Intragenic rearrangements in LARGE and POMGNT1 genes in severe dystroglycanopathies

Dystroglycanopathies are a heterogeneous group of muscular dystrophies with autosomal recessive inheritance characterized by abnormal glycosylation of alpha-dystroglycan. The most severe phenotypes are Walker-Warburg Syndrome (WWS) and muscle-eye-brain disease (MEB) presenting with lissencephaly type II (LIS II) and in which muscular dystrophy is associated with mental retardation and eye abnormalities. To date, six distinct genes, POMT1, POMT2, POMGNT1, FKTN, FKRP, LARGE and recently in one case DPM3, have been shown to be involved in dystroglycanopathies. Genomic sequencing alone is still frequently used for diagnosis purpose, not allowing detection of intragenic rearrangements at the heterozygous state contrarily to RNA analysis, quantitative PCR and CGH array analysis. These latter methods enabled us to identify four new intragenic rearrangements in the LARGE gene in three fetuses with WWS, born to two unrelated families: deletion of exons 9-10 and duplication of introns 1-4 for the first family and deletion of exons 4 and 7 for the second one; and a deletion of the last six exons of the POMGNT1 gene in two unrelated MEB patients. Genomic dosage studies using emerging tools such as CGH array should be included in routine molecular analysis of dystroglycanopathies, not only for the screening of the LARGE gene in which this kind of mutation seems to be more frequent than point mutations, but also for the other involved genes, especially in severe clinical cases.

IRF6 Screening of Syndromic and a priori Non-Syndromic Cleft Lip and Palate Patients: Identification of a New Type of Minor VWS Sign

Van der Woude syndrome (VWS), caused by dominant IRF6 mutation, is the most common cleft syndrome. In 15% of the patients, lip pits are absent and the phenotype mimics isolated clefts. Therefore, we hypothesized that some of the families classified as having non-syndromic inherited cleft lip and palate could have an IRF6 mutation. We screened in total 170 patients with cleft lip with or without cleft palate (CL/P): 75 were syndromic and 95 were a priori part of multiplex non-syndromic families. A mutation was identified in 62.7 and 3.3% of the patients, respectively. In one of the 95 a priori non-syndromic families with an autosomal dominant inheritance (family B), new insights into the family history revealed the presence, at birth, of lower lip pits in two members and the diagnosis was revised as VWS. A novel lower lip sign was observed in one individual in this family. Interestingly, a similar lower lip sign was also observed in one individual from a 2nd family (family A). This consists of 2 nodules below the lower lip on the external side. In a 3rd multiplex family (family C), a de novo mutation was identified in an a priori non-syndromic CL/P patient. Re-examination after mutation screening revealed the presence of a tiny pit-looking lesion on the inner side of the lower lip leading to a revised diagnosis of VWS. On the basis of this data, we conclude that IRF6 should be screened when any doubt rises about the normality of the lower lip and also if a non-syndromic cleft lip patient (with or without cleft palate) has a family history suggestive of autosomal dominant inheritance.

Use of marginal organs in kidney transplantation for marginal recipients: too close to the margins of safety?

Objective

Due to organ shortage, average waiting time for a kidney in Germany is about 4 years after start of dialysis. Number of kidney grafts recovered can only be maintained by accepting older and expanded criteria donors. The aim of this study was to analyse the impact of donor and recipient risk on kidney long-term function.

Methods

All deceased kidney transplantations were considered. We retrospectively studied 332 patients between 2002 and 2006; divided in 4 groups reflecting donor and recipient risk.

Results

Non-marginal recipients were less likely to receive a marginal organ (69 of 207, 33%) as compared to marginal recipients, of whom two-thirds received a marginal organ (p < 0.0001). Graft function significantly differed between the groups, but detrimental effect of marginal recipient status on eGFR after 12 months (-6 ml/min/1.73 qm, 95% CI -2 to -9) was clearly smaller than the effect of marginal donor status (-10 ml/min/1.73 qm, 95% CI -7 to -14).

