Aspartylglucosaminuria (AGU) is a lysosomal, inherited storage disorder caused by defective activity of the enzyme aspartylglycosaminidase (AGA). It has a slow, progressive course with progressive mental retardation, characteristic coarse features, short stature, repeated upper respiratory infections, joint laxity, and hernias in the affected patients. Patients with AGU have a delayed development during infancy and reach a maximal intellectual level and adaptive skills of a 5- to 6-year-old child at an age between 13 and 16 years before a decline of mental abilities ensues (1–3). Lifespan is shortened, and in adulthood approximately one fourth of the patients have behavioral disturbances. The majority of the patients need help with daily living (1–3). Most publications including clinical and molecular characteristics of the disease are published from the Finnish population, where the incidence of AGU is higher than elsewhere (3). In Sweden, AGU is an extremely rare disorder, mostly occurring in the northern part of the country, where Finnish immigrants abe lived for several generations.
In AGU, as in other lysosomal disorders with a known enzyme deficiency, different approaches to therapy have been tried or proposed, such as allogeneic stem-cell transplantation (ASCT), enzyme recombinant therapy (ERT), and gene-therapy (3). The first publication of outcome after bone-marrow transplantation in AGU in two young Finnish patients reported an improved myelination on magnetic resonance imaging (MRI), increased AGA activity in leukocytes, and disappearance of cells with storage vacuoles in rectal mucosa at follow-up between 1.0 to 5.6 years (4). In a later publication (5), the results after ASCT in five AGU patients with neuropsychologic and clinical follow-up were interpreted as not beneficial, and a marked scepticism to this treatment was pronounced. The two siblings in our study, included in the publication above (5), were only followed during 1 year after ASCT. Now, 5 years later, we update the laboratory, clinical, neuropsychology, and neuroradiology data in these children.
MATERIALS AND METHODS
Patient 1, born 1987, is the oldest girl of four siblings in a nonconsanguineous family from northern Sweden. The pregnancy and delivery was normal, with birth weight at 3,650 g. Her early development was normal; she could sit at 7 months and walk at 14 months. Later, a psychomotor delay was suspected, and she could only say a few words at 4 years of age. A mental retardation was confirmed when she was school-aged, at 7 years old. Auditory deficit was early confirmed, and she was given hearing aids. A new investigation in 1997 only showed a mild bilateral sensorineural hearing deficit without need of auditory aids.
Patient 2, the above patient’s younger brother by 3 years and 5 months, was born in 1991 in a normal delivery after a normal pregnancy. His early development was normal, just as his sister’s. He could sit without support at 7 to 8 months and walk at 15 months. At 4 years old, he could say only a few words, had auditory deficits, and was also considered developmentally delayed. A metabolic investigation of the siblings gave the diagnosis of AGU. Both children have received their education in schools for the mentally retarded.
The Wechsler Preschool and Primary Scale Of Intelligence–Revised (WPPSI-R), standardized in 1993, is composed of performance and verbal sections; the sum of both gives a total intelligence quotient (IQ) (6). To evaluate language, auditory, and spatial processing, sections of the Developmental Test of Visual-Motor Integration, Motor Free Visual Perception Test–Revised, and Illinois Test of Psycholinguistic Abilities (7–9) have been used for psychologic evaluation. To assess concentration and social ability, the children were observed during the neuropsychologic investigation and through an interview with the mother.
The activity of aspartylglucosaminidase in leukocytes and the total sialic acid concentration in urine were measured before and yearly after ASCT. The concentration of aspartylglycosamine in urine was measured at the time of diagnosis. Tau-protein, a normal axonal protein, used as a marker of neuronal and axonal degeneration, was analyzed in the cerebrospinal fluid (10).
The patients were examined with MRI using T1, T2, proton density, and flair weighted sequences. No contrast medium was administered. Both patients were examined on six occasions.
Patient 1 received her ASCT, 971010, with an unrelated human leukocyte antigen (HLA)-A, -B, -DRBI genomically identical donor with one DQB mismatch when she was 10 years and 5 months old. She was conditioned with busulphan for 4 days, (the dose was adjusted according to plasma concentrations), cyclophosphamide (63 mg/kg per day) for 4 days, and monoclonal antibody OKT-3 (5 mg/day) during 5 days before ASCT (11–13). She received a bone-marrow cell dose of 3.8×106 CD34+ cells/kg. Her posttransplant course was complicated with severe grade III acute graft-versus-host disease (GvHD) that affected the skin, gastrointestinal tract, and liver. She was treated with high-dose steroids and cyclosporine. In addition, she experienced and was treated for repeated episodes of bacterial, viral, and fungal infections. She suffered from hemorrhagic diarrhea and hemorrhagic cystitis. Six months of inpatient care was required before she was discharged to the outpatient clinic. However, she eventually recovered and showed no signs of chronic GvHD.
