In-depth genetic and molecular characterization of diaphanous related formin 2 (DIAPH2) and its role in the inner ear

Diaphanous related formins are regulatory cytoskeletal protein involved in actin elongation and microtubule stabilization. In humans, defects in two of the three diaphanous genes (DIAPH1 and DIAPH3) have been associated with different types of hearing loss. Here, we investigate the role of the third member of the family, DIAPH2, in nonsyndromic hearing loss, prompted by the identification, by exome sequencing, of a predicted pathogenic missense variant in DIAPH2. This variant occurs at a conserved site and segregated with nonsyndromic X-linked hearing loss in an Italian family. Our immunohistochemical studies indicated that the mouse ortholog protein Diaph2 is expressed during development in the cochlea, specifically in the actin-rich stereocilia of the sensory outer hair cells. In-vitro studies showed a functional impairment of the mutant DIAPH2 protein upon RhoA-dependent activation. Finally, Diaph2 knock-out and knock-in mice were generated by CRISPR/Cas9 technology and auditory brainstem response measurements performed at 4, 8 and 14 weeks. However, no hearing impairment was detected. Our findings indicate that DIAPH2 may play a role in the inner ear; further studies are however needed to clarify the contribution of DIAPH2 to deafness.

Heterozygous COL4A3/COL4A4 mutations: the hidden part of the iceberg?

BACKGROUND

Single mutations in COL4A3/COL4A4 genes have been described in patients with autosomal dominant Alport syndrome and thin basement membrane nephropathy, without a shared definition of these patients within the medical community. We aimed to better categorize this clinical entity by examining clinical manifestations, family history, pathological features and genetics.

METHODS

We retrospectively analyzed patients with causative heterozygous COL4A3/COL4A4 mutations referred to us between 1990 and 2019. Index cases were defined as children who were the first to be diagnosed in their families.

RESULTS

The study included 24 index cases and 29 affected relatives, belonging to 25 families with a heterozygous mutation in the COL4A3/COL4A4 genes. During the follow-up, nine patients developed proteinuria [median age 15.7 years (range 5.6-33)], six at clinical diagnosis and four with progression toward chronic kidney disease (CKD) (three required kidney replacement therapy at 25, 45 and 53 years and one had CKD Stage 2 at 46 years). Extrarenal involvement was observed in 24.5% of patients. Hematuria was transmitted in consecutive generations, while CKD was reported in nonconsecutive generations of 11 families [median age 53 years (range 16-80)]. Seventeen patients (32%) underwent kidney biopsy: findings were consistent with Alport syndrome in 12 cases and with thin basement membrane nephropathy in 5 cases.

CONCLUSIONS

Despite the benign course for these patients described in the literature, a significant percentage is at risk for disease progression. Consequently, we suggest that the assessment of these patients must take into account family history, genetic analysis and pathologic findings. After comparison with the literature, our data suggest that a different definition for Alport syndrome must be considered.

Role of Cytoskeletal Diaphanous-Related Formins in Hearing Loss

Hearing relies on the proper functioning of auditory hair cells and on actin-based cytoskeletal structures. Diaphanous-related formins (DRFs) are evolutionarily conserved cytoskeletal proteins that regulate the nucleation of linear unbranched actin filaments. They play key roles during metazoan development, and they seem particularly pivotal for the correct physiology of the reproductive and auditory systems. Indeed, in Drosophila melanogaster, a single diaphanous (dia) gene is present, and mutants show sterility and impaired response to sound. Vertebrates, instead, have three orthologs of the diaphanous gene: DIAPH1, DIAPH2, and DIAPH3. In humans, defects in DIAPH1 and DIAPH3 have been associated with different types of hearing loss. In particular, heterozygous mutations in DIAPH1 are responsible for autosomal dominant deafness with or without thrombocytopenia (DFNA1, MIM #124900), whereas regulatory mutations inducing the overexpression of DIAPH3 cause autosomal dominant auditory neuropathy 1 (AUNA1, MIM #609129). Here, we provide an overview of the expression and function of DRFs in normal hearing and deafness.

Nutrient supply, cell spatial correlation and Gompertzian tumor growth

Gompertzian tumor growth can be reproduced by mitosis, related to nutrient supply, with local spatial cell correlations. The global energy constraint alone does not reproduce in vivo data by the observed values of the nutrient expenditure for the cell activities. The depletion of the exponential growth, described by the Gompertz law, is obtained by mean field spatial correlations or by a small word network among cells. The well-known interdependence between the two parameters of the Gompertz growth naturally emerges and depends on the cell volume and on the tumor density.

Containment effort reduction and regrowth patterns of the Covid-19 spreading

In all countries the political decisions aim to achieve an almost stable configuration with a small number of new infected individuals per day due to Covid-19. When such a condition is reached, the containment effort is usually reduced in favor of a gradual reopening of the social life and of the various economical sectors. However, in this new phase, the infection spread restarts and, moreover, possible mutations of the virus give rise to a large specific growth rate of the infected people. Therefore, a quantitative analysis of the regrowth pattern is very useful. We discuss a macroscopic approach which, on the basis of the collected data in the first lockdown, after few days from the beginning of the new phase, outlines different scenarios of the Covid-19 diffusion for longer time. The purpose of this paper is a demonstration-of-concept: one takes simple growth models, considers the available data and shows how the future trend of the spread can be obtained. The method applies a time dependent carrying capacity, analogously to many macroscopic growth laws in biology, economics and population dynamics. The illustrative cases of France, Italy and United Kingdom are analyzed.

SLC22A4 Gene in Hereditary Non-syndromic Hearing Loss: Recurrence and Incomplete Penetrance of the p.C113Y Mutation in Northwest Africa

Inherited hearing loss is extremely heterogeneous both clinically and genetically. In addition, the spectrum of deafness-causing genetic variants differs greatly among geographical areas and ethnicities. The identification of the causal mutation in affected families allows early diagnosis, clinical follow-up, and genetic counseling. A large consanguineous family of Moroccan origin affected by autosomal recessive sensorineural hearing loss (ARSNHL) was subjected to genome-wide linkage analysis and exome sequencing. Exome-wide variant analysis and prioritization identified the SLC22A4 p.C113Y missense variant (rs768484124) as the most likely cause of ARSNHL in the family, falling within the unique significant (LOD score>3) linkage region on chromosome 5. Indeed, the same variant was previously reported in two Tunisian ARSNHL pedigrees. The variant is present in the homozygous state in all six affected individuals, but also in one normal-hearing sibling, suggesting incomplete penetrance. The mutation is absent in about 1,000 individuals from the Greater Middle East Variome study cohort, including individuals from the North African population, as well as in an additional seven deaf patients from the same geographical area, recruited and screened for mutations in the SLC22A4 gene. This study represents the first independent replication of the involvement of SLC22A4 in ARSNHL, highlighting the importance of the gene, and of the p.C113Y mutation, at least in the Northwest African population.

