Type 2 Gaucher disease: phenotypic variation and genotypic heterogeneity.

Gaucher disease (GD), the most common lysosomal storage disease, results from a deficiency of the lysosomal enzyme glucocerebrosidase. GD has been classified into 3 types, of which type 2 (the acute neuronopathic form) is the most severe, presenting pre- or perinatally, or in the first few months of life. Traditionally, type 2 GD was considered to have the most uniform clinical phenotype when compared to other GD subtypes. However, case studies over time have demonstrated that type 2 GD, like types 1 and 3, manifests with a spectrum of phenotypes. This review includes case reports that illustrate the broad range of clinical presentations encountered in type 2 GD, as well as a discussion of associated manifestations, pathological findings, diagnostic techniques, and a review of current therapies. While type 2 GD is generally associated with severe mutations in the glucocerebrosidase gene, there is also significant genotypic heterogeneity.

A monozygotic twin pair with highly discordant Gaucher phenotypes.

We describe monozygotic twin sisters, born to consanguineous Moroccan parents, who are highly discordant for the manifestations of Gaucher disease. Both carry Gaucher genotype N188S/N188S. One has severe visceral involvement, epilepsy, and a cerebellar syndrome. Her twin does not manifest any symptoms or signs of Gaucher disease but suffers from type 1 diabetes mellitus. The concurrence of a mild Gaucher mutation with a severe phenotype, as well as the occurrence of highly discordant phenotypes in a pair of monozygotic twins, is discussed.

Mutation of Jak3 in a patient with SCID: essential role of Jak3 in lymphoid development.

Males with X-linked severe combined immunodeficiency (XSCID) have defects in the common cytokine receptor gamma chain (gamma c) gene that encodes a shared, essential component of the receptors of interleukin-2 (IL-2), IL-4, IL-7, IL-9, and IL-15. The Janus family tyrosine kinase Jak3 is the only signaling molecule known to be associated with gamma c, so it was hypothesized that defects in Jak3 might cause an XSCID-like phenotype. A girl with immunological features indistinguishable from those of XSCID was therefore selected for analysis. An Epstein-Barr virus (EBV)-transformed cell line derived from her lymphocytes had normal gamma c expression but lacked Jak3 protein and had greatly diminished Jak3 messenger RNA. Sequencing revealed a different mutation on each allele: a single nucleotide insertion resulting in a frame shift and premature termination in the Jak3 JH4 domain and a nonsense mutation in the Jak3 JH2 domain. The lack of Jak3 expression correlated with impaired B cell signaling, as demonstrated by the inability of IL-4 to activate Stat6 in the EBV-transformed cell line from the patient. These observations indicate that the functions of gamma c are dependent on Jak3 and that Jak3 is essential for lymphoid development and signaling.

The identification of eight novel glucocerebrosidase (GBA) mutations in patients with Gaucher disease.

Mutations in the gene encoding for the lysosomal enzyme glucocerebrosidase (GBA) result in Gaucher disease. In this study, seven novel missense mutations in the glucocerebrosidase gene (A136E, H162P, K198E, Y205C, F251L, Q350X and I402F) and a splice site mutation (IVS10+2T-->A) were identified by direct sequencing of three amplified segments of the glucocerebrosidase gene. Five of the novel mutations were found in patients with neuronopathic forms of Gaucher disease, two of which, K198E and F251L, appear to be associated with type 2 Gaucher disease.

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

In recent years there has been increased recognition of a severe perinatal lethal form of Gaucher disease, the inherited deficiency of lysosomal glucocerebrosidase. We previously reported a case of severe type 2 Gaucher disease which was seen in a medical center in Rotterdam and now present three new cases from two other families seen at the same center. Mutational analyses of these cases revealed two novel mutations, H311R and V398F, located in exons 8 and 9, respectively. The identification of four cases of lethal type 2 Gaucher disease in a single center seems to be a function of increased awareness of this phenotype, rather than of geographic clustering. The actual incidence of lethal type 2 Gaucher disease may be underestimated, as many cases may have been misclassified as collodion babies or hydrops of unknown cause.

