Parental insertional balanced translocations are an important cause of apparently de novo CNVs in patients with developmental anomalies

In several laboratories, genome-wide array analysis has been implemented as the first tier diagnostic test for the identification of copy number changes in patients with mental retardation and/or congenital anomalies. The identification of a pathogenic copy number variant (CNV) is not only important to make a proper diagnosis but also to enable the accurate estimation of the recurrence risk to family members. Upon the identification of a de novo interstitial loss or gain, the risk recurrence is considered very low. However, this risk is 50% if one of the parents is carrier of a balanced insertional translocation (IT). The apparently de novo imbalance in a patient is then the consequence of the unbalanced transmission of a derivative chromosome involved in an IT. To determine the frequency with which insertional balanced translocations would be the origin of submicroscopic imbalances, we investigated the potential presence of an IT in a consecutive series of 477 interstitial CNVs, in which the parental origin has been tested by FISH, among 14,293 patients with developmental abnormalities referred for array. We demonstrate that ITs underlie ~2.1% of the apparently de novo, interstitial CNVs, indicating that submicroscopic ITs are at least sixfold more frequent than cytogenetically visible ITs. This risk estimate should be taken into account during counseling, and warrant parental and proband FISH testing wherever possible in patients with an apparently de novo, interstitial aberration.     

High resolution comparative genomic hybridisation analysis reveals imbalances in dyschromosomal patients with normal or apparently balanced conventional karyotypes

A sensitive technique is needed for screening whole genome imbalances in dyschromosomal patients when G-banding shows normal karyotypes or apparently balanced translocations. In this study we performed highly sensitive comparative genomic hybridisation analysis on a number of such cases and revealed chromosomal imbalances in all.     

Fluorescence in situ hybridization characterization of apparently balanced translocation reveals cryptic complex chromosomal rearrangements with unexpected level of complexity

The great majority of apparently balanced translocations are associated with multiple miscarriages and normal phenotype. Several mechanisms have been proposed to explain how a small percentage of apparently balanced translocations are associated with abnormal phenotypes. One of the proposed mechanisms that have not been well investigated is that apparently balanced translocations may host 'cryptic' complex chromosomal rearrangements (CCRs). To test this hypothesis, this study investigated 20 non-preselected cases with apparently balanced translocations in order to determine the presence of cryptic CCRs. Multiprobe subtelomeric and whole chromosome paint FISH analyses revealed and further characterized three cryptic CCRs. Two out of three CCRs showed an unexpected level of complexity. The results of this study provided evidence that the link between an apparently balanced rearrangement and the appearance of abnormal phenotype may be partly explained by the presence of cryptic CCRs. The results also suggested that what is reported as apparently balanced translocation by classical cytogenetics may host cryptic CCRs, which could be more common than initially thought. Furthermore, the use of both of the above-mentioned FISH methodologies was absolutely necessary to detect the CCRs.     

Disease profile of 400 institutionalized mentally retarded patients in Kuwait

Farag TI, Al-Awadi SA, El-Badramary MH, Aref MA, Kasrawi B, Krishna Murthy DS, El-Khalifa MY, Yadav G, Marafie MJ, Bastaki L, Wahba RA, Mohammed FM, Abul Hasan S, Redha AA, Redha MA, Al-aboud H, Al-Hijji S, Al-Dighashem D, Al-Hashash N, Al-Jeeryan L, Al-Khor-afi H, Qurban EA, Al-Sulaiman I. Disease profile of 400 institutionalized mentally retarded patients in Kuwait.
Clin Genet 1993: 44: 329–334. © Munksgaard, 1993
In this preliminary report we summarize the results of a 4-year multidisciplinary systematic, etiological clinicogenetic survey of 400 institutionalized mentally retarded patients in Kuwait. All had an intelligence quotient below 50. A constitutional disorder, as the direct cause of the mental retardation, was found in 203 patients (50.75%)): a chromosomal abnormality in 37 (9.25%), Mendelian disorders in 137 (34.25%), MCA/MR in 22 (5.55%) and CNS malformations in 7 cases (1.75%). In 157 patients (39.35%) a pre-, peri or postnatal cause was ascertained. No etiological diagnosis was detected in 40 patients (10%). A detailed analysis of the "disease profile" is given and compared with the results of previous diagnostic genetic surveys among different institutionalized mentally retarded populations in Western and developing countries.     

Entamoeba histolytica autochthonous isolates from mentally retarded Italian patients

A total of 77 mentally retarde male inpatients residing in a psychiatric institution in northern Italy were screened for the presence of stool parasites,Entamoeba histolytica particularly. Parasitological stool examination showedEntamoeba spp. (E. histolytica and/orE. dispar) in 26 cases (33.7%). In vitro culture on Robinson's medium was positive in 16 cases (61.1%); in 11 cases we could stabilize and clone the isolates and proceed to electrophoretic assays. In all cases, patterns of pathogenic zymodemes were found (zymodeme II, 3 isolates; zymodeme XII, 4 isolates; zymodeme XIV, 4 isolates). All isolates were therefore identified asE. histolytica.     

