Rima Slim

A defect in harmonin, a PDZ domain-containing protein expressed in the inner ear sensory hair cells, underlies Usher syndrome type 1C

Usher syndrome type 1 (USH1) is an autosomal recessive sensory defect involving congenital profound sensorineural deafness, vestibular dysfunction and blindness (due to progressive retinitis pigmentosa). Six different USH1 loci have been reported. So far, only MYO7A (USH1B), encoding myosin VIIA (ref. 2), has been identified as a gene whose mutation causes the disease. Here, we report a gene underlying USH1C (MIM 276904), a USH1 subtype described in a population of Acadian descendants from Louisiana and in a Lebanese family. We identified this gene (USH1C), encoding a PDZ-domain–containing protein, harmonin, in a subtracted mouse cDNA library derived from inner ear sensory areas. In patients we found a splice-site mutation, a frameshift mutation and the expansion of an intronic variable number of tandem repeat (VNTR). We showed that, in the mouse inner ear, only the sensory hair cells express harmonin. The inner ear Ush1c transcripts predicted several harmonin isoforms, some containing an additional coiled-coil domain and a proline- and serine-rich region. As several of these transcripts were absent from the eye, we propose that USH1C also underlies the DFNB18 form of isolated deafness.

Mutations in NALP7 cause recurrent hydatidiform moles and reproductive wastage in humans

Hydatidiform mole (HM) is an abnormal human pregnancy with no embryo and cystic degeneration of placental villi. We report five mutations in the maternal gene NALP7 in individuals with familial and recurrent HMs. NALP7 is a member of the CATERPILLER protein family involved in inflammation and apoptosis. NALP7 is the first maternal effect gene identified in humans and is also responsible for recurrent spontaneous abortions, stillbirths and intrauterine growth retardation.

The infevers autoinflammatory mutation online registry: update with new genes and functions.

Infevers (Internet Fevers; http://fmf.igh.cnrs.fr/ISSAID/infevers), a website dedicated to mutations responsible for hereditary autoinflammatory diseases, was created in 2002 and has continued to evolve. This new version includes eight genes; six were already present: MEFV, MVK, TNFRSF1A, NLRP3, NOD2, PSTPIP1, and two are new, LPIN2 and NLRP7. Currently, Infevers contains over 540 sequence variants. Several new database functions were recently instituted. The website now accepts confidential data and complex alleles. For each gene, a newly created menu offers: 1) a tabular list of the variants that can be sorted by several parameters; 2) a gene graph providing a schematic representation of the variants along the gene; 3) statistical analysis of the data according to the phenotype, alteration type, and location of the mutation in the gene; 4) the cDNA and gDNA sequences of each gene, showing the nucleotide changes along the sequence, with a color‐based code highlighting the gene domains, the first ATG, and the termination codon; and 5) a “download” menu making all tables and figures available for the users, which, except for the gene graphs, are all automatically generated and updated upon submission of the variants. Finally, the entire database was curated to comply with the HUGO Gene Nomenclature Committee (HGNC) and HGVS nomenclature guidelines, and wherever necessary, an informative note was provided. Infevers has already proven useful for the scientific community with a mean number of visits per month of 200 in 2002 and 800 in 2007, and its new design will lead to a more comprehensive comparative analysis and interpretation of auto‐inflammatory sequence variants. Hum Mutat 29(6), 803–808, 2008. Published 2008, Wiley‐Liss, Inc.

A novel approach identifies new differentially methylated regions (DMRs) associated with imprinted genes

Imprinted genes are critical for normal human growth and neurodevelopment. They are characterized by differentially methylated regions (DMRs) of DNA that confer parent of origin-specific transcription. We developed a new strategy to identify imprinted gene-associated DMRs. Using genome-wide methylation profiling of sodium bisulfite modified DNA from normal human tissues of biparental origin, candidate DMRs were identified by selecting CpGs with methylation levels consistent with putative allelic differential methylation. In parallel, the methylation profiles of tissues of uniparental origin, i.e., paternally-derived androgenetic complete hydatidiform moles (AnCHMs), and maternally-derived mature cystic ovarian teratoma (MCT), were examined and then used to identify CpGs with parent of origin-specific DNA methylation. With this approach, we found known DMRs associated with imprinted genomic regions as well as new DMRs for known imprinted genes, NAP1L5 and ZNF597, and novel candidate imprinted genes. The paternally methylated DMR for one candidate, AXL, a receptor tyrosine kinase, was also validated in experiments with mouse embryos that demonstrated Axl was expressed preferentially from the maternal allele in a DNA methylation-dependent manner.

