Isabel Martínez-Garay

A two base pair deletion in the PQBP1 gene is associated with microphthalmia, microcephaly, and mental retardation

X-linked mental retardation has been traditionally divided into syndromic (S-XLMR) and non-syndromic forms (NS-XLMR), although the borderlines between these phenotypes begin to vanish and mutations in a single gene, for example PQBP1, can cause S-XLMR as well as NS-XLMR. Here, we report two maternal cousins with an apparently X-linked phenotype of mental retardation (MR), microphthalmia, choroid coloboma, microcephaly, renal hypoplasia, and spastic paraplegia. By multipoint linkage analysis with markers spanning the entire X-chromosome we mapped the disease locus to a 28-Mb interval between Xp11.4 and Xq12, including the BCOR gene. A missense mutation in BCOR was described in a family with Lenz microphthalmia syndrome, a phenotype showing substantial overlapping features with that described in the two cousins. However, no mutation in the BCOR gene was found in both patients. Subsequent mutation analysis of PQBP1, located within the delineated linkage interval in Xp11.23, revealed a 2-bp deletion, c.461_462delAG, that cosegregated with the disease. Notably, the same mutation is associated with the Hamel cerebropalatocardiac syndrome, another form of S-XLMR. Haplotype analysis suggests a germline mosaicism of the 2-bp deletion in the maternal grandmother of both affected individuals. In summary, our findings demonstrate for the first time that mutations in PQBP1 are associated with an S-XLMR phenotype including microphthalmia, thereby further extending the clinical spectrum of phenotypes associated with PQBP1 mutations.

Intronic L1 insertion and F268S, novel mutations in RPS6KA3 (RSK2) causing Coffin-Lowry syndrome

Two novel mutations of the ribosomal S6 kinase 2 gene (also known as RSK2) have been identified in two unrelated patients with Coffin–Lowry syndrome. The first mutation consists of a de novo insertion of a 5′‐truncated LINE‐1 element at position −8 of intron 3, which leads to a skipping of exon 4, leading to a shift of the reading frame and a premature stop codon. The L1 fragment (2800 bp) showed a rearrangement with a small deletion, a partial inversion of the ORF 2, flanked by short direct repeats which duplicate the acceptor splice site. However, cDNA analysis of the patient shows that both sites are apparently not functional.

Gypsy endogenous retrovirus maintains potential infectivity in several species of Drosophilids

BackgroundSequences homologous to the gypsy retroelement from Drosophila melanogaster are widely distributed among drosophilids. The structure of gypsy includes an open reading frame resembling the retroviral gene env, which is responsible for the infectious properties of retroviruses.ResultsIn this study we report molecular and phylogeny analysis of the complete env gene from ten species of the obscura group of the genus Drosophila and one species from the genus Scaptomyza.ConclusionThe results indicate that in most cases env sequences could produce a functional Env protein and therefore maintain the infectious capability of gypsy in these species.

Localization of MRX82: A new nonsyndromic X-linked mental retardation locus to Xq24-q25 in a Basque family

Clinical and molecular studies are reported on a Basque family (MRX82) with nonsyndromic X‐linked mental retardation (XLMR) in five affected males. A total of 38 microsatellite markers were typed. The XLMR locus has been linked to DXS8067, DXS1001, DXS425, DXS7877, and DXS1183 with a maximum LOD score of 2.4. The haplotype studies and multipoint linkage analysis suggest a localization of the MRX82 locus to an interval of 7.6 Mb defined by markers DXS6805 and DXS7346, in Xq24 and Xq25, respectively. No gene contained in this interval has been so far associated with nonsyndromic mental retardation, except for GRIA3, disrupted by a balanced translocation in a female patient with bipolar affective disorder and mental retardation. However, the search for mutations of this gene did not showed a pathogenic mutation in the present family. Given that there are other eight MRX families overlapping this interval, none of them with known mutation, we conclude that at least one new gene responsible for nonsyndromic mental retardation is located in this region.

