ALS-associated VRK1 R321C mutation causes proteostatic imbalance and mitochondrial defects in iPSC-derived motor neurons.

Vaccinia-related kinase 1 (VRK1) is a gene which has been implicated in the pathological process of a broad range of neurodevelopmental disorders as well as neuropathies, such as Amyotrophic Lateral Sclerosis (ALS). Here we report a family presenting ALS in an autosomal recessive mode of inheritance, segregating with a homozygous missense mutation located in VRK1 gene (p.R321C; Arg321Cys). Proteomic analyses from iPSC-derived motor neurons identified 720 proteins eligible for subsequent investigation, and our exploration of protein profiles revealed significant enrichments in pathways such as mTOR signaling, E2F, MYC targets, DNA repair response, cell proliferation and energetic metabolism. Functional studies further validated such alterations, showing that affected motor neurons presented decreased levels of global protein output, ER stress and downregulation of mTOR signaling. Mitochondrial alterations also pointed to decreased reserve capacity and increased non-mitochondrial oxygen consumption. Taken together, our results present the main pathological alterations associated with VRK1 mutation in ALS.

Transcriptome of iPSC-derived neuronal cells reveals a module of co-expressed genes consistently associated with autism spectrum disorder.

Evaluation of expression profile in autism spectrum disorder (ASD) patients is an important approach to understand possible similar functional consequences that may underlie disease pathophysiology regardless of its genetic heterogeneity. Induced pluripotent stem cell (iPSC)-derived neuronal models have been useful to explore this question, but larger cohorts and different ASD endophenotypes still need to be investigated. Moreover, whether changes seen in this in vitro model reflect previous findings in ASD postmortem brains and how consistent they are across the studies remain underexplored questions. We examined the transcriptome of iPSC-derived neuronal cells from a normocephalic ASD cohort composed mostly of high-functioning individuals and from non-ASD individuals. ASD patients presented expression dysregulation of a module of co-expressed genes involved in protein synthesis in neuronal progenitor cells (NPC), and a module of genes related to synapse/neurotransmission and a module related to translation in neurons. Proteomic analysis in NPC revealed potential molecular links between the modules dysregulated in NPC and in neurons. Remarkably, the comparison of our results to a series of transcriptome studies revealed that the module related to synapse has been consistently found as upregulated in iPSC-derived neurons-which has an expression profile more closely related to fetal brain-while downregulated in postmortem brain tissue, indicating a reliable association of this network to the disease and suggesting that its dysregulation might occur in different directions across development in ASD individuals. Therefore, the expression pattern of this network might be used as biomarker for ASD and should be experimentally explored as a therapeutic target.

New SMS mutation leads to a striking reduction in spermine synthase protein function and a severe form of Snyder-Robinson X-linked recessive mental retardation syndrome.

We report the identification of a novel mutation at a highly conserved residue within the N-terminal region of spermine synthase (SMS) in a second family with Snyder-Robinson X-linked mental retardation syndrome (OMIM 309583). This missense mutation, p.G56S, greatly reduces SMS activity and leads to severe epilepsy and cognitive impairment. Our findings contribute to a better delineation and expansion of the clinical spectrum of Snyder-Robinson syndrome, support the important role of the N-terminus in the function of the SMS protein, and provide further evidence for the importance of SMS activity in the development of intellectual processing and other aspects of human development.

Decreased cellular uptake and metabolism in Allan-Herndon-Dudley syndrome (AHDS) due to a novel mutation in the MCT8 thyroid hormone transporter.

