Impact of High-to-Moderate Penetrance Genes on Genetic Testing: Looking over Breast Cancer.

Breast cancer (BC) is the most common cancer and the leading cause of cancer death in women worldwide. Since the discovery of the highly penetrant susceptibility genes BRCA1 and BRCA2, many other predisposition genes that confer a moderate risk of BC have been identified. Advances in multigene panel testing have allowed the simultaneous sequencing of BRCA1/2 with these genes in a cost-effective way. Germline DNA from 521 cases with BC fulfilling diagnostic criteria for hereditary BC were screened with multigene NGS testing. Pathogenic (PVs) and likely pathogenic (LPVs) variants in moderate penetrance genes were identified in 15 out of 521 patients (2.9%), including 2 missense, 7 non-sense, 1 indel, and 3 splice variants, as well as two different exon deletions, as follows: ATM (n = 4), CHEK2 (n = 5), PALB2 (n = 2), RAD51C (n = 1), and RAD51D (n = 3). Moreover, the segregation analysis of PVs and LPVs into first-degree relatives allowed the detection of CHEK2 variant carriers diagnosed with in situ melanoma and clear cell renal cell carcinoma (ccRCC), respectively. Extended testing beyond BRCA1/2 identified PVs and LPVs in a further 2.9% of BC patients. In conclusion, panel testing yields more accurate genetic information for appropriate counselling, risk management, and preventive options than assessing BRCA1/2 alone.

The somatic p.T81dup variant in AKT3 gene underlies a mild cerebral phenotype and expands the spectrum including capillary malformation and lateralized overgrowth.

Heterozygous germline or somatic variants in AKT3 gene can cause isolated malformations of cortical development (MCDs) such as focal cortical dysplasia, megalencephaly (MEG), Hemimegalencephaly (HME), dysplastic megalencephaly, and syndromic forms like megalencephaly-polymicrogyria-polydactyly-hydrocephalus syndrome, and megalencephaly-capillary malformation syndrome. This report describes a new case of HME and capillary malformation caused by a somatic AKT3 variant that differs from the common p.E17K variant described in literature. The patient's skin biopsy from the angiomatous region revealed an heterozygous likely pathogenic variant AKT3:c.241_243dup, p.(T81dup) that may affect the binding domain and downstream pathways. Compared to previously reported cases with a common E17K mosaic variant, the phenotype is milder and patients showed segmental overgrowth, an uncommon characteristic in AKT3 variant cases. These findings suggest that the severity of the disease may be influenced not only by the level of mosaicism but also by the type of variant. This report expands the phenotypic spectrum associated with AKT3 variants and highlights the importance of genomic analysis in patients with capillary malformation and MCDs.

Epidemiology of the disorders of the Pik3ca-related overgrowth spectrum (Pros).

PIK3CA pathogenic variants are responsible for a group of overgrowth syndromes, collectively known as PIK3CA-Related Overgrowth Spectrum (PROS). These gain-of-function variants arise postzygotically, and, according to time of onset, kind of embryonal tissue affected and regional body extension, give rise to heterogeneous phenotypes. PROS rarity and heterogeneity hamper the correct estimation of its epidemiology. Our work represents the first attempt to define the prevalence of PROS according to the established diagnostic criteria and molecular analysis and based on solid demographic data. We assessed the prevalence in Piedmont Region (Italy), including in the study all participants diagnosed with PROS born there from 1998 to 2021. The search identified 37 cases of PROS born across the 25-year period, providing a prevalence of 1:22,313 live births. Molecular analysis was positive in 81.0% of participants. Taking into account the cases with a detected variant in PIK3CA (n = 30), prevalence of molecularly positive PROS was 1:27,519.

Genetic and clinical features of familial mediterranean fever (FMF) in a homogeneous cohort of patients from South-Eastern Italy.

