The TNNI3 gene encodes for the cardiac isoform of troponin I, a pivotal component of the sarcomeric structure of the myocardium. While heterozygous TNNI3 missense mutations have long been associated with autosomal dominant hypertrophic and restrictive cardiomyopathies, the role of TNNI3 null mutations has been more debated due to the paucity and weak characterization of reported cases and the low penetrance of heterozygous genotypes. In recent years, however, an increasing amount of evidence has validated the hypothesis that biallelic TNNI3 null mutations cause a severe form of neonatal dilated cardiomyopathy. Here, we expand the case series reporting two unrelated patients afflicted with early onset dilated cardiomyopathy, due to homozygosity for the p.Arg98* TNNI3 variant, which had thus far been documented only in heterozygous patients and apparently healthy carriers, and the recurrent p.Arg69Alafs*8 variant, respectively. A review of previously reported biallelic TNNI3 loss-of-function variants and their associated cardiac phenotypes was also performed.

Since the early 2000s, an ever-increasing subset of missense pathogenic variants in the ACTG1 gene has been associated with an autosomal-dominant, progressive, typically post-lingual non-syndromic hearing loss (NSHL) condition designed as DFNA20/26. ACTG1 gene encodes gamma actin, the predominant actin protein in the cytoskeleton of auditory hair cells; its normal expression and function are essential for the stereocilia maintenance. Different gain-of-function pathogenic variants of ACTG1 have been associated with two major phenotypes: DFNA20/26 and Baraitser–Winter syndrome, a multiple congenital anomaly disorder. Here, we report a novel ACTG1 variant [c.625G>A (p. Val209Met)] in an adult patient with moderate-severe NSHL characterized by a downsloping audiogram. The patient, who had a clinical history of slowly progressive NSHL and tinnitus, was referred to our laboratory for the analysis of a large panel of NSHL-associated genes by next generation sequencing. An extensive review of previously reported ACTG1 variants and their associated phenotypes was also performed.

Background: The melanocortin-1 receptor (MC1R) gene is a major determinant of skin and hair color. Although several MC1R variants increase the risk of skin tumors regardless of pigmentation, their role as genetic modifiers in ocular diseases remains poorly understood. Methods: Here, we analyzed a cohort of 48 Caucasian individuals using a custom next-generation sequencing (NGS) panel targeted for oculocutaneous disorders. Results: MC1R variants were identified in two probands selected from this cohort, exhibiting distinctly divergent pathological phenotypes. The first patient, an adult male with a pheomelanin-related trait and a history of early-onset skin cancer without ocular abnormalities, carried compound heterozygous MC1R variants: the novel frameshift c.537dupC (p.Ile180Hisfs*59) and the known c.880G>C (p.Asp294His). Conversely, the second patient, a young boy with severe vision-threatening features—including congenital nystagmus, foveal hypoplasia, and an atypical visual-pathway misrouting pattern—carried a candidate digenic genotype combining the same MC1R c.880G>C variant with the albinism-related c.1209G>T (p.Arg403Ser) variant in the tyrosinase (TYR) gene. Conclusions: While MC1R variants have previously been proposed as phenotypic modifiers in albinism, primarily in combination with the oculocutaneous type II melanosomal transmembrane protein (OCA2) encoding gene, our findings support a potential role for MC1R as a candidate modifier interacting with TYR in neuroretinal development. Although functional validation is required to establish causality, incorporating MC1R screening in patients with unresolved foveal hypoplasia may help clarify complex oligogenic mechanisms and optimize phenotypic classification.