Rare compound heterozygosity for IVS2 +1G>A and R170P in an Italian patient with Gaucher disease type 1

To the Editor: Gaucher disease (GD), the inherited deficiency of the enzyme glucocerebrosidase (EC 3.2.1.45), is characterized by broad genotypic and phenotypic heterogeneity. The clinical phenotypes of patients with GD, ranging from severely affected infants to asymptomatic adults, have been traditionally divided into three major groups on the basis of the absence (type 1) or the presence and severity of primary involvement of the central nervous system (type 2 and type 3) (1). The gene encoding glucocerebrosidase (GBA; GenBank/EMBL accession no.: J03059) is located on chromosome 1q21 and contains 11 exons; 16kb downstream of the active gene there is a highly (96%) homologous pseudogene (2). To date, more than 200 mutations, including point mutations, deletions, insertions, splicing aberrations and various rearrangements, have been identified within the GBA gene, and attempts to correlate the genotype to the phenotype have been the objective of several studies (3–7). In an Italian patient with GD type I we demonstrated a rare compound heterozygosity for mutations IVS2 þ1G>A and R170P. He was a male born to non-consanguineous parents and had a negative family history. At 6 years of age, he showed the first clinical manifestations of GD, consisting of splenomegaly associated with anaemia and thrombocytopenia. At the same age the patient underwent total splenectomy because of progressive organomegaly, requiring repeated platelet transfusions. At that time, the diagnosis of GD was considered by detection of specific storage cells and was confirmed by glucocerebrosidase deficiency in leucocytes. Two years later, the patient began to suffer from bone pain at the hip and in his hands and legs. In subsequent years the clinical conditions were stationary; his statural growth andmental development were normal. Seven years ago, at 33 years of age, enzymereplacement therapy was initiated at a dose of 60U/kg of imilglucerase every 2weeks, with a significant improvement of anaemia, and a decrease in tiredness as well as in chronic bone pain. Now the patient is 40 years old, married and has one unaffected son. At clinical evaluation he presents with only a diffuse yellow/brown cutaneous pigmentation. Haematological parameters are normal, without anaemia or thrombocytopenia. Bone marrow magnetic resonance imaging (MRI) does not show any infiltration. Liver function is normal, but increased levels of gammaglutamyltransferase and mild hyperbilirubinaemia are present. Pulmonary studies based on posteroanterior and lateral chest radiographs and on pulmonary function tests are normal. Electrophysiological studies, including electroencephalogram (EEG), visual-evoked potentials, median and tibial nerve somatosensory-evoked potentials and brainstem auditory-evoked potentials, are normal. Molecular analysis of the patient’s GBA gene was performed on genomic DNA extracted from peripheral leucocytes using standard methods. The GBA scanning, by single-strand conformation polymorphism (SSCP) analysis, revealed mobility shifts in two genomic regions: the first localized in the sequence spanning exon 2; and the second localized in the sequence spanning exon 6 (Table 1). In order to characterize the nature of these alterations at the genetic level, the DNA fragments of the GBA gene encompassing exon 2, exon 6 and their flanking intronic sequences were amplified by the polymerase chain reaction (PCR) and sequenced. Two different mutations were found: the first was the panethnic IVS2 þ 1G>A causing an aberrant splicing with consequent production of nonfunctional truncated protein (8); the second mutation was the G to C transversion predicting the non-conservative replacement of proline with arginine at codon 170 (R170P). The presence of mutation R170P in the heterozygous form was Clin Genet 2003: 64: 261–262 Copyright # Blackwell Munksgaard 2003 Printed inDenmark. All rights reserved CLINICALGENETICS ISSN 0009-9163