Molecular genetic investigation of hereditary breast and ovarian cancer patients in the Southern Transdanubian region: widening the mutation spectrum and searching for new pathogenic variants using next-generation methods.

Hereditary breast and ovarian cancer is a well-known genetic condition, inherited mainly in an autosomal dominant way, which elevates the risk of developing malignancies at a young age in heterozygous carriers. Advances in new generation sequencing have enabled medical professionals to determine whether a patient is harbouring mutations in moderate- or high penetrance susceptibility genes. We conducted a retrospective analysis among 275 patients who underwent genetic counselling and multigene panel testing for hereditary breast and ovarian cancer syndrome in our department. From these patients 74.5% (205/275) were affected by some type of malignancy, while the remaining 25.5% (70/275) had a positive family history of different cancers, suggesting a genetic predisposition. These tests confirmed a genetic variant in 29.8% and 28.6% of these patient groups respectively. The results also mirrored our general knowledge concerning the genetic background of hereditary breast and ovarian cancer, as variants in either one of the BRCA1 and BRCA2 genes proved to be the most common cause among our patients with 41.5%. Our test also detected a novel mutation in the CDH1 gene and three patients with double heterozygosity in two different susceptibility genes. This study demonstrates the relevance of genetic counselling and non-BRCA gene sequencing among cancer patients and patients who fulfil the criteria for genetic testing, while also providing important details about the genetic profile of Hungarian patients.

Rare Germline Variants in the Adenomatous Polyposis Coli Gene Associated with Dental and Osseous Anomalies.

APC is a tumor suppressor gene that exerts its effect through the regulation of the Wnt signaling pathway. Loss of function mutations of the gene are associated with familial adenomatous polyposis (FAP). Early diagnosis in FAP patients is essential to prevent the development of colorectal cancer. Extraintestinal manifestations often precede the formation of the polyposis; therefore, these manifestations may serve as a clinical indicator for the condition. The aim of this study was to assess genotype-phenotype associations between the location of APC mutations and various extraintestinal features, mainly focusing on osseous and dental anomalies. Analyses of our cases and the mutations available in the literature with these manifestations revealed that mutations in the N-terminal region (amino acids 1-~1000) of the protein are more frequently associated with only osseous anomalies, whereas dental manifestations are more prevalent in mutations in the middle region (amino acids 1000-~2100). In addition, supernumerary teeth were found to be the most common dental feature. Since dental abnormalities often precede intestinal polyposis, dentists have a crucial role in the early identification of patients at risk.

NGS-Based Identification of Two Novel PCDH19 Mutations in Female Patients with Early-Onset Epilepsy.

Developmental and epileptic encephalopathy-9 (DEE9) is characterized by seizure onset in infancy, mild to severe intellectual impairment, and psychiatric features and is caused by a mutation in the PCDH19 gene on chromosome Xq22. The rare, unusual X-linked type of disorder affects heterozygous females and mosaic males; transmitting males are unaffected. In our study, 165 patients with epilepsy were tested by Next Generation Sequencing (NGS)-based panel and exome sequencing using Illumina technology. PCDH19 screening identified three point mutations, one indel, and one 29 bp-long deletion in five unrelated female probands. Two novel mutations, c.1152_1180del (p.Gln385Serfs*6) and c.830_831delinsAA (p.Phe277*), were identified and found to be de novo pathogenic. Moreover, among the three inherited mutations, two originated from asymptomatic mothers and one from an affected father. The PCDH19 c.1682C>T and c.1711G>T mutations were present in the DNA samples of asymptomatic mothers. After targeted parental testing, X chromosome inactivation tests and Sanger sequencing were carried out for mosaicism examination on maternal saliva samples in the two asymptomatic PCDH19 mutation carrier subjects. Tissue mosaicism and X-inactivation tests were negative. Our results support the opportunity for reduced penetrance in DEE9 and contribute to expanding the genotype-phenotype spectrum of PCDH19-related epilepsy.

Case Report of Suspected Gonadal Mosaicism in FOXP1-Related Neurodevelopmental Disorder.

