Variations in the coding and regulatory sequences of the angiogenin (ANG) gene are not associated to ALS (amyotrophic lateral sclerosis) in the Italian population

Abstract

Potentially causative missense variations in the ANG gene and a positive association with the synonymous rs11701-G substitution was detected mainly in Irish and Scottish ALS patients. We screened 262 Italian SOD1 negative ALS patients (250 sporadic) and 415 matched controls for sequence variations in the coding, 3′/5′ UTR and 5′ flanking (642 bp) regions of the ANG gene. We identified 53 sequence variations of which 46 new, 20 with a minor allele frequency (MAF) ≥ 0.01 and only three localised in the coding sequence, namely the missense I46V, identified in one patient and two controls, and the synonymous G86G and T97T corresponding to rs11701 and rs2228653. None of the detected SNPs or of their haplotypic combinations was significantly associated with ALS susceptibility or clinical features. In conclusion, we did not detect the association with rs11701-G or with any other newly detected variation in the ANG regulatory region. Furthermore we did not identify potentially causal mutations in the coding region.

Introduction

Amyotrophic lateral sclerosis (ALS) is an adult onset neurodegenerative disorder characterized by progressive loss of motor neurons in the spinal cord, brainstem, and cerebral cortex. Five to ten percent of ALS cases are familial (FALS), mostly inherited as autosomal dominant, and 14–24% of them have mutations in the gene encoding for Cu/Zn superoxide dismutase (SOD1). However in the majority of familial and sporadic (SALS) ALS patients, the cause of the selective degeneration of motor neurons is unknown.

Recently a positive association with ALS of the G allele of the synonymous SNP rs11701 in the ANG (angiogenin) gene was identified in the Irish population [1]. Genotyping of rs11701 in 1629 ALS patients and 1264 ethnically matched controls from five populations mostly of Northern Europe origin from Ireland, Scotland, USA Boston, Sweden, UK [2], and in 210 Italian SALS patients and 306 Italian controls [3] confirmed the positive association only in the Irish and Scottish populations. Moreover, sequencing of the ANG coding regions in the same patients identified in 15 ALS patients 7 missense mutations of which only one (K17I) was also detected in a healthy 65-year-old male. Six of these missense mutations affect functionally important residues that are evolutionary highly conserved suggesting a potential causative role in ALS pathogenesis. Sixty percent of the patients with a mutation presented with a bulbar site of onset as against 24–28% in the total tested patients, 4 cases reported a family history of ALS and 12 were of Irish/Scottish origin [2]. No mutation was detected in the Italian patients [3]. Thus ANG mutations appeared to be largely restricted to patients from Irish and/or Scottish ancestry.

In order to confirm and extend the above results we tested the involvement of ANG sequence variations in a further large sample of Italian ALS patients and controls. In addition to what performed in previous studies, we also screened for variations the ANG regulatory sequences and tested the association of all the detected variations with ALS susceptibility and clinical presentation.