X-linked congenital ptosis and associated intellectual disability, short stature, microcephaly, cleft palate, digital and genital abnormalities define novel Xq25q26 duplication syndrome.

Submicroscopic duplications along the long arm of the X-chromosome with known phenotypic consequences are relatively rare events. The clinical features resulting from such duplications are various, though they often include intellectual disability, microcephaly, short stature, hypotonia, hypogonadism and feeding difficulties. Female carriers are often phenotypically normal or show a similar but milder phenotype, as in most cases the X-chromosome harbouring the duplication is subject to inactivation. Xq28, which includes MECP2 is the major locus for submicroscopic X-chromosome duplications, whereas duplications in Xq25 and Xq26 have been reported in only a few cases. Using genome-wide array platforms we identified overlapping interstitial Xq25q26 duplications ranging from 0.2 to 4.76 Mb in eight unrelated families with in total five affected males and seven affected females. All affected males shared a common phenotype with intrauterine- and postnatal growth retardation and feeding difficulties in childhood. Three had microcephaly and two out of five suffered from epilepsy. In addition, three males had a distinct facial appearance with congenital bilateral ptosis and large protruding ears and two of them showed a cleft palate. The affected females had various clinical symptoms similar to that of the males with congenital bilateral ptosis in three families as most remarkable feature. Comparison of the gene content of the individual duplications with the respective phenotypes suggested three critical regions with candidate genes (AIFM1, RAB33A, GPC3 and IGSF1) for the common phenotypes, including candidate loci for congenital bilateral ptosis, small head circumference, short stature, genital and digital defects.

Generation of two iPSC lines (MHHi001-A-12 and MHHi001-A-13) carrying biallelic truncating mutations at the 3'-end of SRCAP using CRISPR/Cas9.

Non-Floating Harbour Syndrome (FLHS) neurodevelopmental disorder (NDD) is a recently described disorder caused by mutations in certain regions of the SRCAP gene. We generated two iPSC lines that contain truncating mutation on both alleles at the 3'-end of SRCAP using CRISPR/Cas9 technology. Both cell lines are pluripotent, differentiate into the 3 germ layers and contain no genomic aberrations or off-target modifications. The cell lines form part of a human disease model to investigate the effects of truncating mutations in different regions of SRCAP.

GMCT : a Monte Carlo simulation package for macromolecular receptors.

Generalized Monte Carlo titration (GMCT) is a versatile suite of computer programs for the efficient simulation of complex macromolecular receptor systems as for example proteins. The computational model of the system is based on a microstate description of the receptor and an average description of its surroundings in terms of chemical potentials. The receptor can be modeled in great detail including conformational flexibility and many binding sites with multiple different forms that can bind different ligand types. Membrane embedded systems can be modeled including electrochemical potential gradients. Overall properties of the receptor as well as properties of individual sites can be studied with a variety of different Monte Carlo (MC) simulation methods. Metropolis MC, Wang-Landau MC and efficient free energy calculation methods are included. GMCT is distributed as free open source software at www.bisb.uni-bayreuth.de under the terms of the GNU Affero General Public License.

Genome-wide copy number variation analysis in attention-deficit/hyperactivity disorder: association with neuropeptide Y gene dosage in an extended pedigree.

Attention-deficit/hyperactivity disorder (ADHD) is a common, highly heritable neurodevelopmental syndrome characterized by hyperactivity, inattention and increased impulsivity. To detect micro-deletions and micro-duplications that may have a role in the pathogenesis of ADHD, we carried out a genome-wide screen for copy number variations (CNVs) in a cohort of 99 children and adolescents with severe ADHD. Using high-resolution array comparative genomic hybridization (aCGH), a total of 17 potentially syndrome-associated CNVs were identified. The aberrations comprise 4 deletions and 13 duplications with approximate sizes ranging from 110 kb to 3 Mb. Two CNVs occurred de novo and nine were inherited from a parent with ADHD, whereas five are transmitted by an unaffected parent. Candidates include genes expressing acetylcholine-metabolizing butyrylcholinesterase (BCHE), contained in a de novo chromosome 3q26.1 deletion, and a brain-specific pleckstrin homology domain-containing protein (PLEKHB1), with an established function in primary sensory neurons, in two siblings carrying a 11q13.4 duplication inherited from their affected mother. Other genes potentially influencing ADHD-related psychopathology and involved in aberrations inherited from affected parents are the genes for the mitochondrial NADH dehydrogenase 1 α subcomplex assembly factor 2 (NDUFAF2), the brain-specific phosphodiesterase 4D isoform 6 (PDE4D6) and the neuronal glucose transporter 3 (SLC2A3). The gene encoding neuropeptide Y (NPY) was included in a ∼3 Mb duplication on chromosome 7p15.2-15.3, and investigation of additional family members showed a nominally significant association of this 7p15 duplication with increased NPY plasma concentrations (empirical family-based association test, P=0.023). Lower activation of the left ventral striatum and left posterior insula during anticipation of large rewards or losses elicited by functional magnetic resonance imaging links gene dose-dependent increases in NPY to reward and emotion processing in duplication carriers. These findings implicate CNVs of behaviour-related genes in the pathogenesis of ADHD and are consistent with the notion that both frequent and rare variants influence the development of this common multifactorial syndrome.

