Lorena Santa María

A frameshift insertion in the cone cyclic nucleotide gated cation channel causes complete achromatopsia in a consanguineous family from a rural isolate

Complete achromatopsia is genetically heterogeneous and segregates with mutations in CNGA3 or CNGB3 genes, which respectively encode for α- and β-subunits of the cyclic-nucleotide-gated (CNG) cation channel expressed in cone photoreceptors. High incidence of the disease (1 in 60) was detected in a rural isolate in central Chile. We excluded previously reported mutations in a consanguineous kindred with five affected members. Genotype analysis with short tandem repeat polymorphic (STRP) markers provided evidence to search for the causative mutation in CNGB3. Two sequence variations, c.492_493insT and c.488A>G, flanking an adenosine (A5) repeat in exon 4 were identified. The frameshift mutation creates two consecutive stop codons in exon 5 that would induce premature translation termination. The severely truncated β-subunit is likely to render a nonfunctional cone CNG channel and cause total colour blindness in this kindred.

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 (Rev Med Chile 2003; 131: 1399-404).

Identification of Males with Cryptic Fragile X Alleles by Methylation-Specific Quantitative Melt Analysis

BACKGROUND FMR1 full mutations (FMs) (CGG expansion >200) in males mosaic for a normal (<45 CGG) or gray-zone (GZ) (45-54 CGG) allele can be missed with the standard 2-step fragile X syndrome (FXS) testing protocols, largely because the first-line PCR tests showing a normal or GZ allele are not reflexed to the second-line test that can detect FM. METHODS We used methylation-specific quantitative melt analysis (MS-QMA) to determine the prevalence of cryptic FM alleles in 2 independent cohorts of male patients (994 from Chile and 2392 from Australia) referred for FXS testing from 2006 to 2013. All MS-QMA-positive cases were retested with commercial triplet primed PCR, methylation-sensitive Southern blot, and a methylation-specific EpiTYPER-based test. RESULTS All 38 FMs detected with the standard 2-step protocol were detected with MS-QMA. However, MS-QMA identified methylation mosaicism in an additional 15% and 11% of patients in the Chilean and Australian cohorts, respectively, suggesting the presence of a cryptic FM. Of these additional patients, 57% were confirmed to carry cryptic expanded alleles in blood, buccal mucosa, or saliva samples. Further confirmation was provided by identifying premutation (CGG 55-199) alleles in mothers of probands with methylation-sensitive Southern blot. Neurocognitive assessments showed that low-level mosaicism for cryptic FM alleles was associated with cognitive impairment or autism. CONCLUSIONS A substantial number of mosaic FM males who have cognitive impairment or autism are not diagnosed with the currently recommended 2-step testing protocol and can be identified with MS-QMA as a first-line test.

Update on the Clinical, Radiographic, and Neurobehavioral Manifestations in FXTAS and FMR1 Premutation Carriers

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disorder caused by a repeat expansion in the fragile X mental retardation 1 (FMR1) gene. The disorder is characterized by kinetic tremor and cerebellar ataxia, shows age-dependent penetrance, and occurs more frequently in men. This paper summarizes the key emerging issues in FXTAS as presented at the Second International Conference on the FMR1 Premutation: Basic Mechanisms & Clinical Involvement in 2015. The topics discussed include phenotype-genotype relationships, neurobehavioral function, and updates on FXTAS genetics and imaging.

Caracterización clínico-genético-molecular de 45 pacientes chilenos con Síndrome de Prader Willi

Background: Prader-Willi syndrome (PWS) is a neurogenetic disease characterized by neonatal hypotonia, retarded mental and motor development, hypogonadism, hyperphagia, morbid obesity and dysmorphic facial features. It has an incidence of 1:12.000-15.000 newborns and is caused by abnormalities in genes located in 15q11q13. PWS is one of the most frequent genetic disorders and microdeletion syndromes. It is also the most common cause of obesity from genetic origin and it was the first disease in which imprinting and uniparental disomy were recognized as cause of genetic disorders. Seventy to seventy five percent of PWS cases are due to 15q11q13 deletions, 20-25% to uniparental disomy and 1% to mutations in the imprinting center. Aim: To analyze the clinical, genetic and molecular features of patients with PWS, seen at one institution. Patients and methods: Retrospective review of 45 patients (27 males) with PWS seen at the Genetics Outpatient Clinic at INTA. Results: Twenty three (51.1%) patients had a delection, 13 (28.9%) patients did not have a deletion. In nine patients, fluorescence in situ hybridization (FISH) study was not performed, therefore the presence of deletion was unknown. The clinical score was 8 points for patients younger than 3 years (n=11) and 11.5 points for patients older than 3 years (n=34); for patients aged 12 months or less, the clinical score was 7 points. Mean clinical score was 11 points for patients with deletion and 10 points for patients without deletion. Conclusions: Most patients with PWS have a deletion; the phenotype depends on age and the clinical score is useful for Chilean patients with PWS (Rev Med Chile 2005; 133: 33-41).