智力低下儿童的体格生长

为了解智力低下儿童的体格生长情况，对326名患儿进行了智力、身高、体重、头围和骨龄的测试，结果表明智力低下儿童平均体格生长水平低于正常儿童。虽然智力与生长间未显示出明显的线性关系，但生长迟缓和小头畸形见于严重的智力低下儿。骨龄与智力水平未见显著相关。     

Comparative genomic hybridisation in mentally retarded patients with dysmorphic features and a normal karyotype

Segmental aneusomy for small chromosomal regions has been shown to be a common cause of mental retardation and multiple congenital anomalies. A screening method for such chromosome aberrations that are not detected using standard cytogenetic techniques is needed. Recent studies have focused on detection of subtle terminal chromosome aberrations using subtelomeric probes. This approach however excludes significant regions of the genome where submicroscopic rearrangements are also liable to occur. The aim of the present study was to evaluate the efficiency of comparative genomic hybridisation (CGH) for screening of submicroscopic chromosomal rearrangements. CGH was performed in a cohort of 17 patients (14 families) with mental retardation, dysmorphic features and a normal karyotype. Five subtle unbalanced rearrangements were identified in 7 patients. Subsequent FISH studies confirmed these results. Although no interstitial submicroscopic rearrangement was detected in this small series, the study emphasises the value of CGH as a screening approach to detect subtle chromosome rearrangements in mentally retarded patients with dysmorphic features and a normal karyotype.     

FRAXE mutation in mentally retarded patients using the OxE18 probe

The folate-sensitive fragile site FRAXE is located in proximal Xq28 of the human X chromosome and lies approximately 600 kb distal to the fragile X syndrome (FRAXA) fragile site at Xq27.3. Although FRAXA and FRAXE are indistinguishable by means of conventional cytogenetics, they can now be delineated at the molecular level and provides the basis for a proper diagnosis. The screening for CGG amplifications in the FMR1 gene was based on standard protocols using EcoRI digests on Southern blots and hybridization with the StB12.3 probe. The FRAXE mutation was analyzed by digestion with HindIII and the filters were probed with OxE20. We present the results of 144 patients referred for fragile X testing but negative for the FMR1 gene trinucleotide expansion, that were also screened for the FMR2 expansion. For FRAXE mutation a molecular protocol for OxE18 probe was used, in the DNA samples digested with EcoRI on the same blots as those used for detection of FRAXA. None of the patients tested were positive for the FRAXE expansion. This technique was successfully established into our laboratory routine showing the practical use of testing for FRAXA and FRAXE in a large series of patients.     

Bone mineral in mentally retarded patients receiving long-term anticonvulsive therapy.

A direct photon absorptiometry method was used to measure bone mineral content in a population of mentally retarded subjects, one half of whom were undergoing long-term anticonvulsant drug therapy. The sample consisted of 134 subjects, 60 males and 74 females. Average ages were 22.5 years for the females and 19.7 years for the males. A multiple regression analysis showed there was no apparent effect on anticonvulsant drug therapy on bone mineral content in this mentally retarded and growth retarded population. A comparison with normal standards indicates that bone mineral values for age for both sexes of mentally retarded subjects were depressed from 15-40 percent relative to white standards. The bone mineral depression closely paralleled the growth depression seen in this population. It is suggested that the inability to detect an overall anticonvulsive drug effect on bone mineral values may be due to the general growth retardation seen in this institutionalized mentally retarded population.     

Townes-Brocks syndrome in two mentally retarded youngsters

We report on 2 children with Townes-Brocks syndrome (TBS) and mental retardation. One child had mild hearing loss, but the other only had hearing loss at 8000 Hz. These cases suggest that there may be an increased incidence of mental retardation in individuals with TBS.     

Chromosomal aberrations in 85 mentally retarded patients examined by high resolution banding

Eighty-five mentally retarded patients had their chromosomes examined by using the high resolution banding techniques. Fifty-nine of them had multiple congenital anomalies and/or dysmorphic features. Twenty-six had mental retardation but no major anomalies; they were primarily suspected of having the fragile X syndrome. This suspicion was first excluded. Fifteen patients were found to have a chromosome aberration, interpreted as clinically significant. Eleven of them had been examined earlier by conventional methods. The aberrations found were divided into three groups: (I) those detectable with an accuracy of ca. 300-400 bands (N = 4), (II) those detectable with an accuracy of ca. 400-550 bands (N = 6) and (III) those detectable with an accuracy of ca. 550-850 bands (N = 5). The aberrations are described and discussed.     

The complex nature of constitutional de novo apparently balanced translocations in patients presenting with abnormal phenotypes

Objective: To describe the systematic analysis of constitutional de novo apparently balanced translocations in patients presenting with abnormal phenotypes, characterise the structural chromosome rearrangements, map the translocation breakpoints, and report detectable genomic imbalances.

