Overt renal disease often first presents in male individuals with Fabry disease in early to middle adulthood, but proteinuria and reduced GFR may occur in adolescents and in young children. More recently, kidney biopsy data have shown early renal histologic changes in pediatric patients, and kidney dysfunction, primarily proteinuria, seems to be more common in girls. Renal investigations and their timing in children remain poorly defined. A consensus on renal investigations is necessary to understand the natural progression of the disease and to evaluate the efficacy of treatments such as enzyme replacement therapies. This article addresses three main categories: Use of GFRs, measuring albuminuria, and renal biopsies in children.

BACKGROUND: Studies on renal function in children with Fabry disease have mainly been done using estimated creatinine-based glomerular filtration rate (GFR). The aim of this study was to compare estimated creatinine-based GFR (eGFR) with measured GFR (mGFR) in children with Fabry disease and normal renal function. METHODS: Eighty-two examinations were done in 42 children (24 boys, 18 girls) with Fabry disease from three different centres. The mean age was 12.3 years. GFR was measured with iohexol, Cr(51)-EDTA or iothalamate, and the mean mGFR was 108 ml/min/1.73 m(2). RESULTS: The widely used original Schwartz formula (1976) overestimated GFR substantially by 50.6 ml/min/1.73 m(2) with a very low accuracy, whereas the new abbreviated Schwartz formula (2009) showed relatively good performances with a mean GFR overestimation of 5.3 ml/min/1.73 m(2) and 79% of the eGFR calculated within 20% of mGFR, thus being only slightly superior to the Counahan-Barratt formula. However, less than half of the eGFR calculated by the new abbreviated Schwartz equation were within 10% of the mGFR. When repeated measurements were performed, mGFR showed less variation than eGFR. CONCLUSIONS: The new abbreviated Schwartz formula should replace the original Schwartz formula in the routine follow-up of children with Fabry disease. The current creatinine-based GFR formulas are all hampered by low accuracy in the 'creatinine-blind' GFR range, and early progressive disease may be missed. Supplemental mGFR is, therefore, recommended in patients where changes in GFR have potential impact on important treatment regimens. Cystatin C-based GFR formulas remain to be validated in Fabry children.

Hunter syndrome is a rare, X-linked disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase. In the absence of sufficient enzyme activity, glycosaminoglycans accumulate in the lysosomes of many tissues and organs and contribute to the multisystem, progressive pathologies seen in Hunter syndrome. The nervous, cardiovascular, respiratory, and musculoskeletal systems can be involved in individuals with Hunter syndrome. Although the management of some clinical problems associated with the disease may seem routine, the management is typically complex and requires the physician to be aware of the special issues surrounding the patient with Hunter syndrome, and a multidisciplinary approach should be taken. Subspecialties such as otorhinolaryngology, neurosurgery, orthopedics, cardiology, anesthesiology, pulmonology, and neurodevelopment will all have a role in management, as will specialty areas such as physiotherapy, audiology, and others. The important management topics are discussed in this review, and the use of enzyme-replacement therapy with recombinant human iduronate-2-sulfatase as a specific treatment for Hunter syndrome is presented.

Background: Hearing loss and tinnitus are common symptoms in Fabry disease and increase in prevalence with age. This study aimed to provide an epidemiological description of hearing impairment and tinnitus in children with Fabry disease in the Fabry Outcome Survey (FOS), an international database to assess the natural history of Fabry disease and the efficacy of enzyme replacement therapy with agalsidase alfa. Methods: Signs and symptoms questionnaires were completed for 543 children with Fabry disease. Pure-tone audiograms were obtained from 101 children (53 girls, 48 boys). Results: On questioning, 33% of the children (n = 179) reported subjective hearing impairment. However, when assessed by age-appropriate audiometry, only 19 of 101 patients (19%) had a persistent hearing loss at least one frequency. Of these, 14 had a high-frequency hearing loss, 4 a pan-frequency hearing loss, and 1 a pattern typical of noise-induced loss. Of the 101 children with audiometry, 44 complained of tinnitus. Only 2 children reported sudden hearing loss, which was not verified by audiometry. Children with tinnitus had greater disease severity scores. Conclusions: Hearing loss is a well-known clinical manifestation in patients with Fabry disease. It was reported in significant numbers of children in the FOS signs and symptoms questionnaire, but confirmed in only 19% by formal audiometry. The subjective hearing impairment may have been due to middle-ear effusions in many cases. Tinnitus is a well-recognized symptom in Fabry disease and can present in childhood. The presence of tinnitus correlated with overall disease severity.

