Molecular genetic analysis of 30 families with Joubert syndrome

Joubert syndrome (JS) is rare recessive disorders characterized by the combination of hypoplasia/aplasia of the cerebellar vermis, thickened and elongated superior cerebellar peduncles, and a deep interpeduncular fossa which is defined by neuroimaging and is termed the 'molar tooth sign'. JS is genetically highly heterogeneous, with at least 29 disease genes being involved. To further understand the genetic causes of JS, we performed whole-exome sequencing in 24 newly recruited JS families. Together with six previously reported families, we identified causative mutations in 25 out of 30 (24 + 6) families (83.3%). We identified eight mutated genes in 27 (21 + 6) Japanese families, TMEM67 (7/27, 25.9%) and CEP290 (6/27, 22.2%) were the most commonly mutated. Interestingly, 9 of 12 CEP290 disease alleles were c.6012-12T>A (75.0%), an allele that has not been reported in non-Japanese populations. Therefore c.6012-12T>A is a common allele in the Japanese population. Importantly, one Japanese and one Omani families carried compound biallelic mutations in two distinct genes (TMEM67/RPGRIP1L and TMEM138/BBS1, respectively). BBS1 is the causative gene in Bardet-Biedl syndrome. These concomitant mutations led to severe and/or complex clinical features in the patients, suggesting combined effects of different mutant genes.

Different X-linked KDM5C mutations in affected male siblings: is maternal reversion error involved?

Genetic reversion is the phenomenon of spontaneous gene correction by which gene function is partially or completely rescued. However, it is unknown whether this mechanism always correctly repairs mutations, or is prone to error. We investigated a family of three boys with intellectual disability, and among them we identified two different mutations in KDM5C, located at Xp11.22, using whole-exome sequencing. Two affected boys have c.633delG and the other has c.631delC. We also confirmed de novo germline (c.631delC) and low-prevalence somatic (c.633delG) mutations in their mother. The two mutations are present on the same maternal haplotype, suggesting that a postzygotic somatic mutation or a reversion error occurred at an early embryonic stage in the mother, leading to switched KDM5C mutations in the affected siblings. This event is extremely unlikely to arise spontaneously (with an estimated probability of 0.39-7.5 × 10(-28) ), thus a possible reversion error is proposed here to explain this event. This study provides evidence for reversion error as a novel mechanism for the generation of somatic mutations in human diseases.

Delineation of clinical features in Wiedemann-Steiner syndrome caused by KMT2A mutations

Wiedemann-Steiner syndrome (WSS) is an autosomal dominant congenital anomaly syndrome characterized by hairy elbows, dysmorphic facial appearances (hypertelorism, thick eyebrows, downslanted and vertically narrow palpebral fissures), pre- and post-natal growth deficiency, and psychomotor delay. WSS is caused by heterozygous mutations in KMT2A (also known as MLL), a gene encoding a histone methyltransferase. Here, we identify six novel KMT2A mutations in six WSS patients, with four mutations occurring de novo. Interestingly, some of the patients were initially diagnosed with atypical Kabuki syndrome, which is caused by mutations in KMT2D or KDM6A, genes also involved in histone methylation. KMT2A mutations and clinical features are summarized in our six patients together with eight previously reported patients. Furthermore, clinical comparison of the two syndromes is discussed in detail.

Mutations in COG2 encoding a subunit of the conserved oligomeric golgi complex cause a congenital disorder of glycosylation

The conserved oligomeric Golgi (COG) complex is involved in intra-Golgi retrograde trafficking, and mutations in six of its eight subunits have been reported in congenital disorders of glycosylation (CDG). Here we report a patient showing severe acquired microcephaly, psychomotor retardation, seizures, liver dysfunction, hypocupremia, and hypoceruloplasminemia. Analysis of his serum glycoproteins revealed defects in both sialylation and galactosylation of glycan termini. Trio-based whole-exome sequencing identified two heterozygous mutations in COG2: a de novo frameshift mutation [c.701dup (p.Tyr234*)] and a missense mutation [c.1900T > G (p.Trp634Gly)]. Sequencing of cloned reverse-transcription polymerase chain reaction (RT-PCR) products revealed that both mutations were located on separate alleles, as expected, and that the mutant transcript harboring the frameshift mutation underwent degradation. The c.1900T > G (p.Trp634Gly) mutation is located in a domain highly conserved among vertebrates and was absent from both the public database and our control exomes. Protein expression of COG2, along with COG3 and COG4, was decreased in fibroblasts from the patient. Our data strongly suggest that these compound heterozygous mutations in COG2 are causative of CDG.

