Paola Luzi

Molecular genetics of Krabbe disease (globoid cell leukodystrophy): Diagnostic and clinical implications

Galactocerebrosidase (GALC) is a lysosomal β‐galactosidase responsible for the hydrolysis of the galactosyl moiety from several galactolipids, including galactosylceramide and psychosine. The deficiency of this enzyme results in the autosomal recessive disorder called Krabbe disease. It is also called globoid cell leukodystrophy (GLD), because of the characteristic storage cells found around cerebral blood vessels in the white matter of affected human patients and animal models. Although most patients present with clinical symptoms before 6 months of age, older patients, including adults, have been diagnosed by their severe deficiency of GALC activity. More than 40 mutations have been identified in patients with all clinical types of GLD. While some mutations clearly result in the infantile type if found homozygous or with another severe mutation, it is difficult to predict the phenotype of novel mutations or when mutations are found in the heterozygous state. A high incidence of polymorphic changes on apparent disease‐causing alleles also complicates the interpretation of the effects of mutations. The detection of mutations has greatly improved carrier identification among family members and will permit preimplantation diagnosis for some families. The molecular characterization of the naturally occurring mouse, dog, and monkey models will permit their use in trials to evaluate different modes of therapy. Hum Mutat 10:268–279, 1997.

Extended normal life after AAVrh10-mediated gene therapy in the mouse model of Krabbe disease.

Globoid cell leukodystrophy (GLD) or Krabbe disease is a neurodegenerative disorder caused by the deficiency of the lysosomal enzyme galactocerebrosidase (GALC). This deficiency results in accumulation of certain galactolipids including psychosine which is cytotoxic for myelin-producing cells. Treatment of human patients at this time is limited to hematopoietic stem cell transplantation (HSCT) that appears to slow the progression of the disease when performed in presymptomatic patients. In this study, adeno-associated virus (AAV) serotype rh10-(AAVrh10) expressing mouse GALC was used in treating twitcher (twi) mice, the mouse model of GLD. The combination of intracerebroventricular, intracerebellar, and intravenous (iv) injection of viral particles in neonate twi mice resulted in high GALC activity in brain and cerebellum and moderate to high GALC activity in spinal cord, sciatic nerve, and some peripheral organs. Successfully treated mice maintained their weight with no or very little twitching, living up to 8 months. The physical activities of the long-lived treated mice were comparable to wild type for most of their lives. Treated mice showed normal abilities to mate, to deliver pups, to nurse and to care for the newborns. This strategy alone or in combination with other therapeutic options may be applicable to treatment of human patients.

Insulin-like growth factor-1 provides protection against psychosine-induced apoptosis in cultured mouse oligodendrocyte progenitor cells using primarily the PI3K/Akt pathway.

Psychosine (galactosylsphingosine) is a toxic metabolite that accumulates in globoid cell leukodystrophy (GLD) due to the deficiency of galactocerebrosidase (GALC) activity. This results in subsequent programmed cell death of oligodendrocytes and demyelination in human patients and animal models. We investigated the potential role of insulin-like growth factor-1 (IGF-1) in modifying the apoptotic effect of psychosine in cultured mouse oligodendrocyte progenitor cells (OLP-II). We show that psychosine inhibits the phosphorylation of Akt and Erk1/Erk2 (Erk1/2), which are the main anti-apoptotic pathways of the IGF-1 receptor (IGF-1R). Although IGF-1 sustained phosphorylation of both of these pathways, it provided maximum protection to OLP-II cells from psychosine-induced cell death in a PI3K/Akt-dependent manner. The effects of IGF-1 were dose-dependent and resulted in increased IGF-1R autophosphorylation levels. Although relatively high concentrations of IGF-1 also resulted in the activation of the insulin receptor (IR), its effect was more significant on the IGF-1R.

Two different mutations are responsible for Krabbe disease in the Druze and Moslem Arab populations in Israel.

Infantile Krabbe disease is a severe, fatal autosomal recessive disorder resulting from the deficiency of galactocerebrosidase (GALC) activity. It is relatively common in two separate inbred communities in Israel. In the Druze community in Northern Israel and two Moslem Arab villages located near Jerusalem the incidence of Krabbe disease is about 1 in 100–150 live births. With our cloning of the GALC gene, mutation analysis of these populations was undertaken. The Moslem Arabs were homozygous for two mutations in the GALC gene; a T-to-C transition at cDNA position 1637 (counting from the A of the initiation codon), which is considered a polymorphism, and a G-to-A transition at position 1582, which changes the codon for aspartic acid to one for asparagine. The Druze patients are homozygous for a T-to-G transversion at position 1748, which changes the codon for isoleucine to one for serine. Expression studies confirmed the deleterious nature of these mutations. The development of a simple polymerase chain reaction (PCR) amplification and restriction enzyme digestion method to identify these alleles will lead to accurate carrier testing and improved genetic counseling for interested individuals in these communities.