We report a novel 1 bp deletion (c.1834delC) in the MCT8 gene in a large Brazilian family with Allan-Herndon-Dudley syndrome (AHDS), an X linked condition characterised by severe mental retardation and neurological dysfunction. The c.1834delC segregates with the disease in this family and it was not present in 100 control chromosomes, further confirming its pathogenicity. This mutation causes a frameshift and the inclusion of 64 additional amino acids in the C-terminal region of the protein. Pathogenic mutations in the MCT8 gene, which encodes a thyroid hormone transporter, results in elevated serum triiodothyronine (T3) levels, which were confirmed in four affected males of this family, while normal levels were found among obligate carriers. Through in vitro functional assays, we showed that this mutation decreases cellular T3 uptake and intracellular T3 metabolism. Therefore, the severe neurological defects present in the patients are due not only to deficiency of intracellular T3, but also to altered metabolism of T3 in central neurones. In addition, the severe muscle hypoplasia observed in most AHDS patients may be a consequence of high serum T3 levels.

Molecular analysis of collagen XVIII reveals novel mutations, presence of a third isoform, and possible genetic heterogeneity in Knobloch syndrome.

Knobloch syndrome (KS) is a rare disease characterized by severe ocular alterations, including vitreoretinal degeneration associated with retinal detachment and occipital scalp defect. The responsible gene, COL18A1, has been mapped to 21q22.3, and, on the basis of the analysis of one family, we have demonstrated that a mutation affecting only one of the three COL18A1 isoforms causes this phenotype. We report here the results of the screening of both the entire coding region and the exon-intron boundaries of the COL18A1 gene (which includes 43 exons), in eight unrelated patients with KS. Besides 20 polymorphic changes, we identified 6 different pathogenic changes in both alleles of five unrelated patients with KS (three compound heterozygotes and two homozygotes). All are truncating mutations leading to deficiency of one or all collagen XVIII isoforms and endostatin. We have verified that, in exon 41, the deletion c3514-3515delCT, found in three unrelated alleles, is embedded in different haplotypes, suggesting that this mutation has occurred more than once. In addition, our results provide evidence of nonallelic genetic heterogeneity in KS. We also show that the longest human isoform (NC11-728) is expressed in several tissues (including the human eye) and that lack of either the short variant or all of the collagen XVIII isoforms causes similar phenotypes but that those patients who lack all forms present more-severe ocular alterations. Despite the small sample size, we found low endostatin plasma levels in those patients with mutations leading to deficiency of all isoforms; in addition, it seems that absence of all collagen XVIII isoforms causes predisposition to epilepsy.

A polymorphism in endostatin, an angiogenesis inhibitor, predisposes for the development of prostatic adenocarcinoma.

We have performed association studies between a novel coding single nucleotide polymorphism (D104N) in endostatin, one of the most potent inhibitors of angiogenesis, and prostate cancer. We observed that heterozygous N104 individuals have a 2.5 times increased chance of developing prostate cancer as compared with homozygous D104 subjects (odds ratio, 2.4; 95% confidence interval, 1.4-4.16). Modeling of the endostatin mutant showed that the N104 protein is stable. These results together with the observation that residue 104 is evolutionary conserved lead us to propose that: (a) the DNA segment containing this residue might contain a novel interaction site to a yet unknown receptor; and (b) the presence of N104 impairs the function of endostatin.

Collagen XVIII, containing an endogenous inhibitor of angiogenesis and tumor growth, plays a critical role in the maintenance of retinal structure and in neural tube closure (Knobloch syndrome).

Knobloch syndrome (KS) is an autosomal recessive disorder defined by the occurrence of high myopia, vitreoretinal degeneration with retinal detachment, macular abnormalities and occipital encephalocele. The KS causative gene had been assigned to a 4.3 cM interval at 21q22.3 by linkage analysis of a large consanguineous Brazilian family. We reconstructed the haplotypes of this family with ten additional markers (five were novel) and narrowed the candidate interval to a region of <245 kb, which contains 24 expressed sequence tags, the KIAA0958 gene and the 5' end of the COL18A1 gene. We identified a homozygous mutation at the AG consensus acceptor splice site of COL18A1 intron 1 exclusively among the 12 KS patients, which was not found among 140 control chromosomes. This mutation predicts the creation of a stop codon in exon 4 and therefore the truncation of the alpha1(XVIII) collagen short form, which was expressed in human adult retina. These findings provide evidence that KS is caused by mutations in COL18A1 which, therefore, has a major role in determining the retinal structure as well as in the closure of the neural tube. Therefore, we show for the first time that the absence of a collagen isoform impairs embryonic cell proliferation and/or migration as a primary or secondary effect.