Hypergonadotropic hypogonadism in a patient with inv ins (2;4).

We report on a 30-year-old man with azoospermia, primary hypogonadism and minor dysmorphic features who carried a balanced insertional chromosome translocation inv ins (2p24;4q28.3q31.22)de novo. Molecular cytogenetic analyses of the chromosome breakpoints revealed the localization of the breakpoint in 4q28.3 between BACs RP11-143E9 and RP11-285A15, an interval that harbours the PCDH10 gene. In 4q31.22, a breakpoint-spanning clone (RP11-6L6) was identified which contains the genes LSM6 and SLC10A7. On chromosome 2, BACs RP11-531P14 and RP11-360O18 flank the breakpoint in 2p24, a region void of known genes. In conclusion, the chromosome aberration of this patient suggests a gene locus for primary hypogonadism in 2p24, 4q28.3 or 4q31.2, and three possible candidate genes (LSM6, SLC10A7 and PCDH10) were identified by breakpoint analyses.

A microduplication of the long range SHH limb regulator (ZRS) is associated with triphalangeal thumb-polysyndactyly syndrome.

BACKGROUND: Sonic hedgehog (SHH) plays an important role in defining the anterior-posterior axis in the developing limbs. A highly conserved non-coding sequence about approximately 1 Mb upstream from the sonic hedgehog gene (SHH) was shown to be a long range regulator for SHH expression in the limb bud. Point mutations within this non-coding regulatory region designated ZRS lead to ectopic expression of Shh in the anterior margin of the limb bud, as shown in mice, and cause the human triphalangeal thumb and polysyndactyly (TPT-PS) phenotype. Even though this association is well established, its molecular mechanism remains unclear. METHODS AND RESULTS: We investigated a large pedigree with variable TPT-PS. A single nucleotide exchange within the SHH limb regulator sequence was excluded, but locus specific microsatellite marker analyses confirmed a linkage to this region. Subsequently, array comparative genomic hybridisation (array CGH) was carried out using a submegabase whole human genome tiling path bacterial artificial chromosome (BAC) array revealing a microduplication in 7q36.3 in affected individuals. A duplicated region of 588,819 bp comprising the ZRS was identified by quantitative real-time polymerase chain reaction (qPCR) and direct sequencing. CONCLUSION: A novel microduplication in 7q36.3 results in a similar TPT-PS phenotype as caused by single nucleotide alterations in the ZRS, the limb specific SHH regulatory element. Duplications can be added to the growing list of mechanisms that cause abnormalities of long range transcriptional control.

High frequency of submicroscopic genomic aberrations detected by tiling path array comparative genome hybridisation in patients with isolated congenital heart disease.

BACKGROUND: Congenital heart disease (CHD) is the most common birth defect and affects nearly 1% of newborns. The aetiology of CHD is largely unknown and only a small percentage can be assigned to environmental risk factors such as maternal diseases or exposure to mutagenic agents during pregnancy. Chromosomal imbalances have been identified in many forms of syndromic CHD, but very little is known about the impact of DNA copy number changes in non-syndromic CHD. METHOD: A sub-megabase resolution array comparative genome hybridisation (CGH) screen was carried out on 105 patients with CHD as the sole abnormality at the time of diagnosis. RESULTS: There were 18 chromosomal changes detected, which do not coincide with common DNA copy number variants, including one de novo deletion, two de novo duplications and eight familial copy number variations (one deletion and seven duplications). CONCLUSIONS: Our data show that submicroscopic deletions and duplications play an important role in the aetiology of this condition, either as direct causes or as genetic risk factors for CHD. These findings have immediate consequences for genetic counselling and should pave the way for the elucidation of the pathogenetic mechanisms underlying CHD.

