Marked variation in blood beta-hexosaminidase in Gaucher disease

Cerebrospinal fluid lysosomal enzymes and alpha-synuclein in Parkinson's disease

To assess the discriminating power of multiple cerebrospinal fluid (CSF) biomarkers for Parkinson's disease (PD), we measured several proteins playing an important role in the disease pathogenesis. The activities of β-glucocerebrosidase and other lysosomal enzymes, together with total and oligomeric α-synuclein, and total and phosphorylated tau, were thus assessed in CSF of 71 PD patients and compared to 45 neurological controls. Activities of β-glucocerebrosidase, β-mannosidase, β-hexosaminidase, and β-galactosidase were measured with established enzymatic assays, while α-synuclein and tau biomarkers were evaluated with immunoassays. A subset of PD patients (n = 44) was also screened for mutations in the β-glucocerebrosidase-encoding gene (GBA1). In the PD group, β-glucocerebrosidase activity was reduced (P < 0.05) and patients at earlier stages showed lower enzymatic activity (P < 0.05); conversely, β-hexosaminidase activity was significantly increased (P < 0.05). Eight PD patients (18%) presented GBA1 sequence variations; 3 of them were heterozygous for the N370S mutation. Levels of total α-synuclein were significantly reduced (P < 0.05) in PD, in contrast to increased levels of α-synuclein oligomers, with a higher oligomeric/total α-synuclein ratio in PD patients when compared with controls (P < 0.001). A combination of β-glucocerebrosidase activity, oligomeric/total α-synuclein ratio, and age gave the best performance in discriminating PD from neurological controls (sensitivity 82%; specificity 71%, area under the receiver operating characteristic curve = 0.87). These results demonstrate the possibility of detecting lysosomal dysfunction in CSF and further support the need to combine different biomarkers for improving the diagnostic accuracy of PD.

The biology of the Gaucher cell: the cradle of human chitinases

Gaucher disease (GD) is the most common lysosomal storage disorder and is caused by inherited deficiencies of glucocerebrosidase, the enzyme responsible for the lysosomal breakdown of the lipid glucosylceramide. GD is characterized by the accumulation of pathological, lipid laden macrophages, so-called Gaucher cells. Following the development of enzyme replacement therapy for GD, the search for suitable surrogate disease markers resulted in the identification of a thousand-fold increased chitinase activity in plasma from symptomatic Gaucher patients and that decreases upon successful therapeutic intervention. Biochemical investigations identified a single enzyme, named chitotriosidase, to be responsible for this activity. Chitotriosidase was found to be an excellent marker for lipid laden macrophages in Gaucher patients and is now widely used to assist clinical management of patients. In the wake of the identification of chitotriosidase, the presence of other members of the chitinase family in mammals was discovered. Amongst these is AMCase, an enzyme recently implicated in the pathogenesis of asthma. Chitinases are omnipresent throughout nature and are also produced by vertebrates in which they play important roles in defence against chitin-containing pathogens and in food processing.

Heterozygosity for Tay-Sachs and Sandhoff Diseases in Non-Jewish Americans with Ancestry from Ireland, Great Britain, or Italy

Previous reports have found that non-Jewish Americans with ancestry from Ireland have an increased frequency of heterozygosity for Tay-Sachs disease (TSD), although frequency estimates are substantially different. Our goal in this study was to determine the frequency of heterozygosity for TSD and Sandhoff diseases (SD) among Irish Americans, as well as in persons of English, Scottish, and/or Welsh ancestry and in individuals with Italian heritage, who were referred for determination of their heterozygosity status and who had no known family history of TSD or SD or of heterozygosity for these conditions. Of 610 nonpregnant subjects with Irish background, 24 TSD heterozygotes were identified by biochemical testing, corresponding to a heterozygote frequency of 1 in 25 (4%; 95% CI, 1/39-1/17). In comparison, of 322 nonpregnant individuals with ancestry from England, Scotland, or Wales, two TSD heterozygotes were identified (1 in 161 or 0.62%; 95% CI, 1/328-1/45), and three TSD heterozygotes were ascertained from 436 nonpregnant individuals with Italian heritage (1 in 145 or 0.69%; 95% CI, 1/714-1/50). Samples from 21 Irish heterozygotes were analyzed for HEXA gene mutations. Two (9.5%) Irish heterozygotes had the lethal + 1 IVS-9 G --> A mutation, whereas 9 (42.8%) had a benign pseudodeficiency mutation. No mutation was found in 10 (47.6%) heterozygotes. These data allow for a frequency estimate of deleterious alleles for TSD among Irish Americans of 1 in 305 (95% CI, 1/2517-1/85) to 1 in 41 (95% CI, 1/72-1/35), depending on whether one, respectively, excludes or includes enzyme-defined heterozygotes lacking a defined deleterious mutation. Pseudodeficiency mutations were identified in both of the heterozygotes with ancestry from other countries in the British Isles, suggesting that individuals with ancestry from these countries do not have an increased rate of TSD heterozygosity. Four SD heterozygotes were found among individuals of Italian descent, a frequency of 1 in 109 (0.92%; 95% CI, 1/400-1/43). This frequency was higher than those for other populations, including those with Irish (1 in 305 or 0.33%; 95% CI, 1/252-1/85), English, Scottish, or Welsh (1 in 161 or 0.62%; 95% CI, 1/1328-1/45), or Ashkenazi Jewish (1 in 281 or 0.36%; 95% CI, 1/1361-1/96) ancestry. Individuals of Irish or Italian heritage might benefit from genetic counseling for TSD and SD, respectively.

