Novel Variant IMPDH1 c.134A>G, p.(Tyr45Cys): Phenotype-Genotype Correlation Revealed Likely Benign Clinical Significance.

Pathogenic variants in IMPDH1 are associated with autosomal dominant retinitis pigmentosa 10 (RP10), and Leber congenital amaurosis 11. This case report of a 13-year-old girl with Down's syndrome and keratoglobus is aimed at linking the novel variant IMPDH1 c.134A>G, p.(Tyr45Cys), a variant of uncertain significance, to a clinical phenotype and to provide grounds for the objective assignment of its benign features. RP10 is characterized by the early onset and rapid progression of ocular symptoms, beginning with nyctalopia in childhood, accompanied by typical RP fundus changes. As evidenced via thorough clinical examination and testing, none of the RP10 characteristics were present in our patient. On the contrary, our patient who was heterozygous for IMPDH1 c.134A>G, p.(Tyr45Cys) showed no signs of peripheral retinal dystrophy, and did not manifest any disease characteristics typical of the IMPDH1 gene mutation. Consequently, we conclude that the variant did not contribute to the phenotype. According to standards and guidelines for the interpretation of sequence variants, IMPDH1 c.134A>G, p.(Tyr45Cys) revealed likely benign features.