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Recent studies have established a strong association between KBTBD13 (HGNC:37227) and nemaline myopathy 6 (MONDO_0012237). In a multi‐patient study, 65 evaluated individuals from three independent families were shown to harbor the Dutch founder variant, c.1222C>T (p.Arg408Cys) (PMID:36335629), with robust linkage analysis demonstrating cosegregation of the variant with both neuromuscular and cardiac phenotypes. A further case series reported a similar, albeit distinct, variant, c.1222C>A (p.Arg408Ser), in three patients displaying mild axial, proximal and distal muscle weakness and additional symptoms such as bradykinesia (PMID:39240645). These findings not only extend the mutational spectrum of KBTBD13 but also underscore the recurring nature of pathogenic changes in this gene.
Segregation data from both studies support an autosomal dominant inheritance pattern. The genetic evidence is bolstered by the recurrence of the c.1222C>T (p.Arg408Cys) variant in unrelated probands and the demonstration of a genealogic link spanning nine generations in one case series, thereby reinforcing the validity of the association. In addition, the integration of cardiac features in some patients, including atrial fibrillation and ventricular tachycardia, calls attention to potential pleiotropic effects of KBTBD13 variants.
Functional studies provide important supportive evidence to this association. Experimental work has shown that KBTBD13 participates in a muscle‐specific ubiquitin ligase complex via interaction with Cullin 3, and in vitro assays demonstrate that the p.Arg408Cys change alters sarcomeric function by affecting actin binding and thin‑filament stiffness (PMID:22542517, PMID:31904591). Mouse models further confirm that both the knock‐in of the p.Arg408Cys allele and KBTBD13 deficiency result in distinct contractile dysfunctions. Although experimental findings are largely concordant with the human phenotype, the heterogeneity of neuromuscular presentations and the variable penetrance of cardiac manifestations suggest that additional modifiers might be at play.
Collectively, the combined genetic and functional data provide a coherent narrative linking KBTBD13 to nemaline myopathy 6. The robust segregation evidence, recurrence of the Dutch founder variant, and supportive functional assays justify a strong clinical validity classification that is instrumental for diagnostic decision‑making and gene panel development for both neuromuscular and cardiac evaluations.
Key Take‑Home: KBTBD13 should be integrated into diagnostic panels for nemaline myopathy 6, with attention to potential cardiac involvement, thus facilitating appropriate clinical management and future research.
Gene–Disease AssociationStrong65 evaluated patients across three families demonstrated the Dutch founder variant with robust linkage and segregation evidence (PMID:36335629) and independent replication in additional cases (PMID:39240645). Genetic EvidenceStrongRecurrent observation of the c.1222C>T (p.Arg408Cys) variant in unrelated probands along with supportive familial segregation data strongly establishes the genetic link (PMID:36335629, PMID:39240645). Functional EvidenceModerateExperimental assays, including in vitro functional studies and mouse models, demonstrate that KBTBD13 mutations lead to altered muscle contractility and abnormal ubiquitination activity, supporting a pathogenic mechanism (PMID:22542517, PMID:31904591). |