X-Linked Alport Syndrome in Women: Genotype and Clinical Course in 24 Cases

Objectives: X-linked Alport syndrome (XLAS) females are at risk of developing proteinuria and chronic kidney damage (CKD). The aim of this study is to evaluate the genotype-phenotype correlation in this rare population.

Materials and Methods: This is a prospective, observational study of XLAS females, confirmed by a pathogenic mutation in COL4A5 and renal ultrastructural evaluation. Proteinuria, renal function and extrarenal involvement were monitored during follow-up. Patients were divided in 2 groups, according to mutations in COL4A5: missense (Group 1) and non-missense variants (Group 2).

Results: Twenty-four XLAS females, aged 10.6 ± 10.4 years at clinical onset (mean follow-up: 13.1 ± 12.6 years) were recruited between 2000 and 2017 at a single center. In group 1 there were 10 patients and in group 2, 14 (mean age at the end of follow-up: 24.9 ± 13.6 and 23.2 ± 13.8 years, respectively). One patient in Group 1 and 9 in Group 2 (p = 0.013) developed proteinuria during follow-up. Mean eGFR at last follow-up was lower in Group 2 (p = 0.027), where two patients developed CKD. No differences in hearing loss were documented among the two groups. Two patients in Group 2 carried one mutation in both COL4A5 and COL4A3 (digenic inheritance) and were proteinuric. In one family, the mother presented only hematuria while the daughter was proteinuric and presented a greater inactivation of the X chromosome carrying the wild-type allele.

Conclusions: The appearance of proteinuria and CKD is more frequent in patients with severe variants. Carrying digenic inheritance and skewed XCI seem to be additional risk factors for proteinuria in XLAS females.

Audiovestibular Phenotypes and Advanced Magnetic Resonance Imaging Features of Cochlin Gene Mutation Carriers

OBJECTIVE

To describe clinical and imaging findings in a group of patients affected by nonsyndromic deafness A9 (DFNA9), using advanced magnetic resonance imaging (MRI) with 3-dimensional (3D) fluid-attenuated inversion recovery (FLAIR) sequence.

METHOD

A retrospective case review was conducted in a tertiary referral center in Italy. Four sequential adult DFNA9-affected patients, who had undergone MRI at our Department between January 2017 and June 2018, were enrolled (male = 2, female = 2; median age: 65.6 years; 8 diseased ears analyzed). Three patients were relatives; the fourth was unrelated. The main outcome measures - age, sex, records of audiological and vestibular testing, genetic assessment, MRI findings - were analyzed.

RESULTS

All subjects suffered from bilateral progressive sensorineural hearing loss, more severely at the high frequencies and with a typical clinical pattern of bilateral chronic degenerative cochleovestibular deficit. Aural fullness was reported at the onset of the disease. All patients revealed a pathogenic heterozygous mutation in the Limulus factor C, Coch-5b2 and Lgl1 domain of cochlin. None of the patients showed a significant vestibular and cochlear endolymphatic hydrops at MRI, while high bilateral contrast enhancement on 4-h delayed postcontrast 3D FLAIR sequence was observed in all ears.

CONCLUSIONS

Increased perilymph enhancement on 4-h delayed postcontrast 3D FLAIR sequence is the common imaging feature of DFNA9 ears, suggesting that blood-labyrinthine barrier breakdown may play the main role in the pathophysiology of this disease. Significant hydrops has been excluded by MRI. This finding might be clinically useful in differentiating DFNA9 disease from other pathologies with similar clinical findings like Ménière's disease.

Next-generation sequencing identified SPATC1L as a possible candidate gene for both early-onset and age-related hearing loss

Hereditary hearing loss (HHL) and age-related hearing loss (ARHL) are two major sensory diseases affecting millions of people worldwide. Despite many efforts, additional HHL-genes and ARHL genetic risk factors still need to be identified. To fill this gap a large genomic screening based on next-generation sequencing technologies was performed. Whole exome sequencing in a 3-generation Italian HHL family and targeted re-sequencing in 464 ARHL patients were performed. We detected three variants in SPATC1L: a nonsense allele in an HHL family and a frameshift insertion and a missense variation in two unrelated ARHL patients. In silico molecular modelling of all variants suggested a significant impact on the structural stability of the protein itself, likely leading to deleterious effects and resulting in truncated isoforms. After demonstrating Spatc1l expression in mice inner ear, in vitro functional experiments were performed confirming the results of the molecular modelling studies. Finally, a candidate-gene population-based statistical study in cohorts from Caucasus and Central Asia revealed a statistically significant association of SPATC1L with normal hearing function at low and medium hearing frequencies. Overall, the amount of different genetic data presented here (variants with early-onset and late-onset hearing loss in addition to genetic association with normal hearing function), together with relevant functional evidence, likely suggest a role of SPATC1L in hearing function and loss.

Alport syndrome cold cases: Missing mutations identified by exome sequencing and functional analysis

Alport syndrome (AS) is an inherited progressive renal disease caused by mutations in COL4A3, COL4A4, and COL4A5 genes. Despite simultaneous screening of these genes being widely available, mutation detection still remains incomplete in a non-marginal portion of patients. Here, we applied whole-exome sequencing (WES) in 3 Italian families negative after candidate-gene analyses. In Family 1, we identified a novel heterozygous intronic variant (c.2245-40A>G) -outside the conventionally screened candidate region for diagnosis- potentially disrupting COL4A5 exon29 splicing. Using a minigene-based approach in HEK293 cells we demonstrated that this variant abolishes exon29 branch site, causing exon skipping. Moreover, skewed X-inactivation of the c.2245-40A>G allele correlated with disease severity in heterozygous females. In Family 2, WES highlighted a novel COL4A5 hemizygous missense mutation (p.Gly491Asp), which segregates with the phenotype and impacts on a highly-conserved residue. Finally, in Family 3, we detected a homozygous 24-bp in-frame deletion in COL4A3 exon1 (NM_000091.4:c.30_53del:p.Val11_Leu18del or c.40_63del24:p.Leu14_Leu21del), which is ambiguously annotated in databases, although it corresponds to a recurrent AS mutation. Functional analyses showed that this deletion disrupts COL4A3 signal peptide, possibly altering protein secretion. In conclusion, WES -together with functional studies- was fundamental for molecular diagnosis in 3 AS families, highlighting pathogenic variants that escaped previous screenings.

