Alpha-actin gene mutations and polymorphisms in Italian patients with nemaline myopathy

Nemaline myopathy is a rare neuromuscular disorder, showing striking clinical and genetic heterogeneity. Patients can show a spectrum of disease ranging from severe congenital to an adult-onset mild form. Disease-causing mutations have been reported in five genes encoding sarcomeric thin filament proteins, and inheritance can be either autosomal recessive or dominant. No phenotype-genotype correlation is apparent at the moment. alpha-actin gene mutations are responsible for about 20% of cases. We have collected 18 patients from 17 families. Our patients exhibit an overall marked clinical variability, but 10 out of 18 show typical features of nemaline myopathy (slowly progressive congenital form). We have identified disease-causing mutations in the alpha-actin gene in 5 out of 17 families, through direct sequencing of its whole coding sequence. One patient carried two mutations, thus we describe a total of 6 mutations, all arising de novo. We also describe some intronic polymorphisms which constitute two common alpha-actin gene haplotypes; we show that haplotype characterisation may have a strong impact in mutation detection due to preferential amplification of a chromosome in subjects carrying both haplotypes. Screening of the alpha-actin gene coding sequence may account for the identification of disease-causing mutations in 20-30% of nemaline myopathy patients. Since the chance to identify mutations is independent of the clinical picture, we suggest that it is appropriate to check for mutations in all patients. Demonstration of a de novo origin of the mutation is of great relevance for families seeking genetic counselling.     

Effect of blood transfusions on oxidative stress in preterm infants

OBJECTIVE: To confirm the increase in non-transferrin bound iron (NTBI) after packed red cell (PRC) transfusion and to evaluate the association with increased oxidative stress in preterm infants. METHOD: Twenty healthy preterm infants (gestational age 28.2 (2.2) weeks; birth weight 1047 (230) g), who required blood transfusion for anaemia of prematurity were prospectively studied. Serum concentrations of NTBI, total hydroperoxides (TH), and protein SH groups, and plasma total radical trapping antioxidant capability (TAC) were measured within three hours before and after PRC transfusion. The infants were transfused with 38.6 (23) ml PRCs over 5.8 (1.0) hours, at a mean age of 43.3 (25.1) days. RESULTS: After PRC transfusion, haemoglobin concentration increased from 9.2 (1.1) to 14.6 (1.5) g/l. Mean plasma NTBI concentration after transfusion was significantly higher (0.43 (0.45) v 2.03 (1.31) micromol/l; p = 0.001), while plasma concentrations of TH (212.3 (42.2) v 214.7 (66.3) Carr units/l) and protein SH groups (317.5 (38.8) v 353.8 (57.4) micromol/), and TAC (256.3 (36.1) v 267.1 (42.4) micromol HClO/ml) remained unchanged. CONCLUSION: For three hours after PRC transfusion, plasma NTBI is significantly increased in preterm infants, but this is not associated with significant changes in oxidative stress.     

Clinical and molecular findings in patients with giant axonal neuropathy (GAN)

Giant axonal neuropathy (GAN) is a rare autosomal recessive neurodegenerative disorder of early onset, clinically characterized by a progressive involvement of both peripheral and CNS. The diagnosis is based on the presence of characteristic giant axons, filled with neurofilaments, on nerve biopsy. Recently, the defective protein, gigaxonin, has been identified and different pathogenic mutations in the gigaxonin gene have been reported as the underlying genetic defect. Gigaxonin, a member of the BTB/kelch superfamily proteins, seems to play a crucial role in the cross talk between the intermediate filaments and the membrane network. The authors report clinical and molecular findings in five Italian patients with GAN. This study shows the allelic heterogeneity of GAN and expands the spectrum of mutations in the GAN gene. The frequent occurrence of private mutations stresses the importance of a complete gene analysis.     

Metallochaperones and metal-transporting ATPases: a comparative analysis of sequences and structures

A comparative structural genomic analysis of a new class of metal-trafficking proteins can provide insights into the intracellular chemistry of reactive cofactors such as copper and zinc. Starting from the sequences of the metallochaperone Atx1 and from the first soluble domain of the copper-transporting ATPase Ccc2, both from yeast, a search on the available genomes was performed using a homology criterion and a metal-binding motif x'-x"-C-x'-x'-C. By limiting ourselves to 20% identity with any of the proteins found, several soluble copper-transport proteins were identified, as well as soluble domains of membrane-bound ATPases. Structural models were calculated using high-resolution solution structures as templates, and the models were validated using statistical and energy criteria. Residue conservation and substitution have been interpreted and discussed in terms of structure-function relationship. The potential energy surfaces have been analyzed in terms of protein-protein interactions. We find that metallochaperones and their physiological partner ATPases from several phylogenetic kingdoms recognize one another, via an interplay of electrostatics, hydrogen bonding, and hydrophobic interactions, in a manner that precisely orients the metal-binding side chains for rapid metal transfer between otherwise tight binding sites. Finally, other putative metal-transport proteins are mentioned that have low homology and/or a different metal-binding consensus motif and that appear to use similar structures for recognition and transfer. This analysis highlights the wealth and the complexity of the field.     

Restriction in T-cell receptor repertoire in a patient affected by trichothiodystrophy and CD4+ lymphopenia

Molecular analysis of T-cell receptor (TCR) repertoire, by measuring the CDR3 heterogeneity length of beta-variable regions (spectratyping), is useful for acquiring novel information on the status of immune system in primary immunodeficiency. Here, we evaluate TCR repertoire in a child with trichothiodystrophy (TTD) and combined immunodeficiency (CID). Spectratyping revealed marked alterations of TCR repertoire distribution: 21 and 10 out of 27 TCR Vbeta (TCRBV) families and subfamilies were skewed in CD8+ and CD4+ subsets, respectively. These findings revealed, for the first time in a TTD patient with CID, a marked reduction in the TCR repertoire complexity, which may reflect alterations in the mechanisms regulating the generation and homeostasis of T cells.