Structural aspects of the p.P222Q homozygous mutation of HSD3B2 gene in a patient with congenital adrenal hyperplasia

Type II 3β-hydroxysteroid dehydrogenase/Δ5-Δ4-isomerase (3β-HSD2), encoded by the HSD3B2 gene, is a key enzyme involved in the biosynthesis of all the classes of steroid hormones. Deleterious mutations in the HSD3B2 gene cause the classical deficiency of 3β-HSD2, which is a rare autosomal recessive disease that leads to congenital adrenal hyperplasia (CAH). CAH is the most frequent cause of ambiguous genitalia and adrenal insufficiency in newborn infants with variable degrees of salt losing. Here we report the molecular and structural analysis of the HSD3B2 gene in a 46,XY child, who was born from consanguineous parents, and presented with ambiguous genitalia and salt losing. The patient carries a homozygous nucleotide c.665C>A change in exon 4 that putatively substitutes the proline at codon 222 for glutamine. Molecular homology modeling of normal and mutant 3β-HSD2 enzymes emphasizes codon 222 as an important residue for the folding pattern of the enzyme and validates a suitable model for analysis of new mutations.

Dynamical mutation of dark energy

We discuss the intriguing possibility that dark energy may change its equation of state in situations where large dark energy fluctuations are present. We show indications of this dynamical mutation in some generic models of dark energy.

Generalized epilepsy with febrile seizures plus: Mutation of the sodium channel subunit SCN1B

Generalized epilepsy with febrile seizures plus (GEFS(+)) is an important childhood genetic epilepsy syndrome with heterogeneous phenotypes, including febrile seizures (FS) and generalized epilepsies of variable severity. Forty unrelated GEFS(+) and FS patients were screened for mutations in the sodium channel beta-subunits SCN1B and SCN2B, and the second GEFS(+) family with an SCN1B mutation is described here. The family had 19 affected individuals: 16 with typical GEFS(+) phenotypes and three with other epilepsy phenotypes. Site-specific mutation within SCN1B remains a rare cause of GEFS(+), and the authors found no evidence to implicate SCN2B in this syndrome.

Low-affinity neurotrophin receptor with targeted mutation of exon 3 is capable of mediating the death of axotomized neurons

1. In vivo studies have shown that the low-affinity 75 kDa neurotrophin receptor (p75NTR) is involved in axotomy-induced cell death of sensory and motor neurons. To further examine the importance of p75NTR in mediating neuronal death in vivo , we examined the effect of axotomy in the p75NTR-knockout mouse, which has a disrupted ligand-binding domain. 2. The extent of sensory and motor neuron loss in the p75NTR-knockout mouse following axotomy was not significantly different to that in wild-type mice. This suggests that disruption of the ligand-binding domain is insufficient to block the cell death process in axotomized neurons. 3. Immunohistochemical studies showed that axotomized neurons continue to express this mutant receptor with its intracellular death-signalling moiety intact. 4. Treatment with antisense oligonucleotides targeted against p75NTR resulted in significant reduction in the loss of axotomized neurons in the knockout mouse. 5. These data suggest that the intracellular domain of p75NTR is essential for death-signalling and that p75NTR can signal apoptosis, despite a disrupted ligand-binding domain.

A novel homozygous splice acceptor site mutation of KISS1R in two siblings with normosmic isolated hypogonadotropic hypogonadism

Context: Loss-of-function mutations of the kisspeptin-1 receptor gene, KISS1R, have been identified in patients with normosmic isolated hypogonadotropic hypogonadism (nIHH). Objective: To investigate KISS1R defects in patients with absent or delayed puberty. Patients: We investigated KISS1R gene defects in a cohort of 99 Brazilian patients with nIHH or constitutional delay of puberty (CDP). Methods: The entire coding region of KISS1R was amplified by PCR followed by automatic sequencing. In addition, screening for KISS1R exonic deletions was performed by multiplex ligation-dependent probe amplification. Results: One novel homozygous KISS1R mutation was identified in two siblings with nIHH. This variant was an insertion/deletion (indel) mutation characterized by the deletion of three nucleotides (GCA) at position -2 to -4, and by the insertion of seven nucleotides (ACCGGCT) at the same position, within the 30 splice acceptor site of intron 2 of KISS1R. The brothers who carried this KISS1R mutation had no clinical evidence of pubertal development at the ages of 14 and 20 years. Computational analysis of this indel mutation predicted the generation of an abnormal protein. In addition, a new heterozygous KISS1R variant (p.E252Q) was identified in a male patient with sporadic nIHH. However, in vitro studies of this variant did not demonstrate functional impairment. Only known polymorphisms were identified in patients with CDP. Conclusion: Loss-of-function mutations of KISS1R represents a rare cause of nIHH, and was absent in patients with CDP. We have described a novel KISS1R homozygous splice acceptor site mutation in the familial form of nIHH.

