Marleen Simon

Hypomethylation of the H19 Gene Causes Not Only Silver-Russell Syndrome (SRS) but Also Isolated Asymmetry or an SRS-Like Phenotype

The H19 differentially methylated region (DMR) controls the allele-specific expression of both the imprinted H19 tumor-suppressor gene and the IGF2 growth factor. Hypermethylation of this DMR--and subsequently of the H19 promoter region--is a major cause of the clinical features of gigantism and/or asymmetry seen in Beckwith-Wiedemann syndrome or in isolated hemihypertrophy. Here, we report a series of patients with hypomethylation of the H19 locus. Their main clinical features of asymmetry and growth retardation are the opposite of those seen in patients with hypermethylation of this region. In addition, we show that complete hypomethylation of the H19 promoter is found in two of three patients with the full clinical spectrum of Silver-Russell syndrome. This syndrome is also characterized by growth retardation and asymmetry, among other clinical features. We conclude that patients with these clinical features should be analyzed for H19 hypomethylation.

Hereditary leiomyomatosis and renal cell cancer in families referred for fumarate hydratase germline mutation analysis

Smit DL, Mensenkamp AR, Badeloe S, Breuning MH, Simon MEH, van Spaendonck KY, Aalfs CM, Post JG, Shanley S, Krapels IPC, Hoefsloot LH, van Moorselaar RJA, Starink TM, Bayley J‐P, Frank J, van Steensel MAM, Menko FH. Hereditary leiomyomatosis and renal cell cancer in families referred for fumarate hydratase germline mutation analysis.

PLS3 Mutations in X-Linked Osteoporosis with Fractures

Plastin 3 (PLS3), a protein involved in the formation of filamentous actin (F-actin) bundles, appears to be important in human bone health, on the basis of pathogenic variants in PLS3 in five families with X-linked osteoporosis and osteoporotic fractures that we report here. The bone-regulatory properties of PLS3 were supported by in vivo analyses in zebrafish. Furthermore, in an additional five families (described in less detail) referred for diagnosis or ruling out of osteogenesis imperfecta type I, a rare variant (rs140121121) in PLS3 was found. This variant was also associated with a risk of fracture among elderly heterozygous women that was two times as high as that among noncarriers, which indicates that genetic variation in PLS3 is a novel etiologic factor involved in common, multi-factorial osteoporosis.

Mutations at a single codon in Mad homology 2 domain of SMAD4 cause Myhre syndrome

Myhre syndrome (MIM 139210) is a developmental disorder characterized by short stature, short hands and feet, facial dysmorphism, muscular hypertrophy, deafness and cognitive delay. Using exome sequencing of individuals with Myhre syndrome, we identified SMAD4 as a candidate gene that contributes to this syndrome on the basis of its pivotal role in the bone morphogenetic pathway (BMP) and transforming growth factor (TGF)-β signaling. We identified three distinct heterozygous missense SMAD4 mutations affecting the codon for Ile500 in 11 individuals with Myhre syndrome. All three mutations are located in the region of SMAD4 encoding the Mad homology 2 (MH2) domain near the site of monoubiquitination at Lys519, and we found a defect in SMAD4 ubiquitination in fibroblasts from affected individuals. We also observed decreased expression of downstream TGF-β target genes, supporting the idea of impaired TGF-β–mediated transcriptional control in individuals with Myhre syndrome.

