Mutation Screening of Elongation Factor 2 in Shwachman-Diamond Syndrome Patients Lacking Mutations in the SBDS Gene

Shwachman-Diamond syndrome is an autosomal recessive disorder characterized by bone marrow failure, pancreatic insufficiency, and skeletal abnormalities. Mutations in SBDS gene explain, by literature, 90% of SDS cases. The Italian experience shows that only the 5% of individuals diagnosed as affected by SDS on clinical and hematological grounds lack mutations in the SBDS gene. It is well established that SBDS protein is essential for the assembly of mature ribosomes. The yeast SBDS ortholog functions within a pathway containing elongation factor-like 1, homologous to human GTPase elongation factor-2, to promote the release and recycling of the nucleolar shuttling factor Tif6 from cytoplasmic pre-60S subunits in a cascade targeted to form the active ribosome. We considered that mutations of genes that disrupt pathways shared by SBDS may result in disease with comparable clinical features. EEF2 was evaluated as a candidate gene by mutation screening in clinically defined SDS which lack mutations in the SBDS gene. To date, no deleterious mutations were found in EEF2 in four Italian patients without SBDS mutations, but with a clinical diagnosis of SDS. 1. Introduction Shwachman-Diamond-syndrome- (SDS-)associated mutations were described in a gene-designed Shwachman-Bodian-Diamond syndrome (SBDS) [1] that encodes a member of a highly conserved protein family, with orthologues in diverse species including archaea, plants, and eukaryotes. Structural studies of the Archaeoglobus fulgidus SBDS ortholog [2] revealed the presence of three domains. The N-terminal domain is identical to the single domain yeast protein Yhr087wp that is implicated in RNA metabolism. The protein that is most closely structurally related to the second domain is the C-terminal domain of E. coli, RuvA, that is involved in Holliday junction recognition during the recombination event. The closest structural homologue to C-terminal third domain of Archaeoglobus fulgidus SBDS ortholog is the fifth domain of yeast S. cerevisiae elongation factor 2 [2]. The SBDS mRNA is widely expressed throughout the human tissue [1]; furthermore, immunofluorecence studies showed that the SBDS protein is localized to both the nucleus and the cytoplasm, but is particularly concentrated within the nucleolus [3]. The nucleolus is best known as a site of ribosome biogenesis. An interesting discovery from proteomic studies of the nucleolus [4–6] was that approximately 30% of nucleolar proteins constituted either novel or uncharacterized proteins. It is known that RNA processing factors are localized in the