Modulation of ligand selectivity by mutation of the first extracellular loop of the human C5a receptor

The cyclic C5a receptor antagonist, phenylalanine [L-ornithine-proline-D-cyclohexylalanine-tryptophan-arginine] (F-[OPchaWR]), has similar to 1000-fold less affinity for the C5a receptor (C5aR) on murine polymorphonuclear leukocytes than on human. Analysis of C5aR from different species shows that a possible cause of this difference is the variation in the sequence of the first extracellular loop of the receptor. The mouse receptor contains Y at a position analogous to P-103 in the human receptor, and D at G(105). To test this hypothesis, we expressed human C5aR mutants ((PY)-Y-103, G(105)D and the double mutant, (PY)-Y-103/G(105)D) in RBL-2H3 cells and investigated the effects of these mutations on binding affinity and receptor activation. All three mutant receptors had a higher affinity for human C5a than the wild-type receptor, but showed no significant difference in the ability of F-[OPchaWR] to inhibit human C5a binding. However, all of the mutant receptors had substantially lower affinities for the weak agonist, C5a des Arg(74) (C5adR(74)), and two altered receptors (G(105)D and (PY)-Y-103/G(105)D) had much lower affinities for the C-terminal C5a agonist peptide analogue, L-tyrosine-serine-phenylalanine-lysine-proline-methionine-proline-leucine-D-alanine-arginine (YSFKPMPLaR). Although it is unlikely that differences at these residues are responsible for variations in the potency of F-[OPchaWR] across species, residues in the first extracellular loop are clearly involved in the recognition of both C5a and C5a agonists. The complex effects of mutating these residues on the affinity and response to C5a, C5adR(74), and the peptide analogues provide evidence of different binding modes for these ligands on the C5aR. (C) 2001 Elsevier Science Inc. All rights reserved.

Complete hypogonadotropic hypogonadism associated with a novel inactivating mutation of the gonadotropin-releasing hormone receptor.

In this study, we describe a patient with a phenotype of complete hypogonadotropic hypogonadism who presented primary failure of pulsatile GnRH therapy, but responded to exogenous gonadotropin administration. This patient bore a novel point mutation (T for A) at codon 168 of the gene encoding the GnRH receptor (GnRH-R), resulting in a serine to arginine change in the fourth transmembrane domain of the receptor. This novel mutation was present in the homozygous state in the patient, whereas it was in the heterozygous state in both phenotypically normal parents. When introduced into the complementary DNA coding for the GnRH-R, this mutation resulted in the complete loss of the receptor-mediated signaling response to GnRH. In conclusion, we report the first mutation of the GnRH-R gene that can induce a total loss of function of this receptor and is associated with a phenotype of complete hypogonadotropic hypogonadism.

Genetic male infertility and mutation of CATSPER ion channels.

A clinically significant proportion of couples experience difficulty in conceiving a child. In about half of these cases male infertility is the cause and often genetic factors are involved. Despite advances in clinical diagnostics ∼50% of male infertility cases remain idiopathic. Based on this, further analysis of infertile males is required to identify new genetic factors involved in male infertility. This review focuses on cation channel of sperm (CATSPER)-related male infertility. It is based on PubMed literature searches using the keywords 'CATSPER', 'male infertility', 'male contraception', 'immunocontraception' and 'pharmacologic contraception' (publication dates from January 1979 to December 2009). Previously, contiguous gene deletions including the CATSPER2 gene implicated the sperm-specific CATSPER channel in syndromic male infertility (SMI). Recently, we identified insertion mutations of the CATSPER1 gene in families with recessively inherited nonsyndromic male infertility (NSMI). The CATSPER channel therefore represents a novel human male fertility factor. In this review we summarize the genetic and clinical data showing the role of CATSPER mutation in human forms of NSMI and SMI. In addition, we discuss clinical management and therapeutic options for these patients. Finally, we describe how the CATSPER channel could be used as a target for development of a male contraceptive.

Mutation of yeast Ku genes disrupts the subnuclear organization of telomeres.

The mammalian Ku70 and Ku86 proteins form a heterodimer that binds to the ends of double-stranded DNA in vitro and is required for repair of radiation-induced strand breaks and V(D)J recombination [1,2]. Deletion of the Saccharomyces cerevisiae genes HDF1 and HDF2--encoding yKu70p and yKu80p, respectively--enhances radiation sensitivity in a rad52 background [3,4]. In addition to repair defects, the length of the TG-rich repeat on yeast telomere ends shortens dramatically [5,6]. We have shown previously that in yeast interphase nuclei, telomeres are clustered in a limited number of foci near the nuclear periphery [7], but the elements that mediate this localization remained unknown. We report here that deletion of the genes encoding yKu70p or its partner yKu80p altered the positioning of telomeric DNA in the yeast nucleus. These are the first mutants shown to affect the subnuclear localization of telomeres. Strains deficient for either yKu70p or yKu80p lost telomeric silencing, although they maintained repression at the silent mating-type loci. In addition, the telomere-associated silencing factors Sir3p and Sir4p and the TG-repeat-binding protein Rap1p lost their punctate pattern of staining and became dispersed throughout the nucleoplasm. Our results implicate the yeast Ku proteins directly in aspects of telomere organization, which in turn affects the repression of telomere-proximal genes.

