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Mucolipidosis (ML) (OMIM 607840 & 607838) is a rare autosomal recessive inherited disorder that occurs due to the deficiency of golgi enzyme uridine diphosphate (UDP)- N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase) responsible for tagging mannose-6-phosphate for proper trafficking of lysosomal enzymes to lysosomes. Variants in GlcNAc-phosphotransferase (GNPTAB (α, β subunits) and GNPTG (γ subunits) are known to result in impaired targeting of lysosomal enzymes leading to Mucolipidosis (ML) Type II or Type III. We analyzed 69 Indian families of MLII/III for clinical features and molecular spectrum and performed in silico analysis for novel variants. We identified 38 pathogenic variants in GNPTAB and 5 pathogenic variants in GNPTG genes including missense, frame shift, deletion, duplication and splice site variations. A total of 26 novel variants were identified in GNPTAB and 4 in GNPTG gene. In silico studies using mutation prediction software like SIFT, Polyphen2 and protein structure analysis further confirmed the pathogenic nature of the novel sequence variants detected in our study. Except for a common variant c.3503_3504delTC in early onset MLII, we could not establish any other significant genotype and phenotype correlation. This is one of the largest studies reported till date on Mucolipidosis II/III in order to identify mutation spectrum and any recurrent mutations specific to the Indian ethnic population. The mutational spectrum information in Indian patients will be useful in better genetic counselling, carrier detection and prenatal diagnosis for patients with ML II/III.

Mucolipidosis (ML) (OMIM 607840607838) is a rare autosomal recessive inherited disorder that occurs due to the deficiency of golgi enzyme uridine diphosphate (UDP)- N-acetylglucosamine-1-phosphotransferase (GlcNAc-phosphotransferase) responsible for tagging mannose-6-phosphate for proper trafficking of lysosomal enzymes to lysosomes. Variants in GlcNAc-phosphotransferase (GNPTAB (α, β subunits) and GNPTG (γ subunits) are known to result in impaired targeting of lysosomal enzymes leading to Mucolipidosis (ML) Type II or Type III. We analyzed 69 Indian families of MLII/III for clinical features and molecular spectrum and performed in silico analysis for novel variants. We identified 38 pathogenic variants in GNPTAB and 5 pathogenic variants in GNPTG genes including missense, frame shift, deletion, duplication and splice site variations. A total of 26 novel variants were identified in GNPTAB and 4 in GNPTG gene. In silico studies using mutation prediction software like SIFT, Polyphen2 and protein structure analysis further confirmed the pathogenic nature of the novel sequence variants detected in our study. Except for a common variant c.3503_3504delTC in early onset MLII, we could not establish any other significant genotype and phenotype correlation. This is one of the largest studies reported till date on Mucolipidosis II/III in order to identify mutation spectrum and any recurrent mutations specific to the Indian ethnic population. The mutational spectrum information in Indian patients will be useful in better genetic counselling, carrier detection and prenatal diagnosis for patients with ML II/III.

Background Mucopolysaccharidosis type VII (MPS VII - Sly disease) is a very rare lysosomal storage disorder caused by biallelic variants in the GUSB gene. Materials and methods We report here an Asian Indian family with recurrent non-immune fetal hydrops where lysosomal enzyme analysis in the prenatal sample (cultured amniocytes) revealed the diagnosis of MPS VII and molecular genetic testing of the GUSB gene was performed through next generation sequencing (NGS). Results A novel homozygous likely pathogenic missense variant (c.893C>T; p.Ala298Val) was detected in the GUSB gene. Further in silico analysis of the variant using mutation prediction software and in silico protein modeling was done, to understand the pathogenicity of the variant and its effect on the protein structure. Discussion and conclusion NGS can be used for mutation analysis of genes with multiple pseudogenes, but subsequent Sanger sequencing-based validation through selective amplification of the concerned exon from the actual gene is essential for confirmation. This is the first mutation report of the GUSB gene from India.

MPS VI is an autosomal recessive disorder which occurs due to the deficiency of N-acetyl galactosamine-4-sulfatase (Arylsulfatase B - ARSB) involved in catabolism of dermatan sulfate resulting from disease-causing variations in the ARSB gene. Human Gene Mutation Database (HGMD) search revealed 200 different mutations in ARSB worldwide. In the present study we carried out molecular and functional analyses to characterize the mutations reported by us in Indian population. Mutation analysis of 19 MPS VI patients revealed presence of a total of 15 different mutations of which twelve were novel [p.Asp53Asn (c.157G>A; p.D53N), p.Leu98Arg (c.293T>G; p.L98R), p.Tyr103Serfs*9 (c.306_312delCTACCAG+146del; p.Y103Sfs*9), p.Phe166Leufs*18 (c.496delT; p.F166Lfs*18), p.Ile220Serfs*5 (c.659_660delTA; p.I220Sfs*5), p.Ile350Phe (c.1048A>T; p.I350F), p.Trp353* (c.1059G>A; p.W353*), p.His393Arg (c.1178A>G; p.H393R), p.Ser403Tyrfs* (c.1208delC; p.S403Yfs*), p.Pro445Leu (c.1334C>T; p.P445L), p.Trp450Leu (c.1349G>T; p.W450L) and p.Trp450Cys (c.1350G>C; p.W450C)] and three were known mutations [p.Asp54Asn (c.160G>A; p.D54N), p.Ala237Asp (c.710C>A; p.A237D) and p.Ser320Arg (c.960C>G; p.S320R)]. Functional characterization using site-directed mutagenesis followed by cell transfection assays, immunoblot, reverse transcriptase PCR and immunofluorescence studies for the putative pathogenic variants detected in our MPS VI patient cohort helped us to confirm the pathogenic potential of the variants in ARSB.