Deletion of band 13q21 is compatible with normal phenotype

Cognitive and behavioral phenotype of a young man with a chromosome 13 deletion del(13)(q21.32q31.1)

Cognitive, emotional, and behavioral characterizations have been reported for patients with a few chromosomal imbalances, but not for patients with a 13q deletion. We report the neuropsychological profile and specific linguistic, visual, spatial, constructional, and behavioral disabilities of a young man with a de novo chromosome 13 deletion (13)(q21.32)(q31.1). Karyotyping at 550 G-band resolution showed that the patient's parents did not share the deletion. According to array-comparative genomic hybridization, the deletion spanned about 14 Mb and included 27 genes. A fluorescence in situ hybridization assay revealed an intact 13q telomere on the partially deleted chromosome. The patient had multiple morphologic and ophthalmologic anomalies. A brain magnetic resonance imaging study did not show gross brain defects. Neuropsychological testing showed an acceptable use of everyday language, but mild mental retardation, executive dysfunction, and very poor performance on visual, visuospatial, and constructional tasks. Establishing a neuropsychological profile for a patient with a specific genetic defect can help clinicians, parents, and teachers work to meet the patient's medical, academic, and behavioral needs.

Phenotype and 244k array-CGH characterization of chromosome 13q deletions: an update of the phenotypic map of 13q21.1-qter

Partial deletions of the long arm of chromosome 13 lead to variable phenotypes dependant on the size and position of the deleted region. In order to update the phenotypic map of chromosome 13q21.1-qter deletions, we applied 244k Agilent oligonucleotide-based array-CGH to determine the exact breakpoints in 14 patients with partial deletions of this region. Subsequently, we linked the genotype to the patient's phenotype. Using this approach, we were able to refine the smallest deletion region linked to short stature (13q31.3: 89.5-91.6 Mb), microcephaly (13q33.3-q34), cortical development malformations (13q33.1-qter), Dandy-Walker malformation (DWM) (13q32.2-q33.1), corpus callosum agenesis (CCA) (13q32.3-q33.1), meningocele/encephalocele (13q31.3-qter), DWM, CCA, and neural tube defects (NTDs) taken together (13q32.3-q33.1), ano-/microphthalmia (13q31.3-13qter), cleft lip/palate (13q31.3-13q33.1), lung hypoplasia (13q31.3-13q33.1), and thumb a-/hypoplasia (13q31.3-q33.1 and 13q33.3-q34). Based on observations of this study and previous reports we suggest a new entity, "distal limb anomalies association," linked to 13q31.3q33.1 segment. Most of the individuals with deletion of any part of 13q21qter showed surprisingly similar facial dysmorphic features, and thus, a "13q deletion facial appearance" was suggested. Prominent nasal columella was mapped between 13q31.3 and 13q33.3, and micrognathia between 13q21.33 and 13q31.1. The degree of mental delay did not display a particular phenotype-genotype correlation on chromosome 13. In contrast to previous reports of carriers of 13q32 band deletions as the most seriously affected patients, we present two such individuals with long-term survival, 28 and 2.5 years.

Tall stature and minor facial dysmorphisms in a patient with a 17.5 Mb interstitial deletion of chromosome 13 (q14.3q21.33): clinical report and review

We present a 4-year-old boy with developmental delay and several into minor dysmorphic features due to an interstitial deletion of 17.5 Mb on the long arm of chromosome 13 [46,XY,del (13)(q14.3q21.33)]. The deletion was detected initially during routine cytogenetic screening and further analyzed on a genome-wide BAC array. In contrast to several previous papers reporting a short stature, our patient was tall with a 1 year advanced skeletal age. In this paper, we compare growth and clinical features of this patient with previously reported cases, with a similar interstitial deletion on the long arm of chromosome 13.

