Background/Objectives: Noonan syndrome (NS) is a genetic multisystem disease characterized by distinctive facial features, short stature, chest deformity, and congenital heart defects. NS is caused by gene variants of the RAS/MAPK pathway, with PTPN11 accounting for about 50% of cases. This study aimed to identify PTPN11 pathogenic variants in Mexican patients with NS to enhance our understanding of the disease in this population. Methods: This study included 91 probands and 60 relatives, all of which were clinically evaluated by a geneticist. Sanger sequencing was used to screen the entire PTPN11 gene. Results: Twenty-one previously reported pathogenic variants were identified in 47.3% of the probands. The most frequently occurring were p.Asn308Asp (16.3%) and p.Met504Val (16.3%). Variants p.Tyr279Cys and p.Thr468Met were found exclusively in patients with lentiginosis. Eighty-three percent of patients carried a variant in one of the three exons (3, 8, or 13) where the greatest genetic diversity was observed. Common clinical findings identified in probands included short stature (82%), cardiac anomalies (70.7%), short neck (68.4%), and pectus excavatum (63.2%), although features represented by only one patient each were also detected. Conclusions: This study confirmed the clinical diagnosis of NS in 43 probands and 11 relatives, and further genetic analysis of the remaining 48 probands is required to identify the causal variant. The genetic and clinical variability observed in our cohort was consistent with reports from other populations, underscoring the importance of comprehensive care for all patients. This research provides the most extensive clinical and molecular characterization of NS in Mexican patients, identifying pathogenic variants of PTPN11.

Genetic variants in the zone of polarizing activity regulatory sequence (ZRS) that induce ectopic expression of the SHH gene have been associated with different ZRS-related phenotypes. We report the first patient with a de novo variant, c.423+4916 T>C, in ZRS (previously classified as a variant of uncertain significance) that causes tibial hemimelia-polysyndactyly-triphalangeal thumb syndrome (THPTTS). A two-month-old male patient presented with bilateral preaxial polydactyly, triphalangeal thumb, and tibial agenesis and was heterozygous for the variant c.423+4916T>C (neither of his parents was a carrier). The findings obtained from the family study were sufficient to reclassify the variant from “uncertain significance” to “likely pathogenic” according to three criteria from the American College of Medical Genetics and Genomics guidelines, as follows: (1) absence of gnomAD, (2) confirmation of paternity and maternity, and (3) strong phenotype–genotype association. In ZRS-associated syndromes, a wide clinical spectrum has been observed, ranging from polydactyly to THPTTS; our patient has the most severe and rare phenotype. We did not perform functional assays. However, the c.423+4916T>C variant is flanked by three variants, which have been proven not only to cause the phenotype but also to increase the expression of SHH. Through all this data gathering, we consider the c.423+4916T>C variant to be causative of THPTTS.

Metatropic dysplasia is an autosomal dominant skeletal disorder characterized by progressive kyphoscoliosis, severe platyspondyly, pronounced metaphyseal enlargement, and shortening of the long bones. This condition is caused by pathogenic variants in the TRPV4 (Transient Receptor Potential Vanilloid 4) gene, which encodes a non-selective calcium channel involved in bone homeostasis. Variants in TRPV4 have been associated with two major disease groups: skeletal dysplasias and neuropathies, with recent findings indicating an overlap in their clinical features. We report three patients with metatropic dysplasia, each presenting a distinct severity profile. All exhibited a bell-shaped thorax, significant platyspondyly, and shortened long bones with broad metaphyses. Notably, patients 1 and 3 had more complex clinical courses, including seizures and global developmental delay. Genetic analysis revealed two different TRPV4 variants: p.Asn796del (patient 1) and p.Pro799Leu (patients 2 and 3). These cases illustrate variability in extra-skeletal manifestations, complications, and prognosis. In our patients with TRPV4-related disorders, the co-occurrence of neurological symptoms and skeletal abnormalities suggests a clinically heterogeneous spectrum consistent with a single disease rather than distinct entities. A comprehensive, multidisciplinary approach is essential to optimize management and improve the quality of life for patients.

Background: Griscelli syndrome type 2 is a rare autosomal recessive disorder caused by pathogenic variants in the RAB27A gene, characterized by partial albinism, immunodeficiency, and a high risk of hemophagocytic lymphohistiocytosis (HLH). Case descriptions: We report two unrelated Mexican patients with GS2 harboring the same homozygous RAB27A frameshift variant (c.335del; p.Asn112Thrfs*3) and describe their clinical and immunological features. Both patients presented with silvery-gray hair and subsequently developed HLH, although with variable onset and clinical course. One patient initially manifested with isolated central nervous system involvement, lacking systemic or laboratory abnormalities, which led to diagnostic uncertainty and delayed treatment. The second patient presented early in life with classical systemic features of HLH. Despite treatment with standard HLH-directed therapy, both patients experienced disease reactivation and ultimately died before undergoing hematopoietic stem cell transplantation. The homozygous pathogenic RAB27A variant (c.335del; p.Asn112Thrfs*3) was identified by polymerase chain reaction followed by Sanger sequencing in the two index cases; both sets of parents were heterozygous carriers. Comparison with previously reported cases carrying the same variant highlights notable phenotypic variability despite a shared genotype. The recurrence of this variant exclusively in individuals of Hispanic origin raises the possibility of a founder effect. Conclusions: These findings underscore the importance of early recognition of pigmentary abnormalities, the integration of clinical and molecular diagnostics approaches, and the consideration of HLH in patients presenting with atypical neurological manifestations. Early diagnosis is critical to enable prompt therapeutic intervention and improve clinical outcomes.

Cartilage-hair hypoplasia (CHH) is a rare autosomal recessive skeletal dysplasia caused by variants in RMRP (RNA component of mitochondrial RNA processing endoribonuclease), which encodes a non-coding RNA. Despite its well-established clinical and molecular spectrum in some populations, data from Mexico remain limited. We report eight patients from seven unrelated families with CHH. Clinical and radiographic findings were assessed, and RMRP was analyzed by polymerase chain reaction and Sanger sequencing. All patients exhibited disproportionate short stature; prenatal long-bone shortening and short stature at birth occurred in 50%. Radiographs showed widened long bones and metaphyseal dysplasia in all patients. Extraskeletal manifestations were observed in four patients, each with a distinct feature: immunodeficiency, anemia, Hirschsprung disease, or lymphopenia. RMRP variants were identified in all patients, comprising two homozygous and six compound heterozygous genotypes. Eight variants were detected: three pathogenic (n.6C>T, n.147G>A, and n.72A>G), two likely pathogenic (n.127C>T and n.125C>T), two variants of uncertain significance (n.128G>C and n.215C>T), and a novel promoter deletion (n.-39_-19del) encompassing the RMRP TATA box, classified as likely pathogenic according to the ClinGen RMRP variant interpretation specifications (GN088, Version 1.3). This study expands the clinical and molecular spectrum of CHH in the Mexican population and provides additional evidence for RMRP variant interpretation.