Rocío Sánchez-Alcudia

Targeted Next-Generation Sequencing Improves the Diagnosis of Autosomal Dominant Retinitis Pigmentosa in Spanish Patients

PURPOSE Next-generation sequencing (NGS) has been demonstrated to be an effective strategy for the detection of mutations in retinal dystrophies, a group of inherited diseases that are highly heterogeneous. Therefore, the aim of this study is the application of an NGS-based approach in a Spanish cohort of autosomal dominant retinitis pigmentosa (RP) patients to find out causative mutations. METHODS Index cases of 59 Spanish families with initial diagnosis of autosomal dominant RP and unsuccessfully studied for mutations in the most common RP causal genes, were selected for application of a NGS-based approach with a custom panel for 73 genes related to retinal dystrophies. Candidate variants were select based on frequency, pathogenicity, inherited model, and phenotype. Subsequently, confirmation by Sanger sequencing, cosegregation analysis, and population studies, was applied for determining the implication of those variants in the pathology. RESULTS Overall 31 candidate variants were selected. From them, 17 variants were considered as mutations causative of the disease, 64% (11/17) of them were novel and 36% (6/17) were known RP-related mutations. Therefore, applying this technology16 families were characterized rendering a mutation detection rate of 27% (16/59). Of them, 5% (3/59) of cases displayed mutations in recessive or X-linked genes (ABCA4, RPGR, and RP2) allowing a genetic and clinical reclassification of those families. Furthermore, seven novel variants with uncertain significance and seven novel variants probably not causative of disease were also found. CONCLUSIONS This NGS strategy is a fast, effective, and reliable tool to detect known and novel mutations in autosomal dominant RP patients allowing genetic reclassification in some cases and increasing the knowledge of pathogenesis in retinal dystrophies.

Panel-based NGS Reveals Novel Pathogenic Mutations in Autosomal Recessive Retinitis Pigmentosa.

Retinitis pigmentosa (RP) is a group of inherited progressive retinal dystrophies (RD) characterized by photoreceptor degeneration. RP is highly heterogeneous both clinically and genetically, which complicates the identification of causative genes and mutations. Targeted next-generation sequencing (NGS) has been demonstrated to be an effective strategy for the detection of mutations in RP. In our study, an in-house gene panel comprising 75 known RP genes was used to analyze a cohort of 47 unrelated Spanish families pre-classified as autosomal recessive or isolated RP. Disease-causing mutations were found in 27 out of 47 cases achieving a mutation detection rate of 57.4%. In total, 33 pathogenic mutations were identified, 20 of which were novel mutations (60.6%). Furthermore, not only single nucleotide variations but also copy-number variations, including three large deletions in the USH2A and EYS genes, were identified. Finally seven out of 27 families, displaying mutations in the ABCA4, RP1, RP2 and USH2A genes, could be genetically or clinically reclassified. These results demonstrate the potential of our panel-based NGS strategy in RP diagnosis.

Genotype–phenotype correlations in sepiapterin reductase deficiency. A splicing defect accounts for a new phenotypic variant

Sepiapterin reductase (SR) catalyzes the final step in the de novo synthesis of tetrahydrobiopterin, essential cofactor for phenylalanine, tyrosine, and tryptophan hydroxylases. SR deficiency is a very rare disease resulting in monoamine neurotransmitter depletion. Most patients present with clinical symptoms before the first year of age corresponding to a dopa-responsive dystonia phenotype with diurnal fluctuations, although some patients exhibit more complex motor and neurological phenotypes. Herein, we describe four new cases from Spain, their clinical phenotype and the biochemical and genetic analyses. Two mutations in the SPR gene were functionally expressed to provide a basis to establish genotype–phenotype correlations. Mutation c.751A>T is functionally null, correlating with the severe phenotype observed. The novel mutation c.304G>T was identified in three siblings with a strikingly mild phenotype without cognitive delay and close to asymptomatic in the eldest sister. Minigene analysis demonstrated that this mutation located in the last nucleotide of exon 1 affects splicing although some normal transcripts can be produced, resulting in the missense mutant p.G102C that retains partial activity. These results may account for the mild phenotype and the variable clinical presentations observed, which could depend on interindividual differences in relative abundance of correctly spliced and aberrant transcripts.