Tamizaje clínico y análisis de mutaciones en el gen FMR1 en 99 varones con características clínicas del síndrome de X-frágil

Introduccion: El sindrome de X fragil (SXF) es una causa frecuente de retraso mental (RM), se presenta en 1 de 4 000 hombres y en 1 de 8 000 mujeres. A nivel molecular existen principalmente tres tipos de alteraciones: premutacion, mutacion completa y mosaicos, todas las cuales corresponden a amplificacion del trinucleotido CGG localizado en el primer exon del gen FMR1: las premutaciones presentan entre 52 y 200 repetidos; las mutaciones completas, sobre 200 CGG, presentan hipermetilacion de la region promotora del gen FMR1 e inhibicion de la expresion de la proteina FMRP, causante del RM y dismorfias caracteristicas de este sindrome. Los mosaicos presentan mutacion completa y premutacion o metilacion parcial del gen FMR1. Los pacientes con SXF son diagnosticados clinicamente segun un protocolo de tamizaje que considera 15 caracteristicas clinicas que entrega un puntaje maximo de 30 puntos en individuos afectados. Objetivo: Definir criterios clinicos especificos para poblacion chilena que ayuden a identificar a los individuos que deban ser sometidos a estudios moleculares confirmatorios de SXF. Pacientes y Metodo: Se consideraron 99 pacientes varones referidos al INTA por presentar retraso mental y caracteristicas clinicas sugerentes del SXF; a todos se les realizo evaluacion clinica utilizando el protocolo descrito por Buttler y estudio molecular con analisis directo del gen FMR1 por Southern blot. Resultados: 23 de los 99 pacientes estudiados presentaron una mutacion en FMR1 y puntaje clinico entre 16 y 27 puntos; los 76 casos restantes con puntajes clinicos entre 10 y 26 puntos, no presentaron mutacion en el gen FMR1. Se evaluaron las caracteristicas clinicas en ambos grupos y se observo que 4 de ellas se asocian significativamente a la mutacion, siendo tres de ellas independientes de la edad de los pacientes. Conclusiones: Con estos resultados y a fin de optimizar el estudio molecular directo del gen FMR1, proponemos que el criterio de seleccion de pacientes sea a traves del examen clinico y que todo individuo con puntaje ³ 15 puntos debe ser sometido al estudio molecular

Diagnóstico molecular de los síndromes de Prader-Willi y de Angelman: análisis de metilación, citogenética y FISH

Background: The diagnosis of Prader-Willi and Angelman syndromes is difficult, since their phenotypic manifestations are variable and unspecific. The study of the methylation state of DNA in l5(q11-q13) using polymerase chain reaction, called methylation test, allows the diagnosis of most patients with Prader-Willi and Angelman syndromes, irrespective if the underlying molecular alteration is a deletion, uniparental disomy or a punctual imprinting mutation. Aim: To assess the effectiveness of methylation test in the diagnosis of Prader-Willi and Angelman syndromes. Patients and methods: Thirty seven cases with a presumptive diagnosis of Prader-Willi syndrome and 25 with the presumptive diagnosis of Angelman syndrome were studied. Methylation test was done in genomic DNA obtained from peripheral Iymphocytes. Results: Methylation test confirmed the clinical diagnosis in 11 of 37 patients with PraderWilli (30%) and 6 of 25 patients with Angelman syndrome (24%). Conclusions: Clinical criteria overestimate the diagnosis of Prader-Willi and Angelman syndromes. The initial diagnosis should be confirmed with the methylation test and, if necessary, with FISH that will detect most deletions in the region. (Rev Med Chile 2001, 129: 367-374)

Molecular classes in 209 patients with Prader–Willi or Angelman syndromes: Lessons for genetic counseling

Conflict of Interest: None Correspondence to: Dr. Vı́ctor Faundes, Laboratorio de Genética y Enfermedades Metabólicas, Instituto de Nutrición y Tecnologı́a de los Alimentos (INTA), Universidad de Chile, Av. El Lı́bano 5524, P.O. 7830490, Santiago, Chile. E-mail: vfaundes@inta.cl Article first published online in Wiley Online Library (wileyonlinelibrary.com): 6 October 2014 DOI 10.1002/ajmg.a.36801 TO THE EDITOR:

Distal 7q11.23 Duplication, an Emerging Microduplication Syndrome: A Case Report and Further Characterisation

Chromosome 7q11.23 duplication syndrome is a well-recognised syndrome which involves the duplication of the same genes located in the Williams-Beuren critical region. However, in 2010, 4 patients were reported with a microduplication only in the HIP1 and YWHAG genes. We refer to this as a distal 7q11.23 duplication (dup7q11.23D). Here, we report the fifth de novo patient with dup7q11.23D, whose symptoms may be explained by YWHAG overexpression as was demonstrated recently in mice and obese patients. Finally, further studies will be necessary to delineate this emerging microduplication syndrome.

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.