Spondyloenchondromatosis with D-2-hydroxyglutaric aciduria: a report of a second patient with this unusual combination

An intermediate phenotype in IDH related enchondromatosis spectrum

Mosaic variants of IDH1 (isocitrate dehydrogenase-1) R132 and IDH2 (isocitrate dehydrogenase-2) R172 loci were detected in most of the bone cysts of Ollier and Maffucci series and in the blood and tissue samples of metaphyseal enchondromatosis with D-2-hydroxyglutaric aciduria (MC-HGA) patients. We aimed to report an intermediate phenotype comparing with the reported cases. The proband was a 9-year-old boy with widespread metaphyseal enchondromatosis involving metaphyses of long tubular bones, iliac bones and tubular bones of both hands and feet and sparing spine and flat and short bones. He underwent quad whole exome sequencing (index-both parents-healthy sibling). Sanger sequencing was performed for confirmation and segregation purposes. Heterozygous IDH1 R132H (c.395G > A) variant was detected in his blood via whole exome sequencing and Sanger analysis in mosaic state, 22% of the reads and Sanger signal. He had no D-2-hydroxyglutaric aciduria in urinary organic acid analysis. Our case is unique with the presence of IDH1 R132H variant in blood with metaphyseal enchondromatosis without D-2-hydroxyglutaric aciduria. It was a transitional phenotype. With his phenotype, we expand the IDH1/IDH2 related enchondromatosis phenotypes.

IDH1 mutated acute myeloid leukemia in a child with metaphyseal chondromatosis with D-2-hydroxyglutaric aciduria

D-2-hydroxyglutaric aciduria (D-2-HGA) is a rare metabolic disorder characterized by developmental delay, hypotonia, and bi-allelic mutations in D-2-hydroxyglutarate dehydrogenase (D2HGDH) or a single gain-of-function mutation in isocitrate dehydrogenase 2 (IDH2). Metaphyseal chondromatosis with D-2-hydroxyglutaric aciduria (MC-HGA) is a type of D-2-HGA that has been previously reported in ten patients (OMIM 614875), three of whom had somatic mosaicism for R132 variants in isocitrate dehydrogenase 1 (IDH1). We describe a 3-year-old boy with MC-HGA who subsequently developed acute myeloid leukemia (AML) and was found to have an IDH1 R132C mutation in a leukemic bone marrow sample. Further testing revealed presence of somatic mosaicism for IDH1 R132C variant, suggesting an association of IDH1 in inducing myeloid leukemogenesis.

D-2-Hydroxyglutaric Aciduria with Enchondromatosis and Angiokeratoma Circumscriptum

In this study, we report a four-year-old male with D-2-hydroxyglutaric aciduria (D2HA) and enchondromatosis with a prior history of hyperpigmented, segmental whorls and streaks on his abdomen who later presented with an eruption of angiokeratoma circumscriptum within a similar distribution. His condition can likely be explained by underlying somatic mosaicism; however, a unifying culprit gene mutation has not yet been identified. To date, only 10 reported cases of D2HA with enchondromatosis are available in the literature with three reported skin findings. This is the first reported case of angiokeratoma circumscriptum associated with the rare condition of D2HA and enchondromatosis.

Widespread and debilitating hemangiomas in a patient with enchondromatosis and D-2-hydroxyglutaric aciduria

Metaphyseal chondromatosis with D-2-hydroxyglutaric aciduria (MC-HGA) (OMIM 614875) is a severe chondrodysplasia combined with a urinary excretion of D-2-hydroxyglutaric acid. Here, we reported the tenth case of this disease. A 15-year-old boy had symmetric radiolulencies in the metaphyses of the long bones suggesting enchondromatosis and platyspondyly. Remarkably, he manifested widespread cavernous hemangiomas including scalp, lips, tongue, larynx, and prepuce, with the onset of 3 years of age. Hemangiomas at the larynx had caused dyspnea and those in the oral cavity led to recurrent bleeding, requiring several surgical removals. These multiple and debilitating hemangiomas have never been previously reported in patients with MC-HGA. Mutation analyses including Sanger sequencing of genes involving in enchondromatosis and the metabolic pathway of D-2-hydroxyglutarate including PTHR1, D2HGDH, HOT, and IDH1, as well as whole-exome sequencing for proband-parent trio analysis and paired blood versus hemangioma studies showed no pathogenic variants. In summary, we reported the tenth patient with MC-HGA who manifested widespread and debilitating hemangiomas in several organs, expanding the clinical spectrum of MC-HGA.

