Twenty-five years since the identification of the first SCA gene: history, clinical features and perspectives for SCA1 / Vinte e cinco anos desde a identificação do primeiro gene das SCAs: história, aspectos clínicos e perspectivas para a SCA1

ABSTRACT Spinocerebellar ataxias (SCA) are a clinically and genetically heterogeneous group of monogenic diseases that share ataxia and autosomal dominant inheritance as the core features. An important proportion of SCAs are caused by CAG trinucleotide repeat expansions in the coding region of different genes. In addition to genetic heterogeneity, clinical features transcend motor symptoms, including cognitive, electrophysiological and imaging aspects. Despite all the progress in the past 25 years, the mechanisms that determine how neuronal death is mediated by these unstable expansions are still unclear. The aim of this article is to review, from an historical point of view, the first CAG-related ataxia to be genetically described: SCA 1.

RESUMO As ataxias espinocerebelares (SCA) são um grupo clínico e geneticamente heterogêneo de doenças monogênicas que compartilham ataxia e herança autossômica dominante como características principais. Uma proporção importante de SCAs é causada por expansões de repetição de trinucleotídeos CAG na região de codificação de diferentes genes. Além da heterogeneidade genética, os aspectos clínicos transcendem os sintomas motores, incluindo aspectos cognitivos, eletrofisiológicos e de imagem. Apesar de todo o progresso feito nos últimos 25 anos, os mecanismos que determinam como se dá a morte neuronal mediada por essas expansões instáveis ainda não estão claros. O objetivo deste artigo é revisar, de um ponto de vista histórico, a primeira ataxia geneticamente relacionada com o CAG descrita: SCA 1.

Spinocerebellar ataxia 7 (SCA7) in Indian population: predilection of ATXN7-CAG expansion mutation in an ethnic population.

Background & objectives: spinocerebellar ataxia 7 (SCA7) is a rare form of neurodegenerative disorder with the clinical manifestation of cerebellar ataxia and retinal degeneration. In this study we describe the clinico-genetic characteristics of nine SCA7 families of Indian origin and cross compare these with other available worldwide studies. Methods: Thirty five individuals from nine SCA7 families were clinico-genetically characterized and CAG repeat distribution analysis was carried out in 382 control DNA samples from healthy controls (derived from 21 diverse Indian populations based on ethnic and linguistic and geographical location). Results: Of the nine families studied, 22 affected individuals and one asymptomatic carrier were identified. The average age at disease onset was 23.4±12.6 yr. The length of expanded CAG ranged from 40-94 with mean value of 53.2±13.9. The main clinical findings in affecteds individuals included cerebellar ataxia, and retinal degeneration along with hyper-reflexia (95%), slow saccades (85%) and spasticity (45%). Analysis of the association of number of CAG repeats with disease onset revealed that <49 repeats were associated with earlier age at onset in South East Asians compared to European populations. Further analysis of CAG repeats from 21 diverse Indian populations showed pre-mutable repeats (28-34) alleles in the IE-N-LP2 population. Six of the nine families identified in this study belonged to the same ethnic population. Interpretations & conclusion: Our results show that presenece of SCA7 is relatively rare and confined to one ethnic group from Haryana region of India. We observed a homogeneous phenotypic expression of SCA7 mutation as described earlier and an earlier age of onset in our patients with CAG <49. The identification of pre-mutable allele in IE-N-LP2 suggests this population to be at the risk of SCA7.

No CAG repeat expansion of polymerase gamma is associated with male infertility in Tamil Nadu, South India.

Mitochondria contains a single deoxyribonucleic acid (DNA) polymerase, polymerase gamma (POLG) mapped to long arm of chromosome 15 (15q25), responsible for replication and repair of mitochondrial DNA. Exon 1 of the human POLG contains CAG trinucleotide repeat, which codes for polyglutamate. Ten copies of CAG repeat were found to be uniformly high (0.88) in different ethnic groups and considered as the common allele, whereas the mutant alleles (not -10/not -10 CAG repeats) were found to be associated with oligospermia/oligoasthenospermia in male infertility. Recent data suggested the implication of POLG CAG repeat expansion in infertility, but are debated. The aim of our study was to explore whether the not -10/not -10 variant is associated with spermatogenic failure. As few study on Indian population have been conducted so far to support this view, we investigated the distribution of the POLG CAG repeats in 61 infertile men and 60 normozoospermic control Indian men of Tamil Nadu, from the same ethnic background. This analysis interestingly revealed that the homozygous wild type genotype (10/- 10) was common in infertile men (77% - 47/61) and in normozoospermic control men (71.7% - 43/60). Our study failed to confirm any influence of the POLG gene polymorphism on the efficiency of the spermatogenesis.

