Abstract
BackgroundCryptic chromosome imbalances are increasingly acknowledged as a cause for mental retardation and learning disability. New phenotypes associated with specific rearrangements are also being recognized. Techniques for screening for subtelomeric rearrangements are commercially available, allowing the implementation in a diagnostic service laboratory. We report the diagnostic yield in a series of 132 subjects with mental retardation, and the associated clinical phenotypes.MethodsWe applied commercially available subtelomeric fluorescence in situ hybridization (FISH). All patients referred for subtelomeric screening in a 5-year period were reviewed and abnormal cases were further characterized clinically and if possible molecularly.ResultsWe identified nine chromosomal rearrangements (two of which were in sisters) corresponding to a diagnostic yield of approx. 7%. All had dysmorphic features. Five had imbalances leading to recognizable phenotypes.ConclusionSubtelomeric screening is a useful adjunct to conventional cytogenetic analyses, and should be considered in mentally retarded subjects with dysmorphic features and unknown cause.
Highlights
Cryptic chromosome imbalances are increasingly acknowledged as a cause for mental retardation and learning disability
It is reasonable to believe that genetic factors are involved in many of the undiagnosed cases, since there is a generally increased recurrence risk for siblings [2], and a large number of different gene mutations are known to be associated with mental retardation
The available data indicate that chromosome abnormalities are found in 4–28% of individuals with mental retardation, and that severity of Mental retardation (MR) and the presence of congenital anomalies increase the diagnostic yield of chromosome abnormalities [4]
Summary
Patients A total of 132 cases from 131 families were referred to the John F. He had MR and facial dysmorphic features He showed growth retardation and was found to have a mild delay of motor function at 21 months. Patient 4 The patient was born to healthy, unrelated parents She was born at 40 weeks of gestation with a birth weight of http://www.biomedcentral.com/1471-2350/6/21 out subtelomeric rearrangements. She had an unbalanced karyotype with monosomy 4p de novo. She was severely delayed in development with hypotonia and postnatal growth retardation and developed epilepsy She had dysmorphic features including hypertelorism, Patient 8 The patient was a girl born to healthy, unrelated parents. In this study we analyzed 132 patients (clinical features summarized in table I) by subtelomeric screening, where conventional chromosome analyses were normal in 130 cases. The phenotypically normal mother only had a deletion http://www.biomedcentral.com/1471-2350/6/21 with probe D2S2986, but was not deleted with other probes
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