Computational approach to unravel the impact of missense mutations of proteins (D2HGDH and IDH2) causing D-2-hydroxyglutaric aciduria 2

The 2-hydroxyglutaric aciduria (2-HGA) is a rare neurometabolic disorder that leads to the development of brain damage. It is classified into three categories: D-2-HGA, L-2-HGA, and combined D,L-2-HGA. The D-2-HGA includes two subtypes: type I and type II caused by the mutations in D2HGDH and IDH2 proteins, respectively. In this study, we studied six mutations, four in the D2HGDH (I147S, D375Y, N439D, and V444A) and two in the IDH2 proteins (R140G, R140Q). We performed in silico analysis to investigate the pathogenicity and stability changes of the mutant proteins using pathogenicity (PANTHER, PhD-SNP, SIFT, SNAP, and META-SNP) and stability (i-Mutant, MUpro, and iStable) predictors. All the mutations of both D2HGDH and IDH2 proteins were predicted as disease causing except V444A, which was predicted as neutral by SIFT. All the mutants were also predicted to be destabilizing the protein except the mutants D375Y and N439D. DSSP plugin of the PyMOL and Molecular Dynamics Simulations (MDS) were used to study the structural changes in the mutant proteins. In the case of D2HGDH protein, the mutations I147S and V444A that are positioned in the beta sheet region exhibited higher Root Mean Square Deviation (RMSD), decrease in compactness and number of intramolecular hydrogen bonds compared to the mutations N439D and D375Y that are positioned in the turn and loop region, respectively. While the mutants R140Q and R140QG that are positioned in the alpha helix region of the protein. MDS results revealed the mutation R140Q to be more destabilizing (higher RMSD values, decrease in compactness and number of intramolecular hydrogen bonds) compared to the mutation R140G of the IDH2 protein. This study is expected to serve as a platform for drug development against 2-HGA and pave the way for more accurate variant assessment and classification for patients with genetic diseases.

The oncometabolite D-2-hydroxyglutarate induced by mutant IDH1 or -2 blocks osteoblast differentiation in vitro and in vivo

Mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 are found in a somatic mosaic fashion in patients with multiple enchondromas. Enchondromas are benign cartilaginous tumors arising in the medulla of bone. The mutant IDH1/2 causes elevated levels of D-2-hydroxyglutarate (D-2-HG). Mesenchymal stem cells (MSC) are the precursor of the osteoblastic, chondrogenic and adipocytic lineage and we hypothesized that increased levels of D-2-HG cause multiple enchondromas by affecting differentiation of MSCs. Bone marrow derived MSCs from different donors were differentiated towards osteoblastic, chondrogenic and adipocytic lineage in the presence or absence of 5 mM D-2-HG. Three of four MSCs showed near complete inhibition of calcification after 3 weeks under osteogenic differentiation conditions in the presence of D-2-HG, indicating a block in osteogenic differentiation. Two of four MSCs showed an increase in differentiation towards the chondrogenic lineage. To evaluate the effect of D-2-HG in vivo we monitored bone development in zebrafish, which revealed an impaired development of vertebrate rings in the presence of D-2-HG compared to control conditions (p-value < 0.0001). Our data indicate that increased levels of D-2-HG promote chondrogenic over osteogenic differentiation. Thus, mutations in IDH1/2 lead to a local block in osteogenic differentiation during skeletogenesis causing the development of benign cartilaginous tumors.

