Discussion
Myopia stands as a pivotal focus in ophthalmic research, especially in the realm of HM, which has garnered significant attention due to its escalating prevalence. The emergence of HM is a result of a complex interplay between environmental influences and genetic factors.24 Present investigations underscore strategies aimed at curbing myopia prevalence, such as reducing screen time and encouraging outdoor activities, as potential measures to mitigate its progression.25 Numerous genetic studies have been conducted to understand the genetic underpinnings of myopia, including molecular genetic studies, family aggregation studies and twins studies.26 These investigations have uncovered a substantial genetic predisposition to HM, identifying numerous pathogenic genes or susceptibility loci strongly associated with its development.
In contrast to proband-centred WES, trios-based WES offers a more comprehensive approach. This method not only enables the identification of gene variants and the in-depth assessment of their pathogenicity but also facilitates the exploration of gene variants based on the principles of cogenetic segregation. This approach enhances the establishment of a robust gene–phenotype relationship mapping network and allows for a more thorough investigation into the inheritance patterns of mutated genes. Besides, given the limited genetic research targeting myopia and the imperative for myopia research within the distinct population of Shaanxi province, we have enrolled a cohort of 26 individuals from the Shaanxi region, characterised by eoHM diagnoses predating school age in our study. By employing a trios-based WES approach within this cohort, we aim to delve deeper into the genetic landscape of eoHM, elucidating the interplay between genetic variants and the manifestation of this condition within a familial context.
In our study, we identified a novel missense mutation (c.139C>T: p.Arg47*) in the ARR3 gene of the proband. It is intriguing to observe that the father of the proband, a visually normative individual, carries a hemizygous mutation in the ARR3 gene while the proband’s grandmother is afflicted by eoHM. This constellation of findings bolsters the hypothesis of an X-linked female-limited inheritance pattern in this specific case. ARR3 exhibits a unique expression pattern,27 28 primarily confined to the retina, is crucial for modulating retina-specific signalling mechanisms. Its role in desensitising photoactivated G protein-coupled receptors, with a distinct preference for opsins.29 30 Pathogenic mutations in ARR3 have been inextricably linked with myopia, a condition distinguished by X-linked female-limited inheritance. ARR3 holds a unique position as the second identified instance of an X-linked female-restricted ailment.17 Within a diagnostic WES cohort, the frequency of pathogenic variants in the ARR3 gene has risen to 5%, making it a relatively common trigger for HM.31 Furthermore, when focusing on eoHM, ARR3 stands out as the most frequently implicated gene, accounting for approximately 3.1% of Mendelian eoHM cases.20
The P3H2 gene, also known as LEPREL1, encodes prolyl 3-hydroxylase 2 (P3H2), an essential 2-oxoglutarate-dependent dioxygenase responsible for catalysing the hydroxylation of collagens.32 Prolyl hydroxylation represents a pivotal post-translational modification process primarily associated with fibril-forming collagens, including collagens I, II, IV and V.33 Consequently, the inactivation of P3H2 due to impaired collagen hydroxylation is likely the underlying mechanism for zonular instability, cataract development and an increased susceptibility to retinal tears and detachment in individuals harbouring recessive LEPREL1 mutations.34 Worth noting is the substantial eye enlargement resulting from the disruption of the inner limiting membrane in chick embryos, suggesting that recessive LEPREL1 mutations causing defects in the inner limiting membrane may contribute to paediatric HM.35
P3H2 exhibits a broad expression across diverse ocular structures, encompassing the iris, lens and trabecular meshwork.36 Notably, mutations within the P3H2 gene have been linked to the development of non-syndromic severe myopia, accompanied by the onset of cataracts and vitreoretinal degeneration.34 In our research, we detected previously unreported mutations in P3H2 (c.1865T>C:p.Phe622Ser and c.212T>C:p.Leu71Pro) that were inherited from carrier parents and culminated in the onset of HM in the offspring. These novel mutations require comprehensive investigation to elucidate their functional implications.
Furthermore, our exploration led to the identification of several genetic mutations relevant to syndromic HM, such as the c.2405_2406delAG mutation in the RPGR gene. This detected mutation in the RPGR gene is particularly noteworthy for its location within exon ORF15, a region known for its high recurrence of hotspot mutations.37 Remarkably, it has been postulated that mutations clustered towards the 3' terminus of exon ORF15 in RPGR are frequently associated with cone-rod degeneration.38 Within the context of a specific family, the uncle, on positive gene sequencing, showcased a complete absence of light perception and typified retinitis pigmentosa on fundus evaluation. These genetic screening results offer valuable insights that could lead to the development of preventive measures and early preparedness for prospective fundus pathology in children grappling with this ailment.
Given that the emergence of HM predominantly materialises through the interplay of polygenic microvariations coupled with environmental influences, the cumulative impact of these polygenic microvariations plays a pivotal role in the onset of HM. Our study also includes an examination of documented mutations in HM risk genes, encompassing TTN, RBM25, MST1 and ANGPT1. These genes hold pivotal roles in steering ocular AL elongation, modulating scleral thickness, influencing choroidal blood flow and orchestrating other factors that are germane to the onset of HM. The identification of pathogenic mutations in these genes promises to significantly enrich our understanding of the pathogenesis of HM.19
Crucially, our study is uniquely focused on eoHM families originating from the densely populated Shaanxi province, characterised by a notably high prevalence of HM prevalence in the northwest region. Hitherto, the landscape has been marked by a dearth of holistic genetic studies dedicated to myopia within this specific region. Ergo, our study assumes a vanguard position in charting the genetic spectrum of HM germane to the Shaanxi population, thereby bridging a pivotal gap in our fund of knowledge. Furthermore, the scarcity of research on eoHM in the Chinese populations, especially comprehensive WES analysis within eoHM pedigrees like ours, underscores the novelty and importance of your research. We expect that our research findings will substantially enrich the current body of knowledge in myopia research, providing valuable insights that can guide future studies and inform policy decisions in the field of myopia.
Despite the significant strides achieved by our study in elucidating the genetic foundations of eoHM within Shaanxi population, several challenges and limitations persist. Our sample size, while informative, remains relatively small, potentially limiting our capacity to detect low frequency or rare variants. To enhance the depth of our findings and bolster statistical robustness, future studies should aim to expand participant numbers. Furthermore, while WES effectively captures coding regions, it is crucial to acknowledge the potential influence of non-coding regions on eoHM. Broader sequencing coverage encompassing these non-coding areas is essential for a more comprehensive understanding of the genetic landscape contributing to eoHM. Moreover, additional functional investigations and ex vivo experimental validations are indispensable to corroborate the myriad HM risk genes spotlighted in our study. We need to further demonstrate the correlation between these gene mutations and changes in clinical parameters.
In summary, our study’s meticulous examination of eoHM families from the Shaanxi province addresses a crucial gap in myopia genetic research in this specific region. By consolidating and integrating our findings, we aspire to provide a valuable reference for genetic counselling and personalised treatment approaches.
