Algoritmo para el estudio molecular del síndrome de Bardet-Biedl en España / Algorithm for the molecular analysis of Bardet-Biedl syndrome in Spain

Fundamento y objetivo: El síndrome de Bardet-Biedl (SBB) es una enfermedad genética multisistémica poco frecuente en población caucásica, caracterizada por una pronunciada variabilidad fenotípica y una gran heterogeneidad genética. Pertenece al grupo de las ciliopatías, causadas por defectos en la estructura y/o función ciliar. Dada la gran complejidad diagnóstica del síndrome, el objetivo de este estudio ha sido analizar el conjunto global de afectados recogidos para elaborar un algoritmo que facilite el diagnóstico molecular rutinario del SBB, así como calcular algunos parámetros epidemiológicos para población española. Pacientes y método: Se han analizado 116 afectados de SBB pertenecientes a 89 familias procedentes de toda la geografía española. Todos los probandos cumplían los criterios diagnósticos establecidos para el SBB. Para ello, se utilizaron las siguientes técnicas: microchip de genotipado, secuenciación directa y microchip de homocigosidad para familias consanguíneas. Resultados: Ha sido posible diagnosticar al 47% de las familias (21% mediante el microchip de genotipado, 18% mediante secuenciación directa de genes BBS predominantes y 8% mediante el mapeo de regiones homocigotas). En cuanto a los datos epidemiológicos, se obtuvo un valor de prevalencia del SBB en España de 1:407.000, así como una razón por sexos de 1,4:1 (varones:mujeres). Conclusiones: El algoritmo propuesto, basado en el análisis de genes BBS predominantes combinado con estudios de homocigosidad, ha permitido confirmar el diagnóstico molecular en un porcentaje significativo de familias con sospecha clínica de SBB. Este algoritmo diagnóstico permitirá optimizar el análisis molecular del SBB (AU)

Background and objective: Bardet-Biedl syndrome (BBS) is a multisystemic genetic disorder, which is not widespread among the Caucasian population, characterized by a highly variable phenotype and great genetic heterogeneity. BBS belongs to a group of diseases called ciliopathies, caused by defects in the structure and/or function of cilia. Due to the diagnostic complexity of the syndrome, the objective of this study was to analyse our whole group of patients in order to create an algorithm to facilitate the routine molecular diagnosis of BBS. We also calculated several epidemiological parameters in our cohort. Patients and method: We analysed 116 BBS patients belonging to 89 families from the whole Spanish geography. All probands fulfilled diagnosis criteria established for BBS. For this, we used: genotyping microarray, direct sequencing and homozygosis mapping (in consanguineous families). Results: By means of the different approaches, it was possible to diagnose 47% of families (21% by genotyping microarray, 18% by direct sequencing of predominant BBS genes, and 8% by homozygosis mapping). With regard to epidemiological data, a prevalence value of 1:407,000 was obtained for BBS in Spain, and a sex ratio of 1.4:1 (men:women). Conclusions: The proposed algorithm, based on the analysis of predominant BBS genes combined with homozygosis mapping, allowed us to confirm the molecular diagnosis in a significant percentage of families with clinically suspected BBS. This diagnostic algorithm will be useful for the improvement of the efficiency of molecular analysis in BBS (AU)

[Algorithm for the molecular analysis of Bardet-Biedl syndrome in Spain]. / Algoritmo para el estudio molecular del síndrome de Bardet-Biedl en España.

BACKGROUND AND OBJECTIVE: Bardet-Biedl syndrome (BBS) is a multisystemic genetic disorder, which is not widespread among the Caucasian population, characterized by a highly variable phenotype and great genetic heterogeneity. BBS belongs to a group of diseases called ciliopathies, caused by defects in the structure and/or function of cilia. Due to the diagnostic complexity of the syndrome, the objective of this study was to analyse our whole group of patients in order to create an algorithm to facilitate the routine molecular diagnosis of BBS. We also calculated several epidemiological parameters in our cohort. PATIENTS AND METHOD: We analysed 116 BBS patients belonging to 89 families from the whole Spanish geography. All probands fulfilled diagnosis criteria established for BBS. For this, we used: genotyping microarray, direct sequencing and homozygosis mapping (in consanguineous families). RESULTS: By means of the different approaches, it was possible to diagnose 47% of families (21% by genotyping microarray, 18% by direct sequencing of predominant BBS genes, and 8% by homozygosis mapping). With regard to epidemiological data, a prevalence value of 1:407,000 was obtained for BBS in Spain, and a sex ratio of 1.4:1 (men:women). CONCLUSIONS: The proposed algorithm, based on the analysis of predominant BBS genes combined with homozygosis mapping, allowed us to confirm the molecular diagnosis in a significant percentage of families with clinically suspected BBS. This diagnostic algorithm will be useful for the improvement of the efficiency of molecular analysis in BBS.

Clinical evaluation of two consanguineous families with homozygous mutations in BEST1.

