FMR1 gene mutations in patients with fragile X syndrome and obligate carriers: 30 years of experience in Chile.

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability (ID) and co-morbid autism. It is caused by an amplification of the CGG repeat (>200), which is known as the full mutation, within the 5'UTR of the FMR1 gene. Expansions between 55-200 CGG repeats are termed premutation and are associated with a greater risk for fragile X-associated tremor/ataxia syndrome and fragile X-associated premature ovarian insufficiency. Intermediate alleles, also called the grey zone, include approximately 45-54 repeats and are considered borderline. Individuals with less than 45 repeats have a normal FMR1 gene. We report the occurrence of CGG expansions of the FMR1 gene in Chile among patients with ID and families with a known history of FXS. Here, we present a retrospective review conducted on 2321 cases (2202 probands and 119 relatives) referred for FXS diagnosis and cascade screening at the Institute of Nutrition and Food Technology (INTA), University of Chile. Samples were analysed using traditional cytogenetic methods and/or PCR. Southern blot was used to confirm the diagnosis. Overall frequency of FMR1 expansions observed among probands was 194 (8·8%), the average age of diagnosis was 8·8 ± 5·4 years. Of 119 family members studied, 72 (60%) were diagnosed with a CGG expansion. Our results indicated that the prevalence of CGG expansions of the FMR1 gene among probands is relatively higher than other populations. The average age of diagnosis is also higher than reference values. PCR and Southern blot represent a reliable molecular technique in the diagnosis of FXS.

[Cytogenetic and molecular profile of genetic diseases in Puerto Montt main hospital]. / Caracterización citogenético-molecular de enfermedades genéticas en el Hospital Base de Puerto Montt.

BACKGROUND: Chromosome aberrations (CA) are the main etiology of multiple congenital malformations, recurrent abortions and intellectual disability (ID) specifically of moderate and severe degree. They account for 0.3 to 1% of newborns (NB) and 6 of 10,000 NB have chromosome imbalances with submicroscopic deletions or duplications smaller than 10 MB that are overlooked by conventional cytogenetic studies. AIM: To report the results of cytogenetic and molecular studies performed in patients with a congenital malformation disease or ID with or without dysmorphic features, attended in a regional hospital. PATIENTS AND METHODS: One hundred and eighty patients, 27 with a clinical diagnosis of Down syndrome, derived for the suspicion of a genetic disease, were studied. A karyogram was performed in all of them and in 30 cases additional molecular studies, such as fluorescence in situ hybridization (FISH) or polymerase chain reaction (PCR) were carried out. RESULTS: Among the 153 patients without Down syndrome, 20 (13%) had a genetic abnormality responsible for the altered phenotype. Sixteen had a chromosome aberration (structural and numerical aberrations in 75 and 25% respectively) and four had genetic molecular alterations. Additional studies were performed to confirm or better characterize the chromosome aberration in 13 of the 30 patients in whom these were requested. CONCLUSIONS: Chromosome and specific genetic molecular studies in selected cases help to characterize patients with genetic diseases. The collaboration between academic and health care facilities is crucial.

Caracterización citogenético-molecular de enfermedades genéticas en el Hospital Base de Puerto Montt / Cytogenetic and molecular profile of genetic diseases in Puerto Montt main hospital

Background: Chromosome aberrations (CA) are the main etiology of múltiple congenital malformations, recurrent abortions and intellectual disability (ID) specifically of modérate and severe degree. They accountfor 0.3 to 1 percent of newborns (NB) and 6 of 10,000 NB have chromosome imbalances with submicroscopic deletions or duplications smaller than 10 MB that are overlooked by conventional cytogenetic studies. Aim: To report the results of cytogenetic and molecular studies performed in patients with a congenital malformation disease or ID with or without dysmorphic features, attended in a regional hospital. Patients and Methods: One hundred and eighty patients, 27 with a clinical diagnosis ofDown syndrome, derivedfor the sus-picion of a genetic disease, were studied. A karyogram was performed in all ofthem and in 30 cases additional molecular studies, such as fluorescence in situ hybridization (FISH) orpolymerase chain reaction (PCR) were carried out. Results: Amongthe 153 patients without Down syndrome, 20 (13 percent) had a genetic abnormality responsible for the altered phenotype. Sixteen had a chromosome aberration (structural and numerical aberrations in 75 and 25 percent respectively) andfour had genetic molecular alterations. Additional studies were performed to confirm or better characterize the chromosome aberration in 13 ofthe 30 patients in whom these were requested. Conclusions: Chromosome and specific genetic molecular studies in selected cases help to characterize patients with genetic diseases. The collaboration between academic and health care facilities is crucial.

Búsqueda de afecciones genéticas como etiología de déficit intelectual en individuos que asisten a escuelas de educación especial / Genetic screening to determine an etiologic diagnosis in children with mental retardation

Background: Mental retardation or intellectual disability affects 2 percent ofthe general population, but in 60 percent to 70 percent of cases the real cause ofthis retardation is not known. An early etiologic diagnosis of intellectual disability can lead to opportunities for improved educational interventions, reinforcing weak aáreas and providing a genetic counseling to the family Aim: To search genetic diseases underíying intellectual disabilities of children attending a special education school. Material and methods: A clinical geneticist performed the history and physical examination in one hundred and three students aged between 5 and 24 years (51 males). A blood sample was obtained in 92 of them for a genetic screening that included a standard karyotype, fragile X molecular genetic testing and search for inborn errors of metabolism by tándem mass spectrometry. Results: This approach yielded an etiological diagnosis in as much as 29 patients. Three percent of them had a fragile X syndrome. Inborn errors of metabolism were not detected. Conclusions: This type of screening should be done always in children with intellectual disability to establish an etiological diagnosis.