Linkage analysis in a large Brazilian family with van der Woude syndrome suggests the existence of a susceptibility locus for cleft palate at 17p11.2-11.1.

van der Woude syndrome (VWS), which has been mapped to 1q32-41, is characterized by pits and/or sinuses of the lower lip, cleft lip/palate (CL/P), cleft palate (CP), bifid uvula, and hypodontia (H). The expression of VWS, which has incomplete penetrance, is highly variable. Both the occurrence of CL/P and CP within the same genealogy and a recurrence risk <40% for CP among descendants with VWS have suggested that the development of clefts in this syndrome is influenced by modifying genes at other loci. To test this hypothesis, we have conducted linkage analysis in a large Brazilian kindred with VWS, considering as affected the individuals with CP, regardless of whether it is associated with other clinical signs of VWS. Our results suggest that a gene at 17p11.2-11.1, together with the VWS gene at 1p32-41, enhances the probability of CP in an individual carrying the two at-risk genes. If this hypothesis is confirmed in other VWS pedigrees, it will represent one of the first examples of a gene, mapped through linkage analysis, which modifies the expression of a major gene. It will also have important implications for genetic counseling, particularly for more accurately predicting recurrence risks of clefts among the offspring of patients with VWS.

Clinical spectrum of fibroblast growth factor receptor mutations.

During the last few years, it has been demonstrated that some syndromic craniosynostosis and short-limb dwarfism syndromes, a heterogeneous group comprising of 11 distinct clinical entities, are caused by mutations in one of three fibroblast growth factor receptor genes (FGFR1, FGFR2, and FGFR3). The present review list all mutations described to date in these three genes and the phenotypes associated with them. In addition, the tentative phenotype-genotype correlation is discussed, including the most suggested causative mechanisms for these conditions.

A new three allele polymorphism at distal 21q22.3, a region relatively devoid of polymorphic markers. Mutations in brief no. 212. Online.

We amplified 305bp of the 3'UT region of COL18A1 from 62 healthy chromosomes from Caucasian individuals. SSCP analysis of these PCR products allowed us to identify 3 alleles which were confirmed through sequencing analysis and ASO. The heterozigosity found for this polymorphic region is 74.2%, and mendelian inheritance was demonstrated in 5 two/three generation families. This polymorphism, located in a region relatively devoid of microsatellites, will be very useful for linkage analysis, particularly for narrowing down candidate regions for genes mapped in this area.

Presence of the Apert canonical S252W FGFR2 mutation in a patient without severe syndactyly.

Apert syndrome, characterised by craniosynostosis, craniofacial anomalies, and symmetrical syndactyly of the digits (cutaneous and bony fusion), has been associated with two canonical mutations in the FGFR2 gene (S252W, P253R) in the great majority of cases. Since these two alterations have been observed exclusively among these patients, it has been suggested that the S252W and P253R changes may play an important role in the occurrence of syndactyly. In order to verify whether the mutations S252W and P253R could also cause a milder phenotype, without involvement of the limbs, we have screened 22 patients with clinical characteristics compatible with Crouzon or Pfeiffer syndrome for these two particular changes. Surprisingly, we identified a Pfeiffer-like patient with the mutation S252W, and therefore we have shown for the first time the occurrence of one of the canonical Apert mutations without severe abnormalities of the upper and lower extremities.

Description of a new mutation and characterization of FGFR1, FGFR2, and FGFR3 mutations among Brazilian patients with syndromic craniosynostoses.

