Disorders associated with pathogenic variants in the lysine acetyltransferase 6B (KAT6B) gene, located at chromosome 10q22.2, constitute a clinically heterogeneous group, historically divided into two allelic syndromes: Say–Barber–Biesecker–Young–Simpson syndrome (SBBYSS), regarded as a variant of Ohdo syndrome, and genitopatellar syndrome (GPS). Both conditions typically arise from heterozygous pathogenic variants in the terminal exons of KAT6B. As the number of reported cases with overlapping SBBYSS/GPS phenotypes has increased, these entities are now collectively classified as KAT6B-related disorders or the KAT6B spectrum. Individuals with SBBYSS commonly present with characteristic facial dysmorphic features, generalised hypotonia, joint hypermobility, feeding difficulties, and long thumbs and great toes. Skeletal anomalies, particularly patellar hypoplasia, are frequently observed. Genitopatellar syndrome (GPS) is distinguished by severe developmental delay and genital anomalies. This report describes an 11-month-old male diagnosed with a KAT6B-related disorder following identification of a heterozygous pathogenic missense variant in the KAT6B gene, confirmed by molecular genetic testing. The phenotype included craniofacial dysmorphism, developmental delay and speech impairment, hypotonia, blepharophimosis, long thumbs, skeletal anomalies, a congenital renal anomaly, and seizures. The clinical presentation exhibited a blend of features characteristic of both SBBYSS and GPS. Publication of this case was authorised by written informed consent from the patient’s mother and conducted in accordance with bioethical principles. Conclusion. The constellation of anomalies observed in this patient fulfils clinical criteria for both SBBYSS and GPS, reinforcing the concept of a continuous phenotypic spectrum within KAT6B-related disorders. Further genotype–phenotype correlation studies are warranted to delineate the full clinical variability and refine diagnostic criteria across this spectrum.