Whole Exome Sequencing Reveals ZNF408 as a New Gene Associated With Autosomal Recessive Retinitis Pigmentosa with Vitreal Alterations

Retinitis pigmentosa (RP) is a group of progressive inherited retinal dystrophies that cause visual impairment as a result of photoreceptor cell death. RP is heterogeneous, both clinically and genetically making difficult to establish precise genotype-phenotype correlations. In a Spanish family with autosomal recessive RP (arRP), homozygosity mapping and whole-exome sequencing led to the identification of a homozygous mutation (c.358_359delGT; p.Ala122Leufs*2) in the ZNF408 gene. A screening performed in 217 additional unrelated families revealed another homozygous mutation (c.1621C>T; p.Arg541Cys) in an isolated RP case. ZNF408 encodes a transcription factor that harbors 10 predicted C2H2-type fingers thought to be implicated in DNA binding. To elucidate the ZNF408 role in the retina and the pathogenesis of these mutations we have performed different functional studies. By immunohistochemical analysis in healthy human retina, we identified that ZNF408 is expressed in both cone and rod photoreceptors, in a specific type of amacrine and ganglion cells, and in retinal blood vessels. ZNF408 revealed a cytoplasmic localization and a nuclear distribution in areas corresponding with the euchromatin fraction. Immunolocalization studies showed a partial mislocalization of the p.Arg541Cys mutant protein retaining part of the WT protein in the cytoplasm. Our study demonstrates that ZNF408, previously associated with Familial Exudative Vitreoretinopathy (FEVR), is a new gene causing arRP with vitreous condensations supporting the evidence that this protein plays additional functions into the human retina.

The molecular landscape of propionic acidemia and methylmalonic aciduria in Latin America.

In this work, we review the clinical and genetic data in 14 Latin American propionic acidemia (PA) and 15 methylmalonic aciduria (MMAuria) patients. In the PA patients, we have identified four different changes in the PCCA gene, including one novel one (c.414+5G>A) affecting the splicing process. The PCCB mutational spectrum included two prevalent changes accounting for close to 60% of the mutant alleles studied and one novel change (c.494G>C) which by functional analysis is clearly pathogenic. We have also identified the deep intronic change c.654+462A>G, and the results of the antisense treatment in the patient’s cell line confirmed the functional recovery of PCC activity. All PA patients bearing out-of-frame mutations presented the disease earlier while patients bearing in hemizygous fashion p.E168K and p.R165W presented the disease later. Regarding the MMAuria patients, we have found three novel mutations in the MUT gene (c.1068G>A, c.1587_1594del8 and c.593delA) and one in the MMAB gene (c.349-1 G>C). Two patients with MMAuria with homocystinuria cblC type are carriers of the frequent c.271dupA mutation. All mut0, cblB and cblC patients presented the symptoms early and in general had more neurological complications, while cblA and mut- patients exhibited a late-onset presentation, and in general the long-term outcome was better. The results presented in this work emphasize the importance of the genetic analysis of the patients not only for diagnostic purposes but also to research into novel therapies based on the genotype.

Functional and Structural Analysis of Five Mutations Identified in Methylmalonic Aciduria cbIB Type

ATP:cob(I)alamin adenosyltransferase (ATR, E.C.2.5.1.17) converts reduced cob(I)alamin to the adenosylcobalamin cofactor. Mutations in the MMAB gene encoding ATR are responsible for the cblB type methylmalonic aciduria. Here we report the functional analysis of five cblB mutations to determine the underlying molecular basis of the dysfunction. The transcriptional profile along with minigenes analysis revealed that c.584G>A, c.349‐1G>C, and c.290G>A affect the splicing process. Wild‐type ATR and the p.I96T (c.287T>C) and p.R191W (c.571C>T) mutant proteins were expressed in a prokaryote and a eukaryotic expression systems. The p.I96T protein was enzymatically active with a KM for ATP and KD for cob(I)alamin similar to wild‐type enzyme, but exhibited a 40% reduction in specific activity. Both p.I96T and p.R191W mutant proteins are less stable than the wild‐type protein, with increased stability when expressed under permissive folding conditions. Analysis of the oligomeric state of both mutants showed a structural defect for p.I96T and also a significant impact on the amount of recovered mutant protein that was more pronounced for p.R191W that, along with the structural analysis, suggest they might be misfolded. These results could serve as a basis for the implementation of pharmacological therapies aimed at increasing the residual activity of this type of mutations. Hum Mutat 31:1033–1042, 2010.

