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Open access

Alejandro García-Castaño, Leire Madariaga, Sharona Azriel, Gustavo Pérez de Nanclares, Idoia Martínez de LaPiscina, Rosa Martínez, Inés Urrutia, Aníbal Aguayo, Sonia Gaztambide and Luis Castaño

Summary

Familial hypocalciuric hypercalcemia type I is an autosomal dominant disorder caused by heterozygous loss-of-function mutations in the CASR gene and is characterized by moderately elevated serum calcium concentrations, low urinary calcium excretion and inappropriately normal or mildly elevated parathyroid hormone (PTH) concentrations. We performed a clinical and genetic characterization of one patient suspected of familial hypocalciuric hypercalcemia type I. Patient presented persistent hypercalcemia with normal PTH and 25-hydroxyvitamin D levels. The CASR was screened for mutations by PCR followed by direct Sanger sequencing and, in order to detect large deletions or duplications, multiplex ligation-dependent probe amplification (MLPA) was used. One large deletion of 973 nucleotides in heterozygous state (c.1733-255_2450del) was detected. This is the first large deletion detected by the MLPA technique in the CASR gene.

Learning points:

  • Molecular studies are important to confirm the differential diagnosis of FHH from primary hyperparathyroidism.

  • Large deletions or duplications in the CASR gene can be detected by the MLPA technique.

  • Understanding the functional impact of the mutations is critical for leading pharmacological research and could facilitate the therapy of patients.

Open access

C E Stiles, R Thuraisingham, D Bockenhauer, L Platts, A V Kumar and M Korbonits

Summary

29-year-old female presenting with an 8-year history of unexplained hypomagnesaemia, which was severe enough to warrant intermittent inpatient admission for intravenous magnesium. Urinary magnesium was inappropriately normal in the context of hypomagnesaemia indicating magnesium wasting. Ultrasound imaging demonstrated unilateral renal cysts and computed tomography of kidneys, ureters and bladder showed a bicornuate uterus. Referral to genetic services and subsequent testing revealed a de novo HNF1B deletion.

Learning points:

  • HNF1B loss-of-function mutations are one of the most common monogenic causes of congenital anomalies of the kidney and urinary tract.

  • Those with HNF1B mutations may have some of a constellation of features (renal and hepatic cysts, deranged liver function tests, maturity onset diabetes of the young type 5 (MODY5), bicornuate uterus, hyperparathyroidism, hyperuricaemic gout, but presenting features are highly heterogeneous amongst patients and no genotype/phenotype correlation exists.

  • HNF1B mutations are inherited in an autosomal dominant pattern but up to 50% of cases are de novo.

  • HNF1B mutations can be part of the Chr17q12 deletion syndrome, a contiguous gene deletion syndrome.

  • Inorganic oral magnesium replacements are generally poorly tolerated with side effects of diarrhoea. Organic magnesium compounds, such as magnesium aspartate, are better absorbed oral replacement therapies.

Open access

Katsumi Taki, Takahiko Kogai, Junko Sakumoto, Takashi Namatame and Akira Hishinuma

Summary

A de novo heterozygous inactivating mutation of calcium-sensing receptor (CASR) gene typically causes neonatal hyperparathyroidism (NHPT) with moderate hypercalcemia and hyperparathyroid bone disease. We present a case of asymptomatic hypocalciuric hypercalcemia with a de novo heterozygous mutation in CASR, S591C, which is primarily reported to be responsible for NHPT. A 54-year-old female was referred for investigation of asymptomatic hypercalcemia that was initially found in the 1980s but without a history of bone disease during the perinatal period. She had moderate hypercalcemia (12.4 mg/dl) and relative hypocalciuria (fractional extraction of calcium 1.07%) but normal intact parathyroid hormone and serum 1,25-dihydroxyvitamin D3. Pedigree analysis revealed that she carried a de novo heterozygous mutation of S591C, which she transmitted to an affected child with moderate hypercalcemia but not to other children, who had normal serum calcium levels. A de novo heterozygous CASR mutation that is responsible for NHPT may also present in individuals with asymptomatic hypocalciuric hypercalcemia. Caution is required when predicting course and outcome in a pedigree with CASR mutation, as well as incidental hypercalcemia, because of its variable phenotypes.

Learning points

  • The phenotype and severity of CASR mutations are thought to be dependent on genotypes.

  • We report an asymptomatic case of the de novo heterozygous S591C mutation in CASR, which has previously been reported as a responsible mutation of NHPT with bone diseases.

  • Variable phenotypes of CASR raise a cautionary note about predicting outcome by genotyping in a pedigree with CASR mutation.