Chromosome abnormalities without phenotypic consequences

Some changes in chromosome morphology, detected during cytogenetic analysis, are not associated with clinical defects. Therefore a proper discrimination of harmless variants from true abnormalities, especially during prenatal diagnosis, is crucial to allow precise counseling. In this review we described chromosome variants and examples of chromosome anomalies that are considered to be unrelated to phenotypic consequences. The correlation between the presence of marker chromosomes and a risk of clinical signs is also discussed. Structural rearrangements of heterochromatic material, satellite polymorphism, or fragile sites, are well-known examples of common chromosome variation. However, the absence of clinical effects has also been reported in some cases of chromosome abnormalities concerning euchromatin. Such euchromatic anomalies were divided into 2 categories: unbalanced chromosome abnormalities (UBCAs), such as deletions or duplications, and euchromatic variants (EVs). Recently so-called molecular karyotyping, especially whole-genome screening by the use of high-resolution array-CGH technique, contributed to revealing a high number of previously unknown small genomic variations, which seem to be asymptomatic, as they are present in phenotypically normal individuals.

An innocuous duplication of 11.2 Mb at 13q21 is gene poor: Sub-bands of gene paucity and pervasive CNV characterize thechromosome anomalies

A boy with autistic spectrum disorder without dysmorphisms was found to have a chromosome duplication of part of band 13q21. His mother and grandfather both of normal intellect had the same chromosomal duplication. Comparison was made with the Chromosome anomaly database www.som.soton.ac.uk/research/geneticsdiv/anomaly%20register which revealed similar cases. Mapping on DNA microarray for the proband and mother showed the duplication to be of length 11.2 Mb, encompassing the 13q21.1-13q21.32 region. The duplicated region is profoundly gene poor, with a mean gene density of 0.45 genes/Mb. We estimate, that the mean gene density in the sub-bands of the chromosome anomalies is 2.4-2.5 genes/Mb. In addition the percentages of the sub-bands reported as copy number variants (CNV) was estimated from the Database of Chromosome Genomic Variants (http://projects.tcag.ca/variation/). It was found that for some of these sub-bands, gene paucity was likely to be a major contributor to their innocuous phenotypic effect, for example, the gene densities were for: 1p31.2 (1.25 genes/Mb); 2p12 (1.7); 4p15.31 (1.3); 5p14.1 (0.22); 5p14.3 (0.8); 5q21.2 (0.6); 5q21.3 (1.2); 8p23.2 (0.25); 13q21.1 (0.9); 14q31.1 (1.4); 18q22.1 (1.4); 21q21.1 (1.2); and 21q21.2 (0.7). For other sub-bands the percentage of the band in which CNV have been reported was found to be markedly increased, for example, 8p23.2 (94.7% of the band is defined by reported CNV); 3p26.3 (81.6); 5p14.3 (59.3); 8p22 (48.8); 2p12 (44.0); 5q21.1 (43.6); 6q24.2 (41.4); 9p23 (38.8); 10q21.1 (36.5); 5q21.2 (35.4), and 11q14.3 (33.8). We argue that both gene paucity and pervasive CNV are major indicators of bands conforming to the Chromosome Anomaly phenomenon.

Interstitial Deletion 13q31 Associated with Normal Phenotype: Cytogenetic Study of a Family with Concomitant Segregation of Reciprocal Translocation and Interstitial Deletion

Gain or loss of a fragment in human chromosomes has been associated with abnormal phenotypes in numerous genetic disorders. However, it is also possible that lack or excess of a particular chromosomal segment is a neutral polymorphism among populations and thus does not cause obvious abnormal phenotype. In this study, conventional GTG-banded karyotyping and molecular cytogenetic analyses (including fluorescence in situ hybridization, spectral karyotyping and comparative genomic hybridization) were applied to study the genotype-phenotype correlation in a Taiwanese family, in which a concomitant segregation of del(13)(q31q31) interstitial deletion and t(13;18)(q32;p11.2) reciprocal translocation in a 2-year-old girl (the proband) was noticed. Two family members (the father and grandmother of the proband) who carried the del(13)(q31q31) but not the translocation t(13;18) both revealed a normal phenotype at adulthood. The finding, which appears novel, that interstitial deletion 13q31 could be associated with a normal phenotype, is therefore valuable in genetic counseling.

Interstitial deletion of 6q without phenotypic effect

Cytogenetically detectable euchromatic deletions without phenotypic consequences are rarely encountered. We report on a 34-year-old woman with normal intelligence referred for karyotyping because of recurrent abortions. With the exception of a bicuspid aortic valve without hemodynamic consