ABSTRACT
Males with an expressed mutation in the SH2D1A gene that encodes an SH2 domain protein named SH2D1A or SAP (NP_002342; signaling lymphocyte activating molecule [SLAM]-associated protein), have an X-linked syndrome characterized by an increased vulnerability to infection with Epstein-Barr virus (EBV). We evaluated two related male patients with fatal infectious mononucleosis (FIM) and mutation in the SH2D1A gene. Sequence analysis revealed a hemizygous c.47G>A mutation in one of the patients, and heterozygosity for this mutation in the genomic DNA from his mother and maternal grandmother. This mutation resulted in p.G16D amino acid change in the sequence of the SAP protein. To analyze the effect of this missense mutation on protein function cDNA was generated by site-directed mutagenesis and expressed in COS cells. We found that half-life of the p.G16D protein was comparable to that of wild type SAP. However, the mutant protein was defective in binding to its physiological ligands SLAM and 2B4. These results suggest that a defect in ligand binding contributes to the loss of function of the SAP protein in patients carrying p.G16D mutation.
Subject(s)
Infectious Mononucleosis/genetics , Intracellular Signaling Peptides and Proteins/genetics , Lymphoproliferative Disorders/genetics , Amino Acid Sequence , Animals , Antigens, CD/metabolism , COS Cells , Child , Chlorocebus aethiops , Genetic Predisposition to Disease , Glycoproteins/metabolism , Half-Life , Humans , Immunoglobulins/metabolism , Intracellular Signaling Peptides and Proteins/chemistry , Intracellular Signaling Peptides and Proteins/physiology , Male , Membrane Glycoproteins/metabolism , Molecular Sequence Data , Mutation, Missense , Pedigree , Protein Binding/physiology , Receptors, Cell Surface , Receptors, Immunologic/metabolism , Signaling Lymphocytic Activation Molecule Associated Protein , Signaling Lymphocytic Activation Molecule Family , Signaling Lymphocytic Activation Molecule Family Member 1ABSTRACT
Cleft lip with or without cleft palate is a common birth defect affecting 1 in every 700 live births. Several genetic loci are believed to be involved in the pathogenesis of syndromic and non-syndromic clefting. We identified a pericentric inversion of chromosome 4, inv(4)(p13q21) that segregates with cleft lip in a two-generation family. By using a combination of fluorescence in situ hybridization, yeast artificial chromosome, bacterial artificial chromosome contig mapping, and database searching we mapped and sequenced the inversion breakpoint region. The pericentric inversion disrupts a gene (ACOD4) on chromosome 4q21 that codes for a novel acyl-CoA desaturase enzyme. The 3.0 kb human ACOD4 cDNA spans approximately 170 kb and is composed of five exons of ACOD4. The inversion breakpoint is located in the second exon. The 3.0 kb mRNA is expressed at high level in fetal brain; a lower expression level was found in fetal kidney. No expression of ACOD4 was detected in fetal lung or liver or in adult tissues. The five exons code for a protein of 330 amino acids, with a predicted molecular weight of 37.5 kDa. The protein is highly similar to acyl-CoA desaturases from Drosophila melanogaster to Homo sapiens. The catalytically essential histidine clusters and the potential transmembrane domains are well conserved.
