Molecular Basis and Diagnostic Approach to Isolated and Syndromic Lateralized Overgrowth in Childhood.

OBJECTIVE: To demonstrate a high-yield molecular diagnostic workflow for lateralized overgrowth (LO), a congenital condition with abnormal enlargement of body parts, and to classify it by molecular genetics. STUDY DESIGN: We categorized 186 retrospective cases of LO diagnosed between 2003 and 2023 into suspected Beckwith-Wiedemann spectrum, PIK3CA-related overgrowth spectrum (PROS), vascular overgrowth, or isolated LO, based on initial clinical assessments, to determine the appropriate first-tier molecular tests and tissue for analysis. Patients underwent testing for 11p15 epigenetic abnormalities or somatic variants in genes related to PI3K/AKT/mTOR, vascular proliferation, and RAS-MAPK cascades using blood or skin DNA. For cases with negative initial tests, a sequential cascade molecular approach was employed to improve diagnostic yield. RESULTS: This approach led to a molecular diagnosis in 54% of cases, 89% of cases consistent with initial clinical suspicions, and 11% reclassified. Beckwith-Wiedemann spectrum was the most common cause, with 43% of cases exhibiting 11p15 abnormalities. PIK3CA-related overgrowth spectrum had the highest confirmation rate, with 74% of clinically diagnosed patients showing a PIK3CA variant. Vascular overgrowth demonstrated significant clinical overlap with other syndromes. A molecular diagnosis of isolated LO proved challenging, with only 21% of cases classifiable into a specific condition. CONCLUSIONS: LO is underdiagnosed from a molecular viewpoint and to date has had no diagnostic guidelines, which is crucial for addressing potential cancer predisposition, enabling precision medicine treatments, and guiding management. This study sheds light on the molecular etiology of LO, highlighting the importance of a tailored diagnostic approach and of selecting appropriate testing to achieve the highest diagnostic yield.

A single scalp nodule as the first presentation of acute lymphoblastic leukemia (KMT2A::MLLT3) in a healthy-appearing infant: a case report.

Background: Infant leukemia is a rare form of acute leukemia diagnosed prior to the age of 1 and is characterized by an extremely poor prognosis due to its dismal response to current therapeutic approaches. It comprises about 4% of all childhood cases of acute lymphoblastic leukemia (ALL). Isolated initial cutaneous involvement in ALL is uncommon, and even more so in infant ALL. Case presentation: Here, we present the case of a 2-month-old healthy-appearing infant, initially presenting with a single scalp nodule and subsequently diagnosed with an infant ALL. The leukemia was characterized by the most immature B-lineage immunophenotype [pro-B ALL/B-I, according to the European Group for the Immunological Characterization of Leukaemias (EGIL) classification] and chromosomal translocation t(9;11)(p22;q23), resulting in fusion gene KMTLA2::MLLT3, which is considered a negative prognostic factor. The patient underwent hematopoietic stem cell transplantation and is still in remission. Conclusions: This case is peculiar because of the rare occurrence of isolated initial cutaneous involvement in ALL. Despite the healthy appearance of the patient, every suspicious symptom suggestive of malignancies should be further investigated to anticipate the diagnosis and start treatment early.

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.

Successful treatment of pulmonary arterial hypertension in a 2-month-old female infant with incontinentia pigmenti: A case report.

Incontinentia pigmenti (IP) is a rare X-linked dominant neuroectodermal dysplasia affecting almost exclusively females. It is caused by loss-of-function mutations in the inhibitor of kappa light polypeptide gene enhancer in B cells, kinase gamma gene, formerly known as NF-κB essential modulator. The disorder is typically identified by peculiar skin findings that develop throughout the 1st year of life. Approximately one-third of patients has ocular and neurologic abnormalities causing severe disability. Defects of hair, nails, and teeth can also occur. Among systemic complications, pulmonary arterial hypertension (PAH) is uncommon but potentially life-threatening. Only six cases have been described in the literature so far, and four of them died before reaching 1 year of age. Herein, we report the case of a 2-month-old girl with IP and severe PAH, successfully treated with pulmonary antihypertensive and anti-inflammatory therapy.

Successful treatment with MEK-inhibitor in a patient with NRAS-related cutaneous skeletal hypophosphatemia syndrome.

Cutaneous skeletal hypophosphatemia syndrome (CSHS) is caused by somatic mosaic NRAS variants and characterized by melanocytic/sebaceous naevi, eye, and brain malformations, and FGF23-mediated hypophosphatemic rickets. The MEK inhibitor Trametinib, acting on the RAS/MAPK pathway, is a candidate for CSHS therapy. A 4-year-old boy with seborrheic nevus, eye choristoma, multiple hamartomas, brain malformation, pleural lymphangioma and chylothorax developed severe hypophosphatemic rickets unresponsive to phosphate supplementation. The c.182A > G;p.(Gln61Arg) somatic NRAS variant found in DNA from nevus biopsy allowed diagnosing CSHS. We administered Trametinib for 15 months investigating the transcriptional effects at different time points by whole blood RNA-seq. Treatment resulted in prompt normalization of phosphatemia and phosphaturia, catch-up growth, chylothorax regression, improvement of bone mineral density, reduction of epidermal nevus and hamartomas. Global RNA sequencing on peripheral blood mononucleate cells showed transcriptional changes under MEK inhibition consisting in a strong sustained downregulation of signatures related to RAS/MAPK, PI3 kinase, WNT and YAP/TAZ pathways, reverting previously defined transcriptomic signatures. CSHS was effectively treated with a MEK inhibitor with almost complete recovery of rickets and partial regression of the phenotype. We identified "core" genes modulated by MEK inhibition potentially serving as surrogate markers of Trametinib action.

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.

Kaposiform hemangioendothelioma further broadens the phenotype of PIK3CA-related overgrowth spectrum.

Kaposiform hemangioendothelioma (KHE) is a rare locally aggressive mixed vascular tumor, with typical onset in early childhood and characterized by progressive angio- and lymphangiogenesis. Its etiopathogenesis and molecular bases are still unclear. Here, we report the first case of congenital KHE harboring a PIK3CA mosaic pathogenic variant (c.323G > A, p.Arg108His) in a boy with very subtle PIK3CA-related overgrowth spectrum (PROS) features. This finding provides insights into the pathophysiology of KHE, offering targeted therapeutic options by inhibition of the PI3K/Akt/mTOR pathway. We propose the inclusion of this mixed lymphatic and vascular anomaly within the PROS.