ARHGAP4 and immunodeficiency disease: In this patient, the deleted region included 1.4 kb of intron 1, the first exon of ARHGAP4 and a 2.8 kb sequence between ARHGAP4 and ARD1A; this sequence is highly conserved across species, and Broides et al, speculated that this conserved region was the cause of the immunodeficiency phenotype observed in their patient.