Clinical and genetic analysis of 29 Brazilian patients with Huntington's disease-like phenotype / Análise clínica e genética em 29 pacientes Brasileiros com fenótipo doença de Huntington-símile

Huntington's disease (HD) is a neurodegenerative disorder characterized by chorea, behavioral disturbances and dementia, caused by a pathological expansion of the CAG trinucleotide in the HTT gene. Several patients have been recognized with the typical HD phenotype without the expected mutation. The objective of this study was to assess the occurrence of diseases such as Huntington's disease-like 2 (HDL2), spinocerebellar ataxia (SCA) 1, SCA2, SCA3, SCA7, dentatorubral-pallidoluysian atrophy (DRPLA) and chorea-acanthocytosis (ChAc) among 29 Brazilian patients with a HD-like phenotype. In the group analyzed, we found 3 patients with HDL2 and 2 patients with ChAc. The diagnosis was not reached in 79.3 percent of the patients. HDL2 was the main cause of the HD-like phenotype in the group analyzed, and is attributable to the African ancestry of this population. However, the etiology of the disease remains undetermined in the majority of the HD negative patients with HD-like phenotype.

A doença de Huntington (DH) é uma doença neurodegenerativa caracterizada por coréia, alterações comportamentais e demência, causada por uma expansão patológica do trinucleotídeo CAG no gene HTT. Vários pacientes têm sido descritos com o fenótipo típico para a DH porém sem a mutação esperada. O objetivo deste estudo foi avaliar a ocorrência de doenças como doença de Huntington-símile 2 (DHS-2), ataxias espinocerebelares tipo 1, 2, 3 e 17, atrofia dentatorubral-palidoluisiana e coreo-acantocitose (CAc) entre 29 pacientes brasileiros com fenótipo doença de Huntington-símile. No grupo analisado, encontramos 3 pacientes com DHS-2 e 2 pacientes com CAc. O diagnóstico permaneceu obscuro em 79,3 por cento dos pacientes. DHS-2 foi a principal causa do fenótipo DH-símile no grupo analisado, provavelmente devido a ancestralidade africana na população brasileira. Entretanto, a etiologia permaneceu indeterminada na maioria dos pacientes avaliados.

Spinocerebellar ataxias: microsatellite and allele frequency in unaffected and affected individuals / Ataxias espinocerebelares: freqüência de alelos e microsatélites em indivíduos normais e afetados

The diagnosis and incidence of spinocerebelar ataxias (SCA) is sometimes difficult to analyze due the overlap of phenotypes subtypes and are disorders of mutations caused by CAG trinucleotide repeat expansion. To investigate the incidence of the SCA in Southern Brazil, we analyzed the trinucleotide repeats (CAG)n at the SCA1, SCA2, SCA3, SCA6 and SCA7 loci to identify allele size ranges and frequencies. We examined blood sample from 154 asymptomatic blood donors and 115 individuals with progressive ataxias. PCR products were submitted to capillary electrophoresis. In the blood donors, the ranges of the five loci were: SCA1, 19 to 36 (CAG)n; SCA2, 6 to 28 (CAG)n; SCA3, 12 to 34 (CAG)n; SCA6, 2 to 13 (CAG)n; and SCA7, 2 to 10 (CAG)n. No deviations from Hardy-Weinberg equilibrium were detected. In the ataxia group, we found (CAG)n above the range of the asymptomatic blood donors in SCA3 (21.74 percent) followed by SCA2 (5.22 percent), SCA7 (2.61 percent), SCA6 (0.87 percent), and no cases of SCA1. The remaining 80 cases (69.56 percent) have different diagnoses from the type here studied. These data defined the alleles and their frequencies, as well as demonstrated their stability in the population not affected. The molecular diagnosis test confirmed the clinical diagnosis in 28/45 cases and classified another 7/70 from the clinical unclassified ataxias group.

