Identification of the first large deletion in the CLDN16 gene in a patient with FHHNC and late-onset of chronic kidney disease: case report

Background

Familial hypomagnesemia with hypercalciuria and nephrocalcinosis is a rare autosomal recessive renal disease characterized by tubular disorders at the thick ascending limb of Henle’s loop. It is caused by mutations in the tight junction structural proteins claudin-16 or claudin-19, which are encoded by the CLDN16 and CLDN19 genes, respectively. Patients exhibit excessive wasting of calcium and magnesium, nephrocalcinosis, chronic kidney disease, and early progression to end-stage renal failure during infancy.

Case presentation

We here report the phenotype and molecular analysis of a female Brazilian patient with a novel large homozygous deletion in the CLDN16 gene. The proband, born from consanguineous parents, presented the first symptoms at age 20. Clinical examination revealed hypocalcemia, hypomagnesemia, nephrocalcinosis, mild myopia, high serum levels of uric acid and intact parathyroid hormone, and moderate chronic kidney disease (stage 3). She and her mother were subjected to CLDN16 and CLDN19 mutational analysis. In addition, the multiplex ligation-dependent probe amplification method was used to confirm a CLDN16 multi-exon deletion. Direct sequencing revealed a normal CLDN19 sequence and suggested a large deletion in the CLDN16 gene. Multiplex ligation-dependent probe amplification showed a homozygous CLDN16 multi-exon deletion (E2_E5del). The patient initiated conventional treatment for familial hypomagnesemia with hypercalciuria and nephrocalcinosis and progressed to end-stage kidney disease after five years.

Conclusions

This study provides the first report of a large homozygous deletion in the CLDN16 gene causing familial hypomagnesemia with hypercalciuria and nephrocalcinosis with late onset of the first symptoms. This description expands the phenotypic and genotypic characterization of the disease. The late-onset chronic kidney disease in the presence of a homozygous deletion in the CLDN16 gene reinforces the great variability of genotype-phenotype manifestation in patients with familial hypomagnesemia with hypercalciuria and nephrocalcinosis.

GSTM1, GSTT1, and GSTP1 polymorphisms, breast cancer risk factors and mammographic density in women submitted to breast cancer screening

Genetic polymorphisms in genes related to the metabolism of xenobiotics, such as genes of the glutathione S-transferases (GSTM1, GSTT1, and GSTP1) superfamily have been associated with an increased risk for breast cancer (BC). Considering the high incidence of BC in the city of Porto Alegre in southern Brazil, the purpose of this study was to characterize genotypic and allelic frequencies of polymorphisms in GSTM1, GSTT1, and GSTP1, and correlate these molecular findings with established risk factors for breast cancer including mammographic density, in a sample of 750 asymptomatic women undergoing mammographic screening. Molecular tests were performed using the multiplex polymerase chain reaction (PCR) for GSTM1 and GSTT1, and quantitative PCR for GSTP1 polymorphisms. Overall, the frequencies of GSTM1 and GSTT1 null genotypes were 45% and 21%, respectively. For GSTP1 polymorphism, genotypic frequencies were 44% for the Ile/Ile genotype, 44% for the Ile/Val genotype, and 12% for Val/Val genotype, with an allelic frequency of 66% for the wild type allele in this population, similar to results of previous international publications. There was a statistically significant association between the combined GSTM1 and GSTT1 null genotypes (M-/T-) and mammographic density in post menopausal women (p = 0.031). When the GSTT1 null (T-) genotype was analyzed isolated, the association with mammographic density in post menopausal women and in the overall sample was also statistically significant (p = 0.023 and p = 0.027, respectively). These findings suggest an association of GSTM1 and GSTT1 null genotypes with mammographic density.