Prenatal lethality of a homozygous null mutation in the human glucocerebrosidase gene

Abstract

The complete spectrum of clinical phenotypes resulting from glucocerebrosidase deficiency continues to evolve. While most patients with Gaucher disease have residual glucocerebrosidase activity, we describe a fetus with severe prenatal lethal type 2 (acute neuronopathic) Gaucher disease lacking glucocerebrosidase activity. This 22-week fetus was the result of a first cousin marriage and had hydrops, external abnormalities, hepatosplenomegaly, and Gaucher cells in several organs. Fetal fibroblast DNA was screened for common Gaucher mutations, none of which was detected. Southern blot analysis using the restriction enzymes SstII and SspI ruled out a fusion gene, deletion, or duplication of either allele, and quantitative studies of SspI digested genomic DNA indicated that both alleles were present. Northern blot analysis of total RNA from fetal fibroblasts demonstrated no detectable transcription, although RT-PCR successfully amplified several exons, suggesting the presence of a very unstable mRNA. Direct PCR sequencing of all exons demonstrated a homozygous frameshift mutation (deletion of a C) on codon 139 in exon 5, thereby introducing a premature termination codon in exon 6. The absence of glucocerebrosidase protein was confirmed by Western analysis. This unique case confirms the essential role of glucocerebrosidase in human development and, like the null allele Gaucher mouse, demonstrates the lethality of a homozygous null mutation. The presence of this novel mutation and the resulting unstable mRNA accounts for the severity of the phenotype observed in this fetus, and contributes to the understanding of genotype/phenotype correlation in Gaucher disease.

Is the perinatal lethal form of Gaucher disease more common than classic type 2 Gaucher disease?

“…One such case, a fetus delivered at 22 weeks of gestation to a first cousin couple in Rotterdam, presented with hydrops, dysmorphic features, and hepatosplenomegaly and had a complete absence of glucocerebrosidase activity. 6 We now describe three additional cases of severe type 2 Gaucher disease seen at the same medical center in Rotterdam. Greater awareness of this dramatic phenotype may improve clinical recognition and permit timely genetic counseling.…”

“…[1][2][3][4][5][6][7] Three types of Gaucher disease are recognized: type 1 or non-neuronopathic, type 2 or acute neuronopathic, and type 3 or subacute neuronopathic. Type 2 is the most rare and rapidly progressive type and is classically diagnosed when an infant is several months old and has failure to thrive, hepatosplenomegaly and developmental delay.…”

Non–pseudogene-derived complex acid β-glucosidase mutations causing mild type 1 and severe type 2 Gaucher disease

“…Presumably, the severe type 2 neonatal form of GD is caused by very severe mutations that render the enzyme essentially nonfunctional and/or unstable (5,(24)(25)(26)(27)(28)(29)(30)(31)(32)(33). However, the causative genotype has not been defined in most of these cases (5,(24)(25)(26)(27).…”

“…However, the causative genotype has not been defined in most of these cases (5,(24)(25)(26)(27). In fact, the complete genotype of only one patient with documented skin abnormalities has been determined: homozygosity for the complex mutation RecNciI (5,26).…”

Mice with type 2 and 3 Gaucher disease point mutations generated by a single insertion mutagenesis procedure (SIMP)

“…Homozygosity for a GC null mutation has been shown to result in prenatal lethality in humans (6). GC knockout mice with a total enzyme deficiency die within 24 hr after birth with glucosylceramide storage in brain and liver and severe epidermal abnormalities (7,8).…”