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Molecular analysis of 30 mucopolysaccharidosis type I patients: evaluation of the mutational spectrum in Italian population and identification of 13 novel mutations.

Mucopolysaccharidosis type I (MPS-I orMPS1) is an autosomal recessive condition characterized by a broad range of clinical symptoms. Molecular diagnosis of MPS-I is important for analyzing genotype-phenotype correlation and for selecting patients for innovative therapies. In this study we analyzed 30 Italian MPS-I patients with different phenotypes (20 severe, 6 intermediate, 4 mild) in an attempt to recognize the mutational spectrum in our population and to identify major DNA alterations specific to our country. We identified 93% of mutated alleles (56 out of 60) with the reconstruction of the complete genotype in 26 patients out of 30. Twenty-three different mutations were found, 13 of which are novel while the remaining 10 have been already described. Among the novel mutations we found 5 non conservative missense mutations (A160D, E178K, P183R, G197D, D349Y), one nonsense mutation (C53X), 6 deletions (468-470del3, 486-491del6, 755-759del5, 1251delC, 1839-1867del29, 1902-1903del2), and one splice site mutation (IVS11+5G>A). No common mutation for MPS-I is present in our country. Frequently (40% of the alleles), mutations were found in just one or two patients. However, Q70X, P533R, G51D, and W402X mutations were present in several patients (15%, 13.3%, 13.3%, and 11.6% of the alleles respectively) suggesting a Mediterranean origin of the P533R and G51D mutations. In most cases the patients' genotypes were unique combinations of mutations. The great heterogeneity found in our MPS-I population hampers mutation detection and hinders the genotype-phenotype correlation.

Alleles↗

Prenatal diagnosis of mucopolysaccharidosis I: A special difficulty arising from an unusually low enzyme activity in mother's cells.

We investigated a case (I.I.) of the severe form of mucopolysaccharidosis I (Hurler syndrome). Prenatal diagnosis was requested by the parents and the next pregnancy was monitored. We report here a special difficulty arising in this diagnosis due to the low enzyme activity in the mother's cells (10-15 per cent of controls) as well as in amniotic cells and would like to stress the need for studying the index case as well as the parents' enzyme activities in order to be prepared for possible difficulties at prenatal analysis.

Adult↗

Bone marrow transplant in a case of mucopolysaccharidosis I Scheie phenotype: skin ultrastructure before and after transplantation.

An 11-year-old girl with mucopolysaccharidosis I Scheie phenotype (MPS I-S) received a bone marrow transplant (BMT) from her heterozygous HLA-identical LMC-non-reactive mother. Multidisciplinary studies were carried out and results evaluated 21 months after transplantation. Herein we report the ultrastructural findings pre- and post-BMT in skin. Multidisciplinary studies are commonly used to evaluate the benefits of metabolic correction following BMT in some MPS and other inherited metabolic disorders, and changes in morphology have been described in liver and few other tissues. In this case, we elected skin, since connective tissue is universally involved in MPS and is safely and easily obtainable. Comparison of skin biopsy specimens taken before and after BMT showed a considerable change in dermal fibroblast morphology, with marked reduction in cell size and the number and size of abnormal lysosomes, thus indicating the clearance of storage. Our results demonstrate that dermal cells respond to enzyme replacement therapy in MPS I-S, with the clearance of glycosaminoglycan lysosomal accumulation in connective tissue fibroblasts, which had near-normal morphology 21 months after BMT. Therefore, the practice of skin biopsy after BMT in MPS and other metabolic disorders in which dermal cells are involved should be encouraged.

Bone Marrow Transplantation↗

Clinically relevant aminoglycosides can suppress disease-associated premature stop mutations in the IDUA and P53 cDNAs in a mammalian translation system.

Recent studies have suggested that the use of aminoglycosides to suppress disease-causing nonsense mutations may be a promising new therapy for a large number of genetic diseases. However, gentamicin is currently the only clinically relevant aminoglycoside shown to suppress premature stop mutations in a mammalian system. We compared the ability of the clinically approved aminoglycosides gentamicin, tobramycin, and amikacin to suppress premature stop mutations. Using readthrough reporter constructs as well as mammalian cDNAs containing naturally occurring premature stop mutations, we found that each of these aminoglycosides can suppress many premature stop mutations in a context-dependent manner in a mammalian translation system. Our results indicate that the tetranucleotide termination signal (the stop codon and the nucleotide 3' of the stop codon) is the primary determinant for aminoglycoside-mediated suppression. The levels of termination suppression achieved by tobramycin were substantially lower than those observed with gentamicin. In contrast, amikacin stimulated suppression in a manner that was generally similar to gentamicin. Amikacin produced higher levels of readthrough than gentamicin at some contexts, demonstrating a unique pattern of context dependence. Experiments with mammalian cDNAs confirmed these results and demonstrated that these aminoglycosides can also suppress disease-associated premature stop mutations previously identified in the IDUA gene (responsible for the lysosomal storage disease mucopolysaccharidosis I) and the P53 gene (associated with many forms of cancer). Taken together, these results suggest that amikacin represents an alternative to gentamicin for suppression therapy in certain contexts, thus providing a means of optimizing the efficacy of aminoglycoside-mediated suppression of premature stop mutations.

Amikacin↗

Enzyme replacement therapy in two patients with an advanced severe (Hurler) phenotype of mucopolysaccharidosis I.

UNLABELLED: Although offered, two of our Hurler patients (OMIM 607014) had not undergone bone marrow transplantation at an early stage of their disease. Rapid disease progression had resulted in a range of signs and symptoms representative of advanced neurodegeneration and debilitating somatic Hurler disease. As general palliative care had only little impact on the burden of disease, laronidase (Aldurazyme) treatment was introduced in an attempt to alleviate somatic symptoms and to improve the quality of their lives. Therapeutic benefits from enzyme replacement therapy included improvements in general physical condition and mood, as well as normalisation of the sleep patterns, disappearance of sleep apnoea syndrome and reduction of hepatosplenomegaly. Improvements in the joint mobility were mainly limited to the wrists and hips. In addition, improvements in cardiac function, stool habits, visual acuity, corneal clouding and hearing were observed in one or both patients. Irreversible skeletal changes did not deteriorate. The neurological outcome of these patients is likely not influenced as laronidase is believed not to pass the blood-brain barrier. Therefore, the decision to initiate this therapy in transplant-naïve Hurler patients with an advanced stage of the disease should be taken after careful consideration. CONCLUSION: We are of the opinion that the option of enzyme therapy should not be excluded in severely affected Hurler patients who cannot undergo bone marrow transplantation. Stabilization or amelioration of somatic disease and improvement of the quality of their lives should be embraced as therapeutic goals.

Female↗