Conclusions

As we were able to show expanded criteria donor has a far bigger effect on long-term graft function than the "extra risk" recipient. Although there have been attempts to define groups of recipients who should be offered ECD kidneys primarily the discussion is still ongoing.

Identification of 28 novel mutations in the Bardet-Biedl syndrome genes: the burden of private mutations in an extensively heterogeneous disease

Bardet-Biedl syndrome (BBS), an emblematic disease in the rapidly evolving field of ciliopathies, is characterized by pleiotropic clinical features and extensive genetic heterogeneity. To date, 14 BBS genes have been identified, 3 of which have been found mutated only in a single BBS family each (BBS11/TRIM32, BBS13/MKS1 and BBS14/MKS4/NPHP6). Previous reports of systematic mutation detection in large cohorts of BBS families (n > 90) have dealt only with a single gene, or at most small subsets of the known BBS genes. Here we report extensive analysis of a cohort of 174 BBS families for 12/14 genes, leading to the identification of 28 novel mutations. Two pathogenic mutations in a single gene have been found in 117 families, and a single heterozygous mutation in 17 families (of which 8 involve the BBS1 recurrent mutation, M390R). We confirm that BBS1 and BBS10 are the most frequently mutated genes, followed by BBS12. No mutations have been found in BBS11/TRIM32, the identification of which as a BBS gene only relies on a single missense mutation in a single consanguineous family. While a third variant allele has been observed in a few families, they are in most cases missenses of uncertain pathogenicity, contrasting with the type of mutations observed as two alleles in a single gene. We discuss the various strategies for diagnostic mutation detection, including homozygosity mapping and targeted arrays for the detection of previously reported mutations.

A new highly penetrant form of obesity due to deletions on chromosome 16p11.2

Obesity has become a major worldwide challenge to public health, owing to an interaction between the Western 'obesogenic' environment and a strong genetic contribution. Recent extensive genome-wide association studies (GWASs) have identified numerous single nucleotide polymorphisms associated with obesity, but these loci together account for only a small fraction of the known heritable component. Thus, the 'common disease, common variant' hypothesis is increasingly coming under challenge. Here we report a highly penetrant form of obesity, initially observed in 31 subjects who were heterozygous for deletions of at least 593 kilobases at 16p11.2 and whose ascertainment included cognitive deficits. Nineteen similar deletions were identified from GWAS data in 16,053 individuals from eight European cohorts. These deletions were absent from healthy non-obese controls and accounted for 0.7% of our morbid obesity cases (body mass index (BMI) >or= 40 kg m(-2) or BMI standard deviation score >or= 4; P = 6.4 x 10(-8), odds ratio 43.0), demonstrating the potential importance in common disease of rare variants with strong effects. This highlights a promising strategy for identifying missing heritability in obesity and other complex traits: cohorts with extreme phenotypes are likely to be enriched for rare variants, thereby improving power for their discovery. Subsequent analysis of the loci so identified may well reveal additional rare variants that further contribute to the missing heritability, as recently reported for SIM1 (ref. 3). The most productive approach may therefore be to combine the 'power of the extreme' in small, well-phenotyped cohorts, with targeted follow-up in case-control and population cohorts.

Experimental study comparing meshes made of polypropylene, polypropylene + polyglactin and polypropylene + titanium: inflammatory cytokines, histological changes and morphometric analysis of collagen

PURPOSE

Incisional hernia occurs in approximately 11% of all laparotomies. Changes in collagen have been closely implicated in its pathogenesis. The high recurrence rate (45-54%) after primary suture has stimulated the development of meshes. Currently, meshes are the biomaterials implant group most used in medicine. This study aims to compare the serum and tissue inflammatory responses and collagen deposition caused by meshes made of polypropylene, polypropylene + polyglactin and polypropylene + titanium.