Novel cases of D-2-hydroxyglutaric aciduria with IDH1 or IDH2 mosaic mutations identified by amplicon deep sequencing

BACKGROUND

Mosaic IDH1 mutations are described as the cause of metaphyseal chondromatosis with increased urinary excretion of D-2-hydroxyglutarate (MC-HGA), and mutations in IDH2 as the cause of D-2-hydroxyglutaric aciduria (D-2HGA) type II. Mosaicism for IDH2 mutations has not previously been reported as a cause of D-2HGA. Here we describe three cases: one MC-HGA case with IDH1 mosaic mutations, and two D-2HGA type II cases. In one D-2HGA case we identified mosaicism for an IDH2 mutation as the genetic cause of this disorder; the other D-2HGA case was caused by a heterozygous IDH2 mutation, while the unaffected mother was a mosaic carrier.

METHODS

We performed amplicon deep sequencing using the 454 GS Junior platform, next to Sanger sequencing, to identify and confirm mosaicism of IDH1 or IDH2 mutations in MC-HGA or D-2HGA, respectively.

RESULTS AND CONCLUSIONS

We identified different mutant allele percentages in DNA samples derived from different tissues (blood vs fibroblasts). Furthermore, we found that mutant allele percentages of IDH1 decreased after more passages had occurred in fibroblast cell cultures. We describe a method for the detection and validation of mosaic mutations in IDH1 and IDH2, making quantification with laborious cloning techniques obsolete.

Metaphyseal chondromatosis combined with D-2-hydroxyglutaric aciduria in four patients

We report four patients who presented with a severe form of metaphyseal chondromatosis in association with D-2-hydroxyglutaric aciduria (D-2-HGA). All patients showed splaying columns of irregular ossification defects with bulbous metaphyses of the long tubular bones, as well as remarkable involvement of the short tubular and flat bones. The vertebral bodies revealed platyspondyly with irregular, stippled endplates. D-2-HGA has been described as a neurometabolic disorder manifesting a broad range of impairment in mental and motor development. Although hydroxyglutaric acid was excreted in high amounts in the urine of all four patients described herein, no significant neurologic abnormalities were evident. This unusual combination of characteristic skeletal and metabolic abnormalities has rarely been reported. Thus, our report will facilitate the recognition of this distinctive entity, and we suggest that a urine organic acid screening be obtained in patients who present with generalized enchondromatosis.

Enchondromatosis revisited: new classification with molecular basis

The so-called "enchondromatoses" are skeletal disorders defined by the presence of ectopic cartilaginous tissue within bone tissue. The clinical and radiographic features of the different enchondromatoses are distinct, and grouping them does not reflect a common pathogenesis but simply a similar radiographic appearance and thus the need for a differential diagnosis. Recent advances in the understanding of their molecular and cellular bases confirm the heterogeneous nature of the different enchondromatoses. Some, like Ollier disease, Maffucci disease, metaphyseal chondromatosis with hydroxyglutaric aciduria, and metachondromatosis are produced by a dysregulation of chondrocyte proliferation, while others (such as spondyloenchondrodysplasia or dysspondyloenchondromatosis) are caused by defects in structure or metabolism of cartilage or bone matrix. In other forms (e.g., the dominantly inherited genochondromatoses), the basic defect remains to be determined. The classification, proposed by Spranger and associates in 1978 and tentatively revised twice, was based on the radiographic appearance, the anatomic sites involved, and the mode of inheritance. The new classification proposed here integrates the molecular genetic advances and delineates phenotypic families based on the molecular defects. Reference radiographs are provided to help in the diagnosis of the well-defined forms. In spite of advances, many cases remain difficult to diagnose and classify, implying that more variants remain to be defined at both the clinical and molecular levels.