A novel dominant mutation of the Nav1.4 alpha-subunit domain I leading to sodium channel myotonia.

BACKGROUND: Mutations in SCN4A may lead to myotonia. METHODS: Presentation of a large family with myotonia, including molecular studies and patch clamp experiments using human embryonic kidney 293 cells expressing wild-type and mutated channels. RESULTS: In a large family with historic data on seven generations and a clear phenotype, including myotonia at movement onset, with worsening by cold temperature, pregnancy, mental stress, and especially after rest after intense physical activity, but without weakness, the phenotype was linked with the muscle sodium channel gene (SCN4A) locus, in which a novel p.I141V mutation was found. This modification is located within the first transmembrane segment of domain I of the Na(v)1.4 alpha subunit, a region where no mutation has been reported so far. Patch clamp experiments revealed a mutation-induced hyperpolarizing shift (-12.9 mV) of the voltage dependence of activation, leading to a significant increase (approximately twofold) of the window current amplitude. In addition, the mutation shifted the voltage dependence of slow inactivation by -8.7 mV and accelerated the entry to this state. CONCLUSIONS: We propose that the gain-of-function alteration in activation leads to the observed myotonic phenotype, whereas the enhanced slow inactivation may prevent depolarization-induced paralysis.

Mutation of the BAFF furin cleavage site impairs B-cell homeostasis and antibody responses.

B-cell-activating factor of the TNF family (BAFF)/BLyS contributes to B-cell homeostasis and function in the periphery. BAFF is expressed as a membrane-bound protein or released by proteolytic cleavage, but the functional importance of this processing event is poorly understood. Mice expressing BAFF with a mutated furin consensus cleavage site, i.e. furin-mutant BAFF (fmBAFF), were not different from BAFF-deficient mice with regard to their B-cell populations and responses to immunization. It is however noteworthy that an alternative processing event releases some soluble BAFF in fmBAFF mice. Mild overexpression (∼ 5-fold) of fmBAFF alone generated intermediate levels of B cells without improving humoral responses to immunization. Processed BAFF was however important for B-cell homeostasis, as peripheral B-cell populations and antibody responses were readily restored by administration of soluble BAFF trimers in BAFF-deficient mice. However, the rescue of CD23 expression in B cells of BAFF-deficient mice required both soluble BAFF trimers and fmBAFF, or a polymeric form of soluble BAFF (BAFF 60-mer). These results point to a predominant role of processed BAFF for B-cell homeostasis and function, and indicate possible accessory roles for membrane-bound BAFF.

T cell division and death are segregated by mutation of TCRbeta chain constant domains.

We have studied the role of the T cell receptor (TCR) beta chain transmembrane and cytoplasmic domains (betaTM/Cyto) in T cell signaling. Upon antigen stimulation, T lymphocytes expressing a TCR with mutant and betaTM and Cyto domains accumulate in large numbers and are specifically defective in undergoing activation-induced cell death (AICD). The mutant TCR poorly recruits the protein adaptor Carma-1 and is subsequently impaired in activating NF-kappaB. This signaling defect leads to a reduced expression of Fas ligand (FasL) and to a reduction in AICD. These beta chain domains are involved in discriminating cell division and apoptosis.

Study of chromosome rearrangements associated with the trpE26 mutation of Bacillus subtilis.

Chromosome rearrangements involved in the formation of merodiploid strains in the Bacillus subtilis 168-166 system were explained by postulating the existence of intrachromosomal homology regions. This working hypothesis was tested by analysing sequences and restriction patterns of the, as yet uncharacterized, junctions between chromosome segments undergoing rearrangements in parent, 168 trpC2 and 166 trpE26, as well as in derived merodiploid strains. Identification, at the Ia/Ib chromosome junction of both parent strains, of a 1.3 kb segment nearly identical to a segment of prophage SPbeta established the existence of one of the postulated homology sequences. Inspection of relevant junctions revealed that a set of different homology regions, derived from prophage SPbeta, plays a key role in the formation of so-called trpE30, trpE30+, as well as of new class I merodiploids. Analysis of junctions involved in the transfer of the trpE26 mutation, i.e. simultaneous translocation of chromosome segment C and rotation of the terminal relative to the origin moiety of the chromosome, did not confirm the presence of any sequence suitable for homologous recombination. We propose a model involving simultaneous introduction of four donor DNA molecules, each comprising a different relevant junction, and their pairing with the junction regions of the recipient chromosome. The resolution of this structure, resting on homologous recombination, would confer the donor chromosome structure to the recipient, achieving some kind of 'transstamping'. In addition, a rather regular pattern of inverse and direct short sequence repeats in regions flanking the breaking points could be correlated with the initial, X-ray-induced, rearrangement.