Patient 2 was given granulocyte colony-stimulating factor mobilized peripheral blood stem cells (9.8×106 CD34+ cells/kg) from an unrelated HLA-A, -B, and -DRBI identical unrelated donor with one DQB subtype mismatch in August 1997 when he was 5 years and 10 months old (14). He was conditioned with fractionated total body irradiation, 4 Gy, for 3 consecutive days, followed by cyclophosphamide 60 mg/kg for 2 days before ASCT. He also received two doses of antithymocyte globulin and OKT-3 (15 mg total dose) given over 4 days before transplant. As posttransplant immune prophylaxis, both patients were treated with cyclosporine combined with a short course of methotrexate (15, 16). The patient developed a slight skin rash on day +18 on his face and hands, which promptly responded to steroids. He was discharged from the hospital on day +28 after ASCT. In the outpatient clinic, he experienced an autoimmune hemolytic anemia 5 months after transplant. He was treated with repeated transfusion, high-dose immunoglobulin, steroids, and azathioprine. During this period, he was tired and icteric. His hemolytic anemia resolved 7 months after ASCT. He recovered and showed no signs of chronic GvHD. Details regarding the transplantation procedure were previously published (12–14).
Chimerism analysis was performed by collecting peripheral blood samples from the donor and recipient before transplantation and from the recipient at various time points after transplantation. To evaluate lineage-specific chimerism, CD3-, CD19-, and CD33-positive cells were selected from peripheral blood using immunomagnetic beads (Dynal, Oslo, Norway), as previously reported (17, 18).
At follow-up 5 years after ASCT, patient 1 was 15 years and 5 months old. She can walk and ride a bicycle. She speaks sentences and understands both Finnish and Swedish words, can write her name, and recognize several letters. She can perform simple domestic work. She can dress herself but needs some help with hygiene, and she cannot be left alone. She is clearly mentally retarded, and she does not know her age. She has not lost any abilities since the transplantation, and her temper has improved. Her face has not become coarser. Neurologic examination showed a somewhat clumsy gait, normal muscular tension, and normal tendon reflexes.
Patient 2 was evaluated 5 years after ASCT when he was 11 years old. He could walk long distances, although he had some problems with pain in his left foot. He has not lost any abilities since ASCT and is able to learn new things. He can speak and understand both Finnish and Swedish. He can understand a joke. He is very interested in fine motor activities and is advanced in practical tasks and can drive a tractor in his parents’ farmyard. His face has not become coarser than before ASCT. He is clearly mentally retarded and does not know how old he is. He needs help with his own hygiene. Neurologic examination shows a slight abnormality of the gait, presumably caused by a pronounced valgisation of his left foot. His muscular tension is normal, and the tendon reflexes are slightly depressed. He is not as aggressive as in the previous years and somewhat more cooperative than before when examined. In evaluating the activity stakes, both patients have Lansky scores above 90 and no chronic GvHD, not taking their unchanged mental retardation into account.
Six years posttransplant, chimerism analysis showed complete donor engraftment of CD19, CD3 and CD33 cells in patient 1. Six years posttransplant, patient 2 is a mixed chimera; 40% of the CD19-positive cells (B cells) are of recipient origins, whereas 70% of the CD3-positive cells (T cells) are recipient cells. Forty percent of the myeloic cells (CD33) are also of recipient origin.
Both children were tested by the same psychologist, who performed the tests with use of both Swedish and Finnish language, when needed. Both children were mentally retarded, and both had an uneven profile, with better results in the performance section of WPPSI-R than in the verbal section. Both had marked deficits in attention. The attention ability in both patients was better during the last investigations compared with the previous, and social competence had developed. The psychometric data during 5 years follow-up is given in Table 1.
The activity of aspartylglucosaminidase in leukocytes was normalized within 1 month after ASCT, and a stable expression was found during the whole follow-up period (Table 2). The spinal fluid concentration of Tau-protein peaked at approximately 12 months after ASCT and then declined to almost normal levels (Figs. 1 and 2). The excretion of sialic acid containing glycoconjugates diminished in both patients during 5 years of monitoring (Table 3).
At 10 and 11 years, the signal in T2- and flair-weighted images was moderately increased in the white matter along the lateral walls and roofs of the lateral ventricles. Cysts in the choroid plexa were noted. At 12 and 13 years, a slight increase in signals around the ventricular trigones on the same sequences was noted. At 14 years, a decrease in the pathologic signals had occurred, which remained unchanged at 15 years.
