membrane-associated proteins that may be involved in structure formation. To identify such proteins, we refined existing procedures to isolate an enriched cell wall fraction from the diatom Thalassiosira pseudonana, the first diatom with a sequenced genome. We applied tandem mass spectrometric analysis to this fraction, identifying 31 proteins for further evaluation. mRNA levels for genes encoding these proteins were monitored during synchronized progression through the cell cycle and compared with two previously identified silaffin genes (involved in silica polymerization) having distinct mRNA patterns that served as markers for cell wall formation. Of the 31 proteins identified, 10 had mRNA patterns that correlated with the silaffins, 13 had patterns that did not, and seven had patterns that correlated but also showed additional features. The possible involvements of these proteins in cell wall synthesis are discussed. In particular, glutamate acetyltransferase was identified, prompting an analysis of mRNA patterns for other genes in the polyamine biosynthesis pathway and identification of those induced during cell wall synthesis. Application of a specific enzymatic inhibitor for ornithine decarboxylase resulted in dramatic alteration of silica structure, confirming the involvement of polyamines and demonstrating that manipulation of proteins involved in cell wall synthesis can alter structure. To our knowledge, this is the first proteomic analysis of a diatom, and furthermore we identified new candidate genes involved in structure formation and directly demonstrated the involvement of one enzyme (and its gene) in the structure formation process.

Exclusion of the dymeclin and PAPSS2 genes in a novel form of spondyloepimetaphyseal dysplasia and mental retardation

Spondyloepimetaphyseal dysplasias (SEMD) represent a heterogeneous group of conditions composed of at least 15 well-defined entities. The classification is based on clinical, radiological and molecular findings. Among them, several conditions also include a mental retardation (MR) syndrome, namely Wolcott-Rallison syndrome, Dyggve-Melchior-Clausen syndrome (DMC) and lysosomal storage disorders. Here, we report on a novel form of SEMD with MR in two Pakistani sisters born to first-cousin parents. SEMD, MR, microcephaly, ataxia, facial dysmorphism and hirsutism of back and legs were noted in the two children. Skeletal findings included flat vertebral bodies with irregular vertebral plates, irregular and flared metaphyses with vertical striations, small and irregular epiphyses, small carpal bones and narrow iliac wings without lacy pelvis iliac crest. Similarities with DMC prompted us to test and eventually exclude the DMC gene, dymeclin, by direct sequencing. Similarly, we excluded the PAPSS2 gene (3'-alpha phosphoadenosine 5'-phosphosulphate synthase 2) responsible for SEMD Pakistani type. The combination of features observed in the two sisters does not fit with any previously reported SEMD and represents therefore a novel form of autosomal recessive SEMD with MR.

Recent advances in Dyggve-Melchior-Clausen syndrome

Dyggve-Melchior-Clausen (DMC) is a rare autosomal-recessive disorder characterized by the association of a progressive spondylo-epi-metaphyseal dysplasia and mental retardation ranging from mild to severe. Electron microscopy studies of both DMC chondrocytes and fibroblasts reveal an enlarged endoplasmic reticulum network and a large number of intracytoplasmic membranous vesicles, suggesting that DMC syndrome may be a storage disorder. Indeed, DMC phenotype is often compared to that of type IV mucopolysaccharidosis (Morquio disease), a lysosomal disorder due to either N-acetylgalactosamine-6-sulphatase or beta-galactosidase deficiency. To date, however, the lysosomal pathway appears normal in DMC patients and biochemical analyses failed to reveal any enzymatic deficiency or accumulated substrate. Linkage studies using homozygosity mapping have led to the localization of the disease-causing gene on chromosome 18q21.1. The gene was recently identified as a novel transcript (Dym) encoding a 669-amino acid product (Dymeclin) with no known domains or function. Sixteen different Dym mutations have now been described in 21 unrelated families with at least five founder effects in Morocco, Lebanon, and Guam Island. Smith-MacCort syndrome (SMC), a rare variant of DMC syndrome without mental retardation, was shown to be allelic of DMC syndrome and to result from mutations in Dym that would be less deleterious to the brain. The present review focuses on clinical, radiological, and cellular features and evolution of DMC/SMC syndromes and discusses them with regard to identified Dym mutations and possible roles of the Dym gene product.