Guillermo Antiñolo

EYS, encoding an ortholog of Drosophila spacemaker, is mutated in autosomal recessive retinitis pigmentosa.

Using a positional cloning approach supported by comparative genomics, we have identified a previously unreported gene, EYS, at the RP25 locus on chromosome 6q12 commonly mutated in autosomal recessive retinitis pigmentosa. Spanning over 2 Mb, this is the largest eye-specific gene identified so far. EYS is independently disrupted in four other mammalian lineages, including that of rodents, but is well conserved from Drosophila to man and is likely to have a role in the modeling of retinal architecture.

A Founding Locus within the RET Proto-Oncogene May Account for a Large Proportion of Apparently Sporadic Hirschsprung Disease and a Subset of Cases of Sporadic Medullary Thyroid Carcinoma

Hirschsprung disease (HSCR) is a common congenital disorder characterized by aganglionosis of the gut. The seemingly unrelated multiple endocrine neoplasia type 2 (MEN 2) is an autosomal dominant disorder characterized by medullary thyroid carcinoma (MTC), pheochromocytoma, and hyperparathyroidism. Yet, germline mutations in the RET proto-oncogene are associated with both MEN 2 and HSCR. In the former, gain-of-function mutations in a limited set of codons is found, whereas, in the latter, loss-of-function mutations are found. However, germline RET mutation is associated with only 3% of a population-based series of isolated HSCR, and little is known about susceptibility to sporadic MTC. We have found previously that specific haplotypes comprising RET coding single-nucleotide polymorphisms (SNPs) comprising exon 2 SNP A45A were strongly associated with HSCR, whereas haplotypes associated with exon 14 SNP S836S were associated with MTC. In this study, we describe three novel intron 1 SNPs, and, together with the coding SNP haplotypes, the data suggest the presence of distinct ancestral haplotypes for HSCR and sporadic MTC in linkage disequilibrium with a putative founding susceptibility locus/loci. The data are consistent with the presence of a very ancient, low-penetrance founder locus approximately 20-30 kb upstream of SNP A45A, but the failure of the SNPs to span the locus presents challenges in modeling mode of transmission or ancestry. We postulate that this founding locus is germane to both isolated HSCR and MTC but also that different mutations in this locus would predispose to one or the other.

RET genotypes comprising specific haplotypes of polymorphic variants predispose to isolated Hirschsprung disease

BACKGROUND Hirschsprung disease (HSCR), which may be sporadic or familial, occurs in 1:5000 live births and presents with functional intestinal obstruction secondary to aganglionosis of the hindgut. Germline mutations of theRET proto-oncogene are believed to account for up to 50% of familial cases and up to 30% of isolated cases in most series. However, these series are highly selected for the most obvious and severe cases and large familial aggregations. Population based studies indicate that germline RETmutations account for no more than 3% of isolated HSCR cases. Recently, we and others have noted that specific polymorphic sequence variants, notably A45A (exon 2), are over-represented in isolated HSCR. PURPOSE In order to determine if it is the variant per se, a combination thereof, or another locus in linkage disequilibrium which predisposes to HSCR, we looked for association of RET haplotype(s) and disease in HSCR cases compared to region matched controls. METHODS Seven loci acrossRET were typed and haplotypes formed for HSCR cases, their unaffected parents, and region matched controls. Haplotype and genotype frequencies and distributions were compared among these groups using the transmission disequilibrium test and standard case-control statistic. RESULTS Twelve unique haplotypes, labelled A-L, were obtained. The distributions of haplotypes between cases and controls (χ11 2 =81.4, p<<0.0001) and between cases and non-transmitted parental haplotypes were significantly different (χ2 11=53.1, p<0.0001). Genotypes comprising pairs of haplotypes were formed for cases and controls. There were 38 different genotypes among cases and controls combined. Inspection of the genotypes in these two groups showed that the genotype distribution between cases and controls was distinct (χ37 2=93.8, p<<0.0001). For example, BB, BC, BD, and CD, all of which contain at least one allele with the polymorphic A45A, are prominently represented among HSCR cases, together accounting for >35% of the case genotypes, yet these four genotypes were not represented among the population matched normal controls. Conversely, AA, AG, DD, GG, and GJ, none of which contains A45A, are commonly represented in the controls, together accounting for 43% of the control genotypes, and yet they are never seen among the HSCR cases. CONCLUSIONS Our data suggest that genotypes comprising specific pairs of REThaplotypes are associated with predisposition to HSCR either in a simple autosomal recessive manner or in an additive, dose dependent fashion.

