Background: PPP1CB-related Noonan syndrome-like disorder with loose anagen hair type 2 (NSLH2; OMIM #617506) is a rare RASopathy caused by pathogenic variants in PPP1CB, encoding the catalytic beta subunit of protein phosphatase 1 (PP1C). Since its first description in 2016, only a limited number of patients have been reported, leaving the full phenotypic spectrum and genotype–phenotype correlations largely undefined. Objectives: To systematically review the clinical, molecular, and functional characteristics of NSLH2, we define its phenotypic spectrum, explore genotype–phenotype correlations, and summarize current evidence on therapeutic management. Methods: A systematic literature search was conducted across PubMed/MEDLINE, Embase, Web of Science, and Google Scholar, supplemented by searches of Orphanet, OMIM, and ClinVar, from 2016 to 2026. Studies reporting patients with pathogenic or likely pathogenic variants in PPP1CB were included. Individual patient-level data were extracted and analyzed descriptively. Additionally, we report a novel patient identified at our institution. Results: Thirty patients from 14 publications were included, harboring nine distinct PPP1CB variants. The most frequently identified variant was p.Pro49Arg (n = 17, 56.7%), followed by p.Met182Lys (n = 4, 13.3%) and p.Glu183Ala (n = 3, 10.0%). The majority of variants arose de novo (n = 26, 86.7%). Ectodermal anomalies, predominantly slow-growing and structurally abnormal hair consistent with loose anagen hair, were present in 79.3% of patients. Congenital heart defects were identified in 75.9%, with pulmonary stenosis and atrial septal defect representing the most common lesions. Short stature was documented in 69.2% of cases, and neurodevelopmental delay—encompassing motor and language delay—affected the majority of patients (72.4–84.6%). Brain structural anomalies were detected in 35.7%. Facial dysmorphic features were universal. Macrocephaly was present in 58.6% of cases, intellectual disability was reported in 26.9%, and epilepsy in 6.7%. Three familial cases with inherited p.Met182Lys transmission from an affected mother to three children are described, representing the largest reported familial cluster. Conclusions: NSLH2 is a clinically recognizable RASopathy with a consistent core phenotype comprising loose anagen hair, congenital heart defects, short stature, macrocephaly, and neurodevelopmental delay. The p.Pro49Arg variant accounts for the majority of reported cases and appears associated with a broad phenotypic expression. Larger cohorts and functional studies are needed to fully delineate genotype–phenotype correlations and guide therapeutic strategies.

Pathogenic variants in RAF1 are a common cause of Noonan syndrome (NS), accounting for approximately 5% of cases. Nonetheless, RAF1 -related NS is often associated with severe clinical features, particularly hypertrophic cardiomyopathy (HCM). Although initial studies highlighted the occurrence of genotype-phenotype correlations, a comprehensive analysis specifically focused on RAF1 variants is still lacking. We conducted a retrospective observational study combining newly collected cases of RAF1 -related NS from a national multicenter retrospective cohort (RC) with systematically reviewed cases from literature search (literature cohort, LC). Variants were classified by protein domain, while the most recurrent variant, p.Ser257Leu, was analyzed separately to assess variant- and domain-specific phenotype correlations. A total of 203 cases were included. Variants in the CR2 domain accounted for 83% of cases, with p.Ser257Leu alone representing 53%. HCM was observed in 80.1% of affected individuals confirming its role as the predominant cardiac manifestation in RAF1 -related NS; neurodevelopmental features were reported in 44.5% of patients. The prevalence of clinical features varied significantly according to variant location. HCM was markedly more frequently associated with CR2 variants (89.4%) and in subjects heterozygous for the p.Ser257Leu change (94.2%) compared with non-CR2 variants (37.1%). Conversely, neurodevelopmental features were more common in patients with non-CR2 variants (69.2%) than in those with CR2 variants (38.2%) or p.Ser257Leu (29.4%). CR2 and p.Ser257Leu variants were associated with earlier age at diagnosis and increased mortality. Our findings confirm and document more comprehensively domain- and variant-specific phenotypes in RAF1 -related NS, emphasizing the importance of variant-level interpretation in clinical management and genetic counseling.

Background: Autosomal recessive intellectual developmental disorder-13 (MRT13; OMIM #613192) is a rare neurodevelopmental disorder caused by pathogenic variants in TRAPPC9. Most reported variants are single-nucleotide variants (SNVs), small insertions/deletions, or copy number variants (CNVs), whereas complex structural variants (SVs) remain poorly characterized. Objectives: This study sought to review the clinical and molecular spectrum of TRAPPC9-related disorder, harmonize reported variants, explore genotype–phenotype correlations, and expand the mutational spectrum by reporting a novel patient with a cryptic SV. Methods: We report a novel patient whose diagnostic workup included array-CGH, whole-exome sequencing, karyotyping, and optical genome mapping. Additionally, a systematic literature search was primarily conducted in PubMed/MEDLINE from 2009 to January 2026, with Embase, Web of Science, Google Scholar, Orphanet, OMIM, and ClinVar used as supplementary sources. Patients carrying pathogenic/likely pathogenic TRAPPC9 variants were included. Clinical and molecular data were extracted and descriptively summarized. Genotype–phenotype correlations were explored. Reported variants were re-annotated using MANE Select reference transcripts. Results: The reported patient showed biallelic TRAPPC9 disruption due to two independently inherited structural variants: a maternal ~35 kb intragenic deletion involving exons 10–12, identified by 400K array-CGH, and a paternal balanced translocation t(4;8) disrupting TRAPPC9 within intron 8, characterized by trio-OGM and paired-end whole-genome sequencing (PE-WGS). Thirty-one studies reporting 75 previously published patients were included in the literature review; together with the novel patient described here, the final cohort comprised 76 patients. Intellectual disability was present in 100% of cases, followed by brain MRI abnormalities (95.9%), microcephaly (82.3%), motor delay (71.4%), dysmorphic features (69.8%), obesity (52.8%), behavioral abnormalities/autism spectrum disorder (49.2%/43.8%), and epilepsy (15.9%). Most patients (84.2%) harbored homozygous variants. Thirty-two distinct sequence variants were identified, predominantly loss-of-function. CNVs were identified in 13.2% of patients. No genotype–phenotype correlations were identified. Conclusions: The systematic review provides an updated and harmonized overview of the clinical and molecular spectrum of TRAPPC9-related disorder, supporting the presence of a recognizable phenotype and confirming the predominance of loss-of-function variants. Our case further highlights the contribution of cryptic structural variants to the mutational spectrum of TRAPPC9 and the diagnostic value of advanced genomic approaches.