Relationships between serum markers of monocyte/macrophage activation in type 1 Gaucher's disease

We studied 44 patients with type 1 Gaucher's disease (16 non-treated patients and 28 treated with enzyme replacement therapy). We measured serum levels of chitotriosidase (ChT), neopterin, angiotensin-converting enzyme (ACE), adenosine deaminase (ADA) and beta-hexosaminidase (Hex) and its major isoenzymes Hex A and Hex B. In the untreated group of patients, the increase in serum levels was ChT>neopterin>ACE> ADA>Hex, with all decreasing significantly in treated patients (p< 0.001). Highly significant correlations were obtained between the markers of monocyte/macrophage activation which were tested (p<0.001). However, partial correlations between serum Hex B (with Hex A constant) and ChT, ACE, neopterin and ADA did not reach statistical significance. This suggests that hepatocytes are the major cellular source of this isoenzyme. Similarly, partial correlation of ChT with neopterin, with the other variables constant, was not significant, which would suggest a different expression of these two markers in Gaucher's disease.

Plasma and metabolic abnormalities in Gaucher's disease

An overview of the most important plasma abnormalities that can be found in Gaucher's disease is presented in this chapter. Attention is focussed on their practical applications and possible clinical relevance. In addition, the result of studies on metabolic alterations in Gaucher's disease are reviewed.

Heterozygosity for Tay-Sachs and Sandhoff diseases among Massachusetts residents with French Canadian background

OBJECTIVES

The frequency of Tay-Sachs disease (TSD) heterozygosity is increased among French Canadians in eastern Quebec. A large proportion of the New England population has French Canadian heritage; thus, it is important to determine if they too are at increased risk for TSD heterozygosity. This prospective study was designed to assess the TSD heterozygote frequency among people with French Canadian background living in Massachusetts. A simultaneous screen for heterozygosity for Sandhoff disease, a related genetic disorder, was also undertaken.

METHODS

1260 non-pregnant subjects of French Canadian background were included in the study. beta hexosaminidase activity was measured in blood samples, and results were evaluated for TSD and Sandhoff disease heterozygosity. Samples from the TSD heterozygotes were also subjected to mutation analysis.

RESULTS

Of the 1260 samples studied, 22 (1 in 57; CI 1 in 41, 1 in 98) were identified as TSD heterozygotes by enzymatic analyses and 11 subjects (1 in 114; CI 1 in 72, 1 in 280) were identified as Sandhoff disease heterozygotes. Three of the 22 TSD heterozygotes were found to have benign pseudodeficiency mutations, resulting in a maximum TSD heterozygote frequency of 19 in 1260 (1 in 66; CI 1 in 46, 1 in 120). Together, these data provide a maximum frequency of heterozygosity for TSD or Sandhoff disease of 30 in 1260 (1 in 42; CI 1 in 31, 1 in 64) in this population.

CONCLUSIONS

Simultaneous screening for TSD and Sandhoff disease heterozygosity by assay of beta hexosaminidases A and B activities provides a possible method for use with subjects of French Canadian background. The relevance of some of the novel mutations identified in this group needs further study. However, the comparatively high combined frequency of TSD and Sandhoff disease heterozygosity indicates a need for discussion regarding the appropriateness of carrier testing for these disorders for persons of French Canadian background in Massachusetts.

