Síndrome de X frágil: análisis clínico en 300 pacientes con retardo mental inespecífico en la población chilena / Fragile X syndrome: clinical analysis of 300 Chilean patients with unspecific mental retardation

Background: Fragile X syndrome is the most important cause of sex linked mental retardation and the second of chromosomal origin, after Down syndrome. Aim: To apply the modified Hagerman score to patients with mental retardation and to relate clinical findings with cytogenetic and molecular diagnosis. Patients and methods: The modified Hagerman score was applied to 214 male and 86 female patients with mental retardation. The clinical variables in non fragile X and fragile X cases, determined by molecular and cytogenetic methods, were compared. Results: The score in 210 non fragile X males was 10.5 + 3.7 (range 3 23), compared to 21.4 + 2.1 (range 19 to 23) in the four fragile X patients. All fragile X patients had mental retardation, attention deficits, hyperactivity disorders, hand biting and poor visual contact. Hand biting, flapping and persevering speech were observed in a significantly higher number of fragile X males. Only one of 86 females had fragile X syndrome. Her most relevant findings were a long face and high forehead, an attention deficit, hyperactivity and poor visual contact. No clinical differences with other mentally retarded females were found. Condusions: Approximately 5 percent of institutionalized males with mental retardation have a fragile X syndrome

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