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Haemolysis in sickle cell anaemia: a genotype/phenotype association study

Mon, 01 Oct 2012 00:00:00 GMT

Title: Haemolysis in sickle cell anaemia: a genotype/phenotype association study Authors: Lavinha, João; Coelho, Andreia; Dias, Alexandra; Morais, Anabela; Ferreira, Emanuel; Picanço, Isabel; Nunes, Baltazar; Faustino, Paula Abstract: Sickle-cell anaemia (SCA) is a clinically heterogeneous autosomal recessive monogenic chronic anaemia characterized by recurrent episodes of severe vaso-occlusion, haemolysis and infection. Several genetic and environmental modifiers have been suggested to modulate the onset and course of SCA. As part of a wider research on the development and validation of vaso-occlusion early predictors in SCA, we have studied the association between haemolysis biomarkers (LDH, total bilirrubin and reticulocyte count) and the inheritance of genetic variants of ten candidate genes in a series of 99 paediatric SS patients (median current age of 9.9 years) followed-up in two general hospitals in Greater Lisbon area (median follow-up/patient of 5.0 years). Although in a large number of tests a seemingly significant (i.e., p<0.05) association was observed, only the following ones were confirmed upon correction for the false discovery rate: (a) An elevated LDH was associated to haplotype 7 within VCAM1 gene. (b) A lower total bilirrubin was associated to the 3.7kb deletion at HBA gene, rs2070744_T allele and haplotypes 3 and 4 at NOS3 gene and haplotype 9 within VCAM1 gene and rs3783598_G and rs3917024_T alleles at VCAM1 gene promoter. (c) A diminished reticulocyte count was associated to the 3.7kb deletion at HBA gene, whereas an elevated count was associated to rs1984112_G allele at CD36 gene. Furthermore, at the phenotypic level all three haemolysis biomarkers were positively associated to left ventricle dilation, a common chronic complication of SCA. On the whole, our findings suggest a complex genetic architecture for the haemolytic endophenotype in SCA involving multiple pathways, namely control of erythrocyte volume and haemoglobinisation, vascular cell adhesion, NO synthesis and lipid metabolism. Further mechanistic studies are needed to explore these avenues leading to a better understanding of the inter- and intra-individual clinical variability of SCA. Acknowledgement: Work partially funded by FCT grants PIC/IC/83084/2007 and CIGMH.

Desenvolvimento Neuropsicológico na Síndrome de X-Frágil: interpretar os perfis de desenvolvimento.

Thu, 22 Nov 2012 00:00:00 GMT

Title: Desenvolvimento Neuropsicológico na Síndrome de X-Frágil: interpretar os perfis de desenvolvimento. Authors: Carmona, Carla; Marques, Isabel; Santos, Rosário; Jorge, Paula Abstract: Introdução: A Síndrome de X Frágil (SXF) é uma doença genética causada por uma mutação dinâmica da região repetitiva constituída por tripletos CGG no gene FMR1, que leva à ausência da FMRP. Na população normal o número de CGGs oscila entre os 5 e os 45. A maioria dos doentes com SXF apresenta para além da expansão > 200 CGG, uma inativação do gene FMR1 por metilação do seu promotor (mutação completa). A principal manifestação da SXF é o atraso mental ou défice intelectual que varia de ligeiro a grave. Outros sinais incluem o atraso de desenvolvimento psicomotor, alterações de comportamento, a hiperatividade, o défice de atenção, dificuldades de aprendizagem e comportamento autista. Objetivo e métodos: Existe um grupo de doentes, menos comum, que revela ausência (total ou parcial) de metilação do FMR1 e níveis reduzidos da FMRP, denominados high-functioning males (HFM). Um outro conjunto engloba doentes, designados mosaicos (MoPMMC), que para além da mutação completa apresentam, em algumas células, um número de repetições inferior aos 200 (pré-mutação). Estes subgrupos são, sob o ponto de vista investigacional, particularmente interessantes pois apresentam características fenotípicas e genéticas imprevisíveis. O objetivo deste trabalho é analisar e comparar os níveis de desenvolvimento neuropsicológico, avaliados a partir da escala de desenvolvimento psicomotor e o perfil cognitivo, avaliado com as escalas de inteligência, de portadores da SXF e MoPMMC, de ambos os sexos. Resultados e Discussão: A análise detalhada dos perfis dos testes permite compreender a forma como as diferentes mutações podem influenciar no desenvolvimento psicomotor e cognitivo das crianças com SXF. Esta investigação neurogenética terá um importante impacto na seleção de uma futura aproximação terapêutica, no funcionamento e na qualidade de vida destes indivíduos, bem como ajudar reduzir os encargos para as famílias, seus cuidadores e a sociedade.