Progress in understanding 2-hydroxyglutaric acidurias

The organic acidurias D: -2-hydroxyglutaric aciduria (D-2-HGA), L-2-hydroxyglutaric aciduria (L-2-HGA), and combined D,L-2-hydroxyglutaric aciduria (D,L-2-HGA) cause neurological impairment at young age. Accumulation of D-2-hydroxyglutarate (D-2-HG) and/or L-2-hydroxyglutarate (L-2-HG) in body fluids are the biochemical hallmarks of these disorders. The current review describes the knowledge gathered on 2-hydroxyglutaric acidurias (2-HGA), since the description of the first patients in 1980. We report on the clinical, genetic, enzymatic and metabolic characterization of D-2-HGA type I, D-2-HGA type II, L-2-HGA and D,L-2-HGA, whereas for D-2-HGA type I and type II novel clinical information is presented which was derived from questionnaires.

Metabolic and monogenic causes of seizures in neonates and young infants

Seizures in neonates or young infants present a frequent diagnostic challenge. After exclusion of acquired causes, disturbances of the internal homeostasis and brain malformations, the physician must evaluate for inborn errors of metabolism and for other non-malformative genetic disorders as the cause of seizures. The metabolic causes can be categorized into disorders of neurotransmitter metabolism, disorders of energy production, and synthetic or catabolic disorders associated with brain malformation, dysfunction and degeneration. Other genetic conditions involve channelopathies, and disorders resulting in abnormal growth, differentiation and formation of neuronal populations. These conditions are important given their potential for treatment and the risk for recurrence in the family. In this paper, we will succinctly review the metabolic and genetic non-malformative causes of seizures in neonates and infants less than 6 months of age. We will then provide differential diagnostic clues and a practical paradigm for their evaluation.

IDH1 and IDH2 mutations are frequent events in central chondrosarcoma and central and periosteal chondromas but not in other mesenchymal tumours

Somatic mutations in isocitrate dehydrogenase 1 (IDH1) and IDH2 occur in gliomas and acute myeloid leukaemia (AML). Since patients with multiple enchondromas have occasionally been reported to have these conditions, we hypothesized that the same mutations would occur in cartilaginous neoplasms. Approximately 1200 mesenchymal tumours, including 220 cartilaginous tumours, 222 osteosarcomas and another ∼750 bone and soft tissue tumours, were screened for IDH1 R132 mutations, using Sequenom(®) mass spectrometry. Cartilaginous tumours and chondroblastic osteosarcomas, wild-type for IDH1 R132, were analysed for IDH2 (R172, R140) mutations. Validation was performed by capillary sequencing and restriction enzyme digestion. Heterozygous somatic IDH1/IDH2 mutations, which result in the production of a potential oncometabolite, 2-hydroxyglutarate, were only detected in central and periosteal cartilaginous tumours, and were found in at least 56% of these, ∼40% of which were represented by R132C. IDH1 R132H mutations were confirmed by immunoreactivity for this mutant allele. The ratio of IDH1:IDH2 mutation was 10.6 : 1. No IDH2 R140 mutations were detected. Mutations were detected in enchondromas through to conventional central and dedifferentiated chondrosarcomas, in patients with both solitary and multiple neoplasms. No germline mutations were detected. No mutations were detected in peripheral chondrosarcomas and osteochondromas. In conclusion, IDH1 and IDH2 mutations represent the first common genetic abnormalities to be identified in conventional central and periosteal cartilaginous tumours. As in gliomas and AML, the mutations appear to occur early in tumourigenesis. We speculate that a mosaic pattern of IDH-mutation-bearing cells explains the reports of diverse tumours (gliomas, AML, multiple cartilaginous neoplasms, haemangiomas) occurring in the same patient.

Peripheral neuropathy in a patient with D-2-hydroxyglutaric aciduria

D-2-hydroxyglutaric aciduria (D-2-HGA; OMIM 600721) is a rare autosomal recessive neurometabolic disorder with a wide clinical spectrum. The severe phenotype is homogeneous and is characterized by early infantile-onset epileptic encephalopathy with hypotonia, delayed cerebral visual development, cardiomyopathy and facial dysmorphic features. The mild phenotype has a more variable clinical expression with hypotonia and developmental delay. We present peripheral neuropathy as an additional clinical and electrophysiological feature in a 16-year-old boy with a homozygous missense mutation in exon 3 of the D-2-hydroxyglutarate dehydrogenase gene (D2HGDH) at position c.458T>C. This mutation results in replacement of a methionine residue, which was highly conserved during evolution, by threonine (p.Met153Thr).