A incidência e o diagnóstico das ataxias espinocerebelares (SCA) é algumas vezes difícil de avaliar devido a sobreposição dos diversos subtipos e por algumas serem devido a mutações das expansões do mesmo trinucleotídeo CAG. Para investigar a incidências das SCA no sul do Brasil, analisamos as repetições do trinucleotídeo (CAG)n nos loci das SCA1, SCA2, SCA3, SCA6 e SCA7, a fim de identificar os seus limites e freqüência. Examinamos o sangue de 154 doadores de sangue assintomáticos e 115 pacientes com ataxias progressivas. O produto do PCR do sangue foi submetido a eletroforese capilar. Nos doadores de sangue, as expansões encontradas nos cinco loci foram: SCA1, 19 a 36 (CAG)n; SCA2, 6 a 28 (CAG)n; SCA3, 12 a 34 (CAG)n; SCA6, 2 a 13 (CAG)n; and SCA7, 2 a 10 (CAG)n. Não foi detectado desequilíbrio na equação de Hardy-Weinberg. No grupo das ataxias encontramos repetições CAG acima das freqüências dos doadores de sangue na SCA3 (21,7 por cento), seguido da SCA2 (5,22 por cento), SCA7 (2,61 por cento), SCA6 (0,8 por cento) e não foi encontrado nenhum caso de SCA1. Os 80 casos restantes (69,56 por cento) devem ter uma forma de ataxia diferente das aqui estudadas. Esses dados definem os alelos e suas freqüências, bem como demonstram a sua estabilidade na população não afetada. O diagnóstico molecular confirmou o diagnóstico clínico em 28/45 dos casos e permitiu classificar outros 7/70 que pertenciam ao grupo de ataxias clinicamente não classificadas.

Molecular and Clinical Characteristics of Myotonic Dystrophy Type 1 in Koreans / 대한진단검사의학회지

BACKGROUND: Myotonic dystrophy type 1 (DM1) is an autosomal-dominant muscular dystrophy caused by expansion of cytosine-thymine-guanine (CTG) trinucleotide repeats in the myotonic dystrophy protein kinase (DMPK) gene. The clinical features of DM1 are multisystemic and highly variable, and the unstable nature of CTG expansion causes wide genotypic and phenotypic presentations. The aim of this study was to characterize the molecular and clinical spectra of DM1 in Koreans. METHODS: The CTG repeats of 283 Korean individuals were tested by PCR fragment analysis and Southern blot. The following characteristics were assessed retrospectively: spectrum of CTG expansions, clinical findings, genotype-phenotype correlation, anticipation, and genetic instability. RESULTS: One-hundred twenty-four patients were confirmed as DM1 by molecular tests, and the CTG expansions ranged from 50 to 2,770 repeats (median 480 repeats). The most frequent clinical features were myotonia, muscular weakness, and family history. Patients with muscular weakness or dysfunction of the central nervous system harbored larger CTG expansions than those without each symptom (P<0.05). The age of onset was inversely correlated with the size of the CTG expansion (gamma=-0.422, P<0.001). The instability of CTG expansion representing as the maximum difference between sibships was observed from 50 to 700 repeats in nine families. Clinical anticipation and the increase in CTG repeat were significantly higher in maternally transmitted alleles (P=0.002). CONCLUSIONS: Molecular genetic tests are not only essential for diagnosis, but also helpful for suggesting the spectrum and relationship between genotype and phenotype in Korean DM1 patients.

Non-choreic movement disorders as initial manifestations of Huntington's disease

We describe seven patients with genetically confirmed Huntington's disease (HD) who had non-choreic movement disorders as presenting symptoms or signs. Patients with movement disorders other than chorea in the early stages tended to have larger CAG trinucleotide repeat expansion in comparison with more "typical" HD patients.

Nós descrevemos sete pacientes com doença de Huntington, geneticamente confirmada, cuja apresentação motora inicial foi diferente de coréia. Pacientes com manifestação motora inicial diferente de coréia apresentaram maior número de expansões repetidas de CAG trinucleotídeo quando comparados com aqueles com sintomatologia motora "típica".

