RESUMO
INTRODUCTION AND OBJECTIVES: Niemann-Pick disease type A (NPD-A) and B (NPD-B) are lysosomal storage diseases with a birth prevalence of 0.4-0.6/100,000. They are caused by a deficiency in acid sphingomyelinase, an enzyme encoded by SMPD1. We analyzed the phenotype and genotype of four unrelated Mexican patients, one with NPD-A and three with NPD-B. PATIENTS AND METHODS: Four female patients between 1 and 7 years of age were diagnosed with NPD-A or NPD-B by hepatosplenomegaly, among other clinical characteristics, and by determining the level of acid sphingomyelinase enzymatic activity and sequencing of the SMPD1 gene. Additionally, a 775bp amplicon of SMPD1 (from 11:6393835_6394609, including exons 5 and 6) was analyzed by capillary sequencing in a control group of 50 unrelated healthy Mexican Mestizos. RESULTS: An infrequent variant (c.1343A>G p.Tyr448Cys) was observed in two patients. One is the first NPD-A homozygous patient reported with this variant and the other a compound heterozygous NPD-B patient with the c.1829_1831delGCC p.Arg610del variant. Another compound heterozygous patient had the c.1547A>G p.His516Arg variant (not previously described in affected individuals) along with the c.1805G>A p.Arg602His variant. A new c.1263+8C>T pathogenic variant was encountered in a homozygous state in a NPD-B patient. Among the healthy control individuals there was a heterozygous carrier for the c.1550A>T (rs142787001) pathogenic variant, but none with the known pathogenic variants in the 11:6393835_6394609 region of SMPD1. CONCLUSIONS: The present study provides further NPD-A or B phenotype-genotype correlations. We detected a heterozygous carrier with a pathogenic variant in 1/50 healthy Mexican mestizos.
Assuntos
Doença de Niemann-Pick Tipo A/genética , Doença de Niemann-Pick Tipo B/genética , Esfingomielina Fosfodiesterase/genética , Adolescente , Adulto , Criança , Pré-Escolar , Epistaxe/fisiopatologia , Feminino , Triagem de Portadores Genéticos , Genótipo , Transtornos do Crescimento/fisiopatologia , Voluntários Saudáveis , Hepatomegalia/fisiopatologia , Heterozigoto , Humanos , Lactente , Fígado/patologia , Fígado/ultraestrutura , México , Doença de Niemann-Pick Tipo A/metabolismo , Doença de Niemann-Pick Tipo A/patologia , Doença de Niemann-Pick Tipo A/fisiopatologia , Doença de Niemann-Pick Tipo B/metabolismo , Doença de Niemann-Pick Tipo B/patologia , Doença de Niemann-Pick Tipo B/fisiopatologia , Fenótipo , Esfingomielina Fosfodiesterase/metabolismo , Esplenomegalia/fisiopatologia , Adulto JovemRESUMO
Niemann-Pick disease (NPD) type B is a lysosomal storage disorder caused by a deficiency of acid sphingomyelinase (ASM). We report the clinical follow-up of a 16-year-old Mexican mestizo woman with a NPD type B phenotype who presented hepatosplenomegaly, persitstenly low high-density lipoprotein (HDL) cholesterol and thrombocytopenia, without central nervous system involvement. After of a dengue fever episode with severe anemia and pancytopenia, leading to a bone marrow study n which foamy histiocytes were noticed and diagnosis of NiemannPick disease was suspected; and confirmed by biochemical and molecular tests. The missense c.1343 A>G (p.Tyr448Cys, formerly Y446C) and c. 1426C>T (p.Arg476Trp, formerly R474W) mutations in the SMPD1 gene were identified. These mutations have never been reported in the Mexican population. Since the c.1343 A>G (Y446C) mutation has been previously reported in a Japanese patient with NPD type A, we suggest an attenuator effect of c.1426C>T (R474W) allele (previously associated with the NPD type B phenotype). In conclusion, this is the first description of the concomitant occurrence of Y446C and R476W mutations in a Mexican patient with NPD type B, showing the importance of increased awareness and availability of specialized diagnostic tests in the diagnosis of rare inherited metabolic diseases.
Assuntos
Doença de Niemann-Pick Tipo B/genética , Esfingomielina Fosfodiesterase/genética , Adulto , Feminino , Humanos , México , Doença de Niemann-Pick Tipo B/metabolismo , Doença de Niemann-Pick Tipo B/patologia , Adulto JovemRESUMO
Niemann-Pick disease type B (NPDB) is a rare, inherited lysosomal storage disorder that occurs due to variants in the sphingomyelin phosphodiesterase 1 (SMPD1) gene and the resultant deficiency of acid sphingomyelinase (ASM) activity. While numerous variants causing NPDB have been described, only a small number have been studied in any detail. Herein, we describe the frequency of the p.(Ala359Asp) variant in the healthy Chilean population, and determine the haplotype background of homozygous patients to establish if this variant originated from a common founder. Genomic DNA samples from 1691 healthy individuals were analyzed for the p.(Ala359Asp) variant. The frequency of p.(Ala359Asp) was found to be 1/105.7, predicting a disease incidence of 1/44 960 in Chile, higher than the incidence estimated by the number of confirmed NPDB cases. We also describe the clinical characteristics of 13 patients homozygous for p.(Ala359Asp) and all of them had moderate to severe NPDB disease. In addition, a conserved haplotype and shared 280 Kb region around the SMPD1 gene was observed in the patients analyzed, indicating that the variant originated from a common ancestor. The haplotype frequency and mitochondrial DNA analysis suggest an Amerindian origin for the variant. To assess the effect of the p.(Ala359Asp) variant, we transfected cells with the ASM-p.(Ala359Asp) cDNA and the activity was only 4.2% compared with the wild-type cDNA, definitively demonstrating the causative effect of the variant on ASM function. Information on common variants such as p.(Ala359Asp) is essential to guide the successful implementation for future therapies and benefit to patients.