Mutations in SYNGAP1 in autosomal nonsyndromic mental retardation

Abstract

Although autosomal forms of nonsyndromic mental retardation account for the majority of cases of mental retardation, the genes that are involved remain largely unknown. We sequenced the autosomal gene SYNGAP1, which encodes a ras GTPase-activating protein that is critical for cognition and synapse function, in 94 patients with nonsyndromic mental retardation. We identified de novo truncating mutations (K138X, R579X, and L813RfsX22) in three of these patients. In contrast, we observed no de novo or truncating mutations in SYNGAP1 in samples from 142 subjects with autism spectrum disorders, 143 subjects with schizophrenia, and 190 control subjects. These results indicate that SYNGAP1 disruption is a cause of autosomal dominant nonsyndromic mental retardation.

Figure 1. De Novo SYNGAP1 Mutations in Three Patients with Nonsyndromic Mental Retardation

Panel A shows the localization of de novo SYNGAP1 mutations identified in patients with nonsyndromic mental retardation. Amino acid positions are based on the NCBI Reference Sequence project number NP_006763 (from NM_006772) (for isoform 1, which consists of 1343 amino acids). The various predicted functional domains are highlighted: pleckstrin homology domain (PH; positions 150 to 251), C2 domain (positions 263 to 362), RASGAP (positions 392 to 729), SH3 (positions 785 to 815), CC domain (positions 1189 to 1262), T/SXV type 1 PDZ-binding motif (QTRV) (isoform 2), and CamKII binding (GAAPGPPRHG) (isoform 3). In addition, the last amino acids of isoform 1 (TADH) are shown. The variable C-terminals of the three SYNGAP1 isoforms that are shown here correspond to GenBank complementary DNA accession numbers AB067525 (for isoform 1), AK307888 (for isoform 2), and AL713634 (for isoform 3). The hatched lines for isoforms 2 and 3 indicate that the amino acid sequence has been abbreviated. Panel B shows chromatograms corresponding to the SYNGAP1 sequence for each of the three patients with de novo mutations and for their parents. Wild-type and mutant SYNGAP1 DNA sequences are shown, along with the corresponding amino acids.