Early Volume Expansion and Outcomes of Hemolytic Uremic Syndrome

BACKGROUND

Hemolytic uremic syndrome associated with Shiga toxin-producing Escherichia coli (STEC-HUS) is a severe acute illness without specific treatment except supportive care; fluid management is concentrated on preventing fluid overload for patients, who are often oligoanuric. Hemoconcentration at onset is associated with more severe disease, but the benefits of volume expansion after hemolytic uremic syndrome (HUS) onset have not been explored.

METHODS

All the children with STEC-HUS referred to our center between 2012 and 2014 received intravenous infusion targeted at inducing an early volume expansion (+10% of working weight) to restore circulating volume and reduce ischemic or hypoxic tissue damage. The short- and long-term outcomes of these patients were compared with those of 38 historical patients referred to our center during the years immediately before, when fluid intake was routinely restricted.

RESULTS

Patients undergoing fluid infusion soon after diagnosis showed a mean increase in body weight of 12.5% (vs 0%), had significantly better short-term outcomes with a lower rate of central nervous system involvement (7.9% vs 23.7%, P = .06), had less need for renal replacement therapy (26.3% vs 57.9%, P = .01) or intensive care support (2.0 vs. 8.5 days, P = .02), and needed fewer days of hospitalization (9.0 vs 12.0 days, P = .03). Long-term outcomes were also significantly better in terms of renal and extrarenal sequelae (13.2% vs 39.5%, P = .01).

CONCLUSIONS

Patients with STEC-HUS had great benefit from early volume expansion. It is speculated that early and generous fluid infusions can reduce thrombus formation and ischemic organ damage, thus having positive effects on both short- and long-term disease outcomes.

First independent replication of the involvement of LARS2 in Perrault syndrome by whole-exome sequencing of an Italian family

Perrault syndrome (MIM #233400) is a rare autosomal recessive disorder characterized by ovarian dysgenesis and primary ovarian insufficiency in females, and progressive hearing loss in both genders. Recently, mutations in five genes (HSD17B4, HARS2, CLPP, LARS2, and C10ORF2) were found to be responsible for Perrault syndrome, although they do not account for all cases of this genetically heterogeneous condition.

We used whole-exome sequencing to identify pathogenic variants responsible for Perrault syndrome in an Italian pedigree with two affected siblings. Both patients were compound heterozygous for two novel missense variants within the mitochondrial leucyl-tRNA synthetase (LARS2), NM_015340.3:c.899C>T(p.Thr300Met) and c.1912G>A(p.Glu638Lys). Both variants co-segregated with the phenotype in the family. p.Thr300 and p.Glu638 are evolutionary conserved residues, and are located respectively within the editing domain and immediately before the catalytically important KMSKS motif. Homology modeling using as template the E. coli leucyl-tRNA synthetase provided further insights on the possible pathogenic effects of the identified variants.

This represents the first independent replication of the involvement of LARS2 mutations in Perrault syndrome, contributing valuable information for the further understanding of this disease.

Hemoconcentration: a major risk factor for neurological involvement in hemolytic uremic syndrome

BACKGROUND

Shigatoxin-associated hemolytic uremic syndrome (STEC-HUS) is a common thrombotic microangiopathy (TMA) in which central nervous system (CNS) involvement is responsible for the majority of deaths and for severe long-term sequelae. We have analyzed the role of hemoconcentration in disease severity.

METHODS

This was a retrospective review of the records and laboratory data at presentation of all patients with STEC-HUS cases (n = 61) over a 10-year period. The patients were grouped into three severity classes: group A, comprising patients who did not require dialysis; group B, patients who were dialyzed without CNS involvement; group C, patients with CNS involvement.

RESULTS

Patients with CNS involvement (group C) had a higher mean hemoglobin level (11.2 ± 2.3 g/dL) than those of group A or B ( 9.4 ± 2.1 and 7.5 ± 1.9 g/dL, respectively; p < 0.0001). We also observed that the higher the initial hemoglobin level, the more severe the long-term renal damage (p < 0.007).

CONCLUSIONS

In patients with STEC-HUS, hemoconcentration and hypovolemia may be responsible for more severe ischemic organ damage (both short and long term) at disease onset, and these signs should be regarded as risk factors for CNS damage and for more severe TMA. Therefore, we recommend that hydration status should be actively monitored in HUS patients and that dehydration, when diagnosed, should be promptly corrected.

Usher syndrome: an effective sequencing approach to establish a genetic and clinical diagnosis

Usher syndrome is an autosomal recessive disorder characterized by retinitis pigmentosa, sensorineural hearing loss and, in some cases, vestibular dysfunction. The disorder is clinically and genetically heterogeneous and, to date, mutations in 11 genes have been described. This finding makes difficult to get a precise molecular diagnosis and offer patients accurate genetic counselling. To overcome this problem and to increase our knowledge of the molecular basis of Usher syndrome, we designed a targeted resequencing custom panel. In a first validation step a series of 16 Italian patients with known molecular diagnosis were analysed and 31 out of 32 alleles were detected (97% of accuracy). After this step, 31 patients without a molecular diagnosis were enrolled in the study. Three out of them with an uncertain Usher diagnosis were excluded. One causative allele was detected in 24 out 28 patients (86%) while the presence of both causative alleles characterized 19 patients out 28 (68%). Sixteen novel and 27 known alleles were found in the following genes: USH2A (50%), MYO7A (7%), CDH23 (11%), PCDH15 (7%) and USH1G (2%). Overall, on the 44 patients the protocol was able to characterize 74 alleles out of 88 (84%). These results suggest that our panel is an effective approach for the genetic diagnosis of Usher syndrome leading to: 1) an accurate molecular diagnosis, 2) better genetic counselling, 3) more precise molecular epidemiology data fundamental for future interventional plans.

Enrichment of LOVD-USHbases with 152 USH2A genotypes defines an extensive mutational spectrum and highlights missense hotspots

Alterations of USH2A, encoding usherin, are responsible for more than 70% of cases of Usher syndrome type II (USH2), a recessive disorder that combines moderate to severe hearing loss and retinal degeneration. The longest USH2A transcript encodes usherin isoform b, a 5,202-amino-acid transmembrane protein with an exceptionally large extracellular domain consisting notably of a Laminin N-terminal domain and numerous Laminin EGF-like (LE) and Fibronectin type III (FN3) repeats. Mutations of USH2A are scattered throughout the gene and mostly private. Annotating these variants is therefore of major importance to correctly assign pathogenicity. We have extensively genotyped a novel cohort of 152 Usher patients and identified 158 different mutations, of which 93 are newly described. Pooling this new data with the existing pathogenic variants already incorporated in USHbases reveals several previously unappreciated features of the mutational spectrum. We show that parts of the protein are more likely to tolerate single amino acid variations, whereas others constitute pathogenic missense hotspots. We have found, in repeated LE and FN3 domains, a nonequal distribution of the missense mutations that highlights some crucial positions in usherin with possible consequences for the assessment of the pathogenicity of the numerous missense variants identified in USH2A.