Familial Mediterranean Fever (FMF) is linked with the MEFV gene and is the commonest among monogenic autoinflammatory diseases, with high prevalence in the Mediterranean basin. Although the clinical presentation of FMF has a major role in diagnosis, genotype/phenotype correlations and the role of "benign" gene variants (as R202Q) appear highly variable and incompletely clear, making difficult to select the most effective strategy in the management of patients. Aim of the present study was to investigate the clinical presentation and the genetic background in a homogenous cohort of patients from Apulia (south eastern Italy). We investigated 217 patients with a clinical suspect of autoinflammatory diseases, who were characterized for the occurrence of specific symptoms and with next generation sequencing by a 4-gene panel including MEFV, MVK, NLRP3 and TNFRSF1A. A genetic change was identified in 122 (53.7%) patients, with 161 different MEFV variants recorded in 100 individuals, 10 variants in NLRP3, and 6 each in TNFRSF1A and MVK. The benign variant R202Q was largely prevalent (41.6% of all MEFV variants). When patients were selected according the number of pathogenic MEFV variants (0, 1, or 2 pathogenic variants), results failed to show significant links between the frequency of symptoms and the number of pathogenic variants. Only family history and Pras score (indicative for severity of disease) predicted the presence of pathogenic variants, as compared with carriers of variants considered of uncertain significance or benign. Fever >38 °C and arthralgias appeared more frequently in R202Q-positive patients than in non-R202Q carriers. These two subgroups showed comparable duration of fever, occurrence of myalgia, abdominal and chest pain, Pras, and IFFS scores. In conclusion, results confirm that FMF manifests in mild form in non-middle eastern patients. This possibility partly affects the reliability of clinical criteria/scores. Furthermore, the presence of the R202Q variant might not be completely neutral in selected groups of patients.

Sigma-2 Receptor Ligand Binding Modulates Association between TSPO and TMEM97.

Sigma-2 receptor (S2R) is a S2R ligand-binding site historically associated with reportedly 21.5 kDa proteins that have been linked to several diseases, such as cancer, Alzheimer's disease, and schizophrenia. The S2R is highly expressed in various tumors, where it correlates with the proliferative status of the malignant cells. Recently, S2R was reported to be the transmembrane protein TMEM97. Prior to that, we had been investigating the translocator protein (TSPO) as a potential 21.5 kDa S2R candidate protein with reported heme and sterol associations. Here, we investigate the contributions of TMEM97 and TSPO to S2R activity in MCF7 breast adenocarcinoma and MIA PaCa-2 (MP) pancreatic carcinoma cells. Additionally, the role of the reported S2R-interacting partner PGRMC1 was also elucidated. Proximity ligation assays and co-immunoprecipitation show a functional association between S2R and TSPO. Moreover, a close physical colocalization of TMEM97 and TSPO was found in MP cells. In MCF7 cells, co-immunoprecipitation only occurred with TMEM97 but not with PGRMC1, which was further confirmed by confocal microscopy experiments. Treatment with the TMEM97 ligand 20-(S)-hydroxycholesterol reduced co-immunoprecipitation of both TMEM97 and PGRMC1 in immune pellets of immunoprecipitated TSPO in MP cells. To the best of our knowledge, this is the first suggestion of a (functional) interaction between TSPO and TMEM97 that can be affected by S2R ligands.

What Have We Learned from Patients Who Have Arboleda-Tham Syndrome Due to a De Novo KAT6A Pathogenic Variant with Impaired Histone Acetyltransferase Function? A Precise Clinical Description May Be Critical for Genetic Testing Approach and Final Diagnosis.

Pathogenic variants in genes are involved in histone acetylation and deacetylation resulting in congenital anomalies, with most patients displaying a neurodevelopmental disorder and dysmorphism. Arboleda-Tham syndrome caused by pathogenic variants in KAT6A (Lysine Acetyltransferase 6A; OMIM 601408) has been recently described as a new neurodevelopmental disorder. Herein, we describe a patient characterized by complex phenotype subsequently diagnosed using the clinical exome sequencing (CES) with Arboleda-Tham syndrome (ARTHS; OMIM 616268). The analysis revealed the presence of de novo pathogenic variant in KAT6A gene, a nucleotide c.3385C>T substitution that introduces a premature termination codon (p.Arg1129*). The need for straight multidisciplinary collaboration and accurate clinical description findings (bowel obstruction/megacolon/intestinal malrotation) was emphasized, together with the utility of CES in establishing an etiological basis in clinical and genetical heterogeneous conditions. Therefore, considering the phenotypic characteristics, the condition's rarity and the reviewed literature, we propose additional diagnostic criteria that could help in the development of future clinical diagnostic guidelines. This was possible thanks to objective examinations performed during the long follow-up period, which permitted scrupulous registration of phenotypic changes over time to further assess this rare disorder. Finally, given that different genetic syndromes are associated with distinct genomic DNA methylation patterns used for diagnostic testing and/or as biomarker of disease, a specific episignature for ARTHS has been identified.

Genotypes and phenotypes heterogeneity in PIK3CA-related overgrowth spectrum and overlapping conditions: 150 novel patients and systematic review of 1007 patients with PIK3CA pathogenetic variants.

