The molecular mechanism underlying Roberts syndrome involves loss of ESCO2 acetyltransferase activity.

Roberts syndrome/SC phocomelia (RBS) is an autosomal recessive disorder with growth retardation, craniofacial abnormalities and limb reduction. Cellular alterations in RBS include lack of cohesion at the heterochromatic regions around centromeres and the long arm of the Y chromosome, reduced growth capacity, and hypersensitivity to DNA damaging agents. RBS is caused by mutations in ESCO2, which encodes a protein belonging to the highly conserved Eco1/Ctf7 family of acetyltransferases that is involved in regulating sister chromatid cohesion. We identified 10 new mutations expanding the number to 26 known ESCO2 mutations. We observed that these mutations result in complete or partial loss of the acetyltransferase domain except for the only missense mutation that occurs in this domain (c.1615T>G, W539G). To investigate the mechanism underlying RBS, we analyzed ESCO2 mutations for their effect on enzymatic activity and cellular phenotype. We found that ESCO2 W539G results in loss of autoacetyltransferase activity. The cellular phenotype produced by this mutation causes cohesion defects, proliferation capacity reduction and mitomycin C sensitivity equivalent to those produced by frameshift and nonsense mutations associated with decreased levels of mRNA and absence of protein. We found decreased proliferation capacity in RBS cell lines associated with cell death, but not with increased cell cycle duration, which could be a factor in the development of phocomelia and cleft palate in RBS. In summary, we provide the first evidence that loss of acetyltransferase activity contributes to the pathogenesis of RBS, underscoring the essential role of the enzymatic activity of the Eco1p family of proteins.

Severe Guillain-Barré syndrome associated with chromosome 17p11.2-12 duplication.

We report a patient with Guillain-Barré syndrome (GBS), characterized by severe tetraparesis, bulbar syndrome, and ophthalmoparesis. The nadir was reached within 1 day, followed by respiratory insufficiency requiring mechanical ventilation. Molecular analysis revealed a duplication at chromosome 17p11.2-12, which is a known genetic cause of Charcot-Marie-Tooth disease type 1A (CMT1A). We suggest that this genotype may comprise a previously unrecognized genetic risk factor for GBS.

Mice deficient for RNA-binding protein brunol1 show reduction of spermatogenesis but are fertile.

RNA-binding proteins are involved in post-transcriptional processes like mRNA stabilization, alternative splicing, and transport. Brunol1 is a novel mouse gene related to elav/Bruno family of genes encoding for RNA-binding proteins. We report here the expression and functional analysis of murine Brunol1. Expression analysis of Brunol1 during embryogenesis by RT-PCR showed that Brunol1 expression starts at 9.5 dpc and continues to the later stages of embryonic development. In adult mice, the Brunol1 expression is restricted to brain and testis. We also analyzed the Brunol1 expression in testes of different mutants with spermatogenesis defects: W/W(V), Tfm/y, Leyl(-/-), olt/olt, and qk/qk. Brunol1 transcript was detectable in Leyl(-/-), olt/olt, and qk/qk mutant but not in W/W(V) and Tfm/y mutants. We also showed by transfection of a fusion protein of green fluorescent protein and Brunol1 protein into NIH3T3 cells, that Brunol1 is localized in cytoplasm and nucleus. In order to elucidate the function of the Brunol1 protein in spermatogenesis, we disrupted the Brunol1 locus in mouse by homologous recombination, which resulted in a complete loss of the Brunol1 transcript. Male and female Brunol1(+/-) and Brunol1(-/-) mice from genetic backgrounds C57BL/6J x 129/Sv hybrid and 129X1/SvJ when inbred exhibited normal phenotype and are fertile, although the number and motility of sperms are significantly reduced. An intensive phenotypic analysis showed no gross abnormalities in testis morphology. Collectively our results demonstrate that Brunol1 might be nonessential protein for mouse embryonic development and spermatogenesis.

Charcot-Marie-Tooth neuropathy type 2A: novel mutations in the mitofusin 2 gene (MFN2).

BACKGROUND: Charcot-Marie-Tooth neuropathies are a group of genetically heterogeneous diseases of the peripheral nervous system. Mutations in the MFN2 gene have been reported as the primary cause of Charcot-Marie-Tooth disease type 2A. METHODS: Patients with the clinical diagnosis of Charcot-Marie-Tooth type 2 were screened using single strand conformation polymorphism (SSCP). All DNA samples showing band shifts in the SSCP analysis were amplified from genomic DNA and cycle sequenced. RESULTS: We analyzed a total of 73 unrelated patients with a clinical diagnosis of CMT 2. Overall, novel mutations were detected in 6 patients. c.380G>T (G127V), c.1128G>A (M376I), c.1040A>T (E347V), c.1403G>A (R468H), c.2113G>A (V705I), and c.2258_2259insT (L753fs). CONCLUSION: We confirmed a significant role of mutations in MFN2 in the pathogenesis of Charcot-Marie-Tooth disease type 2.

Electrophoresis of DNA in human genetic diagnostics - state-of-the-art, alternatives and future prospects.

Electrophoretic separation of nucleic acids according to their molecular weights has dominated the methods' spectrum in molecular genetics for nearly half a century. We review the current methodological basis and evaluate its impact with special reference to new developments in the microarray technology. Although electrophoresis may be made redundant for many applications in DNA diagnostics within a few years, a number of electrophoretic vestiges will remain irreplaceable in the foreseeable future.

