Animal models for lysosomal storage disorders

The lysosomal storage disorders (LSD) represent a heterogeneous group of inherited diseases characterized by the accumulation of non-metabolized macromolecules (by-products of cellular turnover) in different tissues and organs. LSDs primarily develop as a consequence of a deficiency in a lysosomal hydrolase or its co-factor. The majority of these enzymes are glycosidases and sulfatases, which in normal conditions participate in degradation of glycoconjugates: glycoproteins, glycosaminoproteoglycans, and glycolipids. Significant insights have been gained from studies of animal models, both in understanding mechanisms of disease and in establishing proof of therapeutic concept. These studies have led to the introduction of therapy for certain LSD subtypes, primarily by enzyme replacement or substrate reduction therapy. Animal models have been useful in elucidating molecular changes, particularly prior to onset of symptoms. On the other hand, it should be noted certain animal (mouse) models may have the underlying biochemical defect, but not show the course of disease observed in human patients. There is interest in examining therapeutic options in the larger spontaneous animal models that may more closely mimic the brain size and pathology of humans. This review will highlight lessons learned from studies of animal models of disease, drawing primarily from publications in 2011-2012.

Krabbe disease: clinical, biochemical and molecular information on six new patients and successful retrospective diagnosis using stored newborn screening cards

PURPOSE

To present clinical, biochemical and molecular information on six new clinically diagnosed Krabbe disease patients and assess the sensitivity of retrospective galactocerebrosidase measurement in their newborn screening samples.

METHODS

Medical records were reviewed. Galactocerebrosidase activity was measured in leukocytes and, retrospectively, in the patients' newborn screening cards (stored for 1.4 to 13.5 years). GALC gene mutation analysis was performed.

RESULTS

Five patients with Krabbe disease, one of whom also had hydrocephalus, became symptomatic during infancy. A sixth patient presented with seizures and developmental regression at age two and had a protracted disease course. Galactocerebrosidase activity in leukocytes ranged from 0.00 to 0.20 nmol/h/mg protein. Low galactocerebrosidase activity (range: 3.2% to 11.1% of the daily mean), consistent with Krabbe disease, was detected in each of the newborn screening samples. GALC molecular analysis identified six previously unreported mutations and two novel sequence variants.

CONCLUSION

Our cases highlight the clinical variability of Krabbe disease. Galactocerebrosidase activity in newborn dried blood spots is a highly sensitive test, even when samples have been stored for many years. The high frequency of private mutations in the GALC gene may limit the use of genetic information for making treatment decisions in the newborn period.

Pathology of GM2 gangliosidosis in Jacob sheep

The G(M2) gangliosidoses are a group of lysosomal storage diseases caused by defects in the genes coding for the enzyme hexosaminidase or the G(M2) activator protein. Four Jacob sheep from the same farm were examined over a 3-year period for a progressive neurologic disease. Two lambs were 6-month-old intact males and 2 were 8-month-old females. Clinical findings included ataxia in all 4 limbs, proprioceptive deficits, and cortical blindness. At necropsy, the nervous system appeared grossly normal. Histologically, most neurons within the brain, spinal cord, and peripheral ganglia were enlarged, and the cytoplasm was distended by foamy to granular material that stained positively with Luxol fast blue and Sudan black B stains. Other neuropathologic findings included widespread astrocytosis, microgliosis, and scattered spheroids. Electron microscopy revealed membranous cytoplasmic bodies within the cytoplasm of neurons. Biochemical and molecular genetic studies confirmed the diagnosis of G(M2) gangliosidosis. This form of G(M2) gangliosidosis in Jacob sheep is very similar to human Tay-Sachs disease and is potentially a useful animal model.