Inborn errors of metabolism for the diagnostic radiologist

Inherited metabolic disorders are becoming more important with the increasing availability of diagnostic methods and therapies for these conditions. The radiologist has become an important link in making the diagnosis or collaborating with the specialist centre to diagnose these disorders and monitor effects of therapy. The modes of presentation, disease-specific groups, classic radiological features and investigations are explored in this article to try and give the general radiologist some crucial background knowledge. The following presentations are covered: acute intoxication, hypoglycaemia, developmental delay and storage features. Specific groups of disorders covered are the abnormalities of intermediary metabolism, disorders of fatty acid oxidation and ketogenesis, mitochondrial disorders, lysosomal storage disorders, and, briefly, other groups such as peroxisomal disorders, disorders of glycosylation, and creatine synthesis disorders. New advances and the demands for monitoring are also briefly explored.

D-2-Hydroxyglutaric aciduria: unravelling the biochemical pathway and the genetic defect

D-2-Hydroxyglutaric aciduria (D-2-HGA) is a neurometabolic inherited disorder first described in 1980. In the following years, it became clear that the clinical phenotype of the disease varies widely from severe neonatal to asymptomatic. However, the sparse biochemical knowledge made D-2-HGA a poorly understood disease. Much progress has been made in the last five years in various studies, revealing two human enzymes that play a role in the metabolism of D-2-hydroxyglutarate (D-2-HG): hydroxyacid-oxoacid transhydrogenase (HOT) and D-2-HG dehydrogenase. HOT is expected to be responsible for the formation of D-2-HG, while D-2-HG dehydrogenase converts D-2-HG into 2-ketoglutarate. We demonstrated pathogenic mutations in the D2HGD gene in patients with D-2-HGA, helping to unravel the primary defect causing D-2-HGA. However, in approximately 50% of the patients with D-2-HGA examined, no pathogenic mutations have yet been found.

Spondyloenchondrodysplasia: clinical variability in three cases

Spondyloenchondrodysplasia is a very rare skeletal dysplasia in which multiple enchondromata exist in the metaphyses of the long bones with platyspondyly. We present three patients (two of them are sibs) with spondyloenchondrodysplasia. The first patient was a 10-year-old boy, who had short stature and enchondromatous-like lesions in the metaphyses of the long bones and platyspondyly on radiography. His older sister (21-years old) had received growth hormone therapy 12 years earlier due to short stature, and her radiological findings were similar but milder than her brother. Both the sibs had normal intelligence and no calcification of the basal ganglia. The third patient was a 6-year-old boy who had short stature, mental retardation, enchondromatous-like lesions in the metaphyses of the long bones and platyspondyly. His cranial BT showed calcification of basal ganglia. The findings of the two sibs in the first family were compatible with spondyloenchondrodysplasia. The difference in clinical severity between the siblings shows the variability within the family. The third case with mental retardation and the presence of intracranial calcifications is compatible with spondyloenchondrodysplasia with basal ganglia calcification. In conclusion, we suggest that family screening and cranial imaging for the presence of intracranial calcifications should be considered in every patient with the diagnosis of spondyloenchondrodysplasia.

Autosomal dominant inheritance of spondyloenchondrodysplasia

Spondyloenchondrodysplasia comprises generalized enchondromatosis with platyspondyly and is thought to be inherited as an autosomal recessive condition. A mother and son are reported with typical features of spondyloenchondrodysplasia. Their similar radiographic and MRI findings are presented. The radiologic appearance of the spine changed over time, illustrating the evolving phenotype of this condition. Transmission from mother to son suggests that dominant pattern of inheritance is possible. A classification of the enchondromatoses is discussed.