Ataxia espinocerebelosa 7: Investigación clínica y genética en una familia argentina / Spinocerebellar ataxia 7: Clinical and genetic investigation in an Argentine family

Las ataxias espino cerebelosas (AEC), constituyen un grupo de trastornos hereditarios neurodegenerativos de herencia autosómica dominante. Se caracterizan principalmente por la presencia clínica de ataxia cerebelosa asociada a oftalmoplejía, disartria, signos piramidales o extrapiramidales y pérdida de la sensibilidad profunda. La AEC 7 pertenece al grupo de las ataxias espinocerebelosas en la cual el trastorno es consecuencia de la expansión del triplete CAG localizado en el cromosoma 3 p12-p21. La característica clínica de dicha ataxia es la pérdida de la agudeza visual y posterior ceguera. Presentamos tres individuos de una familia con ataxia cerebelosa, pérdida de la agudeza visual y otros signos neurológicos. El diagnóstico fue confirmado por medio del análisis genético en el cual se observó la anormalidad característica de la AEC 7. Este es el primer caso de AEC 7 en Argentina confirmado por estudio genético. En la revisión de la literatura (hasta enero 2006) se hallaron sólo dos familias notificadas en América Latina. El objetivo del trabajo es el de enfocar la atención en el diagnóstico de esta enfermedad degenerativa en pacientes que se presentan con ataxia cerebelosa progresiva asociada con disminución de la agudeza visual e historia familiar positiva.

Spino cerebellar ataxia (SCA) are a complex group of hereditary neurodegenerative disturbances of autosomal dominant pattern. They are largely characterized by the clinical presence of cerebellar ataxia related to ophtalmoplegia, dysarthria, pyramidal and extra-pyramidal signs and loss of deep sensitivity. SCA 7 belongs to the SCA group in which the disturbance is a result of the expansion of CAG triplet repetition located in the 3p12-p21 chromosome. The characteristic clinical feature of SCA7 is the loss of visual acuity and blindness. We present here three cases of ataxia, from the same family, with loss of visual acuity and other neurological disorders. The diagnosis was confirmed by a genetic analysis of the index case in whom the characteristic genetic abnormality of SCA7 was discovered. To our knowledge, this is the first case of SCA7 confirmed by genetic study in Argentina. Only two other reports on family cases were found in a review of the literature of Latin America up to January 2006. The purpose of our report is to draw attention to the diagnosis of this degenerative disease in patients with progressive cerebellar ataxia associated with loss of visual acuity symptoms, where a positive family history is found.

Clinical presentation of juvenile Huntington disease

OBJETIVO: Descrever o quadro clínico de um grupo de pacientes com forma juvenil da doença de Huntington.MÉTODO: Os pacientes foram entrevistados seguindo um questionário clínico estruturado; genotipados para a repetição do trinucleotídeo citosina-adenina-guanina (CAG) no gene da doença de Huntington; e realizaram exame de RM de alta resolução. RESULTADOS: Identificamos 4 pacientes com doença de Huntington de início juvenil dentre 50 pacientes com doença de Huntington seguidos prospectivamente em nosso ambulatório de neurogenética. A idade de início variou entre 3 e 13 anos (2 meninos e 2 meninas). Três pacientes tiveram herança paterna da doença. O tamanho do alelo expandido da doença de Huntington variou entre 41 a 69 repetições de trinucleotídeos. As principais manifestações clínicas no início da doença foram rigidez, bradicinesia, distonia, disartria, crises epilépticas e ataxia. A RM mostrou acentuada atrofia dos núcleos caudado e putamem (p=0.001) e redução do volume cerebral e cerebelar (p=0.01). CONCLUSÃO: 8% dos pacientes com doença de Huntington acompanhados em nosso ambulatório apresentaram início juvenil da doença. Estes pacientes não apresentaram a manifestação típica de coréia observada em adultos. Houve predomínio de rigidez, bradicinesia, crises epilépticas e ataxia, o que tem relação com a atrofia cortical e cerebelar precoce na RM.

Tamizaje clínico y análisis de mutaciones en el gen FMR1 en 99 varones con características clínicas del síndrome de X-frágil / Clinical screening and FMR1 gene mutation analysis in male patients with Fragile X syndrome