A familial case of recurrent hydatidiform molar pregnancies with biparental genomic contribution.

Hydatidiform mole is a benign trophoblastic neoplasia characterized by an abnormal development of the embryo and proliferation of placental villi. Using microsatellite markers amplified by the polymerase chain reaction, we have performed a genetic study on eight independent molar tissues occurring in two sisters. Karyotype and genotype data demonstrate a diploid and biparental constitution in seven of the analyzed moles suggesting a common mechanism underlying the etiology of the various molar pregnancies in this family. The data reported here suggest that complete and partial hydatidiform moles are not always separate entities and that women with familial recurrent hydatidiform moles are homozygous for an autosomal recessive mutation.

The genetics of hydatidiform moles: new lights on an ancient disease.

Hydatidiform mole (HM) is a human pregnancy with no embryo but cystic degeneration of chorionic villi. The common form of this condition occurs in 1 in every 1500 pregnancies in western societies and at a higher incidence in some geographic regions and populations. Recurrent moles account for 2% of all molar cases and a few of them occur in more than one family member. By studying a familial form of recurrent moles, a recessive maternal locus responsible for this condition was mapped to 19q13.4 and causative mutations identified. The defective protein, NALP7, is part of the CATERPILLAR protein family with roles in pathogen‐induced inflammation and apoptosis. The exact role of NALP7 in the pathophysiology of molar pregnancies is unknown yet. NALP7 could have a role either in oogenesis or in the endometrium during trophoblast invasion and decidualization. In this review, we outlined recent advances in the field of HMs and reviewed the literature in the light of the new data.

Townes‐Brocks syndrome: Detection of a SALL1 mutation hot spot and evidence for a position effect in one patient

Townes‐Brocks syndrome (TBS) is an autosomal dominant developmental disorder characterized by anal and thumb malformations and by ear anomalies that can affect the three compartments and usually lead to hearing loss. The gene underlying TBS, SALL1, is a human homolog of the Drosophila spalt gene which encodes a transcription factor. A search for SALL1 mutations undertaken in 11 unrelated affected individuals (five familial and six sporadic cases) led to the detection of mutations in nine of them. One nonsense and six different novel frameshift mutations, all located in the second exon, were identified. Together with the previously reported mutations [Kohlhase et al., 1999], they establish that TBS results from haploinsufficiency. The finding of de novo mutations in the sporadic cases is consistent with the proposed complete penetrance of the disease. Moreover, the occurrence of the same 826C>T transition in a CG dimer, in three sporadic cases from the present series and three sporadic cases from the other series [Kohlhase et al., 1999] (i.e., six of the eight mutations identified in sporadic cases), reveals the existence of a mutation hotspot. Six different SALL1 polymorphisms were identified in the course of the present study, three of which are clustered in a particular region of the gene that encodes a stretch of serine residues. Finally, the chromosome 16 breakpoint of a t(5;16)(p15.3;q12.1) translocation carried by a TBS‐affected individual was mapped at least 180 kb telomeric to SALL1, thus indicating that a position effect underlies the disease in this individual. Hum Mutat 14:377–386, 1999.

NLRP7 in the spectrum of reproductive wastage: rare non-synonymous variants confer genetic susceptibility to recurrent reproductive wastage

Background NLRP7 mutations are responsible for recurrent molar pregnancies and associated reproductive wastage. To investigate the role of NLRP7 in sporadic moles and other forms of reproductive wastage, the authors sequenced this gene in a cohort of 135 patients with at least one hydatidiform mole or three spontaneous abortions; 115 of these were new patients. Methods/Results All mutations were reviewed and their number, nature and locations correlated with the reproductive outcomes of the patients and histopathology of their products of conception. The presence of NLRP7 mutations was demonstrated in two patients with recurrent spontaneous abortions, and some rare non-synonymous variants (NSVs), present in the general population, were found to be associated with recurrent reproductive wastage. These rare NSVs were shown to be associated with lower secretion of interleukin 1β and tumour necrosis factor and therefore to have functional consequences similar to those seen in cells from patients with NLRP7 mutations. The authors also attempted to elucidate the cause of stillbirths observed in 13% of the patients with NLRP7 mutations by examining available placentas of the stillborn babies and live births from patients with mutations or rare NSVs. A number of severe to mild placental abnormalities were found, all of which are known risk factors for perinatal morbidity. Conclusions The authors recommend close follow-up of patients with NLRP7 mutations and rare NSVs to prevent the death of the rare or reduced number of babies that reach term.

