RESUMO
We identified two unstable variants in the third exon of α-globin genes: Hb Bernalda/Groene Hart (HBA1:c.358C>T), and Hb Caserta (HBA2:c.79G>A) in cis to Hb Sun Prairie (HBA2:c.391G>C), also named Hb Southern Italy. These mutations occurred in the H helix of the α-globin that is involved in heme contacting, specific recognition of α-hemoglobin-stabilizing protein (AHSP), and α1ß1 interactions. The carriers showed α-thalassemia phenotype, but one also jaundice and cholelithiasis. Molecular identification of clusters of families in Southern Italy encouraged molecular characterization of mRNA, globin chain analyses, molecular modeling studies, and comparison with globin variants to understand the mechanisms causing the α-thalassemia phenotype. A normal amount of Hb Bernalda/Groene Hart mRNA were found, and molecular modeling highlighted additional H bonds with AHSP. For Hb Southern Italy, showing an unexpected α/ß biosynthetic ratio typical of the ß-thalassemia type, two different molecular mechanisms were shown: Reduction of the variant mRNA, likely due to the No-Go Decay for the presence of unused triplet ACG at cod 26, and protein instability due to the impairment of AHSP interaction. The UDP glucuronosyltransferase 1A (UGT1A1) genotyping was conclusive in the case of jaundice and cholelithiasis. Multiple approaches are needed to properly identify the mechanisms leading to unstable variants and the effect of a mutation.
Assuntos
Hemoglobina A/genética , Hemoglobinas Anormais/genética , Mutação , Talassemia/genética , Adolescente , Adulto , Idoso , Sítios de Ligação , Proteínas Sanguíneas/metabolismo , Células Cultivadas , Criança , Feminino , Glucuronosiltransferase/genética , Hemoglobina A/química , Hemoglobina A/metabolismo , Hemoglobinas Anormais/química , Hemoglobinas Anormais/metabolismo , Humanos , Itália , Masculino , Pessoa de Meia-Idade , Chaperonas Moleculares/metabolismo , Fenótipo , Ligação Proteica , Estabilidade Proteica , Estabilidade de RNA , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Talassemia/patologiaRESUMO
OBJECTIVE: To evaluate the role of different polymorphic gene variants involved in homocysteine metabolism and plasma levels of homocysteine, folate and vitamin B12 in families from southern Italy with neural tube defects (NTDs). METHODS: Eighteen fathers, 15 NTD children and 60 women who had conceived NTD foetuses were investigated. A group of 100 adults and 43 apparently healthy children was used as control. At the time of blood draw, none were taking vitamin pills or nutritional supplements. RESULTS: Among controls, 79 (55.2%) were heterozygous for C677T MTHFR variant and 26 (18.2%) were TT homozygous. Among the cases, 35 (61.4%) out of 57 mothers and 7 (38.9%) out of 18 fathers carried the T allele; 12 (21.1%) mothers and 2 (11.1%) fathers had the TT genotype. Four (26.7%) out of 15 probands were TT homozygous and 11 (73.3%) were heterozygous (Fisher exact test p = 0.025). No significant difference between groups was observed for the 1298C MTHFR variant and CBS haplotypes. Median homocysteine in NTD children was significantly higher (10.0 micromol/L) than that of controls (median 4.5 micromol/L, Mann-Whitney p < 0.05). Folate and B12 were not different among groups. CONCLUSIONS: The T677 MTHFR allele is significantly associated with the occurrence of NTDs; no significant association has been observed with other genetic determinants analysed. Homocysteine levels in children with NTDs are significantly higher than those of the paediatric population from the same geographical area.
Assuntos
Predisposição Genética para Doença , Homocisteína/genética , Defeitos do Tubo Neural/genética , Adolescente , Adulto , Estudos de Casos e Controles , Pré-Escolar , Feminino , Homocisteína/sangue , Homocisteína/metabolismo , Humanos , Lactente , Itália , Masculino , Metilenotetra-Hidrofolato Redutase (NADPH2)/genética , Pessoa de Meia-Idade , Mutação , Estado Nutricional , População Branca/genéticaRESUMO
We report a novel mutation, Hb A2-Monreale [delta146(HC3)His-->Arg], detected by cation exchange high performance liquid chromatography in a family from West Sicily. The mutation is due to a CAT-->CGT substitution at codon 146 of the delta-globin gene. The two carriers had reduced levels of normal Hb A2 (1.1%), but comparable levels (0.9%) of the Hb A2 variant. Most likely the new variant has the same characteristics as Hb Cochin-Port Royal [beta146(HC3)His-->Arg], that is stable but has a 75% reduction of the Bohr effect. The finding of the new variant increases the genotype heterogeneity of the delta-globin gene in the Mediterranean area, and is relevant to the study and prevention of Cooley's Anemia.