At 6 years, there was an increased signal on the same sequences in the same areas as with his sibling, but the intensity was lower. Plexus choroideus cysts were also noted. At 7 years, the signal had increased in all areas but especially around the ventricular trigones. At 8 years, the pathologic signal was slightly decreased and at 9 years even more so. At 10 years, there was further slight decrease, although the pathologic signal was still conspicuous. At 11 years, no change was noted. No gray matter abnormality or loss of brain matter was detected in either of the patients.
This report of two patients may be considered anecdotal but is important in light of the rarity of the disease. Five years of follow-up is obviously a short period in view of the 4- to 5-decade course of the disease, and the follow-up must be extended at least 10 years or longer for evaluation. The presented psychometric and clinical data must be seen in the context of the natural development of AGU patients, as reported in literature (1–3). The better performance in the neuropsychologic tests and improved attention ability after ASCT in our patients could thus be interpreted to be part of the normal development and aging. AGU patients are described to reach their maximal intellectual level and the adaptive skills of a 5- to 6-year-old normal child at an age of between 13 and 16 years, followed by a period of slow decline until 25 to 28 years age, when a rapid impairment occurs (1–3). However, the level of Tau-protein in the cerebrospinal fluid, considered to reflect an ongoing neuronal and axonal degeneration in the central nervous system (10), declined during the observation period and indicates an arrest of the disease. The decrease in the excretion of urinary sialic containing glycoconjugates is in accordance with the first presentation of ASCT of two children with AGU, who had clearance of storage material in the rectal mucosa and a decreased excretion of urinary AGU (4). Also, the neuroradiologic findings in our study that showed an improvement of myelination in the youngest patient and an arrest of demyelination in the older one corresponds with a previous study reporting a nearly normal gray to white matter cortical ratio in children who had undergone transplantation, contrary with those who had not (4).
The marked hesitation to recommend ASCT for patients with AGU in the later publication (5) was based on the observation that the patients receiving transplants had a mean lower IQ than those children with AGU not receiving transplants. However, the two siblings in our study and included in that publication had only been followed for 1 year. During that year, posttransplantational complications and a long hospital stay in patient 1 may have influenced the results of the tests. Patient 1 suffered from severe GvHD, especially of the gut, from which she eventually recovered. Patient 2 only experienced grade I acute GvHD (17, 18). However, half a year after transplant, he experienced autoimmune hemolytic anemia, because of which he was very tired and required repeated erythrocyte transfusions and immune therapy before it resolved. This was very stressful for the patient and the family. The severe acute GvHD in patient 1 and the hemolytic anemia in patient 2 may have affected the test results at the time when they were included in the Finnish study. However, since then, the patients have recovered from their posttransplant complications.
In different lysosomal disorders characterized by enzyme deficiency and central nervous system involvement, evaluation of ASCT must be performed for each individual disorder. The outcome depends on how rapid or slow the natural progress of the disease is, at what age ASCT is performed, and the influence of transplant-related complications (19–24). One example is metachromatic leukodystrophy of the late-infantile, juvenile, or adult type. In this disorder, the late-infantile, rapidly progressive form has no benefit of ASCT, in contrast with the juvenile and adult forms, which have a slower course (24–26). Another example can be taken from the mucopolysaccharide (MPS) disorders. In MPS I (Hurlers disease), the mental retardation can be arrested if ASCT is performed before the age of 18 to 24 months, whereas in MPS III (Sanfilippo disease), ASCT cannot prevent the progressive mental retardation even if performed before the age of 2 to 3 years, (24). In adrenoleukodystrophy, intervention at a very early stage of the disease is of utmost significance if ASCT is to be successful (24).
Other treatment strategies in addition to ASCT for enzyme-deficient lysosomal diseases have been proposed or tried, namely gene therapy and ERT. Gene therapy has not, so far, been useful as, previously proposed. ERT for different lysosomal diseases is in a phase of rapid development (27), but there is not yet any solution for the problem of how to get the enzyme across the blood-brain barrier. In ERT treatment, as in after ASCT, there is also a need for very long-term follow-up to determine its efficacy.
ASCT has been used for more than 25 years in selected cases of metabolic diseases to provide a longstanding enzyme supplement. Both mortality and morbidity have improved during the last years (24). As is the case for many other inborn errors of metabolism, transplantation should be performed as early as possible. At best, ASCT may arrest progression and could contribute to a better quality of life in perspective of whole life in individuals with AGU. In summary, we conclude that ASCT in AGU may prevent a further progress of the disease.
The authors thank Anne Koskenniemi for skilful performance of the neuropsychologic tests.
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