Irene Marcos

Germline sequence variant S836S in the RET proto‐oncogene is associated with low level predisposition to sporadic medullary thyroid carcinoma in the Spanish population

OBJECTIVE The molecular basis of sporadic medullary thyroid carcinoma (MTC) remains elusive. While germline gain‐of‐function mutations in the RET proto‐oncogene cause hereditary MTC, somatic activating RET mutations and loss of heterozygosity of markers in various chromosomal regions representing deletions of tumour suppressor genes, have been described in a variable number of sporadic MTC. A previous report suggested that the presence of a germline variant at RET codon 836 (S836S) was associated with the development of sporadic MTC and, furthermore, that the presence of S836S was highly correlated with somatic RET M918T mutation in the MTC. Thus, we sought to determine if the S836S variant would be associated with sporadic MTC from a completely different population base, that of Andalucia.

A major locus for autosomal recessive retinitis pigmentosa on 6q, determined by homozygosity mapping of chromosomal regions that contain gamma-aminobutyric acid-receptor clusters

Retinitis pigmentosa (RP) is the most common inherited retinal dystrophy, with extensive allelic and nonallelic genetic heterogeneity. Autosomal recessive RP (arRP) is the most common form of RP worldwide, with at least nine loci known and accountable for approximately 10%-15% of all cases. Gamma-aminobutyric acid (GABA) is the major inhibitory transmitter in the CNS. Different GABA receptors are expressed in all retinal layers, and inhibition mediated by GABA receptors in the human retina could be related to RP. We have selected chromosomal regions containing genes that encode the different subunits of the GABA receptors, for homozygosity mapping in inbred families affected by arRP. We identify a new locus for arRP, on chromosome 6, between markers D6S257 and D6S1644. Our data suggest that 10%-20% of Spanish families affected by typical arRP could have linkage to this new locus. This region contains subunits GABRR1 and GABRR2 of the GABA-C receptor, which is the effector of lateral inhibition at the retina.

Mutations in USH2A in Spanish patients with autosomal recessive retinitis pigmentosa: high prevalence and phenotypic variation

Retinitis pigmentosa (RP), which occurs in about one in 3000–7000 people in Spain, is inherited in an autosomal dominant manner in 12% of cases, in an autosomal recessive way in 39%, and in an X linked manner in 4% of cases. This leaves 41% of RP cases with a simplex form and 4% in which the transmission pattern is unclear.1 Direct analyses of rhodopsin, the alpha and gamma subunits of rod cGMP-phosphodiesterase, periferin/RDS, rod outer segment membrane protein, recoverin, guanilate cyclase activating protein, S antigen, interstitial retinol binding protein, and NRL have failed to detect any disease causing mutation in non-syndromic ARRP Spanish families. Mutations in the beta subunit of the rod cGMP-phosphodiesterase gene,2–5 in the ATP binding cassette receptor gene,6 and in the TULP1 gene7 account for a small percentage of Spanish ARRP families. These data indicate that genes other than these may be involved in the remaining families, emphasising the genetic heterogeneity of the disease and reinforcing the hypothesis that in ARRP a number of genes rather than one major gene will account individually for a small number of cases. The recent report that a missense mutation in the USH2A gene (C759F) is present in 4.5% of patients with non-syndromic ARRP8 prompted us to analyse the involvement of this mutation in a large set of Spanish ARRP families. A complete mutational analysis of the coding region of the USH2A gene was performed in all cases in which the C759F allele was found. Additional mutations were identified in the USH2A gene in non-syndromic ARRP patients. Interestingly, two C759F homozygotes belonging to a consanguineous ARRP family had no RP symptoms and no hearing impairment. A group of 196 unrelated ARRP patients plus four cases of retinitis punctata albescens were studied. The patients were diagnosed …

Mutation analysis of GABRR1 and GABRR2 in autosomal recessive retinitis pigmentosa.

