CNNM2 mutations cause impaired brain development and seizures in patients with hypomagnesemia.
Intellectual disability and seizures are frequently associated with hypomagnesemia and have an important genetic component. However, to find the genetic origin of intellectual disability and seizures often remains challenging because of considerable genetic heterogeneity and clinical variability. In this study, we have identified new mutations in CNNM2 in five families suffering from mental retardation, seizures, and hypomagnesemia. For the first time, a recessive mode of inheritance of CNNM2 mutations was observed. Importantly, patients with recessive CNNM2 mutations suffer from brain malformations and severe intellectual disability. Additionally, three patients with moderate mental disability were shown to carry de novo heterozygous missense mutations in the CNNM2 gene. To elucidate the physiological role of CNNM2 and explain the pathomechanisms of disease, we studied CNNM2 function combining in vitro activity assays and the zebrafish knockdown model system. Using stable Mg(2+) isotopes, we demonstrated that CNNM2 increases cellular Mg2+ uptake in HEK293 cells and that this process occurs through regulation of the Mg(2+)-permeable cation channel TRPM7. In contrast, cells expressing mutated CNNM2 proteins did not show increased Mg(2+) uptake. Knockdown of cnnm2 isoforms in zebrafish resulted in disturbed brain development including neurodevelopmental impairments such as increased embryonic spontaneous contractions and weak touch-evoked escape behaviour, and reduced body Mg content, indicative of impaired renal Mg(2+) absorption. These phenotypes were rescued by injection of mammalian wild-type Cnnm2 cRNA, whereas mammalian mutant Cnnm2 cRNA did not improve the zebrafish knockdown phenotypes. We therefore concluded that CNNM2 is fundamental for brain development, neurological functioning and Mg(2+) homeostasis. By establishing the loss-of-function zebrafish model for CNNM2 genetic disease, we provide a unique system for testing therapeutic drugs targeting CNNM2 and for monitoring their effects on the brain and kidney phenotype.
Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands.
Francisco J
FJ
Arjona
Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands.
Jeroen H F
JH
de Baaij
Department of General Pediatrics, University Children's Hospital, Münster, Germany.
Karl P
KP
Schlingmann
Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands.
Anke L L
AL
Lameris
Department of Otorhinolaryngology, Radboud university medical center, Nijmegen, The Netherlands.
Erwin
E
van Wijk
Department of Organismal Animal Physiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Nijmegen, The Netherlands.
Gert
G
Flik
Department of General Pediatrics, University Children's Hospital, Münster, Germany.
Sabrina
S
Regele
Department of Neuropediatrics, Children's Hospital, Oldenburg, Germany.
G Christoph
GC
Korenke
Department of Neuropediatrics, St. Anna Children's Hospital, Medical University Vienna, Vienna, Austria.
Birgit
B
Neophytou
Leibniz Institute of Arteriosclerosis Research, University of Münster, Münster, Germany.
Stephan
S
Rust
Institute of Human Genetics, University of Cologne, Cologne, Germany.
Nadine
N
Reintjes
Department of General Pediatrics, University Children's Hospital, Münster, Germany.
Martin
M
Konrad
Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands.
René J M
RJ
Bindels
Department of Physiology, Radboud Institute for Molecular Life Sciences, Radboud university medical center, Nijmegen, The Netherlands.
Joost G J
JG
Hoenderop
D000293:Adolescent; D000818:Animals; D001921:Brain / Q000378:metabolism*; D027682:Cation Transport Proteins; D002460:Cell Line; D016213:Cyclins / Q000235:genetics*; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008607:Intellectual Disability / Q000235:genetics* / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008274:Magnesium / Q000378:metabolism*; D008297:Male; D020125:Mutation, Missense / Q000235:genetics*; D010641:Phenotype; D012640:Seizures / Q000235:genetics* / Q000378:metabolism; D015027:Zebrafish / Q000235:genetics / Q000378:metabolism
C558175:CNNM2 protein, human; D027682:Cation Transport Proteins; D016213:Cyclins; D008274:Magnesium