Large Duplications Can Be Benign Copy Number Variants: A Case of a 3.6-Mb Xq21.33 Duplication

Segmental aneusomies are usually associated with clinical consequences, but an increasing number of nonpathogenic cytogenetically visible as well as large cryptic chromosomal imbalances have been reported. Here, we report a 3.6-Mb Xq21.33 microduplication detected prenatally on a female fetus which was inherited from a phenotypically normal mother and grandfather. It is assumed that male patients harboring Xq or Xp duplication present with syndromic intellectual disability because of functional disomy of the corresponding genes. Female carriers are generally asymptomatic because of preferential inactivation of the abnormal X. In the present case, the 3.6-Mb-duplicated segment encompasses only 2 genes, DIAPH2 and RPL4A. Since the asymptomatic grandfather carries the duplication, we hypothesize that these genes are not dosage sensitive and/or involved in cognitive function. Our observation further illustrates that large copy number variants can be associated with a normal phenotype, especially where gene density is low. Reporting rare cases of large genomic imbalances without a phenotypic effect can be very helpful, especially for genetic counseling in the prenatal setting.

Ca2+ Enhances U-Type Inactivation of N-Type (CaV2.2) Calcium Current in Rat Sympathetic Neurons

Ca2+-dependent inactivation (CDI) has recently been shown in heterologously expressed N-type calcium channels (CaV2.2), but CDI has been inconsistently observed in native N-current. We examined the effect of Ca2+ on N-channel inactivation in rat sympathetic neurons to determine the role of CDI on mammalian N-channels. N-current inactivated with fast (τ ∼ 150 ms) and slow (τ ∼ 3 s) components in Ba2+. Ca2+ differentially affected these components by accelerating the slow component (slow inactivation) and enhancing the amplitude of the fast component (fast inactivation). Lowering intracellular BAPTA concentration from 20 to 0.1 mM accelerated slow inactivation, but only in Ca2+ as expected from CDI. However, low BAPTA accelerated fast inactivation in either Ca2+ or Ba2+, which was unexpected. Fast inactivation was abolished with monovalent cations as the charge carrier, but slow inactivation was similar to that in Ba2+. Increased Ca2+, but not Ba2+, concentration (5–30 mM) enhanced the amplitude of fast inactivation and accelerated slow inactivation. However, the enhancement of fast inactivation was independent of Ca2+ influx, which indicates the relevant site is exposed to the extracellular solution and is inconsistent with CDI. Fast inactivation showed U-shaped voltage dependence in both Ba2+ and Ca2+, which appears to result from preferential inactivation from intermediate closed states (U-type inactivation). Taken together, the data support a role for extracellular divalent cations in modulating U-type inactivation. CDI appears to play a role in N-channel inactivation, but on a slower (sec) time scale.

Morphological Changes and Lysis Induced by β-Lactams Associated with the Characteristic Profiles of Affinities of Penicillin-Binding Proteins in Actinobacillus pleuropneumoniae

ABSTRACT Actinobacillus pleuropneumoniae, which was formerly classified in the genus Haemophilus, is a pathogen causing swine pleuropneumonia. We found that aspoxicillin showed strong activity and that meropenem had better lytic activity against this pathogen. In the present study, we for the first time identified penicillin-binding proteins (PBPs) of A. pleuropneumoniaein order to elucidate the relationship between the antibacterial and lytic activities of β-lactam antibiotics and affinities of the PBPs. The competitive assay using 3H-labeled benzylpenicillin revealed seven PBPs in A. pleuropneumoniae; they were determined to be PBPs 1a, 1b, 2, 3, 4, 5, and 6, and the molecular masses of these PBPs were estimated to be 92, 80, 76, 72, 50, 44, and 30 kDa, respectively, by comparison with those of Haemophilus influenzae. Our detailed analysis of the affinities of the PBPs of A. pleuropneumoniae and of the bacterial lysis kinetics for several β-lactam antibiotics revealed that the strong antibacterial activity of aspoxicillin against this strain could be related to the higher affinity of PBP 3 and that preferential inactivation of PBP 1b could cause rapid lysis.