De novo EEF1A2 mutations in patients with characteristic facial features, intellectual disability, autistic behaviors and epilepsy

Eukaryotic elongation factor 1, alpha-2 (eEF1A2) protein is involved in protein synthesis, suppression of apoptosis, and regulation of actin function and cytoskeletal structure. EEF1A2 gene is highly expressed in the central nervous system and Eef1a2 knockout mice show the neuronal degeneration. Until now, only one missense mutation (c.208G > A, p.Gly70Ser) in EEF1A2 has been reported in two independent patients with neurological disease. In this report, we described two patients with de novo mutations (c.754G > C, p.Asp252His and c.364G > A, p.Glu122Lys) in EEF1A2 found by whole-exome sequencing. Common clinical features are shared by all four individuals: severe intellectual disability, autistic behavior, absent speech, neonatal hypotonia, epilepsy and progressive microcephaly. Furthermore, the two patients share the similar characteristic facial features including a depressed nasal bridge, tented upper lip, everted lower lip and downturned corners of the mouth. These data strongly indicate that a new recognizable disorder is caused by EEF1A2 mutations.

Coffin-Siris syndrome is a SWI/SNF complex disorder

Coffin-Siris syndrome (CSS) is a congenital disorder characterized by intellectual disability, growth deficiency, microcephaly, coarse facial features, and hypoplastic or absent fifth fingernails and/or toenails. We previously reported that five genes are mutated in CSS, all of which encode subunits of the switch/sucrose non-fermenting (SWI/SNF) ATP-dependent chromatin-remodeling complex: SMARCB1, SMARCA4, SMARCE1, ARID1A, and ARID1B. In this study, we examined 49 newly recruited CSS-suspected patients, and re-examined three patients who did not show any mutations (using high-resolution melting analysis) in the previous study, by whole-exome sequencing or targeted resequencing. We found that SMARCB1, SMARCA4, or ARID1B were mutated in 20 patients. By examining available parental samples, we ascertained that 17 occurred de novo. All mutations in SMARCB1 and SMARCA4 were non-truncating (missense or in-frame deletion) whereas those in ARID1B were all truncating (nonsense or frameshift deletion/insertion) in this study as in our previous study. Our data further support that CSS is a SWI/SNF complex disorder.

Exome sequencing in a family with an X-linked lethal malformation syndrome: clinical consequences of hemizygous truncating OFD1 mutations in male patients

Oral-facial-digital syndrome type 1 (OFD1; OMIM #311200) is an X-linked dominant disorder, caused by heterozygous mutations in the OFD1 gene and characterized by facial anomalies, abnormalities in oral tissues, digits, brain, and kidney; and male lethality in the first or second trimester pregnancy. We encountered a family with three affected male neonates having an 'unclassified' X-linked lethal congenital malformation syndrome. Exome sequencing of entire transcripts of the whole X chromosome has identified a novel splicing mutation (c.2388+1G > C) in intron 17 of OFD1, resulting in a premature stop codon at amino acid position 796. The affected males manifested severe multisystem complications in addition to the cardinal features of OFD1 and the carrier female showed only subtle features of OFD1. The present patients and the previously reported male patients from four families (clinical OFD1; Simpson-Golabi-Behmel syndrome, type 2 with an OFD1 mutation; Joubert syndrome-10 with OFD1 mutations) would belong to a single syndrome spectrum caused by truncating OFD1 mutations, presenting with craniofacial features (macrocephaly, depressed or broad nasal bridge, and lip abnormalities), postaxial polydactyly, respiratory insufficiency with recurrent respiratory tract infections in survivors, severe mental or developmental retardation, and brain malformations (hypoplasia or agenesis of corpus callosum and/or cerebellar vermis and posterior fossa abnormalities).

Homozygous c.14576G>A variant of RNF213 predicts early-onset and severe form of moyamoya disease

OBJECTIVE

RNF213 was recently reported as a susceptibility gene for moyamoya disease (MMD). Our aim was to clarify the correlation between the RNF213 genotype and MMD phenotype.

METHODS

The entire coding region of the RNF213 gene was sequenced in 204 patients with MMD, and corresponding variants were checked in 62 pairs of parents, 13 mothers and 4 fathers of the patients, and 283 normal controls. Clinical information was collected. Genotype-phenotype correlations were statistically analyzed.

