Niemann-Pick disease A or B in four pediatric patients and SMPD1 mutation carrier frequency in the Mexican population.

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.

Cytogenetic profile in 1,921 cases of trisomy 21 syndrome.

BACKGROUND AND AIMS: Trisomy 21 is the most frequent genetic cause of intellectual disability. It is caused by different cytogenetic aberrations: free trisomy, Robertsonian translocations, mosaicism, duplication of the critical region and other structural rearrangements of chromosome 21. The aim of the study was to identify in Mexican trisomy 21 patients who attended Hospital Infantil de México Federico Gómez from 1992-2011 the type and frequency of the cytogenetic aberration and to evaluate the effect of maternal age. METHODS: A retrospective analysis of epidemiological data and karyotype reports were carried out; type and frequency of the cytogenetic variants were determined. RESULTS: We identified 2,018 cases referred with a clinical diagnosis of trisomy 21. In 1,921 analyses (95.2%) a cytogenetic variant of trisomy 21 was identified: free trisomy 21 in 1,787 cases (93.02%), four cases (0.21%) had an additional non-contributory aberration; Robertsonian translocations in 92 cases (4.79%); mosaicism in 31 cases (1.61%) and seven cases (0.36%) had other chromosomal abnormalities, five (0.26%) had other contributory structural rearrangements and two corresponded to double aneuploidies (0.10%). Gender distribution was 1,048 (54.56%) males and 873 (45.44%) females. A maternal age effect was observed in patients with free trisomy 21 with mothers >36 years of age. CONCLUSION: The present work reports the experience of a Mexican referral center regarding the karyotype diagnosis of patients with trisomy 21 and is one of the most extensive studies published so far. Percentages of the cytogenetic abnormalities present in our population reflect the ones previously reported for these cytogenetic alterations worldwide.