METHODS

Thirty Wistar rats were divided into three groups. In group I, a high-density polypropylene mesh was positioned on the abdominal wall. In groups II and III, low-density meshes were used in associations with polyglactin and titanium, respectively. Immediately before the operation and on the first, third and fortieth postoperative days, pro-inflammatory cytokines were assayed. On the 40th postoperative day, the region of the inserted prosthesis was biopsied. The tissue inflammatory reaction was evaluated using a scale for objective scoring. For collagen, picrosirius was used with data reading using the Image Tool computer software.

RESULTS

Cytokines: there were no statistically significant differences between the groups.

HISTOLOGY

on the 40th postoperative day in group I, there were fewer inflammatory tissue response and greater collagen deposition (P < 0.01). In group II, there were greater inflammatory tissue response and less collagen deposition (P < 0.01). Group III presented intermediate values between groups I and II.

CONCLUSIONS

There were no significant differences in cytokine levels between the groups in the present study. In the animals with the polypropylene + polyglactin mesh implant there was the most intense inflammatory process with lower tissue maturation and collagen deposition on the 40th postoperative day. The polypropylene mesh presented a less severe late inflammatory process, with greater tissue maturation and collagen deposition. The polypropylene + titanium mesh presented intermediate values between the others.

Mutational spectrum of CDKL5 in early-onset encephalopathies: a study of a large collection of French patients and review of the literature

The CDKL5 gene has been implicated in the molecular etiology of early-onset intractable seizures with infantile spasms (IS), severe hypotonia and atypical Rett syndrome (RTT) features. So far, 48 deleterious alleles have been reported in the literature. We screened the CDKL5 gene in a cohort of 177 patients with early-onset seizures, including 30 men and 10 girls with Aicardi syndrome. The screening was negative for all men as well as for women with Aicardi syndrome, excluding the CDKL5 gene as a candidate for this neurodevelopmental disorder. We report 11 additional de novo mutations in CDKL5 in female patients. For the first time, the MLPA approach allowed the identification of a partial deletion encompassing the promoter and the first two exons of CDKL5. The 10-point mutations consist of five missenses (with recurrent amino acid changes at p.Ala40 and p.Arg178), four splicing variants and a 1-base pair duplication. We present a review of all mutated alleles published in the literature. In our study, the overall frequency of mutations in CDKL5 in women with early-onset seizures is around 8.6%, a result comparable with previous reports. Noteworthy, the CDKL5 mutation rate is high (28%) in women with early-onset seizures and IS.

[Genetics of mental retardation]

Mental retardation affects nearly 3 % of the population. The causes of these disorders are various and are often not identified. Recent advances focused on the molecular basis of mental retardation. Nearly half of mental retardation syndromes have a genetic origin and the description of molecular, cytogenetic and metabolic alterations in these disorders led to the development of diagnostic tools. Indeed, identifying the precise origin of the mental retardation allows to improve patient care and to refine the prognosis. Moreover, these molecular tools will help the geneticist to evaluate the recurrence risk in the family in the genetic counseling step. On a fundamental point of view, the knowledge of molecular basis of mental retardation will help to understand the biological pathway which constitutes the first step before therapeutic strategies. Every patient with mental retardation should be investigated for causal origin of the disease. We will detail the diagnostic methods necessary to investigate a patient presenting with mental retardation. Then different examples of syndromes including a mental retardation will be chosen to illustrate different clinical situations.

MEF2C haploinsufficiency caused by either microdeletion of the 5q14.3 region or mutation is responsible for severe mental retardation with stereotypic movements, epilepsy and/or cerebral malformations

BACKGROUND

Over the last few years, array-comparative genomic hybridisation (CGH) has considerably improved our ability to detect cryptic unbalanced rearrangements in patients with syndromic mental retardation.

METHOD

Molecular karyotyping of six patients with syndromic mental retardation was carried out using whole-genome oligonucleotide array-CGH.

RESULTS

5q14.3 microdeletions ranging from 216 kb to 8.8 Mb were detected in five unrelated patients with the following phenotypic similarities: severe mental retardation with absent speech, hypotonia and stereotypic movements. Facial dysmorphic features, epilepsy and/or cerebral malformations were also present in most of these patients. The minimal common deleted region of these 5q14 microdeletions encompassed only MEF2C, the gene for a protein known to act in brain as a neurogenesis effector, which regulates excitatory synapse number. In a patient with a similar phenotype, an MEF2C nonsense mutation was subsequently identified.