Editor—Retinitis pigmentosa (RP, MIM 268000) is the most frequent form of retinal dystrophy world wide. The clinical findings are night blindness and narrowing of the visual field. Examination of the fundus of the eye in RP patients usually shows bone spicula pigmentation of the retina, waxy pallor of the optic disc, attenuation of the retinal blood vessels, and no results detectable by electroretinogram.1 RP shows notable allelic and non-allelic heterogeneity2(RET-GEN-NET htp://www.sph.uth.tm.edu/Retnet/home.htm). By using classical linkage strategies and the direct and indirect candidate gene approach, the number of RP loci identified has grown increasingly since 1989 and to date more than 30 autosomal RP loci have been identified, including syndromic and non-syndromic forms of the disease. Autosomal recessive RP (ARRP) is the commonest form of RP and to date at least 13 independent ARRP loci have been identified.3-15 Our group proposed the hypothesis that the alteration of functions related to neurotransmission in the external plexiform layer of the retina could be related to RP.14 In order to test this model, we used homozygosity mapping to analyse different genes involved in retinal neurotransmission. Using this indirect candidate gene approach, we identified the locus RP25 in an important subgroup of ARRP patients from our cohort. In fact, around 14% of the ARRP families from southern Spain showed linkage to RP25. 14 RP25 is an ARRP locus located on the long arm of chromosome 6 between markers D6S257 and D6S1644 (MIM 602772). This chromosomal region contains the GABRR1 and GABRR2 genes, both being expressed in the retina. These genes encode the rho1 and rho2 subunits of the C type receptor for γ-aminobutyric acid (GABAc receptor).16 17The GABAc …

Evaluation of germline sequence variants of GFRA1, GFRA2, and GFRA3 genes in a cohort of spanish patients with sporadic medullary thyroid cancer

The etiology of sporadic medullary thyroid carcinoma (sMTC) remains elusive. While germline gain-of-function mutations in the RET proto-oncogene cause hereditary MTC, somatic RET mutations have been described in a variable number of sMTC. So far, S836S of RET, is the only variant whose association with sMTC has been found in several European cohorts. Because RET variants seem to be associated with MTC, it is plausible that variants in genes encoding for RET coreceptors may play a role in the pathogenesis of sMTC. Recently, we described two possible low penetrance susceptibility alleles in the gene encoding RET coreceptor GFRalpha1, -193C > G and 537T > C, in a German series of sMTC. In this study, we have genotyped nine polymorphisms within GFRA1-3 genes for 51 Spanish sMTC, and 100 normal controls. Our results show that no statistical signification was found when Spanish sMTC patients were compared to controls. Taken together with the observations in the German sMTC series, the present findings suggest that GFRA1-193C > G and 537T > C could be in linkage disequilibrium with other loci responsible for the disease with a founder effect in Germany. Alternatively, the combined observations might also suggest that, if indeed the polymorphisms are functional, the effect is small.

Cloning, characterization, and chromosome mapping of the human GlcAT-S gene

AbstractWe report on the structure, map location, and tissue expression of the human GlcAT-S gene. The gene covers approximately 85Kb on chromosome 6 (6q13) between the D6S455 and D6S1673 markers. GlcAT-S is composed of four exons and encodes a 324-amino-acid protein, which shows 89% homology with the rat glcat-s protein and is involved in the biosynthesis of the HNK-1 carbohydrate epitope on glycoproteins. Although GlcAT-S was considered an interesting candidate gene for the RP25 locus, the absence of any pathogenic mutations in probands of RP25-linked families ruled out that candidacy.

Evaluation of the ELOVL4 gene in families with retinitis pigmentosa linked to the RP25 locus

Editor—Retinitis pigmentosa (RP) is the most common form of retinal dystrophy. Patients present with night blindness and progressive narrowing of the visual field, eventually leading to central vision loss. Fundus examination usually shows bone spicula pigmentation, attenuation of blood vessels in the retina, and waxy pallor of the optic disc. Typically, the electroretinogram is notably diminished or even abolished.1 RP shows important allelic and non-allelic genetic heterogeneity (RET-GEN-NET) with different modes of inheritance, including autosomal dominant (AD), autosomal recessive (AR), X linked, and digenic. ARRP is the most common form of RP. A locus for ARRP, RP25 , was mapped in 1998 to the long arm of chromosome 6 between microsatellite markers D6S257 and D6S1644 (MIM 602772).2 Recently, we have excluded two candidates, GABRR1 and GABRR2, as the disease causing gene.3 Several loci with retinal dystrophy phenotypes have been mapped to the pericentromeric region of chromosome 6. They include autosomal dominant Stargardt-like disease ( STGD3 ),4 autosomal dominant macular atrophy ( ADMD ),5autosomal dominant …