Introducción: El síndrome de X frágil (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: premutación, mutación completa y mosaicos, todas las cuales corresponden a amplificación del trinucleótido CGG localizado en el primer exón del gen FMR1: las premutaciones presentan entre 52 y 200 repetidos; las mutaciones completas, sobre 200 CGG, presentan hipermetilación de la región promotora del gen FMR1 e inhibición de la expresión de la proteína FMRP, causante del RM y dismorfias características de este síndrome. Los mosaicos presentan mutación completa y premutación o metilación parcial del gen FMR1. Los pacientes con SXF son diagnosticados clínicamente según un protocolo de tamizaje que considera 15 características clínicas que entrega un puntaje máximo de 30 puntos en individuos afectados. Objetivo: Definir criterios clínicos específicos para población chilena que ayuden a identificar a los individuos que deban ser sometidos a estudios moleculares confirmatorios de SXF. Pacientes y Método: Se consideraron 99 pacientes varones referidos al INTA por presentar retraso mental y características clínicas sugerentes del SXF; a todos se les realizó evaluación clínica utilizando el protocolo descrito por Buttler y estudio molecular con análisis directo del gen FMR1 por Southern blot. Resultados: 23 de los 99 pacientes estudiados presentaron una mutación en FMR1 y puntaje clínico entre 16 y 27 puntos; los 76 casos restantes con puntajes clínicos entre 10 y 26 puntos, no presentaron mutación en el gen FMR1. Se evaluaron las características clínicas en ambos grupos y se observó que 4 de ellas se asocian significativamente a la mutación, 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 selección de pacientes sea a través del examen clínico y que todo individuo con puntaje ³ 15 puntos debe ser sometido al estudio molecular.

Use of methylation sensitive polymerase chain reaction for detection of fragile X full mutation & carrier state in males.

BACKGROUND & OBJECTIVE: Fragile X syndrome is the most common cause of inherited mental retardation. It is characterized by the progressive expansion of polymorphic (CGG) trinucleotide repeats located in the promoter region of the FMRI gene located at Xq27.3. The typical dysmorphic features that help in diagnosis are very often subtle or absent especially in pre-pubertal children. Confirmation is by molecular diagnosis based on repeat size and methylation analysis of the FMR1 gene. The present study was done to evaluate the utility of a methylation sensitive polymerase chain reaction (ms-PCR) method in the molecular diagnosis of fragile X syndrome in a select group of mentally retarded male children. METHODS: We used a methylation sensitive PCR technique, which initially modified DNA by bisulphite treatment. Two sets of PCR primers one each for methylated and unmethylated DNA sequences, were used. In full mutations, PCR specific for the methylated sequences was designed to amplify the CpG dinucleotide region upstream to the CGG repeats in clinically affected males. In healthy males and carriers, the second set of primers would amplify the unmethylated DNA sequences. The amplified PCR product size would help to differentiate between normal and premutation repeat size. RESULTS: In all, 25 blood samples collected from mentally retarded male children and five from normal controls were tested. Analysis of cases revealed one full blown mutation and one carrier state. These were further confirmed by southern blotting. INTERPRETATION & CONCLUSION: Unlike currently used methods, methylation sensitive PCR is a quick and accurate technique which could be used for the rapid screening of fragile X syndrome in mental retardation.

X-linked spinal and bulbar muscular atrophy (Kennedy's disease) with long-term electrophysiological evaluation: case report

Atrofia muscular bulbo-espinal ligada ao cromossomo X (doença de Kennedy) é uma neuronopatia motora em adultos causada por expansões na repetição CAG no gene do receptor andrógeno. Neste relato, descreve-se o caso de homem de 66 anos, com diagnóstico prévio de doença do neurônio motor (DNM) que apresentou quadro agudo e reversível de paresia de prega vocal (disfonia) e de músculos faríngeos à esquerda; posteriormente seguiram-se surtos de fraqueza lentamente progressiva, atrofia e fasciculações em língua, masseter, face, faringe e membros superiores predominantemente proximal, associada a tremor bilateral de mãos e ginecomastia leve. Foram realizadas 5 eletroneuromiografias entre 1989 e 2003 que mostraram reinervação crônica, algumas fasciculações, raras fibrilações e redução progressiva de amplitude ou ausência dos potenciais de ação dos nervos sensitivos (PANS). Técnica de PCR para análise de DNA revelou expansão anormal de repetições CAG, sendo encontrado 44 (normal, 11-34). Este caso teve apresentação clínica aguda e assimétrica relacionada aos motoneurônios bulbares; PANS ausentes ou de baixa amplitude com leve assimetria; envolvimento subclínico ou leve de músculos proximais e distais tanto de membros superiores como inferiores; e, provável evolução com surtos agudos de desnervação aguda, seguida por reinervação eficiente.

