Prevalence of lysosomal storage disorders in Australia from 2009 to 2020.

BACKGROUND: Lysosomal storage disorders (LSD) are a family of genetic diseases that have a devastating impact on the patient and family with a concomitant health burden. Although considered rare disorders, improved diagnostic capabilities, newborn screening programs and public awareness has witnessed the frequency of many LSD increase considerably over recent years. To quantify their footprint, the number of LSD diagnosed in the multicultural Australian population in a 12-year period was determined. The principle objective was to yield contemporary prevalence figures to inform public health policies. METHODS: From the national referral laboratory for LSD diagnoses in Australia, retrospective data from patient referrals and prenatal testing for the period January 1 2009 to December 31 2020 were collated. Diagnosis was established biochemically by enzyme activity and/or metabolite determinations, as well as molecular genetic testing. The incidence of each disorder was determined by dividing the number of postnatal diagnoses by the number of births with prevalence including prenatal diagnoses. FINDINGS: During this 12-year period 766 diagnosis of LSD were confirmed inclusive of 32 prenatal outcomes representing 38 individual disorders. Total diagnosis per 100,000 live births averaged 21 per year (range 16 - 26) with Fabry disease the most prevalent representing 34% of all diagnoses in the current (up to 2020) report. INTERPRETATION: The combined prevalence of LSD for this study period at 1 per 4,800 live births is considerably higher than 1 per 7,700 reported for a 17-year period up to 1996. Additionally, more adults were diagnosed than children, implying that LSD are more common in adulthood than childhood. These data highlight the requirements for physicians to consider LSD in symptomatic adults and should refigure public health policies steering newborn screening programs in the direction of adult-onset conditions. FUNDING: No funding was received for this study.

Chondroitin sulfate disaccharide is a specific and sensitive biomarker for mucopolysaccharidosis type IVA.

Mucopolysaccharidosis type IVA (MPS IVA) is an inborn error of glycosaminoglycan (GAG) catabolism characterized by a deficiency of the lysosomal enzyme, N-acetylgalactosamine 6-sulphatase (GALNS). Consequently, partially degraded GAG, chondroitin 6-sulfate (CS) and keratan sulfate (KS), accumulate in the lysosomes of affected cells, primarily in cartilage resulting in skeletal disease. Excessive urinary excretion of these GAG is often used as the initial biochemical parameter to inform a laboratory diagnosis. Here we present the utility of a CS-disaccharide with a non-reducing 6-sulfated N-acetylgalactosamine residue (HNAc-UA (1S))-the enzyme's substrate-for the diagnosis and biochemical monitoring of MPS IVA patients. Following implementation of this method into the diagnostic laboratory, we identified one MPS IVA patient over 3 years of MPS urine screening, with no false positive results from 2050 urines tested. Uniquely, urinary concentrations of HNAc-UA (1S) are independent of age meaning that age-related reference ranges are not required. Urinary HNAc-UA (1S) was also able to identify two MPS IVA siblings who remained misdiagnosed with spondyloepiphyseal dysplasia for 5 years because of normal urinary GAG. HNAc-UA (1S) could also be used as a biomarker for monitoring response to enzyme replacement therapy (ERT) as there was a drop in urinary concentration following the administration of ERT in all 12 patients and concentrations correlated with urinary KS (R 2 = 0.92). In conclusion, HNAc-UA (1S) is a reliable, sensitive and specific biomarker for the diagnosis of MPS IVA and can be used to biochemically monitor the response to ERT.

Expanding the clinical utility of glucosylsphingosine for Gaucher disease.

Gaucher disease (GD) is an inherited metabolic disorder characterised by impaired catabolism of the glycosphingolipid, glucosylceramide. The deacetylated derivative, glucosylsphingosine (GluSph, lyso-Gb1) has materialised as a biomarker for GD. Further appraisal of the clinical utility of GluSph is required in terms of its prognostic power to inform disease course and pre-symptomatic testing. In this study, we show that plasma GluSph concentrations are significantly higher in GD patients with neuronopathic disease compared with non-neuronopathic disease, even in the neonatal period. A neonate diagnosed at 1 day of age (homozygous for N370S) due to an affected older sibling, returned GluSph of 70 nmol/L compared with 1070-2620 nmol/L for four neuronopathic patients diagnosed <20 days of age. Given this result shows promise for newborn screening, we developed a rapid, simple, and robust assay for GluSph in dried filter paper blood spots (DBS) and were able to detect 23 GD patients from 220 unaffected individuals. Neuronopathic GD patients also had significantly higher DBS concentrations of GluSph than their non-neuronopathic counterparts. We went on to measure GluSph in tissue extracts prepared from chorionic villus sampling and confirmed concentrations were undetectable in unaffected tissue but elevated in GD tissue demonstrating utility in the prenatal setting. Additionally, GluSph is a pharmacodynamic biomarker, revealing a precipitous drop following initiation of enzyme replacement therapy. In conclusion, GluSph is a reliable and specific biomarker for GD and shows promise for prenatal diagnosis and DBS screening programmes.