Emerging ciliopathies: are respiratory cilia compromised in Usher syndrome?

PURPOSE

Usher syndrome is a ciliopathy involving photoreceptors and cochlear hair cells (sensory cilia): since sensory and motor ciliopathies can overlap, we analysed the respiratory cilia (motile) in 17 patients affected by Usher syndrome and 18 healthy control subject.

PATIENTS AND METHODS

We studied the mucociliary transport time with the saccharine test, ciliary motility and ultrastructure of respiratory cilia obtained by nasal brushing; we also recorded the classical respiratory function values by spirometry.

RESULTS

All enrolled subjects showed normal respiratory function values. The mean mucociliary transport time with saccharine was 22.33 ± 17.96 min, which is in the range of normal values. The mean ciliary beat frequency of all subjects was 8.81 ± 2.18 Hz, which is a value approaching the lower physiological limit. None of the classical ciliary alterations characterizing the "ciliary primary dyskinesia" was detected, although two patients showed alterations in number and arrangement of peripheral microtubules and one patient had abnormal ciliary roots.

CONCLUSIONS

Respiratory cilia in Usher patients don't seem to have evident ultrastructural alterations, as expected, but the fact that the ciliary motility appeared slightly reduced could emphasize that a rigid distinction between sensory and motor ciliopathies may not reflect what really occurs.

Nuclear shadowing in the holographic framework

The nucleon structure function F2(N) computed in a holographic framework can be used to describe nuclear deep inelastic scattering effects provided that a rescaling of the Q2 momentum and of the IR hard-wall parameter z0 is made. The ratios RA=F2(A)/F2(N) can be obtained in terms of a single rescaling parameter λA for each nucleus. The resulting ratios agree with the experiment in a wide range of the shadowing region.

Unbiased next generation sequencing analysis confirms the existence of autosomal dominant Alport syndrome in a relevant fraction of cases

The mode of inheritance of Alport syndrome (ATS) has long been controversial. In 1927, the disease was hypothesized as a dominant condition in which males were more severely affected than females. In 1990, it was considered an X-linked (XL) semidominant condition, due to COL4A5 mutations. Later on, a rare autosomal recessive (AR) form due to COL4A3/COL4A4 mutations was identified. An autosomal dominant (AD) form was testified more recently by the description of some large pedigrees but the real existence of this form is still questioned by many and its exact prevalence is unknown. The introduction of next generation sequencing (NGS) allowed us to perform an unbiased simultaneous COL4A3-COL4A4-COL4A5 analysis in 87 Italian families (273 individuals) with clinical suspicion of ATS. In 48 of them (55%), a mutation in one of the three genes was identified: the inheritance was XL semidominant in 65%, recessive in 4% and most interestingly AD in 31% (15 families). The AD form must therefore be seriously taken into account in all pedigrees with affected individuals in each generation. Furthermore, a high frequency of mutations (>50%) was shown in patients with only 1 or 2 clinical criteria, suggesting NGS as first-level analysis in cases with a clinical suspicion of ATS.

Molecular and functional studies of 4 candidate loci in Pendred syndrome and nonsyndromic hearing loss

Patients with PS or non-syndromic deafness were submitted to genetic/functional analyzes of SLC26A4, of its binding domain for FOXI1 (FOXI1-DBD), of the transcription activator FOXI1, and of the potassium channel KCNJ10. SLC26A4 was the most frequently mutated gene. An altered intracellular localization with immunocytochemistry, and a hampered maturation process were demonstrated for two novel SLC26A4 variants. Biochemical and immunocytochemical analyzes led to the development of a more sensitive fluorometric functional assay able to reveal the partial loss-of-function of SLC26A4 mutations. A novel missense variant was found in FOXI1 gene, though functional analysis showed no significant impairment in the transcriptional activation of SLC26A4. Finally, 3 patients were found to harbor a variant in KCNJ10, which was classified as polymorphism. The novelty of the study resides in the analysis of all the 4 candidate genetic loci linked to PS/non-syndromic deafness, and in the precise definition of the thyroid phenotype. PS was invariably associated with biallelic mutations of SLC26A4, whereas the genetic origin of non-syndromic deafness remained largely undetermined, since monoallelic SLC26A4 variants accounted for one fourth of the cases and FOXI1 and KCNJ10 were not involved in this series.

A novel mutation within the MIR96 gene causes non-syndromic inherited hearing loss in an Italian family by altering pre-miRNA processing

The miR-96, miR-182 and miR-183 microRNA (miRNA) family is essential for differentiation and function of the vertebrate inner ear. Recently, point mutations within the seed region of miR-96 were reported in two Spanish families with autosomal dominant non-syndromic sensorineural hearing loss (NSHL) and in a mouse model of NSHL. We screened 882 NSHL patients and 836 normal-hearing Italian controls and identified one putative novel mutation within the miR-96 gene in a family with autosomal dominant NSHL. Although located outside the mature miR-96 sequence, the detected variant replaces a highly conserved nucleotide within the companion miR-96*, and is predicted to reduce the stability of the pre-miRNA hairpin. To evaluate the effect of the detected mutation on miR-96/mir-96* biogenesis, we investigated the maturation of miR-96 by transient expression in mammalian cells, followed by real-time reverse-transcription polymerase chain reaction (PCR). We found that both miR-96 and miR-96* levels were significantly reduced in the mutant, whereas the precursor levels were unaffected. Moreover, miR-96 and miR-96* expression levels could be restored by a compensatory mutation that reconstitutes the secondary structure of the pre-miR-96 hairpin, demonstrating that the mutation hinders precursor processing, probably interfering with Dicer cleavage. Finally, even though the mature miR-96 sequence is not altered, we demonstrated that the identified mutation significantly impacts on miR-96 regulation of selected targets. In conclusion, we provide further evidence of the involvement of miR-96 mutations in human deafness and demonstrate that a quantitative defect of this miRNA may contribute to NSHL.