CONCLUSION

Taken together, these results strongly suggest that haploinsufficiency of MEF2C is responsible for severe mental retardation with stereotypic movements, seizures and/or cerebral malformations.

Impact of modulators of mitochondrial ATP-sensitive potassium channel (mitoK(ATP)) on hypoxic pulmonary vasoconstriction

Previously, we demonstrated that hypoxic pulmonary vasoconstriction (HPV) of intra-acinar arteries (IAA) requires mitochondrial complex II (= succinate dehydrogenase, SDH) activity (citeauthor ch41:paddenberg2006, Respir Res, 7:93, citeyear ch41:paddenberg2006). Interestingly, SDH subunits A and B have recently been described as components of a multiprotein mitochondrial ATP-sensitive potassium channel (mitoK(ATP)), together with mitochondrial ATP-binding cassette protein-1, adenine nucleotide translocator (ANT), ATP synthase, and phosphate carrier (citeauthor ch41:ardehali2004, Proc Natl Acad Sci USA, 101(32):11880-5, citeyear ch41:ardehali2004). Hence, we tested the hypothesis that such an SDH-containing mitoK(ATP) is involved in HPV. For this purpose, the impact of modulators of mitoK(ATP) on HPV of IAA was studied videomorphometrically in precision cut murine lung slices. Inhibitors of mitoK(ATP) (glibenclamide, 5-hydroxydecanoate) completely suppressed HPV, mitoK(ATP) activators (pinacidil, diazoxide) even induced vasodilatation, and ANT inhibitors (bongkrekic acid, atractyloside) attenuated HPV. This pharmacological profile differs clearly from that described for mitoK(ATP). Accordingly, co-immunoprecipitation experiments provided no evidence for association of complex II subunits SDH-A, -B and -C with ANT, ATP synthase or cytochrome c oxidase in murine heart mitochondria. Hence, it is likely that the inhibitory effects on HPV that we observed in our experiments result from modulation of several mitochondrial protein complexes independently involved in the signalling cascade such as ROS-producing complex II and ANT-regulated mitochondrial permeability transition pore.

Clinical and molecular delineation of the 17q21.31 microdeletion syndrome

BACKGROUND

The chromosome 17q21.31 microdeletion syndrome is a novel genomic disorder that has originally been identified using high resolution genome analyses in patients with unexplained mental retardation.

AIM

We report the molecular and/or clinical characterisation of 22 individuals with the 17q21.31 microdeletion syndrome.

RESULTS

We estimate the prevalence of the syndrome to be 1 in 16,000 and show that it is highly underdiagnosed. Extensive clinical examination reveals that developmental delay, hypotonia, facial dysmorphisms including a long face, a tubular or pear-shaped nose and a bulbous nasal tip, and a friendly/amiable behaviour are the most characteristic features. Other clinically important features include epilepsy, heart defects and kidney/urologic anomalies. Using high resolution oligonucleotide arrays we narrow the 17q21.31 critical region to a 424 kb genomic segment (chr17: 41046729-41470954, hg17) encompassing at least six genes, among which is the gene encoding microtubule associated protein tau (MAPT). Mutation screening of MAPT in 122 individuals with a phenotype suggestive of 17q21.31 deletion carriers, but who do not carry the recurrent deletion, failed to identify any disease associated variants. In five deletion carriers we identify a <500 bp rearrangement hotspot at the proximal breakpoint contained within an L2 LINE motif and show that in every case examined the parent originating the deletion carries a common 900 kb 17q21.31 inversion polymorphism, indicating that this inversion is a necessary factor for deletion to occur (p<10(-5)).

CONCLUSION

Our data establish the 17q21.31 microdeletion syndrome as a clinically and molecularly well recognisable genomic disorder.