Duplication of the Williams–Beuren critical region: case report and further delineation of the phenotypic spectrum

Only 12 patients with a duplication of the Williams-Beuren critical region (WBCR) have been reported to date, with variable developmental, psychomotor and language delay, in the absence of marked dysmorphic features. In this paper we present a new WBCR microduplication case, which supports the wide variability displayed by this duplication in the phenotype. The WBCR microduplication may be associated with autistic spectrum disorder, but most reported cases do not show this behavioural disorder, or may even show a hypersociable personality, as with our patient. From the present case and a review of the 12 previously described, we conclude that the phenotype associated with duplication of WBCR can affect the same domains as WBCR deletion, but that they cluster near the polar ends of social relationship (autism-like v hypersociability), language (expressive language impairment v “cocktail party” speech), visuospatial (severe v normal), mental retardation (severe v mild) and dysmorphic (severe v mild) features.

Screening for microdeletions of the X-chromosome in non-specific mental retardation

Small deletions of the X-chromosome have been reported in several cases associated to non-specific mental retardation. In particular, both partial or complete deletion of gene IL1RAPLwere detected in two out of 26 XLMR families, as well as in several contiguous gene syndromes [Carrié et al., 1999]. Two other regions, in Xp22.3 and Xq21, respectively, are also apparently prone to deletion based on the recurrent report of cases with contiguous gene syndromes including mental retardation [Ballabio and Andria, 1992; Yntema et al., 1999; Fukami et al., 2000]. However, a reliable estimation of the frequency of these deletions is unknown in patients with non-specific mental retardation. For this reason, we decided to develop a method based on a multiplexPCR inorder to estimate the frequency of these deletions amongpatientswith idiopathicmental retardationand,more importantly, to assess the implementation of such a method in routine clinical practice (Fig. 1). A total of 450 male patients with idiopathic mental retardation were investigated. The patients were previously referred for fragile-X syndrome diagnosis, and only those cases with the fragile-X expansion were excluded. This series was previously used to estimate the frequency of the fragile-X syndrome [Millán et al., 1999]. Several markers and conditions were assayed to obtain a balanced amplification of four fragments corresponding to the three regions: DXS1218 and exon 11 of gene IL1RAPL are in opposite sites of this gene, where partial deletions were reported [Carrié et al., 1999].RSK4 gene (also knownasRPS6KA6, a paralog of the Coffin–Lowry gene) is a candidate XLMR gene, localized in the critical region in Xq21 [Yntema et al., 1999]. Among the several markers from the Xp22.3 region (K7-2, K2H, DXS1139, DXS1130, and DXS237) only the two latter yielded consistent results in previous studies that were performed in normal controls and in two unrelated patients with a microdeletion in this region causing XLMR and ichthyosis (data not shown). PCR amplification was performed under standard conditions (PCR Supermix, Life Technologies, Invitrogen, Barcelona, Spain) and the primer concentrations indicated in Table I, using the following program: initial denaturation at 948C for 3min, 32 cycles of 958C for 30 s, and 558C for 30 s with a final elongation step at 728C for 7 min. Five microliters of PCR products were loaded in 12% polyacrylamide gels (acrylamide:bis 29:1) of 7 cm length and run at 200V for 2 hr under native conditions. The bands were detected by staining with silver nitrate (Fig. 2). The method that we employed gave reliable results in general. Only degraded DNA samples failed to amplify or yielded spurious absence of amplification, easily determined for affecting the two larger fragments (in different chromosomal regions). Every putative deletion was checked separately and together with another marker. We detected only one deletion in the whole series: a sample showed lack of amplification of exon 3 of the gene RSK4. The study of other polymorphisms near this gene showed deletion of DXS1196, while markers DXS441, DXS6800, and DXS990 were preserved. In accordance, the present deletion spans at least 3.4Mb [NCBI, XXX], although it was not detected by routine cytogenetic analysis. The large size of the deletion at the molecular level, together with the preand peri-natal complications in this particular case (alcohol intake during pregnancy andhypoxia at birth)make the assignment of the genetic contribution to the patient’s phenotype difficult. The patient’s mother could not be studied, but she was referred as having mental disability by the person taking care of the patient. Most of this series was used previously to estimate the incidence of the fragile-X syndrome, where a total of 20 cases were detected. Conversely, the incidence of thesekindofdeletionsamong thenon-syndromicmental retardation is apparently lower: about 0.2% of males Grant sponsor: Fondo de Investigaciones Sanitarias; Grant number: FIS 01/0890.