BACKGROUND: Postzygotic activating PIK3CA variants cause several phenotypes within the PIK3CA-related overgrowth spectrum (PROS). Variant strength, mosaicism level, specific tissue involvement and overlapping disorders are responsible for disease heterogeneity. We explored these factors in 150 novel patients and in an expanded cohort of 1007 PIK3CA-mutated patients, analysing our new data with previous literature to give a comprehensive picture. METHODS: We performed ultradeep targeted next-generation sequencing (NGS) on DNA from skin biopsy, buccal swab or blood using a panel including phosphatidylinositol 3-kinase/AKT/mammalian target of rapamycin pathway genes and GNAQ, GNA11, RASA1 and TEK. Additionally, 914 patients previously reported were systematically reviewed. RESULTS: 93 of our 150 patients had PIK3CA pathogenetic variants. The merged PROS cohort showed that PIK3CA variants span thorough all gene domains, some were exclusively associated with specific PROS phenotypes: weakly activating variants were associated with central nervous system (CNS) involvement, and strongly activating variants with extra-CNS phenotypes. Among the 57 with a wild-type PIK3CA allele, 11 patients with overgrowth and vascular malformations overlapping PROS had variants in GNAQ, GNA11, RASA1 or TEK. CONCLUSION: We confirm that (1) molecular diagnostic yield increases when multiple tissues are tested and by enriching NGS panels with genes of overlapping 'vascular' phenotypes; (2) strongly activating PIK3CA variants are found in affected tissue, rarely in blood: conversely, weakly activating mutations more common in blood; (3) weakly activating variants correlate with CNS involvement, strong variants are more common in cases without; (4) patients with vascular malformations overlapping those of PROS can harbour variants in genes other than PIK3CA.

Lateralized overgrowth with vascular malformation caused by a somatic PTPN11 pathogenic variant: Another piece added to the puzzle of mosaic RASopathies.

Lateralized/segmental overgrowth disorders (LOs) encompass a heterogeneous group of congenital conditions with excessive body tissue growth. Documented molecular alterations in LOs mostly consist of somatic variants in genes of the PI3KCA/AKT/mTOR pathway or of chromosome band 11p15.5 imprinted region anomalies. In some cases, somatic pathogenic variants in genes of the RAS/MAPK pathway have been reported. We present the first case of a somatic pathogenic variant (T507K) in PTPN11 causing a LO phenotype characterized by severe lateralized overgrowth, vascular proliferation, and cerebral astrocytoma. The T507K variant was detected in DNA from overgrown tissue in a leg with capillary malformation. The astrocytoma tissue showed a higher PTPN11 variant allele frequency. A pathogenic variant in FGFR1 was also found in tumor tissue, representing a second hit on the RAS/MAPK pathway. These findings indicate that RAS/MAPK cascade overactivation can cause mosaic overgrowth phenotypes resembling PIK3CA-related overgrowth disorders (PROS) with cancer predisposition and are consistent with the hypothesis that RAS/MAPK hyperactivation can be involved in the pathogenesis of astrocytoma. This observation raises the issue of cancer predisposition in patients with RAS/MAPK pathway gene variants and expands genotype spectrum of LOs and the treatment options for similar cases through inhibition of the RAS/MAPK oversignaling.

Clinical presentation and genetic analyses of neurofibromatosis type 1 in independent patients with monoallelic double de novo closely spaced mutations in the NF1 gene.

Neurofibromatosis type 1 (NF1) belongs to RASopathies, a group of syndromes caused by germline mutations in Ras/MAPK pathway genes. Most NF1 patients exhibit single inactivating pathogenic variants within the NF1 gene. We performed extensive genetic analyses in two NF1 families disclosing the first two cases of double de novo monoallelic NF1 variants. Both index patients described in this study had classical NF1. Probands were born from fathers in their late 30s and presented closely spaced double mutations (<100 bp) in NF1 regions showing an excess of somatic mutations. Closely spaced multiple mutations have been reported in RAS/MAPK signaling genes but never in NF1. Mutagenesis is a quasi-random process in humans, therefore two causative variants in the same gene, moreover in the same allele are exceptional. Here, we discuss possible mechanisms for this ultrarare event. Our findings confirm the possibility of a higher risk of concurrent de novo variants in NF1.

Beyond BRCA1/2: Homologous Recombination Repair Genetic Profile in a Large Cohort of Apulian Ovarian Cancers.