Heterozygous mutations in the FOXP1 gene (OMIM#605515) are responsible for a well-characterized neurodevelopmental syndrome known as "intellectual developmental disorder with language impairment with or without autistic features" (OMIM#613670) or FOXP1 syndrome for short. The main features of the condition are global developmental delay/intellectual disability; speech impairment in all individuals, regardless of their level of cognitive abilities; behavioral abnormalities; congenital anomalies, including subtle dysmorphic features; and strabismus, brain, cardiac, and urogenital abnormalities. Here, we present two siblings with a de novo heterozygous FOXP1 variant, namely, a four-year-old boy and 14-month-old girl. Both children have significantly delayed early psychomotor development, hypotonia, and very similar, slightly dysmorphic facial features. A lack of expressive speech was the leading symptom in the case of the four-year-old boy. We performed whole-exome sequencing on the male patient, which identified a pathogenic heterozygous c.1541G>A (p.Arg514His) FOXP1 mutation. His sister's targeted mutation analysis also showed the same heterozygous FOXP1 variant. Segregation analysis revealed the de novo origin of the mutation, suggesting the presence of parental gonadal mosaicism. To the best of our knowledge, this is the first report of gonadal mosaicism in FOXP1-related neurodevelopmental disorders in the medical literature.

Case report: Initial atypical skeletal symptoms and dental anomalies as first signs of Gardner syndrome: the importance of genetic analysis in the early diagnosis.

Background: Gardner syndrome is a rare genetic cancer predisposition disorder characterized by intestinal polyposis, multiple osteomas, and soft and hard tissue tumors. Dental anomalies are present in approximately 30%-70% of patients with Gardner syndrome and can be discovered during routine dental examinations. However, sometimes the diagnosis is challenging due to the high clinical variability and incomplete clinical picture. Herein, we report a family with various dental and bone anomalies, in which the definitive diagnosis was established with the help of a comprehensive genetic analysis based on state-of-the-art next-generation sequencing technology. Case presentation: A 17-year-old female index patient presented with dental (caries, impacted, retained and anteriorly located teeth) and atypical bone anomalies not resembling Gardner syndrome. She was first referred to our Genetic Counselling Unit at the age of 11 due to an atypical bone abnormality identified by a panoramic X-ray. Tooth 3.6 was surgically removed and the histopathology report revealed a Paget's disease-like bone metabolic disorder with mixed osteoblastic and osteoclastic activity of the mandible. A small lumbar subcutaneous tumor was discovered by physical examination. Ultrasound examination of the tumor raised the possibility of a soft tissue propagation of chondromatosis. Her sister, 2 years younger at the age of 14, had some benign tumors (multiple exostoses, odontomas, epidermoid cysts) and impacted teeth. Their mother had also skeletal symptoms. Her lower teeth did not develop, the 9th-10th ribs were fused, and she complained of intermittent jaw pain. A cranial CT scan showed fibrous dysplasia on the cranial bones. Whole exome sequencing identified a heterozygous pathogenic nonsense mutation (c.4700C>G; p.Ser1567*) in the APC gene in the index patient's DNA. Targeted sequencing revealed the same variant in the DNA of the other affected family members (the sister and the mother). Conclusion: Early diagnosis of this rare, genetically determined syndrome is very important, because of the potentially high malignant transformation of intestinal polyps. Dentists should be familiar with the typical maxillofacial features of this disorder, to be able to refer patients to genetic counseling. Dental anomalies often precede the intestinal polyposis and facilitate the early diagnosis, thereby increasing the patients' chances of survival. Genetic analysis may be necessary in patients with atypical phenotypic signs.

Importance and application of WES in fetal genetic diagnostics: Identification of novel ASPM mutation in a fetus with microcephaly.

Background: Prenatal whole exome sequencing (WES) approaches can provide genetic diagnosis with rapid turnaround time and high diagnostic rate when conventional tests are negative. Here we report a family with multiple pregnancy loss and with repeated occurrence of fetal microcephaly. Methods and results: Because of positive family history and recurrent structural abnormality during the pregnancies that may lead postnatal neurodevelopmental consequences, WES analysis was indicated. Umbilical cord blood sampling was carried out and WES was performed using Twist Human Core Exome Kit and Illumina sequencing technology. The presence of pathogenic variants was confirmed by Sanger sequencing. WES analysis revealed a known pathogenic c.8506_8507delCA (p.Gln2836Glufs*35, rs587783280) and a novel pathogenic c.3134_3135delTC (p.Leu1045Glnfs*17) ASPM mutations in the fetus in compound heterozygous state. The c.3134_3135delTC has never been reported in the literature. Conclusions: Our findings serve additional evidence that WES can be an efficient and relevant tool to diagnose certain genetic disorders with appropriate indication and to assess the recurrence risk of a disease. With the application of WES in combination with pre-implantation genetic tests, we can avoid the transmission of pathogenic mutations and we can achieve a decreased abortion rate in obstetric care.

