{'fraction_non_alphanumeric': 0.046362339514978604, 'fraction_numerical': 0.03209700427960057, 'mean_word_length': 5.261160714285714, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Screening for cryptic chromosomal abnormalities in patients with mental retardation and dysmorphic facial features using telomere fish probes

Three recently published large studies have identified subtelomeric rearrangements in 4 to 9% of individuals with idiopathicmental retardationusingFISH telomere probes [Anderlid et al., 2002; Baker et al., 2002; Clarkson et al., 2002]. Previous telomere studies have shown that cryptic deletions andduplications not visible by routine G-band analysis can occur in up to 7.5% of patients with moderate to severe mental retardation using telomerefluorescence in situhybridization (FISH) probes [Knight et al., 1999; Slavotinek et al., 1999; Rossi et al., 2001]. We initiated a similar IRB-approved study, after receiving parental informed consent, on patients who had mental retardation or developmental delay and dysmorphic facial features, as identified by a clinical geneticist. Among the 17 patients enrolled in the study, three cases had visible cytogenetic abnormalities and one had a single gene mutation. Of the remaining 13 cases studied using FISH telomere probes (Cytocell, Oxfordshire, UK), three abnormal telomere results were found; del(1)(p36.3), der(1)t(1;8)(p36.3;p23), and del(2)(q37). The 1p deletion was confirmed using amore proximal probe, p 58 (Oncor, Gaithersburg, MD). Both parental karyotypes were normal. For the second patient, one of the 8p telomere probe signals showed a split signal between 8p and 1p, the latter which also had a 1p telomere signal. The 8p telomere probe can crosshybridize with 1p, as currently listed on the Cytocell website. As a follow-up, parental blood samples were obtained, and the father’s chromosomes showed the same hybridization pattern for the 8p probe as the child’s, suggesting an inherited polymorphism. For the third patient, the Vysis (Downers Grove, IL) 2q telomere probe, which is proximal to the Cytocell probe, was present on both homologues. This polymorphism has been reported [Ballif et al., 2000] and acknowledged by Cytocell. Our study identified a cryptic chromosomal abnormality in 1/13 or 7.7% (95%C.I., 0.2–36%) of patientswith idiopathic mental retardation and abnormal facial appearance. These results are similar to larger studies that have been reported. Our study emphasizes the importance of confirming the abnormality in the child and parents, using different telomere probes since cross hybridization and polymorphisms exist. In addition, these studies have helped identify recognizable syndromes, including the del(1)(p36.3), which has been identified as a deletion syndrome [Reish et al., 1995], and recently has been estimated to be as frequent as 1/5,000 [Ballif et al., 2001]. Collection of this type of information can help to provide prognostic information to parents.