Molecular Analysis of RIM1 in Autosomal Recessive Retinitis pigmentosa

Retinitis pigmentosa (RP) is a frequent retinal dystrophy characterized by a progressive loss of photoreceptors along with retinal degeneration. RIM1, encoding a presynaptic protein involved in the glutamate neurotransmission, is the responsible gene for autosomal dominant cone-rod dystrophy CORD7, whose locus overlaps partially with a locus of autosomal recessive RP (arRP), RP25. Given the genetic heterogeneity that features RP, it is plausible that mutations in RIM1 are also implicated in the disease in arRP families genetically linked to the CORD7 region. To test our hypothesis we analysed the complete RIM1 gene in 8 arRP families by DNA sequencing. Even though the absence of pathogenic mutations suggests that RIM1 is notinvolved in arRP, a role for this gene in other inherited forms of RP as well as other retinal dystrophies needs to be elucidated.

Short Communication: Fluorescence Resonance Energy Transfer Analysis of the RANTES Polymorphisms -403G → A and -28G → C: Evaluation of Both Variants as Susceptibility Factors to HIV Type 1 Infection in the Spanish Population

The identification of genetic factors predisposing or protecting against HIV-1 infection has been an important aim in AIDS research. Two of these factors are located in the promoter region of the CCL5 gene, which encodes the RANTES (regulated on activation, normal T cells expressed and secreted) chemokine, an inhibitor agent for M-tropic HIV-1 strains. More specifically, the role of single-nucleotide polymorphisms (SNPs) -403G --> A and -28C --> G has been evaluated in the course of HIV-1 infection in several populations with different genetic, geographic, and ethnic backgrounds. Here we present a fast, simple, reliable, and efficient method for the simultaneous genotyping of these two CCL5 variants. A case-control study has been performed to evaluate the role of -403G --> A and -28C --> G as susceptibility factors for HIV-1 infection in the Spanish population. No differences have been found in the allelic frequencies of either variant or in the haplotype/genotype distribution between patients and controls. These data would be consistent with a lack of association between these SNPs and HIV-1 infection in our population.

Molecular genetic analysis of two functional candidate genes in the autosomal recessive retinitis pigmentosa, RP25, locus

Purpose: To identify the disease gene in five Spanish families with autosomal recessive retinitis pigmentosa (arRP) linked to the RP25 locus. Two candidate genes, EEF1A1 and IMPG1, were selected from the region between D6S280 and D6S1644 markers where the families are linked. The genes were selected as good candidates on the basis of their function, tissue expression pattern, and/or genetic data. Methods: A molecular genetic study was performed on DNA extracted from one parent and one affected member of each studied family. The coding exons, splice sites, and the 5′ UTR of the genes were amplified by polymerase chain reaction (PCR). For mutation detection, direct sequence analysis was performed using the ABI 3100 automated sequencer. Segregation of an IMPG1 single nucleotide polymorphism (SNP) in all the families studied was analyzed by restriction enzyme digest of the amplified gene fragments. Results: In total, 15 SNPs were identified of which 7 were novel. Of the identified SNPs, one was insertion, two were deletions, five were intronic, six were missense, and one was located in the 5′ UTR. These changes, however, were also identified in unaffected members of the families and/or 50 control Caucasians. The examined known IMPG1 SNP was not segregating with the disease phenotype but was correlating with the genetic data in all families studied. Conclusions: Our results indicate that neither EEF1A1 nor IMPG1 could be responsible for RP25 in the studied families due to absence of any pathogenic variants. However, it is important to notice that the methodology used in this study cannot detect larger deletions that lie outside the screened regions or primer site mutations that exist in the heterozygous state. A role of both genes in other inherited forms of RP and/or retinal degenerations needs to be elucidated.