Copy Number Variations in Neuropsychiatric Disorders.

Neuropsychiatric disorders are complex conditions that represent a significant global health burden with complex and multifactorial etiologies. Technological advances in recent years have improved our understanding of the genetic architecture of the major neuropsychiatric disorders and the genetic loci involved. Previous studies mainly investigated genome-wide significant SNPs to elucidate the cross-disorder and disorder-specific genetic basis of neuropsychiatric disorders. Although copy number variations represent a major source of genetic variations, they are known risk factors in developing a variety of human disorders, including certain neuropsychiatric diseases. In this review, we demonstrate the current understanding of CNVs contributing to liability for schizophrenia, bipolar disorder, and major depressive disorder.

Identification of an NF1 Microdeletion with Optical Genome Mapping.

Neurofibromatosis type 1 (NF1) is a clinically heterogeneous neurocutaneous disorder inherited in autosomal dominant manner. Approximately 5-10% of the cases are caused by NF1 microdeletions involving the NF1 gene and its flanking regions. Microdeletions, which lead to more severe clinical manifestations, can be subclassified into four different types (type 1, 2, 3 and atypical) according to their size, the genomic location of the breakpoints and the number of genes included within the deletion. Besides the prominent hallmarks of NF1, patients with NF1 microdeletions frequently exhibit specific additional clinical manifestations like dysmorphic facial features, macrocephaly, overgrowth, global developmental delay, cognitive disability and an increased risk of malignancies. It is important to identify the genes co-deleted with NF1, because they are likely to have an effect on the clinical manifestation. Multiplex ligation-dependent probe amplification (MLPA) and microarray analysis are the primary techniques for the investigation of NF1 microdeletions. However, based on previous research, optical genome mapping (OGM) could also serve as an alternative method to identify copy number variations (CNVs). Here, we present a case with NF1 microdeletion identified by means of OGM and demonstrate that this novel technology is a suitable tool for the identification and classification of the NF1 microdeletions.

Three-Year Follow-Up after Intrauterine mTOR Inhibitor Administration for Fetus with TSC-Associated Rhabdomyoma.

Tuberous sclerosis complex (TSC) is a multisystem disorder characterized by seizures, neuropsychiatric disorders, and tumors of the heart, brain, skin, lungs, and kidneys. We present a three-year follow-up of a patient with TSC-associated rhabdomyoma detected in utero. Genetic examination of the fetus and the parents revealed a de novo variant in the TSC2 gene (c.3037delG, p.Asp1013IlefsTer3). Oral everolimus was initiated in the pregnant mother to regress the fetal tumor, which was successful. To the best of our knowledge, there is very little information regarding the use of everolimus therapy during pregnancy. West-syndrome was diagnosed when the proband was four months old. The symptoms were well-manageable, however temporarily. Therapy-resistant focal seizures were frequent. The patient had good vitals and was under regular cardiological control, showed a balanced circulation, and did not require any medication. Subependymal giant cell astrocytoma (SEGA) identified by regular neuroimaging examinations remained unchanged, which may be a consequence of early intrauterine treatment. Early detection of the pathogenic TSC2 variant, followed by in utero administration of everolimus and early vigabatrin therapy, allowed the detection of a milder developmental delay of the proband. Our study emphasizes how early genetic testing and management of epilepsy are pivotal for proper neurodevelopmental impacts and therapeutic strategies.

Superimposed Mosaicism in the Form of Extremely Extended Segmental Plexiform Neurofibroma Caused by a Novel Pathogenic Variant in the NF1 Gene.

Plexiform neurofibromas occurring in approximately 20-50% of all neurofibromatosis type-1 (NF1) cases are histologically benign tumors, but they can be fatal due to compression of vital structures or transformation to malignant sarcomas or malignant peripheral nerve sheath tumors. All sizeable plexiform neurofibromas are thought to result from an early second mutation giving rise to a loss of heterozygosity of the NF1 gene. In this unusual case, a 12-year-old girl presented with a rapidly growing, extremely extensive plexiform neurofibroma with segmental distribution over the entire right arm, extending to the right chest wall and mediastinum, superimposed on classic cutaneous lesions of NF1. After several surgical interventions, the patient was efficiently treated with an oral selective MEK inhibitor, selumetinib, which resulted in a rapid reduction of the tumor volume. Molecular analysis of the NF1 gene revealed a c.2326-2 A>G splice-site mutation in the clinically unaffected skin, peripheral blood sample, and plexiform neurofibroma, which explains the general clinical symptoms. Furthermore, a novel likely pathogenic variant, c.4933dupC (p.Leu1645Profs*7), has been identified exclusively in the girl's plexiform neurofibromas. This second-hit mutation can explain the extremely extensive segmental involvement.