Novel TMEM67 mutations and genotype-phenotype correlates in meckelin-related ciliopathies

Human ciliopathies are hereditary conditions caused by defects of proteins expressed at the primary cilium. Among ciliopathies, Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS) and nephronophthisis (NPH) present clinical and genetic overlap, being allelic at several loci. One of the most interesting gene is TMEM67, encoding the transmembrane protein meckelin. We performed mutation analysis of TMEM67 in 341 probands, including 265 JSRD representative of all clinical subgroups and 76 MKS fetuses. We identified 33 distinct mutations, of which 20 were novel, in 8/10 (80%) JS with liver involvement (COACH phenotype) and 12/76 (16%) MKS fetuses. No mutations were found in other JSRD subtypes, confirming the strong association between TMEM67 mutations and liver involvement. Literature review of all published TMEM67 mutated cases was performed to delineate genotype-phenotype correlates. In particular, comparison of the types of mutations and their distribution along the gene in lethal versus non lethal phenotypes showed in MKS patients a significant enrichment of missense mutations falling in TMEM67 exons 8 to 15, especially when in combination with a truncating mutation. These exons encode for a region of unknown function in the extracellular domain of meckelin.

Expanding CEP290 mutational spectrum in ciliopathies

Ciliopathies are an expanding group of rare conditions characterized by multiorgan involvement, that are caused by mutations in genes encoding for proteins of the primary cilium or its apparatus. Among these genes, CEP290 bears an intriguing allelic spectrum, being commonly mutated in Joubert syndrome and related disorders (JSRD), Meckel syndrome (MKS), Senior-Loken syndrome and isolated Leber congenital amaurosis (LCA). Although these conditions are recessively inherited, in a subset of patients only one CEP290 mutation could be detected. To assess whether genomic rearrangements involving the CEP290 gene could represent a possible mutational mechanism in these cases, exon dosage analysis on genomic DNA was performed in two groups of CEP290 heterozygous patients, including five JSRD/MKS cases and four LCA, respectively. In one JSRD patient, we identified a large heterozygous deletion encompassing CEP290 C-terminus that resulted in marked reduction of mRNA expression. No copy number alterations were identified in the remaining probands. The present work expands the CEP290 genotypic spectrum to include multiexon deletions. Although this mechanism does not appear to be frequent, screening for genomic rearrangements should be considered in patients in whom a single CEP290 mutated allele was identified.

Analysis of the GJB2 and GJB6 genes in Italian patients with nonsyndromic hearing loss: frequencies, novel mutations, genotypes, and degree of hearing loss

Mutations in the GJB2 gene, which encodes the gap-junction protein connexin 26, are the most common cause of nonsyndromic hearing loss (NSHL) and account for about 32% of cases. We analyzed 734 patients and identified mutations in 474/1468 chromosomes. Thirty-six different mutations and five polymorphisms were found in 269 NSHL subjects. Our data confirm 35delG as the most frequent GJB2 mutation in the Italian population, accounting for about 68% of all the mutated GJB2 alleles analyzed. We also identified two novel variants: the V156I mutation and the C>A change at nucleotide 684 in the 3'UTR of the gene. The GJB6 gene deletion, del(GJB6-D13S1830), which can cause HL in combination with GJB2 mutations in trans, was identified in three patients, while the del(GJB6-D13S1854) was not observed in our cohort of patients. We collected audiometric data from 200 patients with biallelic DFNB1 mutations or with dominant mutation in GJB2 to determine the degree of HL to correlate the genotypes with the audiological phenotypes.

Phenotypic variability of patients homozygous for the GJB2 mutation 35delG cannot be explained by the influence of one major modifier gene

Hereditary hearing loss (HL) is a very heterogeneous trait, with 46 gene identifications for non-syndromic HL. Mutations in GJB2 cause up to half of all cases of severe-to-profound congenital autosomal recessive non-syndromic HL, with 35delG being the most frequent mutation in Caucasians. Although a genotype-phenotype correlation has been established for most GJB2 genotypes, the HL of 35delG homozygous patients is mild to profound. We hypothesise that this phenotypic variability is at least partly caused by the influence of modifier genes. By performing a whole-genome association (WGA) study on 35delG homozygotes, we sought to identify modifier genes. The association study was performed by comparing the genotypes of mild/moderate cases and profound cases. The first analysis included a pooling-based WGA study of a first set of 255 samples by using both the Illumina 550K and Affymetrix 500K chips. This analysis resulted in a ranking of all analysed single-nucleotide polymorphisms (SNPs) according to their P-values. The top 250 most significantly associated SNPs were genotyped individually in the same sample set. All 192 SNPs that still had significant P-values were genotyped in a second independent set of 297 samples for replication. The significant P-values were replicated in nine SNPs, with combined P-values between 3 x 10(-3) and 1 x 10(-4). This study suggests that the phenotypic variability in 35delG homozygous patients cannot be explained by the effect of one major modifier gene. Significantly associated SNPs may reflect a small modifying effect on the phenotype. Increasing the power of the study will be of greatest importance to confirm these results.

A multicenter study on the prevalence and spectrum of mutations in the otoferlin gene (OTOF) in subjects with nonsyndromic hearing impairment and auditory neuropathy

Autosomal recessive nonsyndromic hearing impairment (NSHI) is a heterogeneous condition, for which 53 genetic loci have been reported, and 29 genes have been identified to date. One of these, OTOF, encodes otoferlin, a membrane-anchored calcium-binding protein that plays a role in the exocytosis of synaptic vesicles at the auditory inner hair cell ribbon synapse. We have investigated the prevalence and spectrum of deafness-causing mutations in the OTOF gene. Cohorts of 708 Spanish, 83 Colombian, and 30 Argentinean unrelated subjects with autosomal recessive NSHI were screened for the common p.Gln829X mutation. In compound heterozygotes, the second mutant allele was identified by DNA sequencing. In total, 23 Spanish, two Colombian and two Argentinean subjects were shown to carry two mutant alleles of OTOF. Of these, one Colombian and 13 Spanish subjects presented with auditory neuropathy. In addition, a cohort of 20 unrelated subjects with a diagnosis of auditory neuropathy, from several countries, was screened for mutations in OTOF by DNA sequencing. A total of 11 of these subjects were shown to carry two mutant alleles of OTOF. In total, 18 pathogenic and four neutral novel alleles of the OTOF gene were identified. Haplotype analysis for markers close to OTOF suggests a common founder for the novel c.2905_2923delinsCTCCGAGCGCA mutation, frequently found in Argentina. Our results confirm that mutation of the OTOF gene correlates with a phenotype of prelingual, profound NSHI, and indicate that OTOF mutations are a major cause of inherited auditory neuropathy.

Growth laws in cancer: implications for radiotherapy

Comparing the conventional Gompertz tumor growth law (GL) with the "Universal" law (UL), which has recently been proposed and applied to cancer, we have investigated the implications of the growth laws for various radiotherapy regimens. According to the GL, the surviving tumor cell fraction could be reduced ad libitum, independent of the initial tumor mass, simply by increasing the number of treatments. In contrast, if tumor growth dynamics follows the Universal scaling law, there is a lower limit of the surviving fraction that cannot be reduced further regardless of the total number of treatments. This finding can explain the so-called tumor size effect and re-emphasizes the importance of early diagnosis because it implies that radiotherapy may be successful provided that the tumor mass at treatment onset is rather small. Taken together with our previous work, the implications of these findings include revisiting standard radiotherapy regimens and treatment protocols overall.