PURPOSE: To describe the clinical and genetic findings in two consanguineous families with Best vitelliform macular dystrophy (BVMD) and homozygous mutations in the bestrophin-1 (BEST1) gene. METHODS: Ophthalmologic examination was performed in eight members of two families originating from Spain and Denmark. Mutation screening was performed using the Vitelliform Macular Dystrophy mutation array from Asper Biotech, and by the directed genomic sequencing of BEST1. RESULTS: Two homozygous mutations were detected in these families. Mutation c.936C>A (p.Asp312Glu) has been reported previously in a Danish family; here, we describe four additional individuals in this family demonstrating findings compatible with a severe dominant BVMD, albeit with reduced penetrance in heterozygotes. In the Spanish family, a novel homozygous missense mutation in exon 4, c.388 C>A (p.Arg130Ser), was identified in the siblings. Homozygous siblings demonstrated evidence of multifocal vitelliform retinopathy, whereas heterozygous family members presented findings ranging from isolated reduction of the electrooculogram Arden ratio to normal values on all clinical parameters. CONCLUSIONS: As demonstrated in these consanguineous families, a great clinical variability is associated with homozygous mutations in BEST1, ranging from severe dominant BVMD with reduced penetrance in heterozygotes to autosomal recessive bestrophinopathy.

Arrayed primer extension technology simplifies mutation detection in Bardet-Biedl and Alström syndrome.

Bardet-Biedl syndrome (BBS; OMIM no. 209 900) and Alström syndrome (ALMS; OMIM no. 203 800) are rare, multisystem genetic disorders showing both a highly variable phenotype and considerable phenotypic overlap; they are included in the emerging group of diseases called ciliopathies. The genetic heterogeneity of BBS with 14 causal genes described to date, serves to further complicate mutational analysis. The development of the BBS-ALMS array which detects known mutations in these genes has allowed us to detect at least one mutation in 40.5% of BBS families and in 26.7% of ALMS families validating this as an efficient and cost-effective first pass screening modality. Furthermore, using this method, we found two BBS families segregating three BBS alleles further supporting oligogenicity or modifier roles for additional mutations. We did not observe more than two mutations in any ALMS family.

Discovery and functional analysis of a retinitis pigmentosa gene, C2ORF71.

Retinitis pigmentosa is a genetically heterogeneous group of inherited ocular disorders characterized by progressive photoreceptor cell loss, night blindness, constriction of the visual field, and progressive visual disability. Homozygosity mapping and gene expression studies identified a 2 exon gene, C2ORF71. The encoded protein has no homologs and is highly expressed in the eye, where it is specifically expressed in photoreceptor cells. Two mutations were found in C2ORF71 in human RP patients: A nonsense mutation (p.W253X) in the first exon is likely to be a null allele; the second, a missense mutation (p.I201F) within a highly conserved region of the protein, leads to proteosomal degradation. Bioinformatic and functional studies identified and validated sites of lipid modification within the first three amino acids of the C2ORF71 protein. Using morpholino oligonucleotides to knockdown c2orf71 expression in zebrafish results in visual defects, confirming that C2ORF71 plays an important role in the development of normal vision. Finally, localization of C2ORF71 to primary cilia in cultured cells suggests that the protein is likely to localize to the connecting cilium or outer segment of photoreceptor cells.

New mutations in BBS genes in small consanguineous families with Bardet-Biedl syndrome: detection of candidate regions by homozygosity mapping.

PURPOSE: Bardet-Biedl syndrome (BBS, OMIM 209900) is a rare multi-organ disorder in which BBS patients manifest a variable phenotype that includes retinal dystrophy, polydactyly, mental delay, obesity, and also reproductive tract and renal abnormalities. Mutations in 14 genes (BBS1-BBS14) are found in 70% of the patients, indicating that additional mutations in known and new BBS genes remain to be identified. Therefore, the molecular diagnosis of this complex disorder is a challenging task. METHODS: In this study we show the use of the genome-wide homozygosity mapping strategy in the mutation detection of nine Caucasian BBS families, eight of them consanguineous and one from the same geographic area with no proven consanguinity. RESULTS: We identified the disease-causing mutation in six of the families studied, five of which had novel sequence variants in BBS3, BBS6, and BBS12. This is the first null mutation reported in BBS3. Furthermore, this approach defined homozygous candidate regions that could harbor potential candidate genes for BBS in three of the families. CONCLUSIONS: These findings further underline the importance of homozygosity mapping as a useful technology for diagnosis in small consanguineous families with a complex disease like BBS.

Complexity of phenotype-genotype correlations in Spanish patients with RDH12 mutations.

PURPOSE: Several mutations have been described in the RDH12 gene that disturb the activity of the encoded protein, suggesting that RDH12 loss of function disrupts the synthetic pathway of the visual chromophore 11-cis-retinal, therefore resulting in early and progressive retinal degeneration (RD). Mutations in this gene have been related to autosomal recessive Leber congenital amaurosis (LCA) and to a form of autosomal recessive childhood-onset severe retinal dystrophy (CSRD). This study was undertaken to attempt to correlate the genotype and phenotype in Spanish CSRD and LCA patients who harbor RDH12 mutations. METHODS: A complete ophthalmic and electrophysiologic examination was performed according to preexisting protocols. A screening for mutations was then performed using denaturing HPLC on a DNA fragment analysis system. Those fragments bearing an abnormal pattern were sequenced. RESULTS: Ten families bearing RDH12 mutations in homozygous or compound heterozygous form were found. All of them corresponded to patients with severe and early-onset retinal dystrophy. CONCLUSIONS: The RDH12-associated phenotype is not homogeneous, the position and nature of the mutations clearly influence the pathologic expression of this disease.