Mechanosensation is the ability to detect dynamic mechanical stimuli and is essential for many processes, including sense of touch on the skin. PIEZO2 is a functional ion channel assembled by three monomers and is an essential mechanotransducer for touch, proprioception, and interoception. Heterozygous pathogenic variants in PIEZO2 gene are associated with distal arthrogryposis type 3 (MIM:114300) and type 5 (MIM:108145), and with Marden-Walker Syndrome (MIM:248700). Recessive pathogenic variants in PIEZO2 are associated with distal arthrogryposis with impaired proprioception and touch (DAIPT) (MIM:617146). Papers describing patient cohorts in literature are few. Here we described 9 patients from 8 families with a very similar clinical picture characterized by neonatal respiratory distress, hypotonia, delayed motor development, sensory ataxia, foot deformities, hyperlaxity, progressive scoliosis, and skeletal contractures. We also carried out a review of patients reported in literature with recessive PIEZO2 variants. We retrospectively analyzed clinical and genetic results of 5 patients followed at Bambino Gesù Children Hospital and 4 patients followed at Neuropediatric Unit, Clinica Meds, Santiago, Chile. In our cohort, we identified nine patients harbouring PIEZO2 variants. Among them, eight patients carried single nucleotide variants (SNVs): three were compound heterozygous, two were homozygous, and two harboured two heterozygous variants of unknown allelic phase. Additionally, one other patient, who presented with a highly suggestive clinical phenotype, was found to harbour only a single heterozygous maternally inherited, frameshift variant. Only one patient was found to have a large homozygous copy number variant (CNV). Our cohort clinical phenotype, even though of variable severity, is highly concordant between the patients and literature data. To our knowledge this is one of the largest cohort of patients with recessive PIEZO2 variants so far.

Marden-Walker syndrome (MWS; OMIM 248700) is an extremely rare congenital disorder characterized by multiple joint contractures, craniofacial dysmorphism, neurological abnormalities, and multisystem involvement. Although historically diagnosed on clinical grounds, only a few cases have been molecularly confirmed. Here, we describe a Brazilian female infant with classic manifestations of MWS, carrying a heterozygous pathogenic variant in the PIEZO2 gene not previously reported in MWS. To our knowledge, this is the first molecularly confirmed MWS case from Brazil, thus expanding both the genotype-phenotype spectrum and geographic distribution of PIEZO2-related disorders. Comparative analysis of previously reported molecularly confirmed cases reveals shared core features and highlights the prominent neurological involvement observed in our patient. A review of individuals with the same PIEZO2 variant demonstrates marked phenotypic variability-from Gordon syndrome to distal arthrogryposis type 5-underscoring allelic heterogeneity and variable expressivity. This case refines the phenotypic spectrum of PIEZO2-related disorders and illustrates how allelic heterogeneity contributes to wide clinical variability, while also underscoring the importance of including underrepresented populations in variant interpretation.

Developmental and Epileptic Encephalopathy (DEE) is a severe and heterogeneous neurological disorder in infancy/early childhood. DEE's genetic and phenotypic variability complicates diagnosis and treatment. This retrospective study aimed to identify genetic variants and explore genotype-phenotype correlations in children with DEE using a targeted epilepsy gene panel (TGP) and Whole Exome Sequencing (WES). Medical records of children who underwent custom-designed 55-gene TGP and WES were reviewed. The diagnostic yield of each method was determined based on the detection of pathogenic (P) and likely pathogenic (LP) variants. A total of 129 patients (66 males, 63 females) underwent TGP, which identified P/LP variants in 29 cases (22.48%). Variants were detected in SCN1A, KCNQ2, STXBP1, CDKL5, PCDH19, PLCB1, WWOX, SCN2A, FGF12, HCN1, SCN8A, and SLC35A2. WES further identified several variants in children with West syndrome. A TSC1 variant was detected in a patient without cutaneous stigmata of tuberous sclerosis complex. The NALCN variant in a patient was linked to Infantile Hypotonia with Psychomotor Retardation and Characteristic Facies 1. A CTBP1 variant associated with extremely rare Hypotonia, Ataxia, Developmental Delay, and Tooth Enamel Defect Syndrome was detected in another patient. A PIEZO2 variant-associated with Marden-Walker syndrome-was found in a child with Early Infantile Developmental and Epileptic Encephalopathy. These findings highlight the extensive genetic heterogeneity and phenotypic variability of DEE. WES demonstrates substantial value in identifying novel gene-disease associations and may be considered as a first-tier diagnostic tool in epilepsy and DEE.

We report a 24-year-old male with blepharophimosis, psychomotor retardation, brachycephaly, microstomia, immobile face, high arched palate, single palmar crease, kyphoscoliosis, talipes equinovarus, inguinal hernia, pyloric stenosis, recurrent infections, bilateral camptodactyly, wide-set eyes, decreased muscle mass, hypotonia, exotropia, and ptosis in the left eye, growth retardation, multiple congenital contractures, and hyporreflexia. Contractures improved with aging, but intellectual disability and blepharophimosis remained. He also presented epilepsy, outbursts of laughter, and predisposition to drug adverse effects (skin lesions with carbamazepine and secondary parkinsonism).

Distal arthrogryposes (DA) are a group of conditions presenting with multiple congenital contractures in the distal joints. The 10 types of DA are distinguished by different extra-articular manifestations. Heterozygous gain-of-function variants in PIEZO2 are known to cause a spectrum of DA conditions including DA type 3, DA type 5, and possibly Marden Walker syndrome, which are usually distinguished by the presence of cleft palate (DA3), ptosis and restriction in eye movements (DA5), and specific facial abnormalities and central nervous system involvement, respectively. We report on a boy with a recurrent de novo heterozygous PIEZO2 variant in exon 20 (NM_022068.3: c.2994G > A, p.(Met998Ile); NM_001378183.1: c.3069G > A, p.(Met1023Ile)), who presented at birth with DA and later developed respiratory insufficiency. His phenotype broadly fits the PIEZO2 phenotypic spectrum and potentially extends it with novel phenotypic features of pretibial linear vertical crease, immobile skin, immobile tongue, and lipid myopathy.