FXR1 and Intellectual disability: Notably, among these, hyaluronan binding protein 4 (HABP4), encoded by HABP4, is known to bind to FXR1 (fragile X mental retardation-related protein 1),[22] suggesting that HABP4 haploinsufficiency due to heterozygous deletion was involved in the observed pathogenesis (i.e., mental retardation) observed in the Gorlin syndrome patient from family F. This haploinsufficiency might have disrupted the interaction of HABP4 with FXR1, although only one of the two affected family members clearly exhibited this phenotype.