Dominant mutations in three fibroblast growth factor receptor genes (FGFRs1-3) cause Crouzon, Jackson-Weiss, Pfeiffer, and Apert syndromes. In the present study, 50 Brazilian patients with these four syndromes (27 Apert, 17 Crouzon, 5 Pfeiffer, and 1 Jackson-Weiss patients) were screened for mutations in the FGFR1-3 genes. Except for one, all the Apert patients had either S252W (n = 16) or P253R (n = 10) mutations. The remaining Apert case is atypical with a mutation altering the splice site of FGFR2 exon IIIc. The Pfeiffer patients had mutations in one of the FGFR genes: three in FGFR2, one in FGFR1, and one in FGFR3. In contrast, only 8 of the 17 Crouzon patients studied had a mutation in either FGFR2 (n = 7) or FGFR3 locus (n = 1). Mutations in the FGFR2 locus account for most (93%) of our syndromic craniosynostotic cases, whereas 5% had mutations in the FGFR3 locus and only 2% had mutations in the FGFR1 gene. Except for one, all the other mutations were reported previously in craniosynostotic patients from other populations. Interestingly, the mutation C278F, previously described in Crouzon and Pfeiffer cases, was here identified in a familial case with Jackson-Weiss. Also, unexpectedly, a common mutation altering the splice site of the FGFR2 exon IIIc was found in one Apert and two Pfeiffer patients. In addition, we identified a new mutation (A337P) in the FGFR2 exon IIIc associated with Crouzon phenotype.

The seventh form of autosomal recessive limb-girdle muscular dystrophy is mapped to 17q11-12.

The group of autosomal recessive (AR) muscular dystrophies includes, among others, two main clinical entities, the limb-girdle muscular dystrophies (LGMDs) and the distal muscular dystrophies. The former are characterized mainly by muscle wasting of the upper and lower limbs, with a wide range of clinical severity. This clinical heterogeneity has been demonstrated at the molecular level, since the genes for six AR forms have been cloned and/or have been mapped to 15q15.1 (LGMD2A), 2p12-16 (LGMD2B), 13q12 (LGMD2C), 17q12-q21.33 (LGMD2D),4q12 (LGMD2E), and 5q33-34 (LGMD2F). The AR distal muscular dystrophies originally included two subgroups, Miyoshi myopathy, characterized mainly by extremely elevated serum creatine kinase (CK) activity and by a dystrophic muscle pattern, and Nonaka myopathy, which is distinct from the others because of the normal to slightly elevated serum CK levels and a myopathic muscle pattern with rimmed vacuoles. With regard to our unclassified AR LGMD families, analysis of the affected sibs from one of them (family LG61) revealed some clinical and laboratory findings (early involvement of the distal muscles, mildly elevated serum CK levels, and rimmed vacuoles in muscle biopsies) that usually are not observed in the analysis of patients with LGMD2A-LGMD2F. In the present investigation, through a genomewide search in family LG61, we demonstrated linkage of the allele causing this form of muscular dystrophy to a 3-cM region on 17q11-12. We suggest that this form, which, interestingly, clinically resembles AR Kugelberg-Welander disease, should be classified as LGMD2G. In addition, our results indicate the existence of still another locus causing severe LGMD.

A gene which causes severe ocular alterations and occipital encephalocele (Knobloch syndrome) is mapped to 21q22.3.

Knobloch syndrome (KS), characterized by high myopia, vitreoretinal degeneration with retinal detachment, macular abnormalities and occipital encephalocele, was recently confirmed as autosomal recessive. Here we report the assignment of the gene for this syndrome to 21q22.3 with the marker D21S171 through homozygosity mapping in a highly inbred Brazilian family with 11 affected individuals. A total of nine markers spanning a region of 15.2 cM of the chromosome 21q22.3 were tested and the candidate region was restricted to an interval of 4.3 cM.