Microhomology-Mediated Break-Induced Replication: A Possible Molecular Mechanism of the Formation of a Large CNV in FBN1 Gene in a Patient with Marfan Syndrome.

BACKGROUND: Marfan syndrome (MFS) is an autosomal dominant multisystem disorder caused by mutations in the fibrillin-1 gene (FBN1). A small portion of them is copy number variations (CNVs), which can occur through recombination-based, replication-based mechanisms or retrotransposition. Not many have been characterized precisely in MFS. METHODS: A female patient with suspected Marfan syndrome was referred for genetic testing at our institute. After systematic sequencing of FBN1, TGFBR1, and TGFBR2 genes, multiplex ligation-dependent probe amplification was applied. Long-range PCR, subsequent Sanger sequencing with designed primers, and preliminary in silico analysis were applied for the precise characterization of the breakpoints. RESULTS: Primary analysis displayed a de novo large deletion affecting exons 46 and 47 in the FBN1 gene, which resulted in the loss of the 31st and 32nd calcium-binding EGFlike domains. Further examination of the breakpoints showed a 4916 nucleotide long deletion localized in intronic regions. Surprisingly a 'TG' dinucleotide insertion was detected at the junction. We hypothesize that the CNV formation was generated by a rare event based on the known microhomology-mediated break-induced replication (MMBIR). CONCLUSION: An increasing number of CNVs are associated with Mendelian diseases and other traits. Approximately 2-7% of the cases in MFS are caused by CNVs. Up to date, hardly any model was proposed to demonstrate the formation of these genomic rearrangements in the FBN1 gene. Hereby, with the help of previous models and breakpoint analysis, we presented a potential mechanism (based on MMBIR) in the formation of this large deletion.

Co-occurrence of neurofibromatosis type 1 and pseudoachondroplasia - a first case report.

BACKGROUND: Neurofibromatosis type 1 and pseudoachondroplasia are both rare autosomal dominant disorders, caused by pathogenic mutations in NF1 and COMP genes, respectively. Both neurofibromin 1 and cartilage oligomeric matrix protein (COMP) play a role in the development of the skeleton. Carrying both germline mutations has not been previously reported; however, it can affect the developing phenotype. CASE PRESENTATION: The index patient, an 8-year-old female presented with several skeletal and dermatologic anomalies resembling the coexistence of multiple syndromes. Her mother had dermatologic symptoms characteristic for neurofibromatosis type 1, and her father presented with distinct skeletal anomalies. NGS-based analysis revealed a heterozygous pathogenic mutation in genes NF1 and COMP in the index patient. A previously unreported heterozygous variant was detected for the NF1 gene. The sequencing of the COMP gene revealed a previously reported, pathogenic heterozygous variant that is responsible for the development of the pseudoachondroplasia phenotype. CONCLUSIONS: Here, we present the case of a young female carrying pathogenic NF1 and COMP mutations, diagnosed with two distinct heritable disorders, neurofibromatosis type 1 and pseudoachondroplasia. The coincidence of two monogenic autosomal dominant disorders is rare and can pose a differential diagnostic challenge. To the best of our knowledge, this is the first reported co-occurrence of these syndromes.

Correlation between large FBN1 deletions and severe cardiovascular phenotype in Marfan syndrome: Analysis of two novel cases and analytical review of the literature.

BACKGROUND: Marfan syndrome (MFS) is a clinically heterogeneous hereditary connective tissue disorder. Severe cardiovascular manifestations (i.e., aortic aneurysm and dissection) are the most life-threatening complications. Most of the cases are caused by mutations, a minor group of which are copy number variations (CNV), in the FBN1 gene. METHODS: Multiplex ligation-dependent probe amplification test was performed to detect CNVs in 41 MFS patients not carrying disease-causing mutations in FBN1 gene. Moreover, the association was analyzed between the localization of CNVs, the affected regulatory elements and the cardiovascular phenotypes among all cases known from the literature. RESULTS: A large two-exon deletion (exon 46 and 47) was identified in two related patients, which was associated with a mild form of cardiovascular phenotype. Severe cardiovascular symptoms were found significantly more frequent in patients with FBN1 large deletion compared to our patients with intragenic small scale FBN1 mutation. Bioinformatic data analyses of regulatory elements located within the FBN1 gene revealed an association between the deletion of STAT3 transcription factor-binding site and cardiovascular symptoms in five out of 25 patients. CONCLUSION: Our study demonstrated that large CNVs are often associated with severe cardiovascular manifestations in MFS and the localization of these CNVs affect the phenotype severity.