Weaver syndrome and EZH2 mutations: Clarifying the clinical phenotype

Weaver syndrome, first described in 1974, is characterized by tall stature, a typical facial appearance, and variable intellectual disability. In 2011, mutations in the histone methyltransferase, EZH2, were shown to cause Weaver syndrome. To date, we have identified 48 individuals with EZH2 mutations. The mutations were primarily missense mutations occurring throughout the gene, with some clustering in the SET domain (12/48). Truncating mutations were uncommon (4/48) and only identified in the final exon, after the SET domain. Through analyses of clinical data and facial photographs of EZH2 mutation‐positive individuals, we have shown that the facial features can be subtle and the clinical diagnosis of Weaver syndrome is thus challenging, especially in older individuals. However, tall stature is very common, reported in >90% of affected individuals. Intellectual disability is also common, present in ∼80%, but is highly variable and frequently mild. Additional clinical features which may help in stratifying individuals to EZH2 mutation testing include camptodactyly, soft, doughy skin, umbilical hernia, and a low, hoarse cry. Considerable phenotypic overlap between Sotos and Weaver syndromes is also evident. The identification of an EZH2 mutation can therefore provide an objective means of confirming a subtle presentation of Weaver syndrome and/or distinguishing Weaver and Sotos syndromes. As mutation testing becomes increasingly accessible and larger numbers of EZH2 mutation‐positive individuals are identified, knowledge of the clinical spectrum and prognostic implications of EZH2 mutations should improve.

Deletions of the RUNX2 gene are present in about 10% of individuals with cleidocranial dysplasia

Cleidocranial Dysplasia (CCD) is an autosomal dominant skeletal disorder characterized by hypoplastic or absent clavicles, increased head circumference, large fontanels, dental anomalies, and short stature. Hand malformations are also common. Mutations in RUNX2 cause CCD, but are not identified in all CCD patients. In this study we screened 135 unrelated patients with the clinical diagnosis of CCD for RUNX2 mutations by sequencing analysis and demonstrated 82 mutations 48 of which were novel. By quantitative PCR we screened the remaining 53 unrelated patients for copy number variations in the RUNX2 gene. Heterozygous deletions of different size were identified in 13 patients, and a duplication of the exons 1 to 4 of the RUNX2 gene in one patient. Thus, heterozygous deletions or duplications affecting the RUNX2 gene may be present in about 10% of all patients with a clinical diagnosis of CCD which corresponds to 26% of individuals with normal results on sequencing analysis. We therefore suggest that screening for intragenic deletions and duplications by qPCR or MLPA should be considered for patients with CCD phenotype in whom DNA sequencing does not reveal a causative RUNX2 mutation.

A Study of the Clinical and Radiological Features in a Cohort of 93 Patients with a COL2A1 Mutation Causing Spondyloepiphyseal Dysplasia Congenita or a Related Phenotype

Type 2 collagen disorders encompass a diverse group of skeletal dysplasias that are commonly associated with orthopedic, ocular, and hearing problems. However, the frequency of many clinical features has never been determined. We retrospectively investigated the clinical, radiological, and genotypic data in a group of 93 patients with molecularly confirmed SEDC or a related disorder. The majority of the patients (80/93) had short stature, with radiological features of SEDC (n = 64), others having SEMD (n = 5), Kniest dysplasia (n = 7), spondyloperipheral dysplasia (n = 2), or Torrance‐like dysplasia (n = 2). The remaining 13 patients had normal stature with mild SED, Stickler‐like syndrome or multiple epiphyseal dysplasia. Over 50% of the patients had undergone orthopedic surgery, usually for scoliosis, femoral osteotomy or hip replacement. Odontoid hypoplasia was present in 56% (95% CI 38–74) and a correlation between odontoid hypoplasia and short stature was observed. Atlanto‐axial instability, was observed in 5 of the 18 patients (28%, 95% CI 10–54) in whom flexion‐extension films of the cervical spine were available; however, it was rarely accompanied by myelopathy. Myopia was found in 45% (95% CI 35–56), and retinal detachment had occurred in 12% (95% CI 6–21; median age 14 years; youngest age 3.5 years). Thirty‐two patients complained of hearing loss (37%, 95% CI 27–48) of whom 17 required hearing aids. The ophthalmological features and possibly also hearing loss are often relatively frequent and severe in patients with splicing mutations. Based on clinical findings, age at onset and genotype–phenotype correlations in this cohort, we propose guidelines for the management and follow‐up in this group of disorders.