High phenotypic intrafamilial variability in patients with Pendred syndrome and a novel duplication in the SLC26A4 gene: clinical characterization and functional studies of the mutated SLC26A4 protein

OBJECTIVE

Pendred syndrome (PS) is characterized by the association of sensorineural hearing loss (SNHL) and a partial iodide organification defect at the thyroid level. It is caused by mutations in the SLC26A4 gene. The encoded transmembrane protein, called pendrin, has been found to be able to transport chloride and other anions.

DESIGN

The aim of the present study was to characterize a family with PS, which shows a strong intrafamilial phenotypic variability, including kidney atrophy in one member. The age of disease-onset was significantly different in all three affected siblings, ranging from 2 to 21 years for thyroid alterations and from 1.5 to 11 years for SNHL.

METHODS

Clinical and genetic studies were carried out in affected siblings. The functional activity of the novel duplication found was studied by a fluorimetric method in a human renal cell line (HEK293 Phoenix) in which the protein was overexpressed.

RESULTS

All three siblings were found to be compound heterozygotes for the missense mutation (1226G>A, R409H) and for a novel 11 bp duplication (1561_1571CTTGGAATGGC, S523fsX548). The latter mutation creates a frame shift leading to the loss of the entire carboxy-terminus domain. Functional studies of this mutant demonstrated impaired transport of chloride and iodide when expressed in HEK 293 Phoenix cells, when compared with wild type pendrin.

CONCLUSIONS

A novel 11 bp duplication was found in a family with Pendred syndrome, showing a high intrafamilial phenotypic variability. An impaired transmembrane anionic transport of the mutated SLC26A4 protein was demonstrated in functional studies using a heterologous cell system.

A new de novo missense mutation in connexin 26 in a sporadic case of nonsyndromic deafness

OBJECTIVES

Mutations in the GJB2 gene, encoding Connexin 26, can cause nonsyndromic recessive deafness or dominant hearing loss (HL) with or without keratoderma. The objective was to perform a molecular evaluation to establish the inherited pattern of deafness in the sporadic cases afferent to our center.

METHODS

The subject was a 2-year-old Italian girl with nonsyndromic early onset HL. We performed DNA sequencing of the GJB2 gene and deletion analysis of the GJB6 gene in all family members.

RESULTS

Direct sequencing of the gene showed a heterozygous C-->G transition at nucleotide 172 resulting in a proline to alanine amino acid substitution at codon 58 (P58A). The analyses indicate that the P58A mutation appeared de novo in the proband with a possible dominant effect.

CONCLUSIONS

This mutation occurs in the first extracellular domain (EC1), which seems to be very important for connexon-connexon interaction and for the control of voltage gating of the channel. The de novo occurrence of an EC1 mutation in a sporadic case of deafness is consistent with the assumption that P58A can cause dominant HL.

Mechanisms causing imprinting defects in familial Beckwith-Wiedemann syndrome with Wilms' tumour

The imprinted expression of the IGF2 and H19 genes is controlled by the Imprinting Centre 1 (IC1) at chromosome 11p15.5. This is a methylation-sensitive chromatin insulator that works by binding the zinc-finger protein CTCF in a parent-specific manner. Microdeletions abolishing some of the CTCF target sites (CTSs) of IC1 have been associated with the Beckwith-Wiedemann syndrome (BWS). However, the link between these mutations and the molecular and clinical phenotypes was debated. We have identified two novel families with IC1 deletions, in which individuals with the clinical features of the BWS are present in multiple generations. By analysing the methylation pattern at the IGF2-H19 locus together with the clinical phenotypes in the individuals with maternal and those with paternal transmission of five different deletions, we demonstrate that maternal transmission of 1.4-1.8 kb deletions in the IC1 region co-segregates with the hypermethylation of the residual CTSs and BWS phenotype with complete penetrance, whereas normal phenotype is observed upon paternal transmission. Although gene expression could not be assayed in all cases, the methylation detected at the IGF2 DMR2 and H19 promoter suggests that IC1 hypermethylation is consistently associated with biallelic activation of IGF2 and biallelic silencing of H19. Comparison of these deletions with a 2.2 kb one previously reported by another group indicates that the spacing of the CTSs on the deleted allele is critical for the gain of the abnormal methylation and penetrance of the clinical phenotype. Furthermore, we observe that the hypermethylation resulting from the deletions is always mosaic, suggesting that the epigenetic defect at the IGF2-H19 locus is established post-zygotically and may cause body asymmetry and heterogeneity of the clinical phenotype. Finally, the IC1 microdeletions are associated with a high incidence of Wilms' tumour, making their molecular diagnosis particularly important for genetic counselling and tumour surveillance at follow-up.

Classification scheme for phenomenological universalities in growth problems in physics and other sciences

A classification in universality classes of broad categories of phenomenologies, belonging to physics and other disciplines, may be very useful for a cross fertilization among them and for the purpose of pattern recognition and interpretation of experimental data. We present here a simple scheme for the classification of nonlinear growth problems. The success of the scheme in predicting and characterizing the well known Gompertz, West, and logistic models, suggests to us the study of a hitherto unexplored class of nonlinear growth problems.

GJB2 mutations and degree of hearing loss: a multicenter study

Hearing impairment (HI) affects 1 in 650 newborns, which makes it the most common congenital sensory impairment. Despite extraordinary genetic heterogeneity, mutations in one gene, GJB2, which encodes the connexin 26 protein and is involved in inner ear homeostasis, are found in up to 50% of patients with autosomal recessive nonsyndromic hearing loss. Because of the high frequency of GJB2 mutations, mutation analysis of this gene is widely available as a diagnostic test. In this study, we assessed the association between genotype and degree of hearing loss in persons with HI and biallelic GJB2 mutations. We performed cross-sectional analyses of GJB2 genotype and audiometric data from 1,531 persons, from 16 different countries, with autosomal recessive, mild-to-profound nonsyndromic HI. The median age of all participants was 8 years; 90% of persons were within the age range of 0-26 years. Of the 83 different mutations identified, 47 were classified as nontruncating, and 36 as truncating. A total of 153 different genotypes were found, of which 56 were homozygous truncating (T/T), 30 were homozygous nontruncating (NT/NT), and 67 were compound heterozygous truncating/nontruncating (T/NT). The degree of HI associated with biallelic truncating mutations was significantly more severe than the HI associated with biallelic nontruncating mutations (P<.0001). The HI of 48 different genotypes was less severe than that of 35delG homozygotes. Several common mutations (M34T, V37I, and L90P) were associated with mild-to-moderate HI (median 25-40 dB). Two genotypes--35delG/R143W (median 105 dB) and 35delG/dela(GJB6-D13S1830) (median 108 dB)--had significantly more-severe HI than that of 35delG homozygotes.

