Little is known about the genetics of nonsyndromic intellectual disability (NSID). We hypothesized that de novo mutations (DNMs) in synaptic genes explain an important fraction of sporadic NSID cases. In order to investigate this possibility, we sequenced 197 genes encoding glutamate receptors and a large subset of their known interacting proteins in 95 sporadic cases of NSID. We found 11 DNMs, including ten potentially deleterious mutations (three nonsense, two splicing, one frameshift, four missense) and one neutral mutation (silent) in eight different genes. Calculation of point-substitution DNM rates per functional and neutral site showed significant excess of functional DNMs compared to neutral ones. De novo truncating and/or splicing mutations in SYNGAP1, STXBP1, and SHANK3 were found in six patients and are likely to be pathogenic. De novo missense mutations were found in KIF1A, GRIN1, CACNG2, and EPB41L1. Functional studies showed that all these missense mutations affect protein function in cell culture systems, suggesting that they may be pathogenic. Sequencing these four genes in 50 additional sporadic cases of NSID identified a second DNM in GRIN1 (c.1679_1681dup/p.Ser560dup). This mutation also affects protein function, consistent with structural predictions. None of these mutations or any other DNMs were identified in these genes in 285 healthy controls. This study highlights the importance of the glutamate receptor complexes in NSID and further supports the role of DNMs in this disorder.

No abstract

In Figure 2B, the label on the right should be NR1-S560dup/NR2B instead of the alternative terminology NR1 (S560_T561InsS)/NR2B.

A spermidine excretion protein in Escherichia coli was looked for among 33 putative drug exporters thus far identified. Cell toxicity and inhibition of growth due to overaccumulation of spermidine were examined in an E. coli strain deficient in spermidine acetyltransferase, an enzyme that metabolizes spermidine. Toxicity and inhibition of cell growth by spermidine were recovered in cells transformed with pUCmdtJI or pMWmdtJI, encoding MdtJ and MdtI, which belong to the small multidrug resistance family of drug exporters. Both mdtJ and mdtI are necessary for recovery from the toxicity of overaccumulated spermidine. It was also found that the level of mdtJI mRNA was increased by spermidine. The spermidine content in cells cultured in the presence of 2 mM spermidine was decreased, and excretion of spermidine from cells was enhanced by MdtJI, indicating that the MdtJI complex can catalyze excretion of spermidine from cells. Polyamines (putrescine, spermidine, and spermine) are essential for normal cell growth (3,11,12), and their content in cells is regulated by biosynthesis, degradation, uptake, and excretion (5, 9, 10, 26). With regard to transport, the properties of three polyamine transport systems were characterized in Escherichia coli (15,16,40). They include spermidine-preferential and putrescine-specific uptake systems, which belong to the family of ATP binding cassette transporters, and a protein, PotE, involved in the excretion of putrescine by a putrescineornithine antiporter activity. Furthermore, it has been reported that cadaverine and aminopropylcadaverine function as compensatory polyamines for cell growth (13), and CadB, a cadaverine-lysine antiporter, is strongly involved in cell growth at acidic pH, like PotE (23,33,34,41). Analogous to the speF-potE operon (18), cadB is one component of the cadBA operon, in which cadA encodes lysine decarboxylase (22,41) and is induced by acidic pH and lysine (23). The cadBA and speF-potE operons contribute to an increase in the pH of the extracellular medium through excretion of cadaverine and putrescine, the consumption of a proton, and a supply of carbon dioxide during the decarboxylation reaction (33, 38), so the expression of these two operons is important for cell growth at acidic pH.Although PotE and CadB excrete putrescine and cadaverine at acidic pH, they function as uptake proteins for putrescine and cadaverine at neutral pH (16,33). Thus, no polyamine excretion proteins that function at neutral pH have been identified to date. Overaccumulated spermidine is either metabolized by acetylation of spermidine, in a reaction catalyzed by spermidine acetyltransferase (6), or neutralized by the increase in L-glycerol 3-phosphate (27). In this study, we looked for spermidine excretion proteins among putative drug exporters comprising five families (the major facilitator family, the small multidrug resistance [SMR] family, the resistance-nodulationcell division family, the ATP binding cassette family, and the multidrug and toxic compound extrusion family) (25) a...

Serotonin (5HT) plays major roles in the physiological regulation of many behavioral processes, including sleep, feeding, and mood, but the genetic mechanisms by which serotonergic neurons arise during development are poorly understood. In the present study, we have investigated the development of serotonergic neurons in the zebrafish. Neurons exhibiting 5HT-immunoreactivity (5HT-IR) are detected from 45 h postfertilization (hpf) in the ventral hindbrain raphe, the hypothalamus, pineal organ, and pretectal area. Tryptophan hydroxylases encode rate-limiting enzymes that function in the synthesis of 5HT. As part of this study, we cloned and analyzed a novel zebrafish tph gene named tphR. Unlike two other zebrafish tph genes (tphD1 and tphD2), tphR is expressed in serotonergic raphe neurons, similar to tph genes in mammalian species. tphR is also expressed in the pineal organ where it is likely to be involved in the pathway leading to synthesis