title: Alu-Alu Recombination Underlying the First Large Genomic Deletion in GlcNAc-Phosphotransferase Alpha/Beta (GNPTAB) Gene in a MLII Alpha/Beta Patient.
abstract: Mucolipidosis type II α/β is a severe, autosomal recessive lysosomal storage disorder, caused by a defect in the GNPTAB gene that codes for the α/β subunits of the GlcNAc-phosphotransferase. To date, over 100 different mutations have been identified in MLII α/β patients, but no large deletions have been reported. Here we present the first case of a large homozygous intragenic GNPTAB gene deletion (c.3435-386_3602 + 343del897) encompassing exon 19, identified in a ML II α/β patient. Long-range PCR and sequencing methodologies were used to refine the characterization of this rearrangement, leading to the identification of a 21 bp repetitive motif in introns 18 and 19. Further analysis revealed that both the 5' and 3' breakpoints were located within highly homologous Alu elements (Alu-Sz in intron 18 and Alu-Sq2, in intron 19), suggesting that this deletion has probably resulted from Alu-Alu unequal homologous recombination. RT-PCR methods were used to further evaluate the consequences of the alteration for the processing of the mutant pre mRNA GNPTAB, revealing the production of three abnormal transcripts: one without exon 19 (p.Lys1146_Trp1201del); another with an additional loss of exon 20 (p.Arg1145Serfs*2), and a third in which exon 19 was substituted by a pseudoexon inclusion consisting of a 62 bp fragment from intron 18 (p.Arg1145Serfs*16). Interestingly, this 62 bp fragment corresponds to the Alu-Sz element integrated in intron 18.This represents the first description of a large deletion identified in the GNPTAB gene and contributes to enrich the knowledge on the molecular mechanisms underlying causative mutations in ML II.
authors: Research and Development Unit, Department of Genetics, CGMJM, INSA/IPATIMUP, Porto, Portugal.
authors: Maria Francisca
authors: MF
authors: Coutinho
authors: Liliana
authors: L
authors: da Silva Santos
authors: Lúcia
authors: L
authors: Lacerda
authors: Sofia
authors: S
authors: Quental
authors: Flemming
authors: F
authors: Wibrand
authors: Allan M
authors: AM
authors: Lund
authors: Klaus B
authors: KB
authors: Johansen
authors: Maria João
authors: MJ
authors: Prata
authors: Sandra
authors: S
authors: Alves