Triangular tibia with fibular aplasia associated with a microdeletion on 2q11.2 encompassing LAF4.

Nievergelt syndrome (NS) is an autosomal dominant mesomelic dysplasia characterized by specific deformities of the radius, ulna, fibula and a rhomboid shape of the tibia. Phenotypically overlapping conditions such as mesomelic dysplasia, Savarirayan-type (MIM 605274), have been described, but their pathogenesis also remains unknown. We report on a girl with fibular agenesis, severely abnormal, triangular tibiae, urogenital tract malformations, failure to thrive, convulsions and recurrent apnoeas leading to respiratory arrest at the age of 4 months. Her skeletal findings correspond to those of the mesomelic dysplasia, Savarirayan-type recently described in two patients. In addition to the skeletal findings, our patient had central nervous system manifestations and developmental anomalies of the urogenital tract. In the patient described in this study, array comparative genomic hybridization (CGH) analysis revealed a de novo interstitial microdeletion of 500 kb on chromosome 2q11.1 containing the LAF4/AFF3 (lymphoid-nuclear-protein-related AF4) gene. In situ hybridization analysis of Laf4 in mouse embryos revealed expression in the developing brain, in the limb buds and in the zeugopod corresponding to the limb phenotype. Haploinsufficiency for LAF4/AFF3 is associated with limb, brain and urogenital malformations and specific changes of the tibia that are part of the NS spectrum.

Mowat-Wilson syndrome: an underdiagnosed syndrome?

Mowat-Wilson syndrome (MWS) is an autosomal dominant developmental disorder with mental retardation and variable multiple congenital abnormalities due to mutations of the ZEB2 (ZFHX1B) gene at 2q22. MWS was first described in 1998 and the causative gene was delineated in 2001. Since then, 115 different mutations of ZEB2 have been published in association with this syndrome in 161 individuals. However, recent reports suggest that due to the variability of the congenital abnormalities, this syndrome may still be underdiagnosed. We report two unrelated patients with MWS where the clinical diagnosis was established only after finding of disruption of the ZEB2 gene by a balanced translocation breakpoint and an interstitial microdeletion, respectively.

Fine mapping of a de novo interstitial 10q22-q23 duplication in a patient with congenital heart disease and microcephaly.

In this study we report a female patient with an interstitial duplication of a region (10q22-q23) which is rarely reported in the literature. We fine mapped the aberration with array CGH, which revealed an 18.6-Mb duplication, covering 89 annotated genes, at 10q22.2-q23.33. There were no other deletions or duplications elsewhere in the genome. The main clinical features of the patient are microcephaly and congenital heart disease, which are likely to be caused by dosage effect of one or several genes in the duplicated region. Similar phenotypes have been found in other patients with 10q11-q22 duplications and in two out of three patients with 10q22-q25 duplications. However, most of the duplication cases were investigated only by conventional chromosome analyses, and fine mapping of these and other duplications of 10q22-q23 are warranted for genotype-phenotype comparisons.

Analysis of Gene Expression Changes in PHA-M Stimulated Lymphocytes - Unraveling PHA Activity as Prerequisite for Dicentric Chromosome Analysis.