Congenital ichthyosis preceding neurologic symptoms in two sibs with type 2 Gaucher disease.

We describe 2 sibs who presented with ichthyotic skin at birth and subsequently developed neurologic manifestations of type 2 Gaucher disease. Type 2 Gaucher patients with and without ichthyosis manifest ultrastructural and biochemical abnormalities in the epidermis. The 2 patients described here clearly demonstrate that epidermal involvement in type 2 Gaucher disease may precede neurologic symptoms and substantiate the prognostic significance of early skin abnormalities in Gaucher patients. Gaucher disease should be considered in the differential diagnosis of congenital ichthyosis, even if the scaling resolves spontaneously.

55-base pair deletion in certain patients with Gaucher disease complicates screening for common Gaucher alleles.

Mutations in the glucocerebrosidase gene which result in Gaucher disease can originate from the highly homologous glucocerebrosidase pseudogene. A 55-bp deletion in exon 9, which corresponds to a 55-bp segment absent from the pseudogene, has been identified in patients with Gaucher disease. We have developed a simple polymerase chain reaction (PCR)-based method to detect this 55-bp deletion, and have found this mutation in 3 of 75 DNA samples (4%) collected from patients with Gaucher disease. Commonly used PCR-based screening methods for specific Gaucher mutations frequently make use of primers either within or surrounding the 55-bp gap to selectively distinguish the glucocerebrosidase gene from the pseudogene. However, if the 55-bp deletion in exon 9 occurs, primers will either fail to produce an amplification product or will produce a shortened product which will be falsely attributed to the pseudogene. This could lead to inaccurate genotyping and genetic counseling for some Gaucher patients and their families. We therefore recommended that laboratories using PCR-based screening techniques involving primers in this region initially determine whether this 55-bp sequence is present.

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

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.

Glucocerebrosidase mutations among African-American patients with type 1 Gaucher disease.

While the inherited deficiency of the enzyme glucocerebrosidase (Gaucher disease) is panethnic in its distribution, there have not been studies of the mutations encountered in specific ethnic groups in the United States, other than those on Ashkenazi Jews. We present the clinical descriptions and genotypes of seven patients of African-American ancestry with type 1 Gaucher disease, and summarize the published literature regarding the genotypes encountered in this population. All seven of the patients had moderate-to-severe manifestations of the disease, and all developed symptoms by adolescence. Genotypic analyses revealed that no two probands shared the same genotype. The common mutations N370S, c.84-85insG, IVS2+1 G-->A, and R463C were not seen. Mutation L444P was present on one allele in each of the patients; but the same mutation was encountered as a single point mutation in three of the patients, and as part of a recombinant allele in four of the patients. Southern blot analyses revealed a glucocerebrosidase fusion allele in one patient, and a duplication resulting from recombination in the region downstream from the glucocerebrosidase gene in three of the patients. Five different point mutations (A90T, R48W, N117D, R170C, and V352L), one deletion mutation (c.222-224 delTAC), and one insertion mutation (c.153-154 insTACAGC) were encountered. Our results demonstrate that there is significant genotypic heterogeneity among African-American patients with type 1 Gaucher disease, and that recombinations in the glucocerebrosidase gene locus are particularly common in this patient group. Published 2001 Wiley-Liss, Inc.

Type 2 Gaucher disease: the collodion baby phenotype revisited.

The association of Gaucher disease, the inherited deficiency of lysosomal glucocerebrosidase (EC 3.2.1.45), and congenital ichthyosis was first noted a decade ago. Subsequently, a null allele type 2 Gaucher mouse was generated that also exhibited ichthyotic skin, confirming that the skin disorder and enzyme deficiency were directly related. This paper details the clinical and molecular characterisation of 6 cases of type 2 Gaucher disease presenting with the collodion baby phenotype. The identified mutant glucocerebrosidase alleles include two novel mutations (S196P and R131L) and two rare point mutations (R120W and R257Q), as well as alleles resulting from recombination with the nearby glucocerebrosidase pseudogene. There is significant genotypic heterogeneity in this rare subset of patients with type 2 Gaucher disease. Gaucher disease should be considered in the differential diagnosis of congenital ichthyosis in the newborn period.