Disabilities caused by unstable mutations in Costa Rica

Myotonic dystrophy and fragile X syndrome are two genetically determined relatively common disabilities. Both are examples of a new type of mutation mechanism called unstable or dynamic mutations, triple repeats expansions or DNA amplification. Fragile X syndrome is recognized as the main cause of hereditary mental retardation and myotonic dystrophy is considered the most common muscular dystrophy of adults. This is a prospective non randomized study of clinically affected people, in order to confirm the diagnosis with molecular techniques (Southern blot and PCR) and to perform cascade screening of the rest of the family to offer them adequate genetic counseling. We were able to corroborate the initial diagnosis in most clinical cases of myotonic dystrophy, but in the cases of mental retardation more than half studies were negative for fragile X syndrome, stressing the difficulties encountered by medical practitioners to diagnose this syndrome. The reasons for this are several; probable the main culprit is the subtle and unspecific clinical picture affected individuals exhibit, particularly children before puberty. Cascade screening, genetic counseling and selective abortion are the only tools available to prevent these disabling diseases for the moment.

Fragile X syndrome a case report of a family.

Fragile X syndrome is the most common of the inherited disorders causing mental retardation. This disorder results from an abnormal expansion in (CGG)n in repeat found in the coding sequence of the FMRI gene, located at Xq 27.3. Previously it was detected by Karyotyping. With the advent of Molecular Biology PCR, has become the best method in the diagnosis of this disorder. This is a case report of a family with this disorder detected by PCR.

Huntington disease: DNA analysis in brazilian population

Huntington disease (HD) is associated with expansions of a CAG trinucleotide repeat in the HD gene. Accurate measurement of a specific CAG repeat sequence in the HD gene in 92 Brazilian controls without HD, 44 Brazilian subjects with clinical findings suggestive of HD and 40 individuals from 6 putative HD families, showed a range from 7 to 33 repeats in normal subjects and 39 to 88 repeats in affected subjects. A trend between early age at onset of first symptoms and increasing number of repeats was seen. Major increase of repeat size through paternal inheritance than through maternal inheritance was observed. Data generated from this study may have significant implications for the etiology, knowledge of the incidence, diagnosis, prognosis, genetic counseling and treatment of HD Brazilian patients

Repetições CAG: candidatos na gênese das psicoses funcionais / CAG repeats: candidates on the functional psychosis genesis

O autor discorre sobre a instabilidade do DNA em regiões de repetições CAG e sua associação com doenças que afetam o SNC e apresentam o fenômeno da antecipação genética. Revisa também os achados de antecipação em famílias com transtorno bipolar e esquizofrenia, assim como as investigações com o método RED (Repeat Expansion Detection) e com o anticorpo 1C2, que apontam para uma participação desse mecanismo mutacional na determinação genética das psicoses funcionais

Pesquisa molecular y clínica del síndrome de X-frágil en 300 pacientes con retardo mental inespecífico / Clinical and metabolic screening for fragile X syndrome in 300 patients with unspecific mental retardation

Background: Fragile X syndrome is the most freqent cause of mental retardation linked to the X chromosome. In the majority of cases, the mutation responsible for the syndrome is an expansion of the trinucleotide repeat (CGG)n, present in the 5' region of exon 1 of the gene for mental retardation associated with fragile X syndrome (FMR-1). Aim: To report the results of a fragile X screening in patients with mental retardation. Patients and methods: Fragile X screening using polymerase chain reaction methods was done in 386 X chromosomes from 300 patients (214 male), aged 4 to 26 years old. The modified Hagerman test was applied to male patients. Hybridization techniques were applied in a subgroup of 51 patients. Results: (CGG)n 30 was the allele found with the highest frequency in 50.2percent of patients. (CGG)n 29 was found in 29percent of patients. One subject had an allele with 46 CGG repeats, which corresponds to the gray zone. Hybridization studies were highly concordant with PCR, detecting four males with fragile X syndrome and a carrier female. The average clinical score of mental retardation not due to fragile X syndrome was 10.3 ñ 3.4 (range 3 to 23), and 97percent of males had a score below 19. The concordance between scores over 20 and molecular genotype was 98percent. Conclusions: The distribution of (CGG)n repeats, observed in this study, was significantly different to that previously reported for a normal Chilean population. The dispersion of molecular status and clinical score was lower than previously described using cytogenetic techniques