Dicentric chromosome analysis (DCA) is the gold standard for individual radiation dose assessment. However, DCA is limited by the time-consuming phytohemagglutinin (PHA)-mediated lymphocyte activation. In this study using human peripheral blood lymphocytes, we investigated PHA-associated whole genome gene expression changes to elucidate this process and sought to identify suitable gene targets as a means of meeting our long-term objective of accelerating cell cycle kinetics to reduce DCA culture time. Human peripheral whole blood from three healthy donors was separately cultured in RPMI/FCS/antibiotics with BrdU and PHA-M. Diluted whole blood samples were transferred into PAXgene tubes at 0, 12, 24 and 36 h culture time. RNA was isolated and aliquots were used for whole genome gene expression screening. Microarray results were validated using qRT-PCR and differentially expressed genes [significantly (FDR corrected) twofold different from the 0 h value reference] were analyzed using several bioinformatic tools. The cell cycle positions and DNA-synthetic activities of lymphocytes were determined by analyzing the correlated total DNA content and incorporated BrdU level with flow cytometry after continued BrdU incubation. From 42,545 transcripts of the whole genome microarray 47.6%, on average, appeared expressed. The number of differentially expressed genes increased linearly from 855 to 2,858 and 4,607 at 12, 24 and 36 h after PHA addition, respectively. Approximately 2-3 times more up- than downregulated genes were observed with several hundred genes differentially expressed at each time point. Earliest enrichment was observed for gene sets related to the nucleus (12 h) followed by genes assigned to intracellular structures such as organelles (24 h) and finally genes related to the membrane and the extracellular matrix were enriched (36 h). Early gene expression changes at 12 h, in particular, were associated with protein classes such as chemokines/cytokines (e.g., CXCL1, CXCL2) and chaperones. Genes coding for biological processes involved in cell cycle control (e.g., MYBL2, RBL1, CCNA, CCNE) and DNA replication (e.g., POLA, POLE, MCM) appeared enriched at 24 h and later, but many more biological processes (42 altogether) showed enrichment as well. Flow cytometry data fit together with gene expression and bioinformatic analyses as cell cycle transition into S phase was observed with interindividual differences from 12 h onward, whereas progression into G2 as well as into the second G1 occurred from 36 h onward after activation. Gene set enrichment analysis over time identifies, in particular, two molecular categories of PHA-responsive gene targets (cytokine and cell cycle control genes). Based on that analysis target genes for cell cycle acceleration in lymphocytes have been identified ( CDKN1A/B/C, RBL-1/RBL-2, E2F2, Deaf-1), and it remains undetermined whether the time expenditure for DCA can be reduced by influencing gene expression involved in the regulatory circuits controlling PHA-associated cell cycle entry and/or progression at a specific early cell cycle phase.

Two independent chromosomal rearrangements, a very small (550 kb) duplication of the 7q subtelomeric region and an atypical 17q11.2 (NF1) microdeletion, in a girl with neurofibromatosis.

Most patients with neurofibromatosis (NF1) are endowed with heterozygous mutations in the NF1 gene. Approximately 5% show an interstitial deletion of chromosome 17q11.2 (including NF1) and in most cases also a more severe phenotype. Here we report on a 7-year-old girl with classical NF1 signs, and in addition mild overgrowth (97th percentile), relatively low OFC (10th-25th percentile), facial dysmorphy, hoarse voice, and developmental delay. FISH analysis revealed a 17q11.2 microdeletion as well as an unbalanced 7p;13q translocation leading to trisomy of the 7q36.3 subtelomeric region. The patient's mother and grandmother who were phenotypically normal carried the same unbalanced translocation. The 17q11.2 microdeletion had arisen de novo. Array comparative genomic hybridization (CGH) demonstrated gain of a 550-kb segment from 7qter and loss of 2.5 Mb from 17q11.2 (an atypical NF1 microdeletion). We conclude that the patient's phenotype is caused by the atypical NF1 deletion, whereas 7q36.3 trisomy represents a subtelomeric copy number variation without phenotypic consequences. To our knowledge this is the first report that a duplication of the subtelomeric region of chromosome 7q containing functional genes (FAM62B, WDR60, and VIPR2) can be tolerated without phenotypic consequences. The 17q11.2 microdeletion (containing nine more genes than the common NF1 microdeletions) and the 7qter duplication were not accompanied by unexpected clinical features. Most likely the 7qter trisomy and the 17q11.2 microdeletion coincide by chance in our patient.

Simulation of the electron transfer between the tetraheme subunit and the special pair of the photosynthetic reaction center using a microstate description.

Charge transfer through biological macromolecules is essential for many biological processes such as, for instance, photosynthesis and respiration. Protons or electrons are transferred between titratable residues or redox-active cofactors, respectively. Transfer rates between these sites depend on the current charge configuration of neighboring sites. Here, we formulate the kinetics of charge-transfer systems in a microstate formalism. A unique transfer rate constant can be assigned to the interconversion of microstates. Mutual interactions between sites participating in the transfer reactions are naturally taken into account. The formalism is applied to the kinetics of electron transfer in the tetraheme subunit and the special pair of the reaction center of Blastochloris viridis. It is shown that continuum electrostatic calculations can be used in combination with an existing empirical rate law to obtain electron-transfer rate constants. The re-reduction kinetics of the photo-oxidized special pair simulated in a microstate formalism is shown to be in good agreement with experimental data. A flux analysis is used to follow the individual electron-transfer steps.

