Clinical utility of multiplex ligation-dependent probe amplification technique in identification of aetiology of unexplained mental retardation: a study in 203 Indian patients.

BACKGROUND & OBJECTIVES: Developmental delay (DD)/mental retardation also described as intellectual disability (ID), is seen in 1-3 per cent of general population. Diagnosis continues to be a challenge at clinical level. With the advancement of new molecular cytogenetic techniques such as cytogenetic microarray (CMA), multiplex ligation-dependent probe amplification (MLPA) techniques, many microdeletion/microduplication syndromes with DD/ID are now delineated. MLPA technique can probe 40-50 genomic regions in a single reaction and is being used for evaluation of cases with DD/ID. In this study we evaluated the clinical utility of MLPA techniques with different probe sets to identify the aetiology of unexplained mental retardation in patients with ID/DD. METHODS: A total of 203 randomly selected DD/ID cases with/without malformations were studied. MLPA probe sets for subtelomeric regions (P070/P036) and common microdeletions/microduplications (P245-A2) and X-chromosome (P106) were used. Positive cases with MLPA technique were confirmed using either fluorescence in situ hybridization (FISH) or follow up confirmatory MLPA probe sets. RESULTS: The overall detection rate was found to be 9.3 per cent (19 out of 203). The detection rates were 6.9 and 7.4 per cent for common microdeletion/microduplication and subtelomeric probe sets, respectively. No abnormality was detected with probe set for X-linked ID. The subtelomeric abnormalities detected included deletions of 1p36.33, 4p, 5p, 9p, 9q, 13q telomeric regions and duplication of 9pter. The deletions/duplications detected in non telomeric regions include regions for Prader Willi/Angelman regions, Williams syndrome, Smith Magenis syndrome and Velocardiofacial syndrome. INTERPRETATION & CONCLUSIONS: Our results show that the use of P245-A2 and P070/P036-E1 probes gives good diagnostic yield. Though MLPA cannot probe the whole genome like cytogenetic microarray, due to its ease and relative low cost it is an important technique for evaluation of cases with DD/ID.

Exome Sequencing in Monogenic Forms of Rickets.

OBJECTIVE: To understand the phenotypic and genotypic spectrum of genetic forms of rickets in 10 families. METHODS: Detailed clinical, radiographic, and biochemical evaluation of 10 families with phenotypes suggestive of a genetic cause of rickets was performed. Molecular testing using exome sequencing aided in the diagnosis of six different forms of known genetic causes. RESULTS: Eleven disease-causing variants including five previously reported variants (CYP27B1:c.1319_1325dup, p.(Phe443Profs*24), VDR:c.1171C>T, p.(Arg391Cys), PHEX: c.1586_1586+1del, PHEX: c.1482+5G>C, PHEX: c.58C>T, p.(Arg20*)) and six novel variants (CYP27B1:c.974C>T, p.(Thr325Met), CYP27B1: c.1376G>A, p.(Arg459His), CYP2R1: c.595C>T, p.(Arg199*), CYP2R1:c.1330G>C, p.(Gly444Arg),SLC34A3:c.1336-11_1336-1del, SLC2A2: c.589G>C, p.(Val197Leu)) in the genes known to cause monogenic rickets were identified. CONCLUSION: The authors hereby report a case series of individuals from India with a molecular diagnosis of rickets and provide the literature review which would help in enhancing the clinical and molecular profile for rapid and differential diagnosis of rickets.