EFFECTS OF TREATMENTS ON INFLAMMATORY AND APOPTOTIC MARKERS IN THE CNS OF MICE WITH GLOBOID CELL LEUKODYSTROPHY

Globoid cell leukodystrophy (GLD) or Krabbe disease is a neurodegenerative disorder caused by the deficiency of the lysosomal enzyme galactocerebrosidase (GALC). GALC deficiency results in a progressive demyelination of the central and peripheral nervous systems. Inflammatory cells and increased levels of cytokines and chemokines are present in the CNS of GLD mice and may play a significant role in the pathogenesis of the disease. In this study we evaluate the effect of non-steroidal anti-inflammatory drugs, such as indomethacin and ibuprofen, and minocycline, a tetracycline analog with neuroprotective and anti-apoptotic properties, on the progression of the disease using a transgenic mouse model of GLD. Real-time quantitative PCR was used to analyze the expression of several markers of the immune/inflammatory response. IL-6, TNF-alpha, MIP-1beta, MCP-1, iNOS/NOS2, CD11b, CD68, CD4 and CD8 mRNA levels were measured in cortex, cerebellum and spinal cord of untreated and treated affected mice at different ages. In addition, the pharmacological treatments were compared to bone marrow transplantation (BMT). The pharmacological treatments significantly extended the life-span of the treated mice and reduced the levels of several of the immuno-related factors studied. However, BMT produced the most dramatic improvements. In BMT-treated mice, factors in the spinal cord were normalized faster than the cerebellum, with the exception of CD68. There was a decrease in the number of apoptotic cells in the cerebellum of mice receiving anti-inflammatory drugs and BMT. These studies indicate a possible role for combined therapy in the treatment of GLD.

Prevalent mutations in the GALC gene of patients with Krabbe disease of Dutch and other European origin

Sixty-four unrelated patients with infantile Krabbe disease (globoid cell leukodystrophy, GLD) of Dutch (n=41) or other European origin (n=23) were screened for the presence of a large 30kb deletion starting in intron 10 (IVS 10del30kb), a base substitution 1538T(T513M) and a polymorphism, 502T. The deletion and the T513M mutation were present in 52% and 8.5%, respectively, of the 82 GALC alleles of the Dutch patients. The 502T polymorphism, which had an allele frequency of 5.3% in a Dutch control panel, occurred in 65% of the GLD alleles. Analysis of patients and both parents in 26 of the families showed that del30kb was invariably associated with 502T. However, 502T was also present on 40% of the GLD alleles with an as yet unidentified mutation, which is 7.5 times higher than its frequency in controls. This suggests that besides del30kb at least one other relatively frequent mutation has arisen on the 502T GALC allele. A relatively high incidence of del30kb was also found in 23 other European (non-Dutch) patients (allele frequency 35%), but T513M did not occur in this group. Practical examples described in this report illustrate the potential usefulness of mutation analysis in many families with Krabbe disease for heterozygote detection and prenatal diagnosis.

Krabbe Disease: Globoid Cell Leukodystrophy

Abstract Krabbe disease or globoid cell leukodystrophy (GLD) is an autosomal recessive disorder of myelination caused by galactocerebrosidase (GALC) deficiency. This enzyme is essential for the lysosomal degradation of several important galactolipids, including galactosylceramide and psychosine. Most human patients present before 6 months of age but older patients are also recognized. The diagnosis can be made by measuring very low GALC activity in any easily obtainable tissue. Newborn screening has been initiated in an attempt to identify individuals who may develop the disease before symptoms appear. Treatment is limited to hematopoietic stem cell transplantation in presymptomatic infants and mildly affected late-onset patients. The GALC gene has been cloned, and over 140 disease-causing mutations have been identified. GLD has also been identified in a number of animal species, which can be used to examine pathogenic mechanisms and potential methods for treatment including gene therapy, stem cell therapy, and small molecule therapy.

Long-term Improvements in Lifespan and Pathology in CNS and PNS After BMT Plus One Intravenous Injection of AAVrh10-GALC in Twitcher Mice

Krabbe disease is an autosomal recessive disorder resulting from defects in the lysosomal enzyme galactocerebrosidase (GALC). GALC deficiency leads to severe neurological features. The only treatment for presymptomatic infantile patients and later-onset patients is hematopoietic stem cell transplantation (HSCT). This treatment is less than ideal with most patients eventually developing problems with gait and expressive language. Several naturally occurring animal models are available, including twitcher (twi) mice, which have been used for many treatment trials. Previous studies demonstrated that multiple injections of AAVrh10-GALC into the central nervous system (CNS) of neonatal twi mice resulted in significant improvements. Recently we showed that one i.v. injection of AAVrh10-GALC on PND10 resulted in normal GALC activity in the CNS and high activity in the peripheral nervous system (PNS). In the present study, a single i.v. injection of AAVrh10-GALC was given 1 day after bone marrow transplantation (BMT) on PND10. The mice show greatly extended lifespan and normal behavior with improved CNS and PNS findings. Since HSCT is the standard of care in human patients, adding this single i.v. injection of viral vector may greatly improve the treatment outcome.