Analysis of the PRPF31 Gene in Spanish Autosomal Dominant Retinitis Pigmentosa Patients: A Novel Genomic Rearrangement

Purpose The aim was to determine the prevalence of PRPF31 mutations in a cohort of Spanish autosomal dominant retinitis pigmentosa (adRP) families to deepen knowledge of the pathogenic mechanisms underlying the disease and to assess genotype-phenotype correlations. Methods A cohort of 211 adRP patients was screened for variants in PRPF31 by using a combined strategy comprising next-generation sequencing approaches and copy-number variation (CNV) analysis. Quantitative RT-PCR and CNV analysis of the regulatory MSR1 element were also performed to assess PRPF31 gene expression. Phenotype was assessed by using ophthalmologic examination protocols. Results Fifteen different causative mutations and genomic rearrangements were identified, revealing five novel mutations. Prevalence of PRPF31 mutations, genomic rearrangements, and lack of penetrance were 7.6%, 1.9%, and 66.7%, respectively. Interestingly, we identified a tandem duplication and a partial PRPF31 deletion in different affected individuals from the same family. PRPF31 gene expression was significantly decreased in symptomatic cases carrying either PRPF31 duplication or deletion as compared to controls. The 4 MSR1 allele in cis with the PRPF31 wild-type allele was apparently a protective factor. The mutated phenotype varied from no symptoms to typical retinitis pigmentosa with variable onset and course depending on the kind of mutation, with the duplication case the most severe. Conclusions In view of the high genetic heterogeneity of PRPF31 mutations, the screening must include the entire gene, as well as CNV assays, to detect large rearrangements. This is the first report of a variable phenotype correlation as well as a gross duplication and deletion within the same family.

Identification of the Photoreceptor Transcriptional Co-Repressor SAMD11 as Novel Cause of Autosomal Recessive Retinitis Pigmentosa.

Retinitis pigmentosa (RP), the most frequent form of inherited retinal dystrophy is characterized by progressive photoreceptor degeneration. Many genes have been implicated in RP development, but several others remain to be identified. Using a combination of homozygosity mapping, whole-exome and targeted next-generation sequencing, we found a novel homozygous nonsense mutation in SAMD11 in five individuals diagnosed with adult-onset RP from two unrelated consanguineous Spanish families. SAMD11 is ortholog to the mouse major retinal SAM domain (mr-s) protein that is implicated in CRX-mediated transcriptional regulation in the retina. Accordingly, protein-protein network analysis revealed a significant interaction of SAMD11 with CRX. Immunoblotting analysis confirmed strong expression of SAMD11 in human retina. Immunolocalization studies revealed SAMD11 was detected in the three nuclear layers of the human retina and interestingly differential expression between cone and rod photoreceptors was observed. Our study strongly implicates SAMD11 as novel cause of RP playing an important role in the pathogenesis of human degeneration of photoreceptors.

Contribution of mutation load to the intrafamilial genetic heterogeneity in a large cohort of Spanish retinal dystrophies families.

PURPOSE The aim of this study was to deepen our knowledge on the basis of intrafamilial genetic heterogeneity of inherited retinal dystrophies (RD) to further discern the contribution of individual alleles to the pathology. METHODS Families with intrafamilial locus and/or allelic heterogeneity were selected from a cohort of 873 characterized of 2468 unrelated RD families. Clinical examination included visual field assessments, electrophysiology, fundus examination, and audiogram. Molecular characterization was performed using a combination of different methods: genotyping microarray, single strand conformational polymorphism (SSCP), denaturing high pressure liquid chromatography (dHPLC), high resolution melt (HRM), multiplex ligation-dependent probe amplification (MLPA), Sanger sequencing, whole-genome homozygosity mapping, and next-generation sequencing (NGS). RESULTS Overall, intrafamilial genetic heterogeneity was encountered in a total of 8 pedigrees. There were 5 of 873 families (~0.6%) with causative mutations in more than one gene (locus heterogeneity), involving the genes: (1) USH2A, RDH12, and TULP1; (2) PDE6B and a new candidate gene; (3) CERKL and CRB1; (4) BBS1 and C2orf71; and (5) ABCA4 and CRB1. Typically, in these cases, each mutated gene was associated with different phenotypes. In the 3 other families (~0.35%), different mutations in the same gene (allelic heterogeneity) were found, including the frequent RD genes ABCA4 and CRB1. CONCLUSIONS This systematic research estimates that the frequency of overall mutation load promoting RD intrafamilial heterogeneity in our cohort of Spanish families is almost 1%. The identification of the genetic mechanisms underlying RD locus and allelic heterogeneity is essential to discriminate the real contribution of the monoallelic mutations to the disease, especially in the NGS era. Moreover, it is decisive to provide an accurate genetic counseling and in disease treatment.

Corrigendum: Panel-based NGS Reveals Novel Pathogenic Mutations in Autosomal Recessive Retinitis Pigmentosa.

Scientific Reports 6: Article number: 19531; published online: 25 January 2016; updated: 22 April 2016 This Article contains errors. In Table 1, for Family RP-1929 the nucleotide change ‘c.9079dupA’ and protein change ‘p.Arg3027Lysfs*9’ were incorrectly given as ‘c.9142dupA’ and ‘p.Arg3048Lysfs*9’ respectively.