RNA processing defects of the helicase gene RECQL4 in a compound heterozygous Rothmund-Thomson patient

Rothmund-Thomson syndrome (RTS) (OMIM 268400) is an autosomal recessive genodermatosis associated with genomic instability and increased risk of mesenchymal cancers. Mutations in the RECQL4 gene, encoding a protein of the family of Werner (WRN) and Bloom (BLM) helicases, have been identified in a subset of RTS patients. Apart from congenital poikiloderma, the clinical presentation of RTS is widely variable, raising the question of the possible existence of a second locus. Results herein reported on a sporadic Caucasian patient emphasize the concept that mutation analyses at both DNA and RNA level complement the genetic defect suggested by clinical and cytogenetic signs. The patient presented with typical congenital poikiloderma and bone defects and exhibited significant genomic instability in the peripheral blood karyotype. By RECQL4 DNA mutation analysis, he was found to carry a 1473delT (mut 5) on one allele and an AG to AC change at the 3'-splice site of exon 13 (a variant of mut 4) on the second allele. RT-PCR analysis of RECQL4 cDNA encompassing the entire helicase domain showed diffuse splicing defects indicating that the loss of a single 3'-splice signal motif disregulates the correct splice-site selection and affects the overall RNA processing. The presence of an unstable minisatellite which ends at 3'-splice site of IVS12 may enhance the mutation at this site. This genomic feature together with a number of short introns in the RECQL4 gene may account for the common missplicing of RECQL4 mRNA. While it is possible that defects of RECQL4 mRNA processing might account for part of the clinical variability observed for this syndrome, only a thorough analysis at both genomic and RNA level may allow a genotype-phenotype correlation in RTS patients, restricting the search of a second RTS locus to the specific patients.

A novel dominant missense mutation--D179N--in the GJB2 gene (Connexin 26) associated with non-syndromic hearing loss

Mutations of the GJB2 gene, encoding Connexin 26, are the most common cause of hereditary congenital hearing loss in many countries, and account for up to 50% of cases of autosomal-recessive non-syndromic deafness. By contrast, only a few GJB2 mutations have been reported to cause an autosomal-dominant form of non-syndromic deafness. We report on a family from southern Italy in whom dominant, non-syndromic, post-lingual hearing loss is associated with a novel missense mutation in the GJB2 gene. Direct sequencing of the gene showed a heterozygous G-->A transition at nucleotide 535, resulting in an aspartic acid to asparagine amino acid substitution at codon 179 (D179N). This mutation occurred in the second extracellular domain (EC2), which would seem to be very important for connexon-connexon interaction.

[Rothmund-Thomson syndrome, trisomy 8 mosaicism and RECQ4 gene mutation]

BACKGROUND

We report a case of Rothmund-Thomson syndrome associated with a trisomy 8 mosaicism, and RECQ4 gene mutation.

OBSERVATION

An 18-year-old man presented with a poikiloderma affecting photoexposed areas and the buttocks. This lesions appeared during the first year of life and was secondly associated with alopecia, sparse body hair, keratosis, and warts. He also had proportional short stature, thumb and patella aplasia, particular facies, and plantar malformations. Cytogenetic studies evidenced chromosomal instability and trisomy 8 mosaicism. The DNA repair capacity was normal. A mutation in RECQ4 helicase gene was found.

DISCUSSION

Rothmund-Thomson syndrome is a rare hereditary syndrome characterized by early onset of poikiloderma. Patients exhibit variable features including skeletal abnormalities, juvenile cataracts, photosensitivity, and a higher than expected incidence of cutaneous or extracutaneous malignancies. Genetic patterns found in Rothmund-Thomson syndrome are heterogeneous. Normal karyotypes have been demonstrated in many patients. Various karyotypic abnormalities or reduced DNA repair was seen in others. Recently, five patients with Rothmund-Thomson syndrome were shown to segregate for mutations in RECQ4 helicase gene. Thus, clinical and genetic features in Rothmund-Thomson syndrome are polymorphous. Therefore, it could be interesting to correlate genotype and phenotype.

Reproductive follow-up of carriers of familial reciprocal balanced translocations involving chromosome 9 and comparison with predicted outcome

Reproductive follow-up of carriers of familial reciprocal balanced translocations involving chromosome 9 and comparison with predicted outcome: Chromosome 9 is commonly implicated in reciprocal translocations (rcp). Twenty-seven families segregating rcp involving chromosome 9 were selected with the aim of comparing the theoretical risk of Mental Retardation with Congenital Anomalies (MCA/MR) calculated according to Human Cytogenetics Forum with the observed reproductive follow-up. The 27 families include 157 subjects. The reproductive follow-up showed that the majority of mothers underwent full-term pregnancies (88/130), and that there were 37 spontaneous and five voluntary abortions. Eighty-one subjects were karyotyped: 18 had a normal karyotype, 50 carried an rcp, ten had an unbalanced rcp-related karyotype and three an abnormal rcp-unrelated karyotype. Of the 88 live-born individuals, seven had an abnormal rcp-related karyotype with partial chromosome 9 trisomy (four cases) or partial 9p monosomy (three cases), and 48 were rcp carriers, two of whom also presented additional anomalies. The evaluation of reproductive outcomes in the 27 families studied revealed good concordance between the Human Cytogenetics Forum predictions and the observed follow-up in relation to the most probable mode of unbalance at birth, and the higher risk of MCA/MR in rcp carriers with unbalanced live-borns in comparison with those generating healthy progeny

Multicolor FISH in chronic lymphocytic leukemia. An interphase study of patients with early-onset disease

Trisomy 12 and deletions of 13q14.2 and 14q32 are the most common chromosome abnormalities in patients with B-chronic lymphocytic leukemia (B-CLL), but whether specific chromosomal defects influence the course of B-CLL is still a matter of discussion. The aim of our study was to assess the possible correlation between cytogenetic findings and clinical characteristics. Thirty patients with previously untreated early-onset B-CLL were recruited. The incidence of trisomy 12, and observations of 13q14.2 and 14q32 was analyzed in unstimulated bone marrow cells by means of multicolor interphase FISH. No correlation was found between trisomy 12 and the patients' clinical characteristics. The analysis of the patients with trisomy 12 and observations of 13q14.2 and 14q32 revealed heterogeneity of the leukemic cell population, thus indicating that these chromosomal abnormalities are probably a secondary event in CLL leukemogenesis. The finding of RB1 gene nullisomy and 14q32 deletions in patients at an advanced clinical stage suggests a possible correlation between these rearrangements and disease progression. Multicolor FISH analysis in B-CLL provides important diagnostic, clinical, and prognostic information that may help in assessing prognosis and making treatment decisions.

