Katharina M. Roetzer

Rare exonic deletions implicate the synaptic organizer Gephyrin (GPHN) in risk for autism, schizophrenia and seizures

The GPHN gene codes for gephyrin, a key scaffolding protein in the neuronal postsynaptic membrane, responsible for the clustering and localization of glycine and GABA receptors at inhibitory synapses. Gephyrin has well-established functional links with several synaptic proteins that have been implicated in genetic risk for neurodevelopmental disorders such as autism spectrum disorder (ASD), schizophrenia and epilepsy including the neuroligins (NLGN2, NLGN4), the neurexins (NRXN1, NRXN2, NRXN3) and collybistin (ARHGEF9). Moreover, temporal lobe epilepsy has been linked to abnormally spliced GPHN mRNA lacking exons encoding the G-domain of the gephyrin protein, potentially arising due to cellular stress associated with epileptogenesis such as temperature and alkalosis. Here, we present clinical and genomic characterization of six unrelated subjects, with a range of neurodevelopmental diagnoses including ASD, schizophrenia or seizures, who possess rare de novo or inherited hemizygous microdeletions overlapping exons of GPHN at chromosome 14q23.3. The region of common overlap across the deletions encompasses exons 3-5, corresponding to the G-domain of the gephyrin protein. These findings, together with previous reports of homozygous GPHN mutations in connection with autosomal recessive molybdenum cofactor deficiency, will aid in clinical genetic interpretation of the GPHN mutation spectrum. Our data also add to the accumulating evidence implicating neuronal synaptic gene products as key molecular factors underlying the etiologies of a diverse range of neurodevelopmental conditions.

Identification of risk genes for autism spectrum disorder through copy number variation analysis in Austrian families

Autism or autism spectrum disorder (ASD) is a range of neurodevelopmental disorders starting in early childhood and is characterized by impairments in communication and reciprocal social interaction and presence of restricted and repetitive patterns of behavior. The contribution of genetic factors to autism is clear in twin and family studies. It is apparent that, overall, ASD is a complex non-Mendelian disorder. Recent studies suggest that copy number variations (CNVs) play a significant role in the etiology of ASD. For the current work, we recruited 245 family members from 73 ASD families from Styria, Austria. The DNA from probands was genotyped with Affymetrix single nucleotide polymorphism (SNP) 6.0 microarrays to screen for CNVs in their genomes. Analysis of the microarray data was performed using three different algorithms, and a list of stringent calls was compared to existing CNV data from over 2,357 controls of European ancestry. For stringent calls not present in controls, quantitative real-time PCR (qRT-PCR) was used to validate the CNVs in the probands and in their family members. Twenty-two CNVs were validated from this set (five of which are apparently de novo), many of which appear likely to disrupt genes that may be considered as good candidates for neuropsychiatric disorders, including DLG2, S100B, ARX, DIP2A, HPCAL1, and GPHN. Several others disrupt genes that have previously been implicated in autism, such as BDNF, AUTS2, DPP6, and C18orf22, and our data add to the growing evidence of their involvement in ASD.

Novel PHEX Mutation Associated with Hypophosphatemic Rickets

Background: X-linked hypophosphatemia (XLH) is the most prevalent heritable form of rickets. It is a dominantly inherited disorder, characterized by renal phosphate wasting, abnormal vitamin D and PTH metabolism, and defective bone mineralization. Inactivating mutations in the gene encoding PHEX (phosphate-regulating gene with homologies to endopeptidases on the X chromosome) have been found to be associated with XLH. Methods: We report about a 54-year-old male patient who exhibited the typical features of XLH, and in whom mutational analysis using PCR and sequencing was performed. Additionally, extensive laboratory and radiological investigations were carried out. Results: A 1-bp deletion in exon 2 of the PHEX gene was detected (177delC), which, to the best of our knowledge, has not been reported yet. This deletion results in a premature stop codon (C59X), suggesting a truncation of the PHEX protein. Furthermore, elevated FGF23 and PTH levels as well as an increased axial bone mineral density score were measured. Conclusions: We present a male patient with XLH, who harbors a novel mutation in the PHEX gene, which might be the cause for his disease. Our data support previous findings and therefore contribute to the decipherment of the pathogenetic pathways of XLH.

Effects of Tumor-Induced Osteomalacia on the Bone Mineralization Process

Fibroblast growth factor 23 (FGF23) overexpression has been identified as a causative factor for tumor-induced osteomalacia (TIO) characterized by hypophosphatemia due to increased renal phosphate wasting, low 1,25(OH)2D3 serum levels, and low bone density. The effects of long-lasting disturbed phosphate homeostasis on bone mineralization are still not well understood. We report on a patient with a 12-year history of TIO, treated with 1,25(OH)2D3 and phosphate, who finally developed hyperparathyroidism with gland hyperplasia before the tumor could be localized in the scapula and removed. During surgery a transiliac bone biopsy was obtained. FGF23 expression in the tumor cells was confirmed by in situ hybridization. Serum FGF23 levels as measured by ELISA were found to be extremely elevated before and decreased after removal of the tumor. Bone histology/histomorphometry and measurement of bone mineralization density distribution using quantitative backscattered electron imaging were performed on the bone biopsy. The data showed important surface osteoidosis and a slightly increased osteoblast but markedly decreased osteoclast number. The mineralized bone volume (−11%) and mineralized trabecular thickness (−18%) were low. The mean degree of mineralization of the bone matrix (−7%), the most frequent calcium concentration (−4.1%), and the amounts of fully mineralized bone (−40.3%) were distinctly decreased, while the heterogeneity of mineralization (+44.5%) and the areas of primary mineralization (+131.6%) were dramatically increased. We suggest that the elevated levels of FGF23 and/or low phosphate concentrations disturb the mineralization kinetics in vivo without affecting matrix mineralization of pre-existing bone packets.