BACKGROUND: Pathogenic variants in homologous recombination repair (HRR) genes other than BRCA1/2 have been associated with a high risk of ovarian cancer (OC). In current clinical practice, genetic testing is generally limited to BRCA1/2. Herein, we investigated the mutational status of both BRCA1/2 and 5 HRR genes in 69 unselected OC, evaluating the advantage of multigene panel testing in everyday clinical practice. METHODS: We analyzed 69 epithelial OC samples using an NGS custom multigene panel of the 5 HRR pathways genes, beyond the genetic screening routine of BRCA1/2 testing. RESULTS: Overall, 19 pathogenic variants (27.5%) were detected. The majority (21.7%) of patients displayed a deleterious mutation in BRCA1/2, whereas 5.8% harbored a pathogenic variant in one of the HRR genes. Additionally, there were 14 (20.3%) uncertain significant variants (VUS). The assessment of germline mutational status showed that a small number of variants (five) were not detected in the corresponding blood sample. Notably, we detected one BRIP1 and four BRCA1/2 deleterious variants in the low-grade serous and endometrioid histology OC, respectively. CONCLUSION: We demonstrate that using a multigene panel beyond BRCA1/2 improves the diagnostic yield in OC testing, and it could produce clinically relevant results.

Spectrum of Germline Pathogenic Variants in BRCA1/2 Genes in the Apulian Southern Italy Population: Geographic Distribution and Evidence for Targeted Genetic Testing.

BRCA1/2-associated hereditary breast and ovarian cancer is the most common form of hereditary breast and ovarian cancer and occurs in all ethnicities and racial populations. Different BRCA1/BRCA2 pathogenic variants (PVs) have been reported with a wide variety among populations. In this study, we retrospectively analyzed prevalence and geographic distribution of pathogenic germline BRCA1/2 variants in families from Apulia in southern Italy and evaluated the genotype-phenotype correlations. Data were collected from Oncogenetic Services present in Apulian hospitals and a shared database was built containing Apulian native probands (n = 2026) that had undergone genetic testing from 2004 to 2019. PVs were detected in 499 of 2026 (24.6%) probands and 68.5% of them (342 of 499) were in the BRCA1 gene. We found 65 different PVs in BRCA1 and 46 in BRCA2. There were 10 most recurrent PVs and their geographical distribution appears to be significantly specific for each province. We have assumed that these PVs are related to the historical and geopolitical changes that occurred in Apulia over time and/or to a "founder effect". Broader knowledge of BRCA1/2 prevalence and recurring PVs in specific geographic areas could help establish more flexible genetic testing strategies that may enhance our ability to detect high-risk subjects.

The First Case of Congenital Myasthenic Syndrome Caused by a Large Homozygous Deletion in the C-Terminal Region of COLQ (Collagen Like Tail Subunit of Asymmetric Acetylcholinesterase) Protein.

Congenital myasthenic syndromes (CMSs) are caused by mutations in genes that encode proteins involved in the organization, maintenance, function, or modification of the neuromuscular junction. Among these, the collagenic tail of endplate acetylcholinesterase protein (COLQ; MIM 603033) has a crucial role in anchoring the enzyme into the synaptic basal lamina. Here, we report on the first case of a patient with a homozygous deletion affecting the last exons of the COLQ gene in a CMS patient born to consanguineous parents of Pakistani origin. Electromyography (EMG), electroencephalography (EEG), clinical exome sequencing (CES), and single nucleotide polymorphism (SNP) array analyses were performed. The subject was born at term after an uneventful pregnancy and developed significant hypotonia and dystonia, clinical pseudoseizures, and recurring respiratory insufficiency with a need for mechanical ventilation. CES analysis of the patient revealed a homozygous deletion of the COLQ gene located on the 3p25.1 chromosome region. The SNP-array confirmed the presence of deletion that extended from exon 11 to the last exon 17 with a size of 19.5 Kb. Our results add new insights about the underlying pathogenetic mechanisms expanding the spectrum of causative COLQ mutations. It is relevant, considering the therapeutic implications, to apply suitable molecular approaches so that no type of mutation is missed: "each lost mutation means a baby treated improperly".

Novel SCN5A p.W697X Nonsense Mutation Segregation in a Family with Brugada Syndrome.

