X-linked West syndrome, also called "X-linked infantile spasms" (ISSX), is characterized by early-onset generalized seizures, hypsarrhythmia, and mental retardation. Recently, we have shown that the majority of the X-linked families with infantile spasms carry mutations in the aristaless-related homeobox gene (ARX), which maps to the Xp21.3-p22.1 interval, and that the clinical picture in these patients can vary from mild mental retardation to severe ISSX with additional neurological abnormalities. Here, we report a study of two severely affected female patients with apparently de novo balanced X;autosome translocations, both disrupting the serine-threonine kinase 9 (STK9) gene, which maps distal to ARX in the Xp22.3 region. We show that STK9 is subject to X-inactivation in normal female somatic cells and is functionally absent in the two patients, because of preferential inactivation of the normal X. Disruption of the same gene in two unrelated patients who have identical phenotypes (consisting of early-onset severe infantile spasms, profound global developmental arrest, hypsarrhythmia, and severe mental retardation) strongly suggests that lack of functional STK9 protein causes severe ISSX and that STK9 is a second X-chromosomal locus for this disorder.

We have identified truncating mutations in the human DLG3 (neuroendocrine dlg) gene in 4 of 329 families with moderate to severe X-linked mental retardation. DLG3 encodes synapse-associated protein 102 (SAP102), a member of the membrane-associated guanylate kinase protein family. Neuronal SAP102 is expressed during early brain development and is localized to the postsynaptic density of excitatory synapses. It is composed of three amino-terminal PDZ domains, an src homology domain, and a carboxyl-terminal guanylate kinase domain. The PDZ domains interact directly with the NR2 subunits of the NMDA glutamate receptor and with other proteins responsible for NMDA receptor localization, immobilization, and signaling. The mutations identified in this study all introduce premature stop codons within or before the third PDZ domain, and it is likely that this impairs the ability of SAP102 to interact with the NMDA receptor and/or other proteins involved in downstream NMDA receptor signaling pathways. NMDA receptors have been implicated in the induction of certain forms of synaptic plasticity, such as long-term potentiation and long-term depression, and these changes in synaptic efficacy have been proposed as neural mechanisms underlying memory and learning. The disruption of NMDA receptor targeting or signaling, as a result of the loss of SAP102, may lead to altered synaptic plasticity and may explain the intellectual impairment observed in individuals with DLG3 mutations.

We retrospectively examined the relationship between fluoroquinolone use and the susceptibilities of 11 bacterial pathogens to fluoroquinolones in 10 US teaching hospitals from 1991 through 2000. Statistical significance was determined by 2-way analysis of variance, with the number of isolates tested each year as a weighting factor. The analysis of baseline-to-end point change in the percentage of susceptibility and the slope of the regression line (trend line) for logit percentage of susceptibility showed that the overall percentage of susceptibility to fluoroquinolones decreased significantly during the study period (P<.05) and that change in percentage of susceptibility was significantly related to change in fluoroquinolone use (P<.05). Particularly notable were the decreases in the susceptibilities of Pseudomonas aeruginosa, Proteus mirabilis, and Escherichia coli (decreases of 25.1%, 11.9%, and 6.8%, respectively).