Impact of low copy repeats on the generation of balanced and unbalanced chromosomal aberrations in mental retardation.

Low copy repeats (LCRs) are stretches of duplicated DNA that are more than 1 kb in size and share a sequence similarity that exceeds 90%. Non-allelic homologous recombination (NAHR) between highly similar LCRs has been implicated in numerous genomic disorders. This study aimed at defining the impact of LCRs on the generation of balanced and unbalanced chromosomal rearrangements in mentally retarded patients. A cohort of 22 patients, preselected for the presence of submicroscopic imbalances, was analysed using submegabase resolution tiling path array CGH and the results were compared with a set of 41 patients with balanced translocations and breakpoints that were mapped to the BAC level by FISH. Our data indicate an accumulation of LCRs at breakpoints of both balanced and unbalanced rearrangements. LCRs with high sequence similarity in both breakpoint regions, suggesting NAHR as the most likely cause of rearrangement, were observed in 6/22 patients with chromosomal imbalances, but not in any of the balanced translocation cases studied. In case of chromosomal imbalances, the likelihood of NAHR seems to be inversely related to the size of the aberration. Our data also suggest the presence of additional mechanisms coinciding with or dependent on the presence of LCRs that may induce an increased instability at these chromosomal sites.

Characterization of a de novo complex chromosome rearrangement (CCR) involving chromosomes 2 and 12, associated with mental retardation and impaired speech development.

We report on a currently six-year-old patient with a de novo complex chromosome rearrangement (CCR) involving chromosomes 2 and 12. A translocation 2;12 that appeared to be reciprocal after standard banding turned out to be a complex event with seven breaks after molecular cytogenetic analyses. Array CGH analysis showed no imbalances at the breakpoints but revealed an additional microdeletion of about 80 kb on chromosome 11. The same deletion was also present in the phenotypically normal father. The patient showed relatively mild mental retardation, defined mainly as impaired speech development (orofacial dyspraxia) and psychomotor retardation. In addition, mild dysmorphic facial features like hypertelorism, a prominent philtrum and down-turned corners of the mouth were observed. We narrowed down all breakpoint regions to about 100 kb, using a panel of mapped bacterial artificial chromosome (BAC) clones for fluorescence in situ hybridization (FISH). BACs spanning or flanking all seven breakpoints were identified and no chromosomal imbalances were found consistent with the array CGH results. Our investigations resulted in the following karyotype: 46,XY,t(2;12)(2pter-->2p25.3::2p23.3-->2p25.2::2p23.3-->2p14::2q14.3-->2p14::2q14.3-->2q14.3::12q 12-->12qter;12pter-->12q12::2p25.3-->2p25.2::2q14.3-->2qter).

Charge-Neutral Constant pH Molecular Dynamics Simulations Using a Parsimonious Proton Buffer.

In constant pH molecular dynamics simulations, the protonation states of titratable sites can respond to changes of the pH and of their electrostatic environment. Consequently, the number of protons bound to the biomolecule, and therefore the overall charge of the system, fluctuates during the simulation. To avoid artifacts associated with a non-neutral simulation system, we introduce an approach to maintain neutrality of the simulation box in constant pH molecular dynamics simulations, while maintaining an accurate description of all protonation fluctuations. Specifically, we introduce a proton buffer that, like a buffer in experiment, can exchange protons with the biomolecule enabling its charge to fluctuate. To keep the total charge of the system constant, the uptake and release of protons by the buffer are coupled to the titration of the biomolecule with a constraint. We find that, because the fluctuation of the total charge (number of protons) of a typical biomolecule is much smaller than the number of titratable sites of the biomolecule, the number of buffer sites required to maintain overall charge neutrality without compromising the charge fluctuations of the biomolecule, is typically much smaller than the number of titratable sites, implying markedly enhanced simulation and sampling efficiency.

Novel rearrangement of chromosome band 22q11.2 causing 22q11 microdeletion syndrome-like phenotype and rhabdoid tumor of the kidney.