RESULTS

The c.14576G>A variant was identified in 95.1% of patients with familial MMD, 79.2% of patients with sporadic MMD, and 1.8% of controls, thus confirming its association with MMD, with an odds ratio of 259 and p < 0.001 for either heterozygotes or homozygotes. Homozygous c.14576G>A was observed in 15 patients but not in the controls and unaffected parents. The incidence rate for homozygotes was calculated to be >78%. Homozygotes had a significantly earlier age at onset compared with heterozygotes or wild types (median age at onset 3, 7, and 8 years, respectively). Of homozygotes, 60% were diagnosed with MMD before age 4, and all had infarctions as the first symptom. Infarctions at initial presentation and involvement of posterior cerebral arteries, both known as poor prognostic factors for MMD, were of significantly higher frequency in homozygotes than in heterozygotes and wild types. Variants other than c.14576G>A were not associated with clinical phenotypes.

CONCLUSIONS

The homozygous c.14576G>A variant in RNF213 could be a good DNA biomarker for predicting the severe type of MMD, for which early medical/surgical intervention is recommended, and may provide a better monitoring and prevention strategy.

Exome sequencing of two patients in a family with atypical X-linked leukodystrophy

We encountered a family with two boys similarly showing brain atrophy with reduced white matter, hypoplasia of the brain stem and corpus callosum, spastic paralysis, and severe growth and mental retardation without speaking a word. The phenotype of these patients was not compatible with any known type of syndromic leukodystrophy. Presuming an X-linked disorder, we performed next-generation sequencing (NGS) of the transcripts of the entire X chromosome. A single lane of exome NGS in each patient was sufficient. Six potential mutations were found in both affected boys. Two missense mutations, including c.92T>C (p.V31A) in L1CAM, were potentially pathogenic, but this remained inconclusive. The other four could be excluded. Because the patients did not show adducted thumbs or hydrocephalus, the L1CAM change in this family can be interpreted as different scenarios. Personal genome analysis using NGS is certainly powerful, but interpretation of the data can be a substantial challenge requiring a lot of tasks.

Paternal mosaicism of an STXBP1 mutation in OS

Ohtahara syndrome (OS) is one of the most severe and earliest forms of epilepsy. We have recently identified that the de novo mutations of STXBP1 are important causes for OS. Here we report a paternal somatic mosaicism of an STXBP1 mutation. The affected daughter had onset of spasms at 1 month of age, and interictal electroencephalogram showed suppression-burst pattern, leading to the diagnosis of OS. She had a heterozygous c.902+5G>A mutation of STXBP1, which affects donor splicing of exon 10, resulting in 138-bp insertion of intron 10 sequences in the transcript. The mutant transcript had a premature stop codon, and was degraded by nonsense-mediated mRNA decay in lymphoblastoid cells derived from the patient. High-resolution melting analysis of clinically unaffected parental DNAs suggested that the father was somatic mosaic for the mutation, which was also suggested by sequencing. Cloning of PCR products amplified with the paternal DNA samples extracted from blood, saliva, buccal cells, and nails suggested that 5.3%, 8.7%, 11.9%, and 16.9% of alleles harbored the mutation, respectively. This is a first report of somatic mosaicism of an STXBP1 mutation, which has implications in genetic counseling of OS.

Suppressive effect of endogenous regucalcin on guanosine triphosphatase activity in rat liver nucleus

The effect of regucalcin, a regulatory protein of Ca2+ signaling, on guanosine triphosphatase (GTPase) activity in the nuclei of rat liver was investigated. GTPase activity was significantly increased by the addition of CaCl2 (50 microm) in the enzyme reaction mixture. This increase was not seen in the presence of trifluoperazine (25 microM), an antagonist of calmodulin, which could decrease nuclear GTPase activity, suggesting that nuclear endogenous calmodulin is involved in an increase in the enzyme activity related to Ca2+ addition. The presence of regucalcin (0.5 microM) in the enzyme reaction mixture caused a significant decrease in nuclear GTPase activity. The enzyme activity was significantly raised in the presence of anti-regucalcin monoclonal antibody (25 and 50 ng/ml) in the reaction mixture. This increase was completely abolished by the addition of regucalcin (0.5 microM). Also, the effect of regucalcin addition in increasing nuclear GTPase activity was seen in the presence of EGTA (0.1 mM), a chelator of Ca2+. The present study demonstrates that endogenous regucalcin has a suppressive effect on GTPase activity in the nuclei of rat liver.