Spontaneous appearance of Tay-Sachs disease in an animal model

Tay-Sachs disease (TSD) is a progressive neurodegenerative disorder due to an autosomal recessively inherited deficiency of beta-hexosaminidase A (Hex A). Deficiency of Hex A in TSD is caused by a defect of the alpha-subunit resulting from mutations of the HEXA gene. To date, there is no effective treatment for TSD. Animal models of genetic diseases, similar to those known to exist in humans, are valuable and essential research tools for the study of potentially effective therapies. However, there is no ideal animal model of TSD available for use in therapeutic trials. In the present study, we report an animal model (American flamingo; Phoenicopterus ruber) of TSD with Hex A deficiency occurring spontaneously in nature, with accumulation of G(M2)-ganglioside, deficiency of Hex A enzymatic activity, and a homozygous P469L mutation in exon 12 of the hexa gene. In addition, we have isolated the full-length cDNA sequence of the flamingo, which consists of 1581 nucleotides encoding a protein of 527 amino acids. Its coding sequence indicates approximately 71% identity at the nucleotide level and about 72.5% identity at the amino acid level with the encoding region of the human HEXA gene. This animal model, with many of the same features as TSD in humans, could represent a valuable resource for investigating therapy of TSD.

Rapid detection of three large novel deletions of the aspartoacylase gene in non-Jewish patients with Canavan disease

Canavan disease (CD), an autosomal recessive neurodegenerative disorder, is caused by mutations in the aspartoacylase (ASPA) gene. In the present study, the ASPA gene was analyzed in 24 non-Jewish patients with CD from 23 unrelated families. Within this cohort, we found three large novel deletions of approximate 92, 56, and 12.13 kb in length, using both self-ligation of restriction endonuclease-digested DNA fragments with long-distance inverse PCR and multiplex dosage quantitative PCR analysis of genomic DNA. The 92 kb large deletion results in complete absence of the ASPA gene in one homozygous and one compound heterozygous patient, respectively. The 56 kb large deletion causes absence of the majority of the ASPA gene except for exon 1 alone in a compound heterozygous patient. The 12.13 kb deletion involves deletion of the ASPA gene from intron 3 to intron 5 including exons 4 and 5 (I3 to E4E5I5) in a compound heterozygous patient. Patients with the three large deletions clinically manifested severe symptoms at birth, including seizures. Our study showed that the combined use of long-distance inverse PCR and multiplex dosage quantitative PCR analysis of genomic DNA is a helpful and rapid technique to search for large deletions, particularly for detection of large deletions in compound heterozygous patients.

Globoid cell leukodystrophy (Krabbe disease): normal umbilical cord blood galactocerebrosidase activity and polymorphic mutations

Globoid cell leukodystrophy is an inherited metabolic disorder of the central nervous system caused by deficiency of the lysosomal enzyme galactocerebrosidase. Haematopoietic stem cell transplantation is the only available effective treatment. The engraftment from normal donors provides competent cells able to correct the metabolic defect. Umbilical cord blood cells have proved to significantly decrease complications and improve engraftment rate compared to adult marrow cells in haematopoietic stem cell transplantation. Umbilical cord blood cells must be of sufficient activity to provide central nervous system recovery after engraftment is obtained. Galactocerebrosidase activity is known to be affected by two polymorphic alleles found at nucleotides 502 and 1637 of the cDNA for this gene. This enzyme activity and the polymorphic alleles noted above were analysed in 83 random samples of umbilical cord blood. The activity, assayed with the fluorogenic substrate 6-hexadecanoylamino-4-methylumbelliferyl-beta-galactopyranoside, in those with neither polymorphic allele was 4.6 +/- 1.7 units (nmol/h per mg protein). This optimal choice of cord blood was found in only 24% of specimens. Homozygotes for 1637T > C with activity of only 1.5 +/- 0.4 units represented 16% of the samples. Those heterozygous for 1637T > C with slightly better activity (2.3 +/- 0.7 units) represented 52% of the samples. Choice of umbilical cord blood for haematopoietic stem cell transplantation, therefore, requires consideration not only of cell quantity and HLA compatibility but also selection for normal alleles to obtain maximal enzymatic activity for central nervous system correction.

[Usefulness of colonoscopy in the diagnosis of colonic diseases in childhood]

We present here our experience in colonoscopy performed in 93 children between 1984-1988 at hospital J. M. de los Ríos de Caracas. Mean age was 5.44 y/o and the range was 2-13 y/o. Rectal bleeding in 91.36% of the cases was the most common indication of the procedure. Rectal and sigmoid polyps were found in 24.73%. Vascular malformations in 16.13%, studies informs as normal 13.98% and ulcerative colitis in 10.75% No complications were observed so we can suggest colonoscopy as the first tool in diagnosis and treatment of the colonic pathology in children of any age.