title: Novel TRPM6 mutations in 21 families with primary hypomagnesemia and secondary hypocalcemia.
abstract: Primary hypomagnesemia with secondary hypocalcemia is a rare autosomal recessive disorder characterized by profound hypomagnesemia associated with hypocalcemia. Pathophysiology is related to impaired intestinal absorption of magnesium accompanied by renal magnesium wasting as a result of a reabsorption defect in the distal convoluted tubule. Recently, mutations in the TRPM6 gene coding for TRPM6, a member of the transient receptor potential (TRP) family of cation channels, were identified as the underlying genetic defect. Here, the results of a TRPM6 mutational analysis of 21 families with 28 affected individuals are presented. In this large patient cohort, a retrospective clinical evaluation based on a standardized questionnaire was also performed. Genotype analysis revealed TRPM6 mutations in 37 of 42 expected mutant alleles. Sixteen new TRPM6 mutations were identified, including stop mutations, frame-shift mutations, splice-site mutations, and deletions of exons. Electrophysiologic analysis of mutated ion channels after heterologous expression in Xenopus oocytes proved complete loss of function of TRPM6. Clinical evaluation revealed a homogeneous clinical picture at manifestation with onset in early infancy with generalized cerebral convulsions. Initial laboratory evaluation yielded extremely low serum magnesium levels, low serum calcium levels, and inadequately low parathyroid hormone levels. Treatment usually consisted of acute intravenous magnesium supplementation leading to relief of clinical symptoms and normocalcemia, followed by lifelong oral magnesium supplementation. Serum magnesium levels remained in the subnormal range despite adequate therapy. This is best explained by a disturbed magnesium conservation in the distal convoluted tubule, which emerged in all patients upon magnesium supplementation. Delay of diagnosis resulted in permanent neurologic damage in three patients.
authors.affiliation: University Children's Hospital Marburg, Deutschhausstrasse 12, 35037 Marburg, Germany. schlingm@staff.uni-marburg.de
authors.forename: Karl P
authors.initials: KP
authors.lastname: Schlingmann
authors.forename: Martin C
authors.initials: MC
authors.lastname: Sassen
authors.forename: Stefanie
authors.initials: S
authors.lastname: Weber
authors.forename: Ulla
authors.initials: U
authors.lastname: Pechmann
authors.forename: Kerstin
authors.initials: K
authors.lastname: Kusch
authors.forename: Lutz
authors.initials: L
authors.lastname: Pelken
authors.forename: Daniel
authors.initials: D
authors.lastname: Lotan
authors.forename: Maria
authors.initials: M
authors.lastname: Syrrou
authors.forename: Jeffrey J
authors.initials: JJ
authors.lastname: Prebble
authors.forename: David E C
authors.initials: DE
authors.lastname: Cole
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Metzger
authors.forename: Shamima
authors.initials: S
authors.lastname: Rahman
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Tajima
authors.forename: San-Ging
authors.initials: SG
authors.lastname: Shu
authors.forename: Siegfried
authors.initials: S
authors.lastname: Waldegger
authors.forename: Hannsjoerg W
authors.initials: HW
authors.lastname: Seyberth
authors.forename: Martin
authors.initials: M
authors.lastname: Konrad
mesh_terms: D004252:DNA Mutational Analysis; D005260:Female; D006801:Humans; D006996:Hypocalcemia / Q000150:complications / Q000235:genetics*; D007223:Infant; D007231:Infant, Newborn; D008274:Magnesium / Q000097:blood / Q000378:metabolism*; D008297:Male; D008659:Metabolic Diseases / Q000150:complications / Q000235:genetics*; D009154:Mutation; D010375:Pedigree; D012189:Retrospective Studies; D050053:TRPM Cation Channels / Q000235:genetics*
chemical_list: D050053:TRPM Cation Channels; C459082:TRPM6 protein, human; D008274:Magnesium