ObjectiveTo investigate and analyze the relationship between genotype and phenotype in patients with early-onset high myopia (eoHM) associated with hereditary eye diseases. MethodsA family-based study was conducted among 30 families diagnosed with eoHM at Department of Ophthalmology of People's Hospital of Ningxia Hui Autonomous Region from January 2022 to June 2023. Seven families (23.3%, 7/30), all probands, and their 14 parents were included. These seven families were unrelated. Detailed patient and family histories were collected. All participants underwent comprehensive ophthalmic examinations, including best-corrected visual acuity, color vision testing, fundus color photography, optical coherence tomography, fluorescein fundus angiography, and fundus autofluorescence imaging. Full-field electroretinography was performed in three cases. Peripheral venous blood samples were collected from patients and their parents for whole-genome DNA extraction and whole-exome sequencing. Potential pathogenic variants were identified, and their pathogenicity was analyzed and confirmed by Sanger sequencing. The pathogenicity of newly discovered gene variants was evaluated according to the guidelines of the American College of Medical Genetics and Genomics (ACMG). Literature on previously reported eoHM associated with hereditary eye diseases was reviewed to analyze the relationship between variant genes and clinical phenotypes. ResultsAmong the seven families, three exhibited X-linked inheritance, two showed autosomal recessive inheritance, and two demonstrated autosomal dominant inheritance. All the patients were male. Among the seven patients, one case each was identified with congenital stationary night blindness (CSNB), Bornholm eye disease, X-linked retinitis pigmentosa (RP), cone-rod dystrophy, Knobloch syndrome, familial exudative vitreoretinopathy (FEVR), and Stickler syndrome. Genetic testing revealed nine gene variants highly correlated with the observed phenotypes. The genetic testing results revealed that all patients were found to carry nine gene variants highly associated with the phenotype, including: a hemizygous missense variant NYX c.647A>T (p.N216I) (M1), an OPN1LW LIAVA haplotype variant (M2), a hemizygous frameshift variant RPGR c.3096_3097del (p.E1033RfsTer45) (M3), compound heterozygous variants TTLL5 c.1588_1589del (p.L531EfsTer24) and c.850G>C (p.D284H) (M4, M5), compound heterozygous variants COL18A1 c.2118dup (p.G707RfsTer23) and c.3523_3524del (p.L1175VfsTer72) (M6, M7), a heterozygous missense mutation FZD4 c.1499C>T (p.T500I) (M8), and a heterozygous frameshift variant COL11A2 c.966dup (p.T323HfsTer19) (M9). Among them, M2, M4, M5, M8 and M9 were newly discovered mutation sites, and M1, M3, M6 and M7 were known mutation sites. According to the classification standards and guidelines of genetic variation issued by ACMG, M2, M3, M4, M6, M7, and M9 were judged to be pathogenic variants, while M1, M5, and M8 were of unknown clinical significance. Through literature review, it was found that eoHM was more common among the clinical phenotypes of 4 types of hereditary retinal diseases, including CSNB, Stickler syndrome, FEVR and RP. ConclusioneoHM is intricately associated with inherited eye diseases and may serve as the earliest indicator of such conditions.