Novel case of dup(3q) syndrome due to a de novo interstitial duplication 3q24-q26.31 with minimal overlap to the dup(3q) critical region.

Dup(3q) syndrome is characterized by typical facial features, mental and growth retardation, often with congenital heart defects. The syndrome has attracted special attention because of the clinical overlap with Cornelia de Lange syndrome (CDLS). Patients with dup(3q) syndrome are trisomic for segments of the long arm of chromosome 3, most often within the region 3q21 to 3qter. Most cases have arisen as unbalanced translocations and do involve other chromosomes also. A dup(3q) minimal region has been defined at 3q26.3-q27. We report here a 15-month-old boy with a de novo interstitial inverted duplication of 3q24-q26.31. Clinical evaluation revealed mild but typical features of dup(3q) syndrome. The duplication was characterized by conventional and molecular cytogenetics. The results allow further narrowing of the dup(3q) critical region at its distal end and suggest the existence of one or several major genes responsible for the dup(3q) syndrome in the proximal half of 3q26.31. Moreover, the results of fluorescence in situ hybridization (FISH) analysis with BAC probes suggest a disruption of the NLGN1 gene at the distal end of the duplication in 3q26.31 in the patient. The breakpoint within NLGN1 is unique for this patient, and the contribution of NLGN1 disruption to the phenotype of this patient remains unclear. Yet since NLGN1 is involved in synaptogenesis in the central nervous system, altered gene dosage is a good candidate for mental retardation as a recurrent feature of dup(3q) syndrome.

A novel GFAP mutation and disseminated white matter lesions: adult Alexander disease?

The recent discovery of heterozygous de novo mutations in the glial fibrillary acidic protein (GFAP) gene as the cause of infantile and juvenile Alexander disease has shed new light on the long-standing debate whether the adult subtype has the same etiology as infantile and juvenile Alexander disease. A 40-year-old man presented with subacute left hemiplegia and ataxia. Cranial MRI revealed disseminated patchy white matter changes involving the corpus callosum, basal ganglia and brainstem. CSF investigation demonstrated elevated total protein but was otherwise normal. Mutation analysis of the GFAP gene was performed in the patient, his mother and healthy brother. A novel heterozygous mutation in exon 4, 681G-->C, predicting an amino acid substitution E223Q in the rod region of GFAP was detected in the patient and his mother but not in his healthy brother or 150 control chromosomes. We conclude that the patient is actually afflicted with Alexander disease. Mutation analysis of GFAP should be considered in patients with remitting neurological deficits, disseminated white matter lesions and absence of inflammatory CSF changes.

Cerebral proton magnetic resonance spectroscopy in infantile Alexander disease.

Alexander disease (AD) is a rare genetic disorder of the central nervous system due to a dysfunction of astrocytes. The most common infantile form presents as a progressive leukodystrophy with macrocephalus. Recently, heterozygous de novo mutations in the gene encoding glial fibrillary acidic protein (GFAP) have been demonstrated to be associated with AD. We used localized proton magnetic resonance spectroscopy (MRS) to assess metabolic abnormalities in grey and white matter, basal ganglia, and cerebellum of 4 patients with infantile AD and GFAP mutations. Strongly elevated concentrations of myo-inositol in conjunction with normal or increased choline-containing compounds in all regions investigated point to astrocytosis and demyelination. Neuroaxonal degeneration, as reflected by a reduction of N-acetylaspartate, was most pronounced in cerebral and cerebellar white matter. The accumulation of lactate in affected white matter is in line with infiltrating macrophages. Metabolic alterations demonstrated by in vivo proton MRS are in excellent agreement with known neuropathological features of AD.

Evaluation of Cx26/GJB2 in German hearing impaired persons: mutation spectrum and detection of disequilibrium between M34T (c.101T>C) and -493del10.

Mutations in the connexin 26 gene (GJB2) are responsible for the major part of nonsyndromic autosomal recessive or apparently sporadic prelingual deafness in Caucasians (DFNB1). We screened 228 German hearing-impaired persons for mutations in the GJB2 gene by sequence analysis. Homozygous or compound heterozygous GJB2 mutations were detected in 38/228 (16.7%) of hearing impaired persons. The most frequently occurring mutation was the c.35delG mutation, which was found in 71.1% of the mutated alleles. The next frequent mutation detected in the group of hearing impaired persons was the c.101T>C mutation (9/76 alleles; 11.8%). One new mutation, c.567delA, was observed. We further studied the presence of a 10bp deletion in the 5' UTR of the GJB2 gene (c.-493del10) which was assumed to occur together with the c.101T>C mutation. Ten out of thirteen patients (76.9%) were found to be carriers of both the c.101T>C mutation and the 10bp variant and in 7/14 alleles a linkage disequilibrium between c.101T>C and the 10bp deletion was proven. In 4/14 alleles the linkage was ruled out and for the remaining 3 cases the phase determination was not possible. Seventy one controls were screened for the prevalence of Cx26 mutations and for the c.-493del10 variant. Heterozygosity frequency in the control group was for c.35delG 4.2%, for c.101T>C 1.4% and for c.-493del10 it was 5.6%.