Translocation of regucalcin to rat liver nucleus: involvement of nuclear protein kinase and protein phosphatase regulation

The translocation of regucalcin to the nuclei of normal rat liver was investigated. The existence of endogenous regucalcin in isolated liver nuclei was confirmed by Western blotting using anti-regucalcin antibody. Nuclear translocation of regucalcin was estimated by sodium sulfate-polyacrylamide gel electrophoresis analysis. When isolated liver nuclei were incubated in the presence of exogenous regucalcin (50 microg/ml; 1.5 microM), potent band for regucalcin was found in the nuclei, indicating that the protein is translocated into the nucleus. This translocation was an early event. Nuclear regucalcin translocation was not appreciably changed in the presence of adenosine 5'-triphosphate (2 mM), guanosine 5'-triphosphate (2 mM), calcium chloride (0.1 mM), and the lectin wheat germ agglutinin (50 or 100 microg/ml), suggesting that its translocation is not mediated through nuclear localization signal. Moreover, Ca2+-dependent protein kinase and protein tyrosine phosphatase activities in isolated liver nuclei were significantly increased in the presence of anti-regucalcin monoclonal antibody (100 ng/ml) in the enzyme reaction mixture, and these increases were completely abolished by the addition of regucalcin (50 microg/ml). This study demonstrates that regucalcin is translocated into liver nucleus, and that it can regulate the nuclear function.

Insight into acid-mediated asymmetric spirocyclization in the presence of a chiral diol

Asymmetric spirocyclization based on intramolecular conjugate addition using a combination of a Lewis acid and an optically active cyclohexane-1,2-diol has been studied in connection with 1) the effect of substituents on the cyclohexane-1,2-diol and 2) the effect of substituents on the substrate. This reaction was found to be both thermodynamically and kinetically controlled under restricted conditions.

Suppressive effect of endogenous regucalcin on the enhancement of protein synthesis and aminoacyl-tRNA synthetase activity in regenerating rat liver

The effect of regucalcin, which is a regulatory protein in Ca2+ signaling, on protein synthesis in regenerating rat liver was investigated. Protein synthesis was assayed in a reaction mixture containing the 5500 g supernatant fraction in the presence of [3H]leucine. The presence of anti-regucalcin monoclonal antibody (100 and 150 ng/ml) in the reaction mixture caused a significant elevation of in vitro protein synthesis. This elevation was completely prevented by the addition of regucalcin (1.0 microM). Regenerating liver after partial hepatectomy (HPX) induced a significant increase in protein synthesis. This increase was significantly enhanced by the presence of anti-regucalcin monoclonal antibody (100 ng/ ml). This enhancement was remarkable at 24 and 48 h after HPX. [3H]Leucyl-tRNA synthetase activity in the 105000 g supernatant fraction (cytosol) of the liver homogenate from normal rats was significantly raised by the presence of antibody (100 and 150 ng/ml) in the enzyme reaction mixture. Regenerating liver caused a significant elevation of the enzyme activity at 24, 48, and 72 h after HPX. This elevating was significantly enhanced in the presence of antibody (100 ng/ml). The present study suggests that endogenous regucalcin has a suppressive effect on the enhancement of protein synthesis in regenerating rat liver with a proliferative cells.

Role of endogenous regucalcin in the regulation of Ca(2+)-ATPase activity in rat liver nuclei

The role of endogenous regucalcin in the regulation of Ca(2+)-ATPase, a Ca(2+) sequestrating enzyme, in rat liver nuclei was investigated. Nuclear Ca(2+)-ATPase activity was significantly reduced by the addition of regucalcin (0.1-0.5 microM) into the enzyme reaction mixture. The presence of anti-regucalcin monoclonal antibody (25 or 50 ng/ml) caused a significant elevation of Ca(2+)-ATPase activity; this effect was completely abolished by the addition of regucalcin (0.1 microM). The effect of anti-regucalcin antibody (50 ng/ml) in increasing Ca(2+)-ATPase activity was completely prevented by the presence of thapsigargin (10(-6) M), an inhibitor of Ca(2+) sequestrating enzyme, N-ethylmaleimide (1 mM), a modifying reagent of thiol groups, or vanadate (10(-5) M), an inhibitor of phosphorylation of the enzyme by ATP, which revealed an inhibitory effect on nuclear Ca(2+)-ATPase activity. Meanwhile, the effect of anti-regucalcin antibody (50 ng/ml) was significantly enhanced by the addition of calmodulin (5 microg/ml), which could increase nuclear Ca(2+)-ATPase activity. In addition, the effect of antibody (50 ng/ml) was significantly reduced by the presence of trifluoperazine (20 microM), an antagonist of calmodulin. These results suggest that the endogenous regucalcin in liver nuclei has a suppressive effect on nuclear Ca(2+)-ATPase activity, and that regucalcin can inhibit an activating effect of calmodulin on the enzyme.