Background/Objectives: Contiguous Xq26.2 deletions involving FRMD7 and IGSF1 are rare and incompletely characterized. FRMD7 loss causes X-linked idiopathic infantile nystagmus (IIN), whereas IGSF1 loss causes central hypothyroidism and other pituitary-related abnormalities. We aimed to define the clinical and molecular spectrum of an Xq26.2 contiguous gene deletion in a large Bedouin kindred with infantile nystagmus. Methods: We clinically evaluated ten family members (3 males and 7 females); genomic analyses included chromosomal microarrays, whole-exome and whole-genome sequencing, breakpoint PCR, and Sanger sequencing. Results: We identified a novel 1.44-Mb Xq26.1-q26.2 deletion, NC_000023.11:g.130756102_132199443del (GRCh38), encompassing complete loss of FRMD7, IGSF1, ARHGAP36, OR13H1, and STK26 and partial deletion of the 5′ end of ENOX2. The deletion was molecularly confirmed in six family members. The kindred exhibited a broad phenotypic spectrum, from an asymptomatic confirmed female carrier to isolated nystagmus and combined ocular–endocrine manifestations. Nystagmus was highly penetrant, whereas endocrine abnormalities were less frequent and variable. Hypoprolactinemia occurred in one confirmed female carrier, and a confirmed hemizygous boy had low-normal free T4 without overt central hypothyroidism. The only relative with overt central hypothyroidism was not genotyped; therefore, co-segregation could not be established. Conclusions: These findings further delineate the clinical spectrum of Xq26.2 deletions, highlight marked intrafamilial variability, and support structural variant analysis in unexplained IIN and/or endocrine abnormalities. Longitudinal endocrine assessment of individuals with Xq26.2 deletions and at-risk relatives in affected families may enable early detection and treatment of hypothyroidism.

The development of antisense oligonucleotide (AON) therapy for monogenic diseases such as retinitis pigmentosa (RP) is effective but labor-intensive. Rapid, efficient technologies to identify optimal AONs are needed. We present a novel approach focusing on intronic splicing mutations. We identified a novel heterozygous intronic non-canonical splice variant in PRPF3 causing dominant RP in a four-generation pedigree. Using a Dual Fluorescence Reporter Assay, we transfected HEK293T cells with a reporter plasmid containing either the wildtype intron (resulting in GFP fluorescence due to normal splicing) or the mutant intron (showing no fluorescence due to splicing defects). As an alternative to standard AONs, we used uridine-rich 7 (U7) small nuclear RNA (snRNA) derivatives with optimized Sm protein-binding site and a modified antisense sequence (U7 Sm OPT snRNA) as modulators of pre-mRNA splicing. Eight AONs were designed to target the aberrant PRPF3 transcript, to restore normal splicing and gene function. To evaluate treatment efficacy, HEK293T cells with the reporter GFP plasmid were co-transfected with U7snRNA cassettes, each containing an incorporated AON sequence. FACS analysis quantified splicing modulation and gene expression rescue, identifying the most effective AON. Our study broadens the genetic understanding of RP, highlighting the significance of personalized medicine in genetic disorder treatment.