Evidence of diffuse brain pathology and unspecific genetic characterization in a patient with an atypical form of adult-onset Krabbe disease

Sirs: Krabbe disease (KD) is a rare autosomal recessive disorder due to a diminished activity of the lysosomal enzyme galactocerebrosidase (GALC) [7, 13]. The demonstration of a severe deficiency in GALC activity in leukocytes or fibroblasts is the basis for diagnosis. The human GALC gene (mapped to chromosome 14q24.3– q32.1, see [14] for details) has been cloned, and a number of KD-causing mutations have been identified. Recent studies have reported an unusual, slowly progressive adult form of KD characterized by spastic paraparesis and magnetic resonance imaging (MRI) findings of bilateral corticospinal tract demyelination [11, 12]. It has been suggested that the new homozygous point mutation T1835C (L618S) found in the GALC gene of one of these patients [11] is characteristic of this form of late-onset KD. We describe a 44-year-old woman who was hospitalized because of slowly progressive gait disturbance. There was no family history of neurological disease. Her birth and delivery were uncomplicated, and development milestones were normal. She did not have neurological symptoms until the age of 42 years, when she began to complain of an unsteadiness of gait. Neurological examination showed mild spastic paraparesis with increased muscle tone in the legs. All deep-tendon reflexes were symmetrically brisk, with bilateral Babinski sign. Sense of joint position and sensation to light touch and pinprick were normal, while vibration sense was mildly decreased in the legs. Mental functions were normal. Blood laboratory examinations showed an iron deficiency anemia. Urine tests were normal. Electromyography and nerve conduction studies showed evidence of demyelinating sensorimotor neuropathy. A sural nerve biopsy specimen revealed mild signs of demyelination, with the presence of inclusions within Schwann’s cells on electron microscopy. The activity of a number of lysosomal enzymes was screened in the patient’s cultured skin fibroblasts [15], and only the GALC activity was decreased (0.26 nmol h–1 mg–1 protein, <10% of the normal mean). DNA was isolated from cultured cells as previously described [10]. The patient was found to be heterozygous for two previously reported mutations: G > A at cDNA position 809 (G270D) and 1026del10. The first mutation, G > A at cDNA position 809 (G270D), has been identified previously in other patients with adult-onset KD [3, 6, 14]. The second mutation, previously identified in another Italian patient with infantile KD [14], consists of a 10 basepair deletion starting in exon 10 at nucleotide 1026. This results in a frame shift and premature stop codon and most likely would not produce any active enzyme since there would be no production of the 30-kDa subunit necessary for activity. Combined brain proton MRI and magnetic resonance spectroscopic imaging (MRSI) was performed using a Philips Gyroscan NT operating at 1.5 T. Multislice spin-echo images were obtained in coronal and transverse planes perpendicular and parallel to the anterior commissure (AC) and posterior commissure (PC) line, LETTER TO THE EDITORS J Neurol (2000) 247 :226–228

Intravenous injection of AAVrh10-GALC after the neonatal period in twitcher mice results in significant expression in the central and peripheral nervous systems and improvement of clinical features.

Globoid cell leukodystrophy (GLD) or Krabbe disease is an autosomal recessive disorder resulting from the defective lysosomal enzyme galactocerebrosidase (GALC). The lack of GALC enzyme leads to severe neurological symptoms. While most human patients are infants who do not survive beyond 2 years of age, older patients are also diagnosed. In addition to human patients, several naturally occurring animal models, including dog, mouse, and monkey, have also been identified. The mouse model of Krabbe disease, twitcher (twi) mouse has been used for many treatment trials including gene therapy. Using the combination of intracerebroventricular, intracerebellar, and intravenous (iv) injection of the adeno-associated virus serotype rh10 (AAVrh10) expressing mouse GALC in neonate twi mice we previously have demonstrated a significantly extended normal life and exhibition of normal behavior in treated mice. In spite of the prolonged healthy life of these treated mice and improved myelination, it is unlikely that using multiple injection sites for viral administration will be approved for treatment of human patients. In this study, we have explored the outcome of the single iv injection of viral vector at post-natal day 10 (PND10). This has resulted in increased GALC activity in the central nervous system (CNS) and high GALC activity in the peripheral nervous system (PNS). As we have shown previously, an iv injection of AAVrh10 at PND2 results in a small extension of life beyond the typical lifespan of the untreated twi mice (~40 days). In this study, we report that mice receiving a single iv injection at PND10 had no tremor and continued to gain weight until a few weeks before they died. On average, they lived 20-25 days longer than untreated mice. We anticipate that this strategy in combination with other therapeutic options may be beneficial and applicable to treatment of human patients.