Trisomy 4 leading to duplication of a mutated KIT allele in acute myeloid leukemia with mast cell involvement

A G-->T transversion at nucleotide 2467 of the c-KIT gene leading to Asp816-->Tyr (D816Y) substitution in the phosphotransferase domain has been previously identified in a patient with rapidly progressing AML-M2 and mast cell involvement; the patient's blasts had a 47,XY, +4,t(8;21)(q22;q22) karyotype. Herein we confirm the simultaneous presence of both major chromosomal changes by multicolor fluorescence in situ hybridization (FISH) on interphase CD34+ mononuclear cells. By setting up culture leukemic blasts, spontaneous differentiation of adherent cells with mast-cell like features was proved by histochemical and immunoenzymatic analyses. Fluorescence in situ hybridization evidence of trisomy 4 confirmed the origin of differentiated cells from the leukemic blasts. Semiquantitative polymerase chain reaction (PCR) and phosphoimage densitometry of wild-type and mutated KIT alleles on bone marrow blasts made it possible to demonstrate that chromosome 4 trisomy led to a double dosage of the mutated KIT allele. This finding, and that of trisomy 7 and MET mutation in hereditary renal carcinoma represent the only cases of human tumors in which an increased number of chromosomes carrying an oncogene activated by point mutation have been detected.

NF1 microdeletion syndrome: refined FISH characterization of sporadic and familial deletions with locus-specific probes

Two familial and seven sporadic patients with neurofibromatosis 1-who showed dysmorphism, learning disabilities/mental retardation, and additional signs and carried deletions of the NF1 gene-were investigated by use of a two-step FISH approach to characterize the deletions. With FISH of YAC clones belonging to a 7-Mb 17q11.2 contig, we estimated the extension of all of the deletions and identified the genomic regions harboring the breakpoints. Mosaicism accounted for the mild phenotype in two patients. In subsequent FISH experiments, performed with locus-specific probes generated from the same YACs by means of a novel procedure, we identified the smallest region of overlapping (SRO), mapped the deletion breakpoints, and identified the genes that map to each deletion interval. From centromere to telomere, the approximately 0.8-Mb SRO includes sequence-tagged site 64381, the SUPT6H gene (encoding a transcription factor involved in chromatin structure), and NF1. Extending telomerically from the SRO, two additional genes-BLMH, encoding a hydrolase involved in bleomycin resistance, and ACCN1, encoding an amiloride-sensitive cation channel expressed in the CNS-were located in the deleted intervals of seven and three patients, respectively. An apparently common centromeric deletion breakpoint was shared by all of the patients, whereas a different telomeric breakpoint defined a deletion interval of 0.8-3 Mb. There was no apparent correlation between the extent of the deletion and the phenotype. This characterization of gross NF1 deletions provides the premise for addressing correctly any genotype-phenotype correlation in the subset of patients with NF1 deletions.

Chromosomal instability in fibroblasts and mesenchymal tumors from 2 sibs with Rothmund-Thomson syndrome

Rothmund-Thomson syndrome (RTS) is a rare autosomal recessive genodermatosis associated with increased risk of mesenchymal tumors. The putative gene has been provisionally assigned to chromosome 8. Using a cytogenetic-molecular approach, we studied lymphocytes, fibroblasts, osteosarcoma (OS) and malignant fibrous histiocytoma (MFH) from 2 affected fraternal twins, looking for constitutive markers of chromosome instability and tumor chromosomal changes which might reflect the common genetic background. The rate of spontaneous chromosome aberrations was not increased in lymphocytes. Conversely, karyotyping of primary fibroblasts from one sib evidenced chromosome breaks and both numerical and structural chromosome changes in 24% and 17% of the metaphases respectively. FISH of a 8q21.3 cosmid allowed us to detect trisomy of the target region on 7% of fibroblast nuclei from both sibs, 47% and 12% of OS and MFH cells. Pronounced chromosomal instability and clonal rearrangements leading to different chromosome-8 derivatives were detected in both tumors. CGH experiments showed multiple gains/losses, among which del(6q), also revealed by cytogenetics, and 7p gain were common, whereas 8q amplification was present only in OS. Chromosomal instability, observed in fibroblasts from the RTS patients studied, accounts for the increased risk of mesenchymal tumors in these patients.

Genotype-phenotype correlation in two sets of monozygotic twins with Williams syndrome

We report on two sets of monozygotic (MZ) twins with Williams syndrome (WS), following the 6 pairs already reported in the literature. We have confirmed monozygosity of both pairs of twins by DNA microsatellite analysis and the clinical diagnosis by fluorescence in situ hybridization using a WS-specific probe. Analysis of the concordance of different clinical signs between members of each pair of twins benefitted from a lengthy clinical follow-up, from 24 months to 7 years in one pair, and from the age of 15 years with reevaluation after 2 years in the other pair. Most clinical signs were concordant in the twins of each pair, with differences present at younger ages, mainly minor facial anomalies, being attenuated with time. Developmental delay was substantially concordant, but the degree differed slightly between twins in each pair. Inguinal hernia was present in a single twin in pair 1. Facial anomalies and other signs attributable to connective tissue abnormalities were also displayed by only one twin in both sets, suggesting that the WS genotype has only a predisposing role in the development of these signs.

Characterization of a cytogenetic 17q11.2 deletion in an NF1 patient with a contiguous gene syndrome

We report on a rare patient screened as a putative carrier of a contiguous gene syndrome on the basis of a complex phenotype characterized by sporadic neurofibromatosis type 1 (NF1), dysmorphism, mental retardation and severe skeletal anomalies. A cytogenetically visible 17q11.2 deletion was detected in the patient's karyotype by high-resolution banding and confirmed by fluorescence in situ hybridization with yeast artificial chromosomes targeting the NF1 region. Analysis of the segregation from parents to proband of 13 polymorphic DNA markers, either contiguous or contained within the NF1 gene, showed that the patient is hemizygous at sites within the NF1 gene-the AAAT-Alu repeat in the 5' region of intron 27b, the CA/GT microsatellite in the 3' region of intron 27b, and the CA/GT microsatellite in intron 38- and at the extragenic D17S798 locus, distal to the 3' end of NF1. The patient may be an important resource in the identification of genes downstream of NF1 that may contribute to some of his extra-NF1 clinical signs.