FRAXE molecular diagnosis in individuals referred for FRAXA screening

Thu, 22 Nov 2012 00:00:00 GMT

Title: FRAXE molecular diagnosis in individuals referred for FRAXA screening Authors: Javed, Ali; G., Ali; Caicedo, Lina; Marques, Isabel; Santos, Rosário; Jorge, Paula Abstract: Introduction: FRAXE mental retardation is a form of mild to moderate intellectual disability generally associated with learning difficulties, communication deficits, attention problems, hyperactivity and autistic behavior. The folate-sensitive fragile site FRAXE (AFF2/ FMR2 gene) is ~600 kb distal to FRAXA (FMR1 gene), which is the most common cause of inherited mental retardation. Normal individuals present 4–39 copies of the polymorphic CCG repeat in AFF2, while individuals expressing the fragile site have >200 copies and the CpG island is fully methylated. Goal and methods: Reports of full expansions and pre-mutations in AFF2 are rarely documented. In this respect, it has been very difficult to determine to what extent the alleles with CCG repeats in the range of 36 to 199, have a pathogenic effect. Intellectually disabled individuals are primarily referred for FRAXA screening and individuals who are negative for FRAXA are possible candidates for FRAXE screening. In order to complement our PCR analysis with Southern blot and hybridization, we cloned a segment of the AFF2 gene that could be used as a labeled probe to determine more accurately the extent of expansion of the CCG repeats. Results and discussion: We have developed a probe to be used for Southern blot analysis that reliably detects the AFF2 CCG triple repeat amplification. We present validation data and results of AFF2 molecular analysis in a subpopulation of 5000 individuals originally referred for FRAXA screening. The presence of pre-mutated and fully expanded alleles in either gender was confirmed by Southern blot analysis, which also enabled evaluation of methylation status and exclusion of repeat number mosaics or PCR failure. We recommend the use of this probe as a method of choice for the detection of AFF2 pre-mutations, full mutations and mosaics, specifically in individuals found to be negative upon FRAXA screening.

Fragile X syndrome: intergenerational allele instability and associated phenotypes in families

Thu, 22 Nov 2012 00:00:00 GMT

Title: Fragile X syndrome: intergenerational allele instability and associated phenotypes in families Authors: Joana, Loureiro; Marques, Isabel; Santos, Rosário; Seixas, Ana; Martins, Márcia; Vale, José; Sequeiros, Jorge; Silveira, Isabel Abstract: Fragile X syndrome (FXS) is the most common hereditary form of intellectual disability with an estimated frequency of 1/4000 males and 1/8000 females. This disease is caused by a (CGG)n expansion in the 5’UTR of the FMR1 gene, which as a result is methylated and gene silenced. Four classes of alleles can be found based on CGG repeat length: normal (5-44), intermediate (45-54), premutation (55-200) and full mutation (>200). In premutation carriers, both FMR1-related primary ovarian insufficiency (FXPOI) and fragile-X associated tremor/ataxia syndrome (FXTAS) have been described. To gain insights into instability of FMR1 CGG repeats and associated phenotypes, we studied 541 individuals from 128 FXS Portuguese families. DNA samples were genotyped by PCR and Southern blot analysis. Additional clinical evaluation was performed in premutation carriers. Among FXS families, 5.3% intermediate, 29.9% premutation and 26.6% full mutation alleles were found. Normal and intermediate alleles were stable upon transmission. For 115 maternal premutation transmissions, 26 (23%) with alleles ranging 60-98 CGGs remained in premutation size with an average expansion of 17 repeat units, whereas 89 (77%) with alleles ranging from 66-199 CGGs expanded to full mutation. In 44 transmissions of maternal full mutation, the offspring inherited alleles in the full mutation range. For 10 paternal transmissions of premutations, ranging 56-120 CGGs, all daughters inherited a premutation allele, with an average expansion of 7 repeat units. After clinical evaluation of 7 premutation carriers, 1 male with FXTAS and 2 females with FXPOI were identified; however the remaining premutation individuals were not yet examined. In Portuguese FXS families, allele instability upon transmission is in agreement with previous reports. The risk of premutation to full mutation expansion increases with maternal premutation size.