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.

Retinitis pigmentosa in Spain

Retinitis pigmentosa is a term commonly given to a group of inherited and progressive disorders which affect the photoreceptors of the retina. As part of an ongoing research programme throughout Spain, clinical, epide‐miological, and genetic studies have been carried out on these diseases. Here, we report the relative frequencies of the different genetic types in 503 non‐syndromic and 89 syndromic RP families of Spanish origin. The most frequent syndromic RP forms were Usher syndrome type 1 (20/ 89 families=30%) and Usher syndrome type 2 (44 families=49%). Among non‐syndromic RP forms, 12% were autosomal dominant, 39% autosomal recessive and 4% X‐linked. Forty‐one percent were isolated or simplex cases and in 4% the genetic type could not be established.

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.

Identification of 14 novel mutations in the long isoform of USH2A in Spanish patients with Usher syndrome type II

Mutations in USH2A gene have been shown to be responsible for Usher syndrome type II, an autosomal recessive disorder characterised by hearing loss and retinitis pigmentosa. USH2A was firstly described as consisting of 21 exons, but 52 novel exons at the 3’ end of the gene were recently identified. In this report, a mutation analysis of the new 52 exons of USH2A gene was carried out in 32 unrelated patients in which both disease-causing mutations could not be found after the screening of the first 21 exons of the USH2A gene. On analysing the new 52 exons, fourteen novel mutations were identified in 14 out of the 32 cases studied, including 7 missense, 5 frameshift, 1 duplication and a putative splice-site mutation.

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 …

Microarray-based mutation analysis of 183 Spanish families with Usher syndrome.

PURPOSE The purpose of this study was to test the ability of the genotyping microarray for Usher syndrome (USH) to identify the mutations responsible for the disease in a cohort of 183 patients with USH. METHODS DNA from 183 patients with Usher syndrome from the Spanish population was analyzed using a genotyping microarray containing 429 previously identified disease-associated variants in eight USH genes. Mutations detected by the array were confirmed by direct sequencing. Haplotype analysis was also performed in families carrying common Spanish mutations. RESULTS The genotyping microarray identified 43 different variants, divided into 32 disease causative and 11 probably nonpathologic. Mutations were detected in 62 patients with USH (33.9%). According to the clinical classification of patients, pathologic variants were detected in 31.4% patients with USH1, 39.4% of with USH2, 22.2% with USH3 and 15.8% with unclassified Usher syndrome. Ninety-seven pathologic alleles were detected, corresponding to 26.5% of expected alleles. The USH2A mutations p.C3267R and p.T3571M were revealed as common in the Spanish population, and two major haplotypes linked to these mutations were observed. CONCLUSIONS The genotyping microarray is a robust, low-cost, rapid technique that is effective for the genetic study of patients with USH. However, it also indicates variants of unclear pathologic nature and detection failures have also been observed. Results must be confirmed by direct sequencing to avoid misdiagnosis, and continuous updates of the microarray should be performed to increase the efficiency and rate of detection of mutations.

EYS is a major gene for rod‐cone dystrophies in France

Autosomal‐recessive retinitis pigmentosa (arRP) was recently associated with mutations in a novel gene EYS, spanning over 2 Mb, making it the largest known gene expressed in the human eye. The purpose of this study was to establish the prevalence and nature of EYS mutations in a clinically well‐characterized cohort of 239 sporadic and arRP French cases. Direct sequencing of EYS was performed in 186 subjects for whom known mutations had previously been excluded by applying microarray technology. We mostly identified novel mutations in EYS in a total of 29 patients: Fifteen of the mutations were predicted to create premature stop codons and two represent exonic deletions. In addition, twenty missense, silent or splice‐site mutations were detected. Patients revealed homozygous or compound heterozygous mutations and in some cases, only a single mutation. Most patients showed classical signs of RP with relatively preserved central vision and visual field until late in the course of the disorder. One patient showed predominance of the disease in the inferior part of the retina suggesting potential phenotypic variability. With a prevalence of 12% or more we provide evidence that EYS is a major gene for RP in France and probably elsewhere.