Brugada syndrome (BrS) is marked by an elevated ST-segment elevation and increased risk of sudden cardiac death. Variants in the SCN5A gene are considered to be molecular confirmation of the syndrome in about one third of cases, while the genetics remain a mystery in about half of the cases, with the remaining cases being attributed to variants in any of a number of genes. Before research models can be developed, it is imperative to understand the genetics in patients. Even data from humans is complicated, since variants in the most common gene in BrS, SCN5A, are associated with a number of pathologies, or could even be considered benign, depending on the variant. Here, we provide crucial human data on a novel NM_198056.2:c.2091G>A (p.Trp697X) point-nonsense heterozygous variant in the SCN5A gene, as well as its segregation with BrS. The results herein suggest a pathogenic effect of this variant. These results could be used as a stepping stone for functional studies to better understand the molecular effects of this variant in BrS.

Old treatments for new genetic conditions: Sirolimus therapy in a child affected by mosaic overgrowth with fibroadipose hyperplasia.

PIK3CA-related overgrowth spectrum (PROS) are overgrowth diseases involving mesenchymal tissues caused by postzygotic variants in the PIK3CA gene. Fibro-Adipose hyperplasia or Overgrowth (FAO) belongs to PROS. We reported the beneficial effect of oral low-dose sirolimus therapy in a child affected by progressive FAO in term of stabilization of the disease, good tolerability, and easy management.

The longevity SNP rs2802292 uncovered: HSF1 activates stress-dependent expression of FOXO3 through an intronic enhancer.

The HSF and FOXO families of transcription factors play evolutionarily conserved roles in stress resistance and lifespan. In humans, the rs2802292 G-allele at FOXO3 locus has been associated with longevity in all human populations tested; moreover, its copy number correlated with reduced frequency of age-related diseases in centenarians. At the molecular level, the intronic rs2802292 G-allele correlated with increased expression of FOXO3, suggesting that FOXO3 intron 2 may represent a regulatory region. Here we show that the 90-bp sequence around the intronic single nucleotide polymorphism rs2802292 has enhancer functions, and that the rs2802292 G-allele creates a novel HSE binding site for HSF1, which induces FOXO3 expression in response to diverse stress stimuli. At the molecular level, HSF1 mediates the occurrence of a promoter-enhancer interaction at FOXO3 locus involving the 5'UTR and the rs2802292 region. These data were confirmed in various cellular models including human HAP1 isogenic cell lines (G/T). Our functional studies highlighted the importance of the HSF1-FOXO3-SOD2/CAT/GADD45A cascade in cellular stress response and survival by promoting ROS detoxification, redox balance and DNA repair. Our findings suggest the existence of an HSF1-FOXO3 axis in human cells that could be involved in stress response pathways functionally regulating lifespan and disease susceptibility.

Accurate Classification of NF1 Gene Variants in 84 Italian Patients with Neurofibromatosis Type 1.

Neurofibromatosis type 1 (NF1) is one of the most common autosomal dominant genetic diseases. It is caused by mutations in the NF1 gene encoding for the large protein, neurofibromin. Genetic testing of NF1 is cumbersome because 50% of cases are sporadic, and there are no mutation hot spots. In addition, the most recognizable NF1 clinical features—café-au-lait (CALs) spots and axillary and/or inguinal freckling—appear early in childhood but are rather non-specific. Thus, the identification of causative variants is extremely important for early diagnosis, especially in paediatric patients. Here, we aimed to identify the underlying genetic defects in 72 index patients referred to our centre for NF1. Causative mutations were identified in 58 subjects, with 29 being novel changes. We evaluated missense and non-canonical splicing mutations with both protein and splicing prediction algorithms. The ratio of splicing mutations detected was higher than that reported in recent patients’ series and in the Human Gene Mutation Database (HGMD). After applying in silico predictive tools to 41 previously reported missense variants, we demonstrated that 46.3% of these putatively missense mutations were forecasted to alter splicing instead. Our data suggest that mutations affecting splicing can be frequently underscored if not analysed in depth. We confirm that hamartomas can be useful for diagnosing NF1 in children. Lisch nodules and cutaneous neurofibromas were more frequent in patients with frameshifting mutations. In conclusion, we demonstrated that comprehensive in silico analysis can be a highly specific method for predicting the nature of NF1 mutations and may help in assuring proper patient care.

Association of autoimmune thyroiditis and celiac disease with Juvenile Polyposis due to 10q23.1q23.31 deletion: Potential role of PI3K/Akt pathway dysregulation.

