Clinical and Molecular Genetic Analyses of a Girl With Isolated Nephrogenic Diabetes Insipidus due to Contiguous Gene Deletion Involving AVPR2 and L1CAM

Loss-of-function mutations of AVPR2 and L1CAM result in nephrogenic diabetes insipidus (NDI) and L1 syndrome. These diseases are inherited in an X-linked recessive manner. Females with heterozygous variants can be affected owing to skewed X-chromosome inactivation (XCI). A 3-year-old girl with normal development was presented with polydipsia and polyuria, and diagnosed of NDI through an improper response to water restriction and desmopressin administration. A targeted genome capture sequencing for X chromosome confirmed Xq28 microdeletion involving AVPR2 and L1CAM, derived from mother with mosaicism of the deletion. No pathogenic variants were identified in the paternal X allele nor in AQP2, another causative gene of NDI. XCI was exclusively skewed toward the maternal X chromosome in hair, oral mucosa, and blood, while it was random in nails and renal tubular epithelial cells (RTECs). Both AVPR2 and L1CAM mRNA expression in the patient's RTECs were significantly reduced compared to those of controls, with AVPR2 showing a more pronounced decrease. Thus, we demonstrated for the first time that NDI can develop in a female with a AVPR2 deletion despite of random XCI. Moreover, the absence of L1 syndrome in the female patient was caused most probably through organ-dependent skewed XCI in the deletion allele.