[Neurofibromatosis-1 microdeletion syndrome.] / Neurofibromatosis-1 microdeletiós szindróma.

Neurofibromatosis type 1 is a clinically extremely heterogeneous neurocutaneous disorder, inherited in autosomal dominant manner. It is primarily caused by intragenic loss-of-function mutations in the NF1 gene, however, as a result of improvements in molecular diagnostics, copy number variants affecting the NF1 gene and its flanking regions are increasingly being detected. Based on genotype-phenotype analyses, two groups can be distinguished: neurofibromatosis type 1 caused by point mutations and the so-called 17q11.2 microdeletion syndrome caused by microdeletions. Microdeletions are observed in 5-10% of cases and can be divided into four different types (type 1, 2, 3 and atypical) according to the size of the deletion, the genomic location of the breakpoints and the affected gene content. Patients with microdeletions often have a more severe course of the disease, with an increased risk of malignancies. With this review, which summarizes the main characteristics and molecular genetic background of neurofibromatosis-1 microdeletion syndrome, we would like to emphasize the importance of early diagnosis of patients with microdeletion syndrome and draw attention to the importance of close follow-up. Orv Hetil. 2022; 163(51): 2041-2051.

Genetic Polymorphisms in miR-137 and Its Target Genes, TCF4 and CACNA1C, Contribute to the Risk of Bipolar Disorder: A Preliminary Case-Control Study and Bioinformatics Analysis.

Accumulating evidence has suggested that miR-137 and its target genes, CACNA1C, and TCF4, are amongst the most robustly implicated genes in psychiatric disorders. This preliminary study is aimed at investigating the effects of genetic variations in miR-137 (rs1625579A/C), TCF4 (rs1261084C/T), and CACNA1C (rs10774053A/G and rs10466907G/T) on BD susceptibility. We recruited 252 BD patients and 213 healthy subjects as the control group. Genotyping was performed using PCR-RFLP and ARMS-PCR methods. Enhanced risk of BD was found under the codominant homozygous, dominant, and allelic models of TCF4 rs1261084C/T, codominant homozygous and allelic models of CACNA1C rs10466907G/T polymorphisms, as well as codominant homozygous, dominant, recessive, and allelic models of the CACNA1C rs10774053A/G. Moreover, both TT/AG/GT/AA and TT/GG/GT/AC genotype combinations strongly increased the risk of BD in the participants. The bioinformatics analyses revealed that rs1261084C/T and rs10466907G/T created and disrupted binding sites of some miRNAs in the 3'-untranslated region of TCF4 and CACNA1C genes. In contrast, the rs10774053A/G created a new binding site for a major splicing factor and might have an effective role in the function of the CACNA1C protein. We have found that all the studied SNPs are positively associated with BD susceptibility. Replicated studies on different ethnicities are required to confirm these findings.

Age-Associated B Cell Features of the Murine High-Grade B Cell Lymphoma Bc.DLFL1 and Its Extranodal Expansion in Abdominal Adipose Tissues.

Diffuse large B cell lymphoma comprises a heterogeneous group of B cell-derived tumors, with different degrees of aggressiveness, as defined by their cellular origin and tissue microenvironment. Using the spontaneous Bc.DLFL1 lymphoma originating from a BALB/c mouse as a diffuse large B cell lymphoma model, in this study we demonstrate that the lymphoma cells display surface phenotype, IgH V-region somatic mutations, transcription factor characteristics and in vivo location to splenic extrafollicular regions of age-associated B cells (ABCs), corresponding to T-bet+ and Blimp-1+/CD138- plasmablasts derivation. The expansion of lymphoma cells within lymphoid tissues took place in a close arrangement with CD11c+ dendritic cells, whereas the extranodal infiltration occurred selectively in the mesentery and omentum containing resident gp38/podoplanin+ fibroblastic reticular cells. Antagonizing BAFF-R activity by mBR3-Fc soluble receptor fusion protein led to a significant delay of disease progression. The extranodal expansion of Bc.DLFL1 lymphoma within the omental and mesenteric adipose tissues was coupled with a significant change of the tissue cytokine landscape, including both shared alterations and tissue-specific variations. Our findings indicate that while Bc.DLFL1 cells of ABC origin retain the positioning pattern within lymphoid tissues of their physiological counterpart, they also expand in non-lymphoid tissues in a BAFF-dependent manner, where they may alter the adipose tissue microenvironment to support their extranodal growth.

