Structure of the SLC7A7 Gene and Mutational Analysis of Patients Affected by Lysinuric Protein Intolerance

Abstract

Lysinuric protein intolerance (LPI) is a rare autosomal recessive defect of cationic amino acid transport caused by mutations in the SLC7A7 gene. We report the genomic structure of the gene and the results of the mutational analysis in Italian, Tunisian, and Japanese patients. The SLC7A7 gene consists of 10 exons; sequences of all of the exon-intron boundaries are reported here. All of the mutant alleles were characterized and eight novel mutations were detected, including two missense mutations, 242A-->C (M1L) and 1399C-->A (S386R); a nonsense mutation 967G-->A (W242X); two splice mutations IVS3 +1G-->A and IVS6 +1G-->T; a single-base insertion, 786insT; and two 4-bp deletions, 455delCTCT and 1425delTTCT. In addition, a previously reported mutation, 1625insATCA, was found in one patient. It is noteworthy that 242A-->C causes the change of Met1 to Leu, a rare mutational event previously found in a few inherited conditions. We failed to establish a genotype/phenotype correlation. In fact, both intrafamilial and interfamilial phenotypic variability were observed in homozygotes for the same mutation. The DNA-based tests are now easily accessible for molecular diagnosis, genetic counseling, and prenatal diagnosis of LPI.

Novel SLC7A7 large rearrangements in lysinuric protein intolerance patients involving the same AluY repeat

“…Mutational screening of the whole coding region and all intron/exon boundaries was performed by PCR and direct sequencing, with PCR conditions and primers reported earlier. 3 The promoter localized in intron 1, which is the active promoter in tissues with strong defects in LPI patients, 16 was also amplified with primers (5 0 -CTGGCCTGATTTCCTCATATT-3 0 ) and [5 0 -GAGGGTTAGCAAGGTAAGTGG-3 0 ), following standard methods. The reaction started with an initial denaturation of 5 min at 941C, followed by 36 cycles of 941C 30 s, 581C 30 s, 741C 1 min and 5 min at 741C.…”

“…12 -15 It contains 11 exons (9 coding exons), 10 introns and two promoter regions spanning B46.5 kb of the genomic DNA. 3,4,16 The cDNA is 2477 bp long with a 527 bp 5 0 -UTR and a 385 bp 3 0 -UTR, with a polyA site located at 2447. 6 It encodes the y þ LAT1 protein (RefSeq: NP_003973), which has 511 predicted amino acids and a molecular weight of B56 kDa.…”

A y+LAT-1 mutant protein interferes with y+LAT-2 activity: implications for the molecular pathogenesis of lysinuric protein intolerance

“…9 Direct sequencing was carried out on PCR products and both strands were sequenced by an automated system (ABI 377 DNA, Applied Biosystems, Monza, Italy).…”

“…The variability of the phenotype cannot be explained by either a straightforward correlation with the genotype or variable compliance to the therapy. 9,10 For example, two of the most severe genotypes reported so far, that is, homozygosity for a large deletion of the gene (patient IV-2, family 1 in Borsani et al 2 ) or homozygosity for the M1L mutation (patients 1A and 1B in Sperandeo et al 9 ), both of which result in absent protein, were found in patients with a very mild phenotype under treatment. The ubiquitous expression of SLC7A6 and the overlapping transport activity suggest that y þ LAT-2 may compensate when y þ LAT-1 is defective.…”

Lysinuric protein intolerance: identification and functional analysis of mutations of the SLC7A7 gene

“…All exons and intron-exon boundaries of the SLC7A7 gene were amplified from genomic DNA extracted from peripheral blood samples of all family members as previously reported (Sperandeo et al, 2000). Direct sequencing was performed on two distinct PCR products, and both strands were sequenced by an automated system (ABI 377 DNA, Applied Biosystems, Monza, Italy).…”