Homozygosity mapping of a Dyggve-Melchior-Clausen syndrome gene to chromosome 18q21.1

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.

Clinical, radiological and molecular studies in 24 individuals with Dyggve-Melchior-Clausen dysplasia and Smith-McCort dysplasia from India

BACKGROUND

Dyggve-Melchior-Clausen dysplasia (DMC) and Smith-McCort dysplasia (SMC types 1 and 2) are rare spondyloepimetaphyseal dysplasias with identical radiological findings. The presence of intellectual disability in DMC and normal intellect in SMC differentiates the two. DMC and SMC1 are allelic and caused by homozygous or compound heterozygous variants in DYM. SMC2 is caused by variations in RAB33B. Both DYM and RAB33B are important in intravesicular transport and function in the Golgi apparatus.

METHODS

Detailed clinical phenotyping and skeletal radiography followed by molecular testing were performed in all affected individuals. Next-generation sequencing and Sanger sequencing were used to confirm DYM and RAB33B variants. Sanger sequencing of familial variants was done in all parents.

RESULTS

24 affected individuals from seven centres are described. 18 had DMC and 6 had SMC2. Parental consanguinity was present in 15 of 19 (79%). Height <3 SD and gait abnormalities were seen in 20 and 14 individuals, respectively. The characteristic radiological findings of lacy iliac crests and double-humped vertebral bodies were seen in 96% and 88% of the affected. Radiological findings became attenuated with age. 23 individuals harboured biallelic variants in either DYM or RAB33B. Fourteen different variants were identified, out of which 10 were novel. The most frequently occurring variants in this group were c.719 C>A (3), c.1488_1489del (2), c.1484dup (2) and c.1563+2T>C (2) in DYM and c.400C>T (2) and c.186del (2) in RAB33B. The majority of these have not been reported previously.

CONCLUSION

This large cohort from India contributes to the increasing knowledge of clinical and molecular findings in these rare 'Golgipathies'.

An extremely rare association of dyggve-melchior-clausen syndrome with mania: coincidence or comorbidity

Dyggve-Melchior-Clausen syndrome is a progressive spondylo-epi-metaphyseal dysplasia associated with mental retardation, characterized by a triad of skeletal deformities (short trunk dwarfism, scoliosis, microcephaly, and limb deformities), facial dysmorphism, and intellectual disability. It an extremely rare condition. Till now, there was no evidence of association of Dyggve-Melchior-Clausen Syndrome with mood disorder. This case report highlights the extremely rare association of Dyggve-Melchior-Clausen syndrome with bipolar affective disorder. The patient had responded well to the combination of mood stabilizer and antipsychotics (sodium valproate and risperidone). To the best of author's knowledge, this is the first case report depicting such association. Both Dyggve-Melchior-Clausen syndrome and bipolar affective disorder are associated with 18q chromosome. This background information raises the possibility of co-morbid association of two disorders rather than a chance association due to genetic linkage.

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.

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.

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.

Fine mapping of a locus for nonsyndromic mental retardation on chromosome 19p13

Mental retardation (MR) occurs in approximately 3% of the population and therefore significantly impacts public health. Despite this relatively high prevalence, the specific causes of MR remain unknown in most cases, although both genetic and environmental factors are known to contribute. We describe a consanguineous family with autosomal recessive (AR) nonsyndromic MR (NSMR). Because the consanguinity of this family is complex, we explore alternative approaches for generating accurate estimates of the evidence for linkage in this family, and demonstrate evidence for linkage to chromosome 19p13 (lod score ranging from 1.2 to 3.5, depending on assumptions of allele frequencies). Fine mapping of the linked region defined a critical region of 3.6 Mb, which overlaps with a previously reported gene (CC2D1A) for MR. However, no mutations in the coding region of this gene are present in the family we describe. These results suggest that another gene causing autosomal recessive nonsyndromic MR (ARNSMR) is located within this genomic region.

[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.

MRI findings in Dyggve-Melchior-Clausen syndrome, a rare spondyloepiphyseal dysplasia

We present the case of an 8-year-old female patient with bone dysplasia as part of Dyggve-Melchior-Clausen syndrome (DMCS). MRI was used to evaluate the case. In the spine, odontoid apophysis aplasia was found with no ossification nucleus, vertebrae with central hump, disk protrusions, hypertrophy of the posterior common vertebral ligament, and hidden spina bifida at the S4 level. Morphological anomalies were found in the hips both in the proximal femoral epiphysis, which was located excentrically and laterally to the femoral neck, and in the Y-cartilage, which was greatly enlarged. In the knees, anterior crossed ligaments were not seen, although there were some indirect signs that indicated congenital absence, including hypoplasia of the femoral trochlea and the intercondylar notch. There was bilateral medial patellar plicae and asymmetry in the height of the distal femoral and proximal tibial physes, as well as dysplasia of the facets of the patella. In comparison with radiography, MRI provides a much clearer definition of the aspects of bone dysplasia that are related to DMCS, including morphological changes in the soft tissue and cartilage of the spine, hips, and knees. MRI can enhance our understanding of the pathogenesis and evolution of deformities.

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.

Mental retardation and abnormal skeletal development (Dyggve-Melchior-Clausen dysplasia) due to mutations in a novel, evolutionarily conserved gene

Dyggve-Melchior-Clausen dysplasia (DMC) and Smith-McCort dysplasia (SMC) are similar, rare autosomal recessive osteochondrodysplasias. The radiographic features and cartilage histology in DMC and SMC are identical. However, patients with DMC exhibit significant developmental delay and mental retardation, the major features that distinguish the two conditions. Linkage studies localized the SMC and DMC disease genes to chromosome 18q12-21.1, providing evidence suggesting that they are allelic disorders. Sequence analysis of the coding exons of the FLJ90130 gene, a highly evolutionarily conserved gene within the recombination interval defined in the linkage study, identified mutations in SMC and DMC patients. The affected individuals in two consanguinous DMC families were homozygous for a stop codon mutation and a frameshift mutation, respectively, demonstrating that DMC represents the FLJ90130-null phenotype. The data confirm the hypothesis that SMC and DMC are allelic disorders and identify a gene necessary for normal skeletal development and brain function.