Altered bone matrix mineralization in a patient with Rett syndrome

Rett syndrome (RTT) is a common X-linked neurodevelopmental disorder caused by mutations in the coding region of methyl-CpG-binding 2 (MECP2) gene. Patients with RTT have a low bone mineral density and increased risk of fracture. However, very little is known if bone matrix mineralization is altered in RTT. A 17-year-old girl with a classical form of RTT with a heterozygous nonsense mutation in exon 3 in the MECP2-gene was treated in our hospital. Her femoral neck BMD is 43.3% below the 3rd percentile when compared to age and sex-matched controls. She underwent surgery for correction of her scoliosis, which provided a unique opportunity to obtain bone tissue to study bone matrix mineralization (Bone Mineralization Density Distribution-BMDD) using quantitative backscattered electron imaging (qBEI) and histomorphometry. BMDD outcomes were compared to recently published normative reference data for young individuals. qBEI analysis showed a significant shift to lower matrix mineralization despite histomorphometric indices indicate a low bone turnover. There was a reduction in CaMean (-7.92%) and CaPeak (-3.97%), which describe the degree of mineralization. Furthermore the fraction of low mineralized matrix (CaLow: +261.84%) was dramatically increased, which was accompanied with an increase in the heterogeneity of mineralization (CaWidth: +86.34%). Our findings show a significantly altered bone matrix mineralization of a typical patient with RTT. This may partly explain the low bone density seen in these patients. These results also warrant further studies on the molecular role of MECP2 in bone matrix mineralization.

Further evidence for the pathogenicity of 15q24 microduplications distal to the minimal critical regions

DNA copy number alterations in 15q24 have repeatedly been reported in patients exhibiting mild to moderate developmental delay and dysmorphic features. To date, mainly microdeletions have been described, and comparison of overlapping regions allowed the definition of minimal critical regions (MCRs) for microdeletions as well as microduplications. These MCRs are associated with distinct phenotypes. Recently, a family with a new microduplication distal to these MCRs was reported. However, for this alteration the typical phenotypical consequences could not yet be determined. Here we present another family with a nearly identical microduplication exhibiting a broad clinical spectrum including developmental delay, autistic traits and dysmorphic features. Our data suggest that microduplications adjacent and distal to the known MCRs are variable in expressivity and are associated with distinct features. They might represent a novel and recurrent microduplication syndrome.

A patient with Melorheostosis manifesting with features similar to tricho-dento-osseous syndrome: a case report

IntroductionA case of melorheostosis in association with tricho-dento-osseous (TDO) syndrome has been encountered.Case presentationThe clinical and the radiographic manifestations of melorheostosis have been encountered in a 41-year-old man. Mutations in the 13 exons and flanking intronic regions of the LEMD3-gene have not been detected. His phenotypic features were consistent but not completely diagnostic for tricho-dento-osseous syndrome (TDO). We report what might be a novel syndromic association.ConclusionMelorheostosis has not previously been reported to be a part of TDO and an extensive review of the literature suggests that the constellation of hair, tooth and bone abnormalities found in our patient either represents an unusual variant of tricho-dento-osseous syndrome or a new syndrome.

Extra phenotypic features in a girl with Miller syndrome.

A 4-year-old girl, the child of nonconsanguineous parents was referred for clinical assessment because of postaxial limb defects associated with mild facial dysmorphism. The overall phenotypic features were compatible with the Miller syndrome. The proband manifested distinctive bone defects, consisting of triangular-shaped terminal phalanges and cone-shaped epiphyses of the middle phalanges of the feet. Using the sequence analysis of the DHODH gene we identified compound heterozygous mutations in the proband. Furthermore, both the parents were found to be heterozygous carriers of one of the two mutations found in the proband. Interestingly, the father had a history of postaxial polydactyly. We speculated that the postaxial polydactyly in the father was either a heterozygote manifestation or is unrelated.

CDK10 Mutations in Humans and Mice Cause Severe Growth Retardation, Spine Malformations, and Developmental Delays

In five separate families, we identified nine individuals affected by a previously unidentified syndrome characterized by growth retardation, spine malformation, facial dysmorphisms, and developmental delays. Using homozygosity mapping, array CGH, and exome sequencing, we uncovered bi-allelic loss-of-function CDK10 mutations segregating with this disease. CDK10 is a protein kinase that partners with cyclin M to phosphorylate substrates such as ETS2 and PKN2 in order to modulate cellular growth. To validate and model the pathogenicity of these CDK10 germline mutations, we generated conditional-knockout mice. Homozygous Cdk10-knockout mice died postnatally with severe growth retardation, skeletal defects, and kidney and lung abnormalities, symptoms that partly resemble the diseases effect in humans. Fibroblasts derived from affected individuals and Cdk10-knockout mouse embryonic fibroblasts (MEFs) proliferated normally; however, Cdk10-knockout MEFs developed longer cilia. Comparative transcriptomic analysis of mutant and wild-type mouse organs revealed lipid metabolic changes consistent with growth impairment and altered ciliogenesis in the absence of CDK10. Our results document the CDK10 loss-of-function phenotype and point to a function for CDK10 in transducing signals received at the primary cilia to sustain embryonic and postnatal development.

Vertebral hyperostosis, ankylosed vertebral fracture and atlantoaxial rotatory subluxation in an elderly patient with a history of infantile idiopathic scoliosis; a case report

This is a case report of a 48-year-old-woman with scoliosis since early childhood. Recent radiographic spinal assessment revealed the presence of distinctive spinal abnormalities. To the best of our knowledge this is the first clinical report describing a constellation of unusual changes in an elderly woman with a history of infantile idiopathic scoliosis.