Diagnosing Gaucher disease. Early recognition, implications for treatment, and genetic counseling.

The diagnosis of Gaucher disease, the inherited deficiency of glucocerebrosidase and the most common inherited disorder of Ashkenazi Jews, can often be missed by clinicians. Medical records from patients with Gaucher disease were reviewed, revealing a wide range of initial misdiagnoses and the frequent use of unnecessary invasive diagnostic procedures. The diagnosis of Gaucher disease is readily established by enzymatic or DNA analyses in conjunction with a thorough history and physical examination. Consequently, greater awareness of the symptoms encountered in these patients could alleviate unnecessary anxiety, testing, and confusion. A definitive diagnosis of Gaucher disease has important implications for genetic counseling and treatment.

Gene rearranagement on 1q21 introducing a duplication of the glucocerebrosidase pseudogene and a metaxin fusion gene.

The genes for glucocerebrosidase and metaxin, both located on chromosome 1q21, each have a highly homologous pseudogene sequence nearby. We describe a novel recombinant allele consisting of a duplication of the glucocerebrosidase pseudogene and a fusion between the metaxin gene and its pseudogene, resulting from a crossover between metaxin and pseudometaxin in the region downstream of the glucocerebrosidase gene. We also show that certain individuals have a metaxin-pseudometaxin fusion gene without a duplication, resulting from the same crossover. DNA from patients with Gaucher disease and normal controls were screened for recombinant alleles by Southern blot analyses prepared with the restriction enzymes SspI and HincII and by direct sequencing. Downstream alterations were identified in eight of the 398 patient alleles studied and in seven of the 200 normal control alleles examined, and were encountered more frequently among patients and controls of African-American ancestry. This is the first recognition of a duplicated allele in the glucocerebrosidase gene region, and its presence may contribute to genotype-phenotype studies in Gaucher disease.

Genotype D399N/R463C in a patient with type 3 Gaucher disease previously assigned genotype N370S/R463C.

A patient with type 3 Gaucher disease is described with a novel genotype, D399N/R463C, established by DNA sequencing. This patient was previously reported as having genotype N370S/R463C. This communication now establishes that no patients reported with mutation N370S have the neuronopathic forms of Gaucher disease and has important implications for genetic counseling.

Glucocerebrosidase gene mutations in patients with type 2 Gaucher disease.

Gaucher disease, the most common lysosomal storage disorder, results from the inherited deficiency of the enzyme glucocerebrosidase. Three clinical types are recognized: type 1, non-neuronopathic; type 2, acute neuronopathic; and type 3, subacute neuronopathic. Type 2 Gaucher disease, the rarest type, is progressive and fatal. We have performed molecular analyses of a cohort of 31 patients with type 2 Gaucher disease. The cases studied included fetuses presenting prenatally with hydrops fetalis, infants with the collodion baby phenotype, and infants diagnosed after several months of life. All 62 mutant glucocerebrosidase (GBA) alleles were identified. Thirty-three different mutant alleles were found, including point mutations, splice junction mutations, deletions, fusion alleles and recombinant alleles. Eleven novel mutations were identified in these patients: R131L, H255Q, R285H, S196P, H311R, c.330delA, V398F, F259L, c.533delC, Y304C and A190E. Mutation L444P was found on 25 patient alleles. Southern blots and direct sequencing demonstrated that mutation L444P occurred alone on 9 alleles, with E326K on one allele and as part of a recombinant allele on 15 alleles. There were no homozygotes for point mutation L444P. The recombinant alleles that included L444P resulted from either reciprocal recombination or gene conversion with the nearby glucocerebrosidase pseudogene, and seven different sites of recombination were identified. Homozygosity for a recombinant allele was associated with early lethality. We have also summarized the literature describing mutations associated with type 2 disease, and list 50 different mutations. This report constitutes the most comprehensive molecular study to date of type 2 Gaucher disease, and it demonstrates that there is significant phenotypic and genotypic heterogeneity among patients with type 2 Gaucher disease. Hum Mutat 15:181-188, 2000. Published 2000 Wiley-Liss, Inc.