The unfolding clinical spectrum of holoprosencephaly due to mutations in SHH, ZIC2, SIX3 and TGIF genes

Holoprosencephaly is a severe malformation of the brain characterized by abnormal formation and separation of the developing central nervous system. The prevalence is 1:250 during early embryogenesis, the live-born prevalence is 1:16 000. The etiology of HPE is extremely heterogeneous and can be teratogenic or genetic. We screened four known HPE genes in a Dutch cohort of 86 non-syndromic HPE index cases, including 53 family members. We detected 21 mutations (24.4%), 3 in SHH, 9 in ZIC2 and 9 in SIX3. Eight mutations involved amino-acid substitutions, 7 ins/del mutations, 1 frame-shift, 3 identical poly-alanine tract expansions and 2 gene deletions. Pathogenicity of mutations was presumed based on de novo character, predicted non-functionality of mutated proteins, segregation of mutations with affected family-members or combinations of these features. Two mutations were reported previously. SNP array confirmed detected deletions; one spanning the ZIC2/ZIC5 genes (approx. 100 kb) the other a 1.45 Mb deletion including SIX2/SIX3 genes. The mutation percentage (24%) is comparable with previous reports, but we detected significantly less mutations in SHH: 3.5 vs 10.7% (P=0.043) and significantly more in SIX3: 10.5 vs 4.3% (P=0.018). For TGIF1 and ZIC2 mutation the rate was in conformity with earlier reports. About half of the mutations were de novo, one was a germ line mosaic. The familial mutations displayed extensive heterogeneity in clinical manifestation. Of seven familial index patients only two parental carriers showed minor HPE signs, five were completely asymptomatic. Therefore, each novel mutation should be considered as a risk factor for clinically manifest HPE, with the caveat of reduced clinical penetrance.

Limb anomalies in patients with CHARGE syndrome: an expansion of the phenotype.

CHARGE syndrome is characterized by a wide clinical variability. During the past years the phenotypic spectrum was markedly expanded. Limb anomalies were initially not recognized as part of the phenotype but more recently mild limb anomalies were described in approximately 30% of the patients. We report on three patients with several major features of CHARGE syndrome who, in addition, presented severe limb anomalies including monodactyly, tibia aplasia, and bifid femora. Three different heterozygous truncating mutations in the CHD7 gene were detected. It has been hypothesized before that the CHARGE syndrome is caused by a disruption of mesenchymal‐epithelial interaction. Given the expression of the CHD7 gene in the developing limb bud, it was anticipated that limb defects would belong to the spectrum of manifestations of CHARGE syndrome. The present observations provide further support to this hypothesis.

17q24.2 microdeletions: a new syndromal entity with intellectual disability, truncal obesity, mood swings and hallucinations

Although microdeletions of the long arm of chromosome 17 are being reported with increasing frequency, deletions of chromosome band 17q24.2 are rare. Here we report four patients with a microdeletion encompassing chromosome band 17q24.2 with a smallest region of overlap of 713 kb containing five Refseq genes and one miRNA. The patients share the phenotypic characteristics, such as intellectual disability (4/4), speech delay (4/4), truncal obesity (4/4), seizures (2/4), hearing loss (3/4) and a particular facial gestalt. Hallucinations and mood swings were also noted in two patients. The PRKCA gene is a very interesting candidate gene for many of the observed phenotypic features, as this gene plays an important role in many cellular processes. Deletion of this gene might explain the observed truncal obesity and could also account for the hallucinations and mood swings seen in two patients, whereas deletion of a CACNG gene cluster might be responsible for the seizures observed in two patients. In one of the patients, the PRKAR1A gene responsible for Carney Complex and the KCNJ2 gene causal for Andersen syndrome are deleted. This is the first report of a patient with a whole gene deletion of the KCNJ2 gene.