In order to explain ID, Caselli et al. [1] suggested a critical region in 13q14, containing at least 30 genes, among which four genes were considered as good functional candidates for neurodevelopmental delay: NUFIP1 (nuclear fragile X mental retardation protein 1), HTR2A (serotonin receptor 2A), PCDH8 (protocadherin 8), and PCDH17 (protocadherin 17). The gene discussed is PCDH17; the disease is Neurodevelopmental delay.