Multi Centric Collaborative Study Of The Clinical Biochemical and Molecular Characterization Of Lysosomal Storage Disorders In India. The Indian Initiative For Research in Lysosomal Storage Disorders
Lysosomal storage disorders (LSD) result from the inherited deficiency of 1 or more of the mostly catabolic enzymes that are located within the Lysosome. Their prevalence in India is yet unknown. As a group, LSDs occur in approximately one in 5000 live births. However, the treatable disorders are extremely rare and have incidence ranging from 1 in 40,000 to 1 in 100,000 births (1) .
If the above data is extrapolated ,in India, every year, around 500 babies born every year are likely to be affected by treatable LSDs where as approximately 3000 new cases of LSD are born every year . The number actually diagnosed with an LSD would be much lesser, as a significant proportion may not come to light owing to poor index of suspicion amongst our medical fraternity, poor diagnostic facilities. So it may be reasonable to assume that approximately 100 such patients may be added to the pool every year. Even the global data reflect that around 10,000 patients are currently receiving enzyme replacement therapy. In Delhi, 3-5 babies born every year are expected to be diagnosed with treatable LSDs.
Accurate diagnosis is imperative for genetic counseling for future pregnancies because most of the LSD are autosomal recessively inherited. With the development of new treatments for several of the LSDs, the diagnostic requirements are also changing. The efficiency of many of the proposed treatments relies heavily on early detection and initiation of treatment before onset of irreversible pathology.
Although many of the clinical presentations of different LSD primarily result from substrate storage, these presentations vary greatly depending upon type, quantity and site of the accumulated storage material. Because there is an overlap of clinical features in many of the LSD it is difficult to establish a diagnosis solely based on clinical presentation. There is paucity of centers geared up to diagnose these disorders, difficulties in transport of blood samples, duplicity of efforts and absence of a clearcut defined group motivated to look into these largely heterogeneous group of disorders, hence the NIRI- LSD group would attempt to look into the various aspects of LSDs.
1. To establish a smooth network of referral and counseling facilities for affected families.
Lysosomal storage disorders are rare inborn errors of metabolism, with a combined incidence of 1in 1500 to 7000 live births. These relatively rare disorders are seldom considered when evaluating a sick child with organomegaly, developmental delay or neurocognitive decline. A significant number of the >50 different lysosomal storage disorders are now known. Although many of the lysosomal storage disorders are characterized by a range in phenotypes, the focus of this project is on the specific types of LSDs which have a relatively higher prevalence and may present with a plethora of neurologic, respiratory, endocrine, and cardiovascular manifestations, dysmorphic features, hepatosplenomegaly, skin orocular involvement, and hydrops fetalis/congenital ascites. A greater awareness of these features in the collaborating group and their undergraduate and post graduates may help to reduce misdiagnosis and promote the early detection of lysosomal storage disorders. Implementing therapy at the earliest stage possible is crucial for several of the lysosomal storage disorders; hence, an early appreciation of these disorders by physicians involved is essential. Diagnostic testing can be done withA) Urine:- Elevated levels of the solvated substrate material are used to screen for example glycosaminoglycans(GAGs) and oligosaccharides in patients having suspected MPS or disorders that present with Oligosaccharides such as I cell disease mucolipidosis type 3, GM1 gangliosidosis type 2, fucosidosis α manosidosis , sialidosis , galactosemia. GAGs can be determined by spectrophotometric technique. Urine screens are sensitive but these are reports of affected individuals having normal screens.
B) Enzyme assay: - Enzyme assays can be performed on a combination of leucocytes and plasma and predominantly include enzymes involved in digestion of glucose phenotypes and oligosaccharides. Diseases tested for include Gauchers Disease; Neimann Pick disease types A & B and lipase deficiency, GM1 and GM2 gangliosidosis, Krabbes disease, Metachromatic leucodystrophy, mucolipidosis type 2 & 3, Fucosidosis, α - manosidosis, MPS type 3 and Schindler disease. Although measurement of enzyme activity in leucocytes and plasma enables the diagnosis of most LSD a proportion may not be detected by this method for example in Sialodosis and Pompe disease, the distinction between normal and affected could be very narrow and the diagnostic analysis should be performed on cultured fibroblast. When leucocytes assays are not reliable the another method of enzyme analysis to assay hair roots that develop form progenitor cells. Since individually rare, the testing needs to be performed at laboratories dedicated for it completely. Transport of blood or leucocytes in thawed state from India is a difficult task in summers.. Although free thawed WBCs are usually good enough, dry ice is required which is not freely available. There is also a wide CV on the tested methods and in between labs.
C) Dried blood spots:- Since the introduction of dried blood spots for the use of multiple enzyme assay by Tandem Mass Spectrometry using 5mm DBS, there has been a revolution in the diagnosis of LSDs. The assays have proved to be reproducible and reliable for the differentiations of normal and disease specific samples. Due to ease of transport of these dried blood samples and reproducibility they have also gained momentum in newborn screening for IMDs specifically for the treatable IMDs
D) Role of Biomarkers:- Many LSDs are currently treatable and a reliable biomarkers may be a useful tool to monitor therapy. Since the discovery of chitotriosidase which is secreted massively by Gaucher cell and is used is an important tool to monitor therapy, new chemokines are being evaluated and include CCL18/PARC, Heparin thrombin co-factor, LAMB 1 & LAMB 2.
E) Role of Molecular Tools:-Enzyme assay, the primary tool for diagnosis has till date been utilized for diagnosis of carries and accurate prenatal diagnosis. This tool has a lot of disadvantages. There is a large amount of overlap in enzyme levels among carrier and normal people; hence it is very difficult to detect carriers by enzyme assay. Knowing the mutation may also be very useful in prenatal diagnosis and genotype , phenotype correlation.
Utility of a smooth referral approach:-Individually rare but collectively common, most parents and treating physicians are unaware of centers geared for diagnosis, confirmation and monitoring also there are genetecists who are duplicating efforts on same disorders. If a common consensus regarding diagnosis and treatment can be achieved it will be a remarkable achievement which will prevent duplicity of efforts, maintain individuality of each insulation who can further perfect each component of research in the individual disease
Quality Control , External Quality Control will be organized through EMQN for molecular Genetic testing and ERNDIM for Biochemical tests
To summarize the draft proposal deals with organization of research in the field of Lysosomal Storage Disorders, the commonest inborn metabolic disorders of the large molecule type. It also aims at a particular level of diagnostic accuracy in the field of LSDs with interlab and intralab IQA, development of registry and a parent support group and to study geoethnic aspect of genotype phenotype correlations in Lysosomal Storage Disorders. It is practically designed to omit duplication, ensure quality channel and propagate further research and form an open forum for patient physician interaction built in private public partnership context.