Gaucher disease, the most common lysosomal storage disorder, encompasses a wide spectrum of clinical symptoms. The perinatal lethal form is very rare and is considered a distinct form of classic type 2 Gaucher disease. Prominent features of the severe perinatal form are hepatosplenomegaly variable, associated with hydrops fetalis and ichthyosis. Here, we describe a child who presented generalized ichthyosis and died at 25 days of age. Genotype analysis revealed compound heterozygosity for the complex allele [L444P;E326K] and mutation P182L, described for the first time in this patient. Mutations E326K and L444P were on the same chromosome. Expression studies of mutant glucocerebrosidases showed that the double mutant allele had lower activity, 8.5% of wild type, in contrast to the activity of individual E326K and L444P mutant enzymes, 42.7% and 14.1%, respectively. The P182L mutant enzyme showed no glucocerebrosidase activity. A revision of the genotypes identified in a series of Spanish patients with type 2 Gaucher disease showed that the complex allele [L444P;E326K] accounted for 19.2% of patient alleles and that homozygosity for this allele or its heterozygosity with mutation L444P, or another severe mutation such as P182L, was associated with the perinatal lethal presentation of the disease. In contrast, the [L444P;E326K] allele was not detected in patients with classic type 2 diagnosed when several months old. The high frequency of the E326K substitution observed in patients with type 2 as compared to the general population (0.5%) suggests that this change may have a modulating negative effect on the clinical condition of these Gaucher disease patients when present in combination with mutation L444P. The relatively high prevalence of the double mutant allele in Spanish patients prompted us to perform a haplotype analysis, using four polymorphic markers, which suggest a common origin for this allele. During the mutational analysis of the series of type 2 patients, a novel mutation, I260T (c.896T>C), was identified.