title: Hypomagnesemia with secondary hypocalcemia in a female with balanced X;9 translocation: mapping of the Xp22 chromosome breakpoint.
abstract: Magnesium-dependent hypocalcaemia (HSH), a rare inherited disease, is caused by selective disorders of magnesium absorption. Both X-linked and autosomal recessive modes of inheritance have been reported for HSH; this suggests a genetically heterogeneous condition. A balanced de novo t(X;9)(p22;q12) translocation has been reported in a female manifesting hypomagnesemia with secondary hypocalcemia. In a lymphoblastoid cell line, derived from this patient, the normal X chromosome is preferentially inactivated, suggesting that the patient's phenotype is caused by disruption of an HSH gene in Xp22. In an attempt to define more precisely the position of the X breakpoint, we have constructed a hybrid cell line retaining the der(X)(Xqter-Xp22.2::9q12-9qter) in the absence of the der(9) and the normal X chromosome. Southern blot analysis of this hybrid and in situ hybridization on metaphase chromosomes have localized the breakpoint between DXS16 and the cluster (DXS207, DXS43), in Xp22.2. Thus, if a gene involved in HSH residues at or near the translocation breakpoint, our findings should greatly facilitate its isolation.
authors.affiliation: Laboratoire de Génétique des Eucaryotes du CNRS, Unité 184 de Biologie Moléculaire et de Génie Génétique de l'INSERM, Faculté de Médicine, Strasbourg, France.
authors.forename: M
authors.initials: M
authors.lastname: Chery
authors.forename: V
authors.initials: V
authors.lastname: Biancalana
authors.forename: C
authors.initials: C
authors.lastname: Philippe
authors.forename: G
authors.initials: G
authors.lastname: Malpuech
authors.forename: H
authors.initials: H
authors.lastname: Carla
authors.forename: S
authors.initials: S
authors.lastname: Gilgenkrantz
authors.forename: J L
authors.initials: JL
authors.lastname: Mandel
authors.forename: A
authors.initials: A
authors.lastname: Hanauer
mesh_terms: D015139:Blotting, Southern; D002472:Cell Transformation, Viral; D002869:Chromosome Aberrations; D002874:Chromosome Mapping; D002899:Chromosomes, Human, Pair 9; D005260:Female; D006801:Humans; D006996:Hypocalcemia / Q000150:complications / Q000235:genetics*; D017403:In Situ Hybridization; D008275:Magnesium Deficiency / Q000150:complications / Q000235:genetics*; D014178:Translocation, Genetic; D014960:X Chromosome