title: Severe combined immunodeficiency and microcephaly in siblings with hypomorphic mutations in DNA ligase IV.
abstract: DNA double-strand breaks (dsb) during V(D)J recombination of T and B lymphocyte receptor genes are resolved by the non-homologous DNA end joining pathway (NHEJ) including at least six factors: Ku70, Ku80, DNA-PK(cs), Artemis, Xrcc4, and DNA ligase IV (Lig4). Artemis and Lig4 are the only known V(D)J/NHEJ factors found deficient in human genetic disorders. Null mutations of the Artemis gene result in a complete absence of T and B lymphocytes and increased cellular sensitivity to ionizing radiations, causing radiosensitive-SCID. Mutations of Lig4 are exclusively hypomorphic and have only been described in six patients, four exhibiting mild immunodeficiency associated with microcephaly and developmental delay, while two patient had leukemia. Here we report a SCID associated with microcephaly caused by compound heterozygous hypomorphic mutations in Lig4. Residual activity of Lig4 in these patients is underscored by a normal pattern of TCR-alpha and -beta junctions in the T cells of the patients and a moderate impairment of V(D)J recombination as tested in vitro. These observations contrast with the severity of the clinical immunodeficiency, suggesting that Lig4 may have additional critical roles in lymphocyte survival beyond V(D)J recombination.
authors.affiliation: INSERM, Hôpital Necker Enfants-Malades, U429, Unité Développement Normal et Pathologique du Système Immunitaire, Paris, France.
authors.forename: Dietke
authors.initials: D
authors.lastname: Buck
authors.forename: Despina
authors.initials: D
authors.lastname: Moshous
authors.forename: Régina
authors.initials: R
authors.lastname: de Chasseval
authors.forename: Yunmei
authors.initials: Y
authors.lastname: Ma
authors.forename: Françoise
authors.initials: F
authors.lastname: le Deist
authors.forename: Marina
authors.initials: M
authors.lastname: Cavazzana-Calvo
authors.forename: Alain
authors.initials: A
authors.lastname: Fischer
authors.forename: Jean-Laurent
authors.initials: JL
authors.lastname: Casanova
authors.forename: Michael R
authors.initials: MR
authors.lastname: Lieber
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: de Villartay
mesh_terms: D001483:Base Sequence; D015153:Blotting, Western; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000235:genetics*; D005260:Female; D015322:Gene Rearrangement, B-Lymphocyte; D015329:Gene Rearrangement, T-Lymphocyte; D006801:Humans; D007135:Immunoglobulin Variable Region; D008297:Male; D008831:Microcephaly / Q000150:complications / Q000235:genetics*; D008969:Molecular Sequence Data; D009154:Mutation; D010375:Pedigree; D011836:Radiation Tolerance; D016511:Severe Combined Immunodeficiency / Q000150:complications / Q000235:genetics*
chemical_list: D007135:Immunoglobulin Variable Region; C000607893:LIG4 protein, human; D011088:DNA Ligases; D000072481:DNA Ligase ATP