Juvenile Polyposis (JP) is a rare hereditary condition characterized by diffuse hamartomatous gastrointestinal polyposis, associated with a significantly increased risk of neoplastic transformation. Most of the cases are caused by SMAD and BMPR1A mutations, while 10q23 microdeletions, encompassing both PTEN and BMPR1A oncogenes, are extremely rare, typically associated with more aggressive JP, and extraintestinal features overlapping with PTEN Hamartoma Tumor Syndrome. We present the first case of a young female with multiple autoimmune disorders (i.e. thyroiditis and celiac disease), associated with JP, cardiac defects and epilepsy, who carries a de novo heterozygous 10q23.1q23.31 deletion. The dysregulation of the PI3K/Akt pathway is advanced as the putative mechanism connecting autoimmune, malformative and neoplastic disorders. A literature review of clinical manifestation, gene alterations and the treatment of patients with 10q23 deletion is also provided, highlighting the importance of comprehensive, long-term, multi-disciplinary management, aimed at early identification and treatment of both intestinal and extraintestinal disorders.

Loss of STK11 expression is an early event in prostate carcinogenesis and predicts therapeutic response to targeted therapy against MAPK/p38.

Prostate cancer (PCa) is the second leading cause of cancer-related death in men; however, the molecular mechanisms leading to its development and progression are not yet fully elucidated. Of note, it has been recently shown that conditional stk11 knockout mice develop atypical hyperplasia and prostate intraepithelial neoplasia (PIN). We recently reported an inverse correlation between the activity of the STK11/AMPK pathway and the MAPK/p38 cascade in HIF1A-dependent malignancies. Furthermore, MAPK/p38 overactivation was detected in benign prostate hyperplasia, PIN and PCa in mice and humans. Here we report that STK11 expression is significantly decreased in PCa compared to normal tissues. Moreover, STK11 protein levels decreased throughout prostate carcinogenesis. To gain insight into the role of STK11-MAPK/p38 activity balance in PCa, we treated PCa cell lines and primary biopsies with a well-established MAPK14-MAPK11 inhibitor (SB202190), which has been extensively used in vitro and in vivo. Our results indicate that inhibition of MAPK/p38 significantly affects PCa cell survival in an STK11-dependent manner. Indeed, we found that pharmacologic inactivation of MAPK/p38 does not affect viability of STK11-proficient PCa cells due to the triggering of the AMPK-dependent autophagic pathway, while it induces apoptosis in STK11-deficient cells irrespective of androgen receptor (AR) status. Of note, AMPK inactivation or autophagy inhibition in STK11-proficient cells sensitize SB202190-treated PCa cells to apoptosis. On the other end, reconstitution of functional STK11 in STK11-deficient PCa cells abrogates apoptosis. Collectively, our data show that STK11 is a key factor involved in the early phases of prostate carcinogenesis, and suggest that it might be used as a predictive marker of therapeutic response to MAPK/p38 inhibitors in PCa patients.

Molecular and Functional Characterization of Three Different Postzygotic Mutations in PIK3CA-Related Overgrowth Spectrum (PROS) Patients: Effects on PI3K/AKT/mTOR Signaling and Sensitivity to PIK3 Inhibitors.

BACKGROUND: PIK3CA-related overgrowth spectrum (PROS) include a group of disorders that affect only the terminal portion of a limb, such as type I macrodactyly, and conditions like fibroadipose overgrowth (FAO), megalencephaly-capillary malformation (MCAP) syndrome, congenital lipomatous asymmetric overgrowth of the trunk, lymphatic, capillary, venous, and combined-type vascular malformations, epidermal nevi, skeletal and spinal anomalies (CLOVES) syndrome and Hemihyperplasia Multiple Lipomatosis (HHML). Heterozygous postzygotic PIK3CA mutations are frequently identified in these syndromes, while timing and tissue specificity of the mutational event are likely responsible for the extreme phenotypic variability observed. METHODS: We carried out a combination of Sanger sequencing and targeted deep sequencing of genes involved in the PI3K/AKT/mTOR pathway in three patients (1 MCAP and 2 FAO) to identify causative mutations, and performed immunoblot analyses to assay the phosphorylation status of AKT and P70S6K in affected dermal fibroblasts. In addition, we evaluated their ability to grow in the absence of serum and their response to the PI3K inhibitors wortmannin and LY294002 in vitro. RESULTS AND CONCLUSION: Our data indicate that patients' cells showed constitutive activation of the PI3K/Akt pathway. Of note, PI3K pharmacological blockade resulted in a significant reduction of the proliferation rate in culture, suggesting that inhibition of PI3K might prove beneficial in future therapies for PROS patients.