Mapping genomic loci implicates genes and synaptic biology in schizophrenia.

Schizophrenia has a heritability of 60-80%1, much of which is attributable to common risk alleles. Here, in a two-stage genome-wide association study of up to 76,755 individuals with schizophrenia and 243,649 control individuals, we report common variant associations at 287 distinct genomic loci. Associations were concentrated in genes that are expressed in excitatory and inhibitory neurons of the central nervous system, but not in other tissues or cell types. Using fine-mapping and functional genomic data, we identify 120 genes (106 protein-coding) that are likely to underpin associations at some of these loci, including 16 genes with credible causal non-synonymous or untranslated region variation. We also implicate fundamental processes related to neuronal function, including synaptic organization, differentiation and transmission. Fine-mapped candidates were enriched for genes associated with rare disruptive coding variants in people with schizophrenia, including the glutamate receptor subunit GRIN2A and transcription factor SP4, and were also enriched for genes implicated by such variants in neurodevelopmental disorders. We identify biological processes relevant to schizophrenia pathophysiology; show convergence of common and rare variant associations in schizophrenia and neurodevelopmental disorders; and provide a resource of prioritized genes and variants to advance mechanistic studies.

TUBB4B gene mutation in Leber phenotype of congenital amaurosis syndrome associated with early-onset deafness.

Beta-tubulin 4B isotype is one of the subunits of microtubules encoded by TUBB4B gene on chromosome 9, which is responsible for the maintenance of microtubule stability. In humans, mutations in microtubule-encoding genes have been associated with several tubulinopathies with very heterogeneous symptoms. So far, only two missense mutations in TUBB4B gene have been found to have pathological implications in this disorder. Here we report a Hungarian family with three affected members, mother and her 12- and 14-year-old children, who suffer from ophthalmologic and hearing impairments probably due to c.1171C > T missense variant in the TUBB4B gene. The presented case is the second report, and unique in the literature because of three affected family members carrying the same mutation and the family provides evidence for a quite similar but not identical phenotype of LCAEOD in subjects carrying this mutation.

Genotype-Phenotype Associations in Patients With Type-1, Type-2, and Atypical NF1 Microdeletions.

Neurofibromatosis type 1 is a tumor predisposition syndrome inherited in autosomal dominant manner. Besides the intragenic loss-of-function mutations in NF1 gene, large deletions encompassing the NF1 gene and its flanking regions are responsible for the development of the variable clinical phenotype. These large deletions titled as NF1 microdeletions lead to a more severe clinical phenotype than those observed in patients with intragenic NF1 mutations. Around 5-10% of the cases harbor large deletion and four major types of NF1 microdeletions (type 1, 2, 3 and atypical) have been identified so far. They are distinguishable in term of their size and the location of the breakpoints, by the frequency of somatic mosaicism with normal cells not harboring the deletion and by the number of the affected genes within the deleted region. In our study genotype-phenotype analyses have been performed in 17 mostly pediatric patients with NF1 microdeletion syndrome identified by multiplex ligation-dependent probe amplification after systematic sequencing of the NF1 gene. Confirmation and classification of the NF1 large deletions were performed using array comparative genomic hybridization, where it was feasible. In our patient cohort 70% of the patients possess type-1 deletion, one patient harbors type-2 deletion and 23% of our cases have atypical NF1 deletion. All the atypical deletions identified in this study proved to be novel. One patient with atypical deletion displayed mosaicism. In our study NF1 microdeletion patients presented dysmorphic facial features, macrocephaly, large hands and feet, delayed cognitive development and/or learning difficulties, speech difficulties, overgrowth more often than patients with intragenic NF1 mutations. Moreover, neurobehavior problems, macrocephaly and overgrowth were less frequent in atypical cases compared to type-1 deletion. Proper diagnosis is challenging in certain patients since several clinical manifestations show age-dependency. Large tumor load exhibited more frequently in this type of disorder, therefore better understanding of genotype-phenotype correlations and progress of the disease is essential for individuals suffering from neurofibromatosis to improve the quality of their life. Our study presented additional clinical data related to NF1 microdeletion patients especially for pediatric cases and it contributes to the better understanding of this type of disorder.