Use of 4-methylumbelliferyl-6-sulpho-2-acetamido-2-deoxy-beta- D-glucopyranoside for prenatal diagnosis of Tay-Sachs disease using chorionic villi

Canine GM2-Gangliosidosis Sandhoff Disease Associated with a 3-Base Pair Deletion in the HEXB Gene

BACKGROUND

GM2-gangliosidosis is a fatal neurodegenerative lysosomal storage disease (LSD) caused by deficiency of either β-hexosaminidase A (Hex-A) and β-hexosaminidase B (Hex-B) together, or the GM2 activator protein. Clinical signs can be variable and are not pathognomonic for the specific, causal deficiency.

OBJECTIVES

To characterize the phenotype and genotype of GM2-gangliosidosis disease in an affected dog.

ANIMALS

One affected Shiba Inu and a clinically healthy dog.

METHODS

Clinical and neurologic evaluation, brain magnetic resonance imaging (MRI), assays of lysosomal enzyme activities, and sequencing of all coding regions of HEXA, HEXB, and GM2A genes.

RESULTS

A 14-month-old, female Shiba Inu presented with clinical signs resembling GM2-gangliosidosis in humans and GM1-gangliosidosis in the Shiba Inu. Magnetic resonance imaging (MRI) of the dog's brain indicated neurodegenerative disease, and evaluation of cerebrospinal fluid (CSF) identified storage granules in leukocytes. Lysosomal enzyme assays of plasma and leukocytes showed deficiencies of Hex-A and Hex-B activities in both tissues. Genetic analysis identified a homozygous, 3-base pair deletion in the HEXB gene (c.618-620delCCT).

CONCLUSIONS AND CLINICAL IMPORTANCE

Clinical, biochemical, and molecular features are characterized in a Shiba Inu with GM2-gangliosidosis. The deletion of 3 adjacent base pairs in HEXB predicts the loss of a leucine residue at amino acid position 207 (p.Leu207del) supporting the hypothesis that GM2-gangliosidosis seen in this dog is the Sandhoff type. Because GM1-gangliosidosis also exists in this breed with almost identical clinical signs, genetic testing for both GM1- and GM2-gangliosidosis should be considered to make a definitive diagnosis.

Emerging sulfated flavonoids and other polyphenols as drugs: nature as an inspiration

Nature uses sulfation of endogenous and exogenous molecules mainly to avoid potential toxicity. The growing importance of natural sulfated molecules, as modulators of a number of physiological and pathological processes, has inspired the synthesis of non-natural sulfated scaffolds. Until the 1990s, the synthesis of sulfated small molecules was almost restricted to derivatives of flavonoids and aimed mainly at structure elucidation and plant biosynthesis studies. Currently, the synthesis of this type of compounds concerns structurally diverse scaffolds and is aimed at the development of potential drugs and/or exploitation of the biological effects of sulfated metabolites. Some important hit compounds are emerging from sulfated flavonoids and other polyphenols mainly as anticoagulant and antiviral agents. When compared with polymeric macromolecules such as heparins, sulfated small molecules could be of value in therapeutics due to their hydrophobic nature that can contribute to improve the bioavailability. This review highlights the synthetic approaches that were applied to obtain monosulfated or polysulfated phenolic small molecules and compiles the diverse biological activities already reported for this type of derivatives. Toxicity and pharmacokinetic parameters of this emerging class of derivatives will also be considered, emphasizing their value for therapeutic applications.

Use of 4-trifluoromethylumbelliferyl-alpha-L-iduronide as a new substrate for detection of alpha-L-iduronidase deficiency in human tissues and for rapid prenatal diagnosis of Hurler disease

Results are presented of alpha-L-iduronidase assays in the leukocytes of normal individuals, patients with Hurler disease and heterozygous carriers. The assays were carried out using 4-methylumbelliferyl-alpha-L-iduronide and 4-trifluoromethylumbelliferyl-alpha-L-iduronide as substrates. It was shown that 4-trifluoromethylumbelliferyl-alpha-L-iduronide, along with the commonly used 4-methylumbelliferyl-alpha-L-iduronide, can serve as a specific substrate for alpha-L-iduronidase and is therefore suitable for demonstrating the enzyme deficiency in patients with Hurler disease, as well as the decrease of enzyme activity in heterozygous disease carriers. Using the two substrates a prenatal diagnosis of Hurler disease in a fetus was made on the basis of the lack of enzyme activity in amniotic fluid cell cultures. The diagnosis was confirmed by the results of alpha-L-iduronidase activity assay in fetal liver and kidney. It was found that 4-trifluoromethylumbelliferyl-alpha-L-iduronide is highly efficient for the rapid detection of alpha-L-iduronidase deficiency directly in pieces of tissues and in placenta, which is important for the prenatal diagnosis of Hurler disease.

First trimester prenatal diagnosis of Tay-Sachs disease using the sulfated synthetic substrate for hexosaminidase A

Uncultured and cultured embryonic trophoblastic tissue obtained by chorionic villus sampling (CVS) displays enzyme activity towards 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranosyl-6-sulfate (MUGS), a specific substrate for Hexosaminidase A (Hex A), the enzyme deficient in Tay-Sachs disease (TSD). Specific activity is comparable to that found in cultured amniocytes and fibroblasts. The enzyme activity has a pH optimum of 4.1 and an apparent Km of 6 x 10(-4) mol/L. Thirteen pregnancies in eight families at risk for TSD were monitored by CVS using MUGS as the Hex A substrate. Four fetuses were proven affected by enzyme analysis of fetal tissues and cultured fetal fibroblasts obtained at the time of termination of the pregnancies. Nine fetuses were judged to be unaffected. Eight babies were clinically normal while the other pregnancy is continuing. The use of MUGS as substrate for Hex A makes prenatal diagnosis by CVS of families at risk for TSD simple, direct and accurate.

The biochemical diagnosis of lysosomal storage diseases--a review of five years experience

The inherited lysosomal storage diseases are a distinct group of inborn errors of metabolism characterised by deficiencies in specific lysosomal enzymes. As many as 40 such disorders have now been described in man. We have measured the activities of up to 16 lysosomal acid hydrolases in plasma and/or extracts of leucocytes and cultured skin fibroblasts from 198 patients referred from throughout Ireland. These 16 assays allowed the biochemical diagnosis of 20 lysosomal storage diseases. Activities were compared with reference ranges to determine homozygotes and heterozygotes. Of the 44 patients with positive results, 15 were diagnosed as being homozygous for a specific lysosomal enzyme deficiency, 4 were identified as having multiple enzyme deficiencies (mucolipidosis Type II/I-cell disease) and 25 had heterozygote (carrier) enzyme levels. Of the latter, 24 were either parents (obligate heterozygotes) or siblings of homozygotes and one was a heterozygote for the X-linked recessively inherited Fabry's disease.

Identification of an intermediate form of beta-N-acetylhexosaminidase in chorionic villi

A minor form of beta-N-acetylhexosaminidase has been found in chorionic villi, in addition to the major forms A and B. This form does not hydrolyze the 4-methylumbelliferyl-2-acetamido-2-deoxy-beta-D-glucopyranoside-6-sulpha te substrate, is thermostable, has a higher mol mass (120,000) than A and B (100,000) and on analytical isoelectric focusing, it shows a microheterogeneity with values ranging between 6.3 and 7.0. For these characteristics, it resembles beta-N-Acetylhexosaminidase P from pregnancy serum, from which is chromatographically indistinguishable.