Identification of three additional genes contiguous to the glucocerebrosidase locus on chromosome 1q21: implications for Gaucher disease.

Gaucher disease results from the deficiency of the lysosomal enzyme glucocerebrosidase (EC 3.2.1.45). Although the functional gene for glucocerebrosidase (GBA) and its pseudogene (psGBA), located in close proximity on chromosome 1q21, have been studied extensively, the flanking sequence has not been well characterized. The recent identification of human metaxin (MTX) immediately downstream of psGBA prompted a closer analysis of the sequence of the entire region surrounding the GBA gene. We now report the genomic DNA sequence and organization of a 75-kb region around GBA, including the duplicated region containing GBA and MTX. The origin and endpoints of the duplication leading to the pseudogenes for GBA and MTX are now clearly established. We also have identified three new genes within the 32 kb of sequence upstream to GBA, all of which are transcribed in the same direction as GBA. Of these three genes, the gene most distal to GBA is a protein kinase (clk2). The second gene, propin1, has a 1.5-kb cDNA and shares homology to a rat secretory carrier membrane protein 37 (SCAMP37). Finally, cote1, a gene of unknown function lies most proximal to GBA. The possible contributions of these closely arrayed genes to the more atypical presentations of Gaucher disease is now under investigation.

cDNA cloning and characterization of the human interleukin 13 receptor alpha chain.

We have cloned cDNAs corresponding to the human interleukin 13 receptor alpha chain (IL-13Ralpha). The protein has 76% homology to murine IL-13Ralpha, with 95% amino acid identity in the cytoplasmic domain. Only weak IL-13 binding activity was found in cells transfected with only IL-13Ralpha; however, the combination of both IL-13Ralpha and IL-4Ralpha resulted in substantial binding activity, with a Kd of approximately 400 pM, indicating that both chains are essential components of the IL-13 receptor. Whereas IL-13Ralpha serves as an alternative accessory protein to the common cytokine receptor gamma chain (gammac) for IL-4 signaling, it could not replace the function of gammac in allowing enhanced IL-2 binding activity. Nevertheless, the overall size and length of the cytoplasmic domain of IL-13Ralpha and gammac are similar, and like gammac, IL-13Ralpha is located on chromosome X.

Gaucher disease and parkinsonism: a phenotypic and genotypic characterization.

Among the many phenotypes associated with Gaucher disease, the inherited deficiency of glucocerebrosidase, are reports of patients with parkinsonian symptoms. The basis for this association is unknown, but could be due to alterations in the gene or gene region. The human glucocerebrosidase gene, located on chromosome 1q21, has a nearby pseudogene that shares 96% identity. Immediately adjacent to the glucocerebrosidase pseudogene is a convergently transcribed gene, metaxin, which has a pseudogene that is located just downstream to the glucocerebrosidase gene. We describe a patient with mild Gaucher disease but impaired horizontal saccadic eye movements who developed a tremor at age 42, followed by rapid deterioration of her gait. A pallidotomy at age 47 was unsuccessful. Her motor and cognitive deterioration progressed despite enzyme replacement therapy. Sequencing of the glucocerebrosidase gene identified mutations L444P and D409H. Southern blot analysis using the enzyme SspI showed that the maternal allele had an additional 17-kb band. PCR amplifications and sequencing of this fragment demonstrated a duplication which included the glucocerebrosidase pseudogene, metaxin gene, and a pseudometaxin/metaxin fusion. Gene alterations associated with this novel rearrangement, resulting from a crossover between the gene for metaxin and its pseudogene, could contribute to the atypical phenotype encountered in this patient.