The 22q11.2 microdeletion syndrome is the most frequent microdeletion syndrome in humans, yet its genetic basis is complex and is still not fully understood. Most patients harbor a 3-Mb deletion (typically deleted region [TDR]), but occasionally patients with atypical deletions, some of which do not overlap with each other and/or the TDR, have been described. Microduplication of the TDR leads to a phenotype similar, albeit not identical, to the deletion of this region. Here we present a child initially suspected of having 22q11 microdeletion syndrome, who in addition developed a fatal malignant rhabdoid tumor of the kidney. Detailed cytogenetic and molecular analyses revealed a complex de novo rearrangement of band q11 of the paternally derived chromosome 22. This aberration exhibited two novel features. First, a microduplication of the 22q11 TDR was associated with an atypical 22q11 microdeletion immediately telomeric of the duplicated region. Second, this deletion was considerably larger than previously reported atypical 22q11 deletions, spanning 2.8 Mb and extending beyond the SMARCB1/SNF5/INI1 tumor suppressor gene, whose second allele harbored a somatic frameshift-causing sequence alteration in the patient's tumor. Two nonallelic homologous recombination events between low-copy repeats (LCRs) could explain the emergence of this novel and complex mutation associated with the phenotype of 22q11 microdeletion syndrome.

Can the physician diagnose hyperactivity in the office?

Office diagnosis of hyperactivity can present a problem to the pediatrician because only about 20% of the potential patients show hyperactive behavior during office examination. Exclusion of the children who appear normal in the physician's office can eliminate from medical treatment a large number of patients for whom treatment is appropriate. Eighty percent of the children ultimately accepted into the project on the basis of home and school reports showed exemplary behavior and no sign of hyperactivity in the office. Nonetheless, at a three-year follow-up, these children were rated the same as those who were obviously hyperactive in the presence of the pediatrician. The groups appeared no different on school grade, teachers' ratings of classroom behavior, amount of stimulant medication prescribed, or duration of drug treatment. The reported outcome data indicate that the physician can have confidence in historical information from the parents combined with current teacher reports as reliable aids in the diagnostic process with hyperactive children.

Comparative genomic hybridization and cytogenetic analysis in a bronchial adenoma: three clones with different chromosomal aberrations.

Classical chromosomal analysis and comparative genomic hybridization (CGH) were performed in a tubular bronchial gland adenoma. Trisomy of chromosomes 2, 11, 18 and 20 and clonal loss of Y were found in cultured cells derived from two different kryotubes; this was also confirmed by CGH from one of these tubes. Cells from two other tubes, investigated by CGH only, showed gains and losses of parts of chromosome 11q in one, and in the second additional gain of the distal portion of 9q and 17q, respectively. CGH analysis of tumor DNA extracted from paraffin-embedded sections showed no chromosomal imbalances. In cell culture growth the advantage of specific clones probably altered the clone distribution. This study highlights the risk of cytogenetic analysis based on cell cultures only.

Loss of heterozygosity on chromosome arm 11q in lung carcinoids.

Neuroendocrine lung tumors such as typical carcinoid, atypical carcinoid, small-cell lung carcinoma, and large-cell neuroendocrine carcinoma represent a variable group with different biologic characteristics and unclear genetical relationships. We investigated the pattern of allelic loss on chromosome arm 11q in 20 sporadic carcinoid tumors of the lung using 10 microsatellite markers. Loss of heterozygosity was found in 13 of 20 tumors. In 5 of 9 typical carcinoids, 3 distinct regions of allelic loss were identified: 11q13.1 (D11S1883), 11q14.3-11q21 (D11S906), and 11q25 (D11S910). Atypical carcinoids showed loss of heterozygosity at 4 different regions: the first, most proximal region at 11q13 between markers PYGM and D11S937; the second at 11q14.3-11q21 (D11S906); and the third and fourth defined by markers D11S939 (11q23.2-23.3) and D11S910 (11q25). However, the region 11q13 harboring the MEN1 gene was more frequently affected in atypical carcinoids (7 of 11) than in typical carcinoids (2 of 9). The high rate of allelic losses within chromosomal region 11q13 in atypical carcinoids emphasizes the importance of this region for tumor development. We also recognized that more aggressive atypical carcinoids defined by high mitotic counts, vascular invasion, and/or organ metastasis are combined with increased allelic losses. HUM PATHOL 32:333-338.