ATP6V1B1 and nephrolithiasis: Finally, the fly orthologs of two genes associated with nephrolithiasis, ATPase H+ Transporting V1 Subunit B1 (ATP6V1B1) and ATP6V0A4 (Vacuolar H+-ATPase 55kD subunit [Vha55] and Vha100-2 in flies), are highly expressed in Malpighian tubule principal cells.