Report of four new patients with protein-truncating mutations in C6orf221/KHDC3L and colocalization with NLRP7

To date, two maternal-effect genes have been shown to have causative roles in recurrent hydatidiform moles (RHMs); NLRP7 that is mutated in 48–60% of patients with RHMs and C6orf221 (HUGO-approved nomenclature is now KHDC3L), a recently identified gene, that is mutated in 14% of patients with RHMs who are negative for NLRP7 mutations. We sequenced KHDC3L in 97 patients with RHMs and reproductive loss who are mostly negative for NLRP7 mutations. We identified three unrelated patients, each homozygous for one of the two protein-truncating mutations, a novel 4-bp deletion resulting in a frameshift, c.299_302delTCAA, p.Ile100Argfs*2, and a previously described 4-bp deletion, c.322_325delGACT, p.Asp108Ilefs*30, transmitted on a shared haplotype to three patients from different populations. We show that five HM tissues from one of these patients are diploid and biparental similar to HMs from patients with two defective NLRP7 mutations. Using immunofluorescence, we show that KHDC3L protein displays a juxta perinuclear signal and colocalizes with NLRP7 in lymphoblastoid cell lines from normal subjects. Using cell lines from patients, we demonstrate that the KHDC3L mutations do not change the subcellular localization of the protein in hematopoietic cells. Our data highlight the similarities between the two causative genes for RHMs, KHDC3L and NLRP7, in their subcellular localization, the parental contribution to the HM tissues caused by them, and the presence of several founder mutations and variants in both of them indicating positive selection and adaptation.

NLRP7, a Nucleotide Oligomerization Domain-like Receptor Protein, Is Required for Normal Cytokine Secretion and Co-localizes with Golgi and the Microtubule-organizing Center

Background: NLRP7 is responsible for recurrent hydatidiform moles, but its functional role is unknown. Results: NLRP7 mutations impair IL-1β and TNF secretion but do not affect IL-1β processing. NLRP7 co-localizes with the microtubule organizing center, and mutations impair cytokine trafficking. Conclusion: Patients with NLRP7 mutations have abnormal tolerance to aberrant pregnancies. Significance: We unravel a new mechanism for reproductive wastage. A hydatidiform mole (HM) is a human pregnancy with hyperproliferative placenta and abnormal embryonic development. Mutations in NLRP7, a member of the nucleotide oligomerization domain-like receptor family of proteins with roles in inflammation and apoptosis, are responsible for recurrent HMs. However, little is known about the functional role of NLRP7. Here, we demonstrate that peripheral blood mononuclear cells from patients with NLRP7 mutations and rare variants secrete low levels of IL-1β and TNF in response to LPS. We show that the cells from patients, carrying mutations or rare variants, have variable levels of increased intracellular pro-IL-1β indicating that normal NLRP7 down-regulates pro-IL-1β synthesis in response to LPS. Using transient transfections, we confirm the role of normal NLRP7 in inhibiting pro-IL-1β and demonstrate that this inhibitory function is abolished by protein-truncating mutations after the Pyrin domain. Within peripheral blood mononuclear cells, NLRP7 co-localizes with the Golgi and the microtubule-organizing center and is associated with microtubules. This suggests that NLRP7 mutations may affect cytokine secretion by interfering, directly or indirectly, with their trafficking. We propose that the impaired cytokine trafficking and secretion caused by NLRP7 defects makes the patients tolerant to the growth of these earlier arrested conceptions with no fetal vessels and that the retention of these conceptions until the end of the first trimester contribute to the molar phenotype. Our data will impact our understanding of postmolar choriocarcinomas, the only allograft non-self tumors that are able to invade maternal tissues.