Revisiting LSDMCA: male lethality escape and genotype-phenotype correlations

Mitochondrial disorders (MDs) are a diverse group of genetic conditions primarily affecting the oxidative phosphorylation (OXPHOS) system and cellular energy production. Among MDs, Linear Skin Defects with Multiple Congenital Anomalies (LSDMCA), or Microphthalmia with Linear Skin Lesions (MLS) syndrome, is a rare X-linked dominant male-lethal disorder characterized by ocular malformations, linear skin defects, and multisystem developmental anomalies. These features are associated with pathogenic variants in genes related to mitochondrial function, including HCCS, COX7B, and NDUFB11 or chromosomal rearrangements of the Xp22 region encompassing HCCS. Despite progress, genotype-phenotype correlations remain insufficiently defined. In this study, we report three novel mutations in three patients with LSDMCA, broadening the phenotypic spectrum of the disorder. Whole exome sequencing revealed pathogenic missense variants in HCCS [NM_005333.5: c.625 G > C; p.(Asp209His)] and COX7B [NM_001866.3: c.221 C > T; p.(Pro74Leu)] in two unrelated patients. Functional studies confirmed that the COX7B variant impairs mitochondrial respiratory chain (MRC) function. A third patient harbored a novel frameshift pathogenic variant in NDUFB11 [NM_001135998.3: c.145_152dup; p.(Thr52Glnfs*66)], further implicating mitochondrial dysfunction in LSDMCA pathogenesis. Notably, the COX7B variant was identified in a biological male (46, XY) without X-chromosome structural rearrangements, marking the first such reported case of LSDMCA. Our data suggest that certain missense variants, resulting in mild impairment of the gene product, may allow male survival, thereby expanding the known phenotype of this rare disorder. This report advances our understanding of genotype-phenotype correlations in LSDMCA and highlights the impact of mitochondrial dysfunction during embryonic development.