Methods: DNA microarrays were used with a resolution of 1 Mb for the detailed genome-wide analysis of the patients. Array CGH was used to screen for genomic imbalance and array painting to map chromosome breakpoints rapidly. These two methods facilitate rapid analysis of translocation breakpoints and screening for cryptic chromosome imbalance. Breakpoints of rearrangements were further refined (to the level of spanning clones) using fluorescence in situ hybridisation where appropriate.

Results: Unexpected additional complexity or genome imbalance was found in six of 10 patients studied. The patients could be grouped according to the general nature of the karyotype rearrangement as follows: (A) three cases with complex multiple rearrangements including deletions, inversions, and insertions at or near one or both breakpoints; (B) three cases in which, while the translocations appeared to be balanced, microarray analysis identified previously unrecognised imbalance on chromosomes unrelated to the translocation; (C) four cases in which the translocation breakpoints appeared simple and balanced at the resolution used.

Conclusions: This high level of unexpected rearrangement complexity, if generally confirmed in the study of further patients, will have an impact on current diagnostic investigations of this type and provides an argument for the more widespread adoption of microarray analysis or other high resolution genome-wide screens for chromosome imbalance and rearrangement.

     

增智胶囊治疗小儿智力低下的研究

１９８７年７月至１９９２年６月间，应用新研制的具有健脑、补肾、强身作用的营养性治疗药物增智胶囊治疗小儿智力低下３８１例，一般用药１至２个疗程，以智商（ＩＱ）提高观察疗效。增智胶囊治疗组３８１例，总有效率为８７．６７％，无效１２．３３％，脑复康治疗对照组３６例，总有效率１９．４４％，无效８０．５６％。经另外四家医院二期临床验证２３３例，总有效率８２．８３％，脑复康对照组７８例，总有效率２５．６４％。结果表明增智胶囊是治疗小儿智力低下的有效药物。该研究为小儿智力低下治疗的可能性提供了新的理论和实践依据。     

Hypogonadotropic hypogonadism in mentally retarded adults with microphthalmia and clinical anophthalmia

Five of 13 patients with microphthalmia or clinical anophthalmia studied in an institution of 650 mentally retarded adults had hypogonadotropic hypogonadism. Four males had low testosterone levels and sexual infantilism, manifesting as micropenis with small testes or cryptorchidism. One female had primary amenorrhea. All 5 patients had low gonadotropin levels, confirming a hypothalamic or pituitary basis for their hypogonadism. Thyroxin, thyroid stimulating hormone, prolactin, and A.M. cortisol were also measured and were normal. All patients with hypogonadotropic hypogonadism were chromosomally normal and had variable central nervous system defects, suggesting that they comprise a heterogeneous group of disorders. Microphthalmia or anophthalmia in a mentally retarded patient is associated with hypogonadotropic hypogonadism.     

Chromosomal variants in mentally retarded and normal men

The possible phenotypic effect of chromosomal variants is as yet an unsolved problem. QM- and C-banded chromosomes of 100 male patients with idiopathic mental retardation were compared with chromosomes of 100 Royal Military College cadets, as controls. Increased size of 9qh seems to be a factor with possible negative effects. 9qh- was found to be more common in the control sample. Another variant found more often in the retarded subjects was 16qh-. Increased frequencies of Yq+ or small inversions in chromosomes 3 and 9 were not found in the retarded.     

MECP2 analysis in mentally retarded patients: implications for routine DNA diagnostics

Rett syndrome (RTT) is one of the most common neurodevelopmental disorders in females. The disease is caused by mutations in the methyl-CpG-binding protein 2 gene (MECP2), and various mutations have been reported. The phenotypic spectrum in both female and male patients is diverse, ranging from very mild to congenital encephalopathy and prenatal lethality. In this study, the question was addressed as to whether implementation of systematic screening of MECP2 in patients with an unexplained mental retardation in DNA diagnostics would be reasonable, and the spectrum of phenotypes resulting from mutations in this gene was further explored. Mutational analysis of MECP2 was performed in mentally retarded female patients who were negative for FMR1 CGG repeat expansion, in male and female patients with clinical features suggestive of either Angelman or Prader-Willi syndrome without methylation defects on chromosome 15q11-q13. In the cohort of females negative for the molecular Fragile-X studies (N=92), one nonsense mutation (p.Q406X) was found. In the cohort of Angelman-negative patients (N=63), two missense mutations (p.R133C in a female patient and a mosaic p.T158M in a male patient) were found, which have been reported many times in patients with classical RTT syndrome. In the Prader-Willi-negative group (N=98), no pathogenic mutations were found. The results support testing of patients with features suggestive of Angelman syndrome, but without methylation defects on chromosome 15q11-q13 for mutations in MECP2. In the remaining patients with unexplained mental retardation, additional clinical features should determine whether analysis of MECP2 is indicated.