Rapid One-Step Carrier Detection Assay of Mucolipidosis IV Mutations in the Ashkenazi Jewish Population

Two mutations in the MCOLN1 mucolipidosis IV (ML IV) gene represent approximately 95% of the mutations in Ashkenazi-Jewish patients with ML IV. The mutations, a splice site mutation (IVS3-2AG) and an approximately 6.4-kb deletion (511del6434), account for 72% and 23% of ML IV alleles in this population, respectively. An automated high-throughput assay was developed using the 5'-nuclease (TaqMan) method for the simultaneous detection of both mutations in a single reaction. Three fluorescent probes specifically detected wild-type, IVS3-2AG, and 511del6434 alleles in each reaction real-time. Data collected were automatically analyzed, and genotype results were uploaded into a laboratory information management system. The assay was validated using genomic controls, demonstrating high robustness and accuracy. Carrier screening of 10,527 samples revealed 77 heterozygote carriers of IVS3-2AG, 25 heterozygote carriers of 511del6434, and two compound heterozygote of both mutant alleles. The frequency of mutated alleles was 0.73% for IVS3-2AG and 0.24% for 511del6434. The combined carrier frequency was 1:103 with predicted disease incidence of 1:42,436 individuals in this population, slightly lower than previously described frequencies. This automated high-throughput assay is labor saving, because two mutations can be detected in a single reaction. The method has potential for use in other assays requiring simultaneous detection of two mutations.