Mucopolysaccharidosis type II (MPS II or Hunter syndrome) is a progressive, multisystemic disease caused by a deficiency of iduronate-2-sulfatase. Patients with the severe form of the disease have cognitive impairment and typically die in the second decade of life. Patients with the less severe form do not experience significant cognitive involvement and may survive until the fifth or sixth decade of life. We studied the relationship of both severity of MPS II and the time period in which patients died with age at death in 129 patients for whom data were entered retrospectively into HOS (Hunter Outcome Survey), the only large-scale, multinational observational study of patients with MPS II. Median age at death was significantly lower in patients with cognitive involvement compared with those without cognitive involvement (11.7 versus 14.1 years; p = 0.024). These data indicate that cognitive involvement is indicative of more severe disease and lower life expectancy in patients with MPS II. Median age at death was significantly lower in patients who died in or before 1985 compared with those who died after 1985 (11.3 versus 14.1 years; p alpha 0.001). The difference in age at death between patients dying in or before, relative to after, the selected cut-off date of 1985 may reflect improvements in patient identification, care and management over the past two decades. Data from patients who died after 1985 could serve as a control in analyses of the effects of enzyme replacement therapy with idursulfase on mortality in patients with MPS II.

Alterations in GLB1, the gene coding for acid beta-D-galactosidase (beta-Gal), can result in GM1 gangliosidosis (GM1), a neurodegenerative disorder, or in Morquio B disease (MBD), a phenotype with dysostosis multiplex and normal central nervous system (CNS) function. While most MBD patients carry a common allele, c.817TG>CT (p.W273L), only few of the >100 mutations known in GM1 can be related to a certain phenotype. In 25 multiethnic patients with GM1 or MBD, 11 missense mutations were found as well as one novel insertion and a transversion causing aberrant gene products. Except c.602G>A (p.R201H) and two novel alleles, c.592G>T (p.D198Y) and c.1189C>G (p.P397A), all mutants resulted in significantly reduced beta-Gal activities (<10% of normal) upon expression in COS-1 cells. Although c.997T>C (p.Y333H) expressed 3% of normal activity, the mutant protein was localized in the lysosomal-endosomal compartment. A homozygous case presented with late infantile GM1, while a heterozygous, juvenile case carried p.Y333H together with p.R201H. This allele, recently found in homozygous MBD, gives rise to rough endoplasmic reticulum (RER)-located beta-Gal precursors. Thus, unlike classical MBD, the phenotype of heterozygotes carrying p.R201H may rather be determined by poorly active, properly transported products of the counter allele than by the mislocalized p.R201H precursors. Hum Mutat 30, 1-8, 2009.(c) 2009 Wiley-Liss, Inc.

Fabry disease is a rare X-linked disorder that leads to widespread and progressive disease manifestations, with patients at risk of premature mortality as a result of renal, cardiovascular or cerebrovascular complications. In recent years there has been a growing awareness that the first signs and symptoms of Fabry disease may begin during childhood. Studies show that clinical manifestations such as pain, hypohidrosis, gastrointestinal disturbances, angiokeratomas, cornea verticillata and acroparaesthesiae may be common in childhood and that such manifestations may become apparent during the first few years of life. Despite the early onset of these signs and symptoms, however, diagnosis is often delayed. Interest is now focused on whether enzyme replacement therapy can slow or prevent the onset of these disease manifestations. Preliminary data from two studies suggest that treatment with agalsidase alfa is well tolerated in children and that it may have beneficial clinical effects; however, further research is needed to determine whether enzyme replacement therapy can prevent the development of disease manifestations. Conclusion: The manifestations of Fabry disease first become apparent during childhood. It is well known that disease-associated manifestations are progressive; however, it has yet to be determined whether specific treatment with enzyme replacement therapy can prevent the development of the associated severe and life-threatening complications.

Glycogen storage disease type IX (GSD type IX) results from a deficiency of hepatic phosphorylase kinase activity. The phosphorylase kinase holoenzyme is made up of four copies of each of four subunits (alpha, beta, gamma and delta). The liver isoforms of the alpha-, beta- and gamma-subunits are encoded by PHKA2, PHKB and PHKG2, respectively. Mutation within these genes has been shown to result in GSD type IX. The diagnosis of GSD type IX is complicated by the spectrum of clinical symptoms, variation in tissue specificity and severity, and its inheritance, either X-linked or autosomal recessive. We investigated 15 patients from 12 families with suspected GSD type IX. Accurate diagnosis had been hampered by enzymology not being diagnostic in five cases. Clinical symptoms included combinations of hypoglycaemia, hepatosplenomegaly, short stature, hepatopathy, weakness, fatigue and motor delay. Biochemical findings included elevated lactate, urate and lipids. We characterised causative mutations in the PHKA2 gene in ten patients from eight families, in PHKG2 in two unrelated patients and in the PHKB gene in three patients from two families. Seven novel mutations were identified in PHKA2 (p.I337X, p.P498L, p.P869R, p.Y116_T120dup, p.R1070del, p.R916W and p.M113I), two in PHKG2 (p.L144P and p.H48QfsX5) and two in PHKB (p.Y419X and c.2336+965A>C). There was a severe phenotype in patients with PHKG2 mutations, a mild phenotype with patients PHKB mutations and a broad spectrum associated with PHKA2 mutations. Molecular analysis allows accurate diagnosis where enzymology is uninformative and identifies the pattern of inheritance permitting counselling and family studies.