Assay of serum/plasma beta-N-acetylhexosaminidase isoenzymes by heat inactivation using a continuous spectrophotometric method adapted to a centrifugal analyzer

Activity of serum/plasma beta-N-acetylhexosaminidase (EC 3.2.1.52) was determined by means of a continuous spectrophotometric method using 3,3'-dichlorophenylsulphonphthaleinyl-N-acetyl-beta-D-glucosaminid e as substrate, with very satisfactory results. Incubation of an undiluted aliquot (1 ml) of samples at 52 degrees C for 8 hours with an adjusted pH 5.5-6.0 provoked only the inactivation of isoenzyme A, thus allowing the evaluation of beta-N-acetylhexosaminidase isoenzyme composition. In 25 serum samples from control subjects and pregnant women, a good correlation between the percentage of isoenzyme B obtained by this procedure and the fluorimetric assay of O'Brien et al. (New Engl J Med 1970; 273:15-20) was found (r = 0.983, S(yx) = 1.51), with no statistically significant difference between the means (43.2 vs 42.8%). In 84 healthy adult subjects, an average value of 30.3% for the proportion of isoenzyme B was obtained, with an interval of 25.4-35.0%, in agreement with results reported by other authors.

Plasma hyaluronidase activity in mucolipidoses II and III: marked differences from other lysosomal enzymes

A nearly pathognomonic finding of the lysosomal storage disorders mucolipidoses II and III is the marked increase of plasma lysosomal enzyme activities. The genetic lesion in ML II and III causes defective function of the enzyme UDP-GlcNAc:lysosomal enzyme N-acetylglucosamine-1-phosphotransferase. Defective function of this enzyme results in deficient phosphorylation of lysosomal enzyme asparagine-linked oligosaccharides and a consequent misrouting of many newly synthesized lysosomal enzymes. These enzymes are secreted from cells instead of being targeted to lysosomes, with resultant marked elevations of multiple lysosomal enzyme activities in plasma. We report here that plasma hyaluronidase activity, an endoglycosidase of presumably lysosomal origin, is not increased in the plasma from individuals with mucolipidoses II and III, unlike most lysosomal enzymes. Our data suggest the possibility that hyaluronidase is not targeted to lysosomes by a lysosomal enzyme phosphosmannosyl recognition mechanism. Alternatively, hyaluronidase activity may not be present in the cell type(s) responsible for the lysosomal enzyme hypersecretion in mucolipidoses II and III which, along with its deficiency in fibroblasts and leukocytes, would constitute an unusual tissue distribution of activity for a soluble lysosomal enzyme.

Heterozygosity for Tay-Sachs disease in non-Jewish Americans with ancestry from Ireland or Great Britain

We performed a genetic epidemiological analysis of American non-Jewish people with ancestry from Ireland or Great Britain with regard to heterozgosity for Tay-Sachs disease (TSD). This study was prompted by a recent report that the frequency of heterozygosity for TSD among Irish Americans was 1 in 8, a frequency much higher than that recognised for any other population group. We identified 19 of 576 (3.3%) people of Irish background as TSD heterozygotes by the standard thermolability assay for beta-hexosaminidase A (Hex A) activity. Three of 289 people of non-Irish British Isles background (1%) were also identified as heterozygotes by biochemical testing. Specimens from the biochemically identified Irish heterozygotes were analysed for seven different Hex A alpha subunit gene mutations; three (15.8%) had a lethal +1 IVS-9 G to A mutation, previously noted to be a common mutation among TSD heterozygotes of Irish ancestry. Eight of 19 (42.1%) had one of two benign or pseudodeficiency mutations, and no mutation was found in 42.1% of the heterozygotes analysed. These data indicate that non-Jewish Americans with Irish background have a significantly increased frequency of heterozygosity at the Hex A alpha subunit gene locus, but that approximately 42% of the biochemically ascertained heterozygotes have clinically benign mutations. A pseudodeficiency mutation was identified in one of the three TSD heterozygotes of non-Irish British Isles background; no mutations were found in the other two. The data allow for a frequency estimate of deleterious alleles for TSD among Irish Americans of 1 in 192 to 1 in 52. Non-Jewish Americans with ancestry from Great Britain have a minimal, if any, increase in rate of heterozygosity at the TSD gene locus relative to the general population.