Methylation status in healthy subjects with normal and high serum folate concentration.

OBJECTIVE: We assessed the impact of high serum folate concentration on erythrocyte S-adenosylmethionine (SAM), S-adenosylhomocysteine (SAH) concentrations, SAM/SAH ratio, CpG methylation levels across the promoter region of the extracellular superoxide dismutase (ec-SOD) gene, and ec-SOD activity in healthy men. METHODS: Serum folate levels were measured in 111 subjects who were categorized in quintiles according to their folate status. Subjects located at the lowest, middle, and upper quintiles were selected for assessment of SAM and SAH by high-performance liquid chromatography, C677T genotype of the 5,10-methylenetetrahydrofolate reductase (MTHFR) gene, ec-SOD methylation of CpG sites in lymphocytes genomic DNA by bisulfate treatment, and ec-SOD activity by a chemical assay. RESULTS: Sixteen subjects were in the lowest serum folate quintile (<23.6 nmol/L), 17 in the middle (>34-<42 nmol/L), and 14 in the highest (>45nmol/L). SAM concentration was higher in the upper than in the middle and lowest quintiles (5.57 +/- 1.58, 2.52 +/- 0.97, 2.29 +/- 1.2 micromol/L; P < 0.0001). SAH concentration was higher in the upper compared with the lowest quintile (0.76 +/- 0.24 versus 0.52 +/- 0.23 micromol/L, P < 0.001). There were no differences in the SAM/SAH ratio, ec-SOD activity, methylation status of CpG sites of the ec-SOD gene, and TMTHFR C677T genotype between groups. CONCLUSION: Serum folate concentrations in the highest quintile among healthy humans are associated with increased erythrocyte SAM and SAH concentrations, but not with SAM/SAH ratio or with methylation levels of CpG sites across the promoter region of the ec-SOD gene. Further research is required to determine if these findings are beneficial or harmful.

[Genetic screening to determine an etiologic diagnosis in children with mental retardation]. / Búsqueda de afecciones genéticas como etiología de déficit intelectual en individuos que asisten a escuelas de educación especial.

BACKGROUND: Mental retardation or intellectual disability affects 2% of the general population, but in 60% to 70% of cases the real cause of this retardation is not known. An early etiologic diagnosis of intellectual disability can lead to opportunities for improved educational interventions, reinforcing weak areas and providing a genetic counseling to the family. AIM: To search genetic diseases underlying intellectual disabilities of children attending a special education school. MATERIAL AND METHODS: A clinical geneticist performed the history and physical examination in one hundred and three students aged between 5 and 24 years (51 males). A blood sample was obtained in 92 of them for a genetic screening that included a standard karyotype, fragile X molecular genetic testing and search for inborn errors of metabolism by tandem mass spectrometry. RESULTS: This approach yielded an etiological diagnosis in as much as 29 patients. Three percent of them had a fragile X syndrome. Inborn errors of metabolism were not detected. CONCLUSIONS: This type of screening should be done always in children with intellectual disability to establish an etiological diagnosis.

[Frequency of C677T polymorphism of 5, 10-methylenetetrahydrofolate reductase (MTHFR) in Chilean mothers of spina bifida cases and controls ]. / Frecuencia del polimorfismo C677T de la 5, 10-metilentetrahidrofolato reductasa (MTHFR) en mujeres chilenas madres de afectados con espina bífida y en controles normales.

BACKGROUND: Several population studies have shown that patients with neural tube defects (NTD), have a higher frequency of a genetic mutation related with thermolability of the enzyme 5,10-metylentetrahydrofolate reductase (MTHFR). There are regional and ethnic variations in the genotypic or allelic frequency of this mutation and its possible relationship with NTD and others congenital anomalies. AIM: To estimate the frequency of the C677T polymorphism of MTHFR in control women and mothers of spina bifida cases. PATIENTS AND METHODS: We analyzed 58 blood samples from mothers who had a child diagnosed with spina bifida. A group of 184 healthy mothers matched by age and with no NTD offspring served as controls. We determined the C677T polymorphism on the MTHFR gene by means of PCR and the analysis of the digestion pattern of HinfI restriction enzyme. RESULTS: The genotypic frequencies showed concordance with Hardy-Weinberg equilibrium, in controls (p = 0.35), and in mothers of the cases (p = 0.95). The odds ratio to the TT genotype compared with the CC genotype (reference category) was estimated as 1.54 (IC 95%: 0.66-3.61), while the odds ratio for the TC genotype compared with CC genotype was 1.06 (IC 95%: 0.48-2.33). CONCLUSION: No differences in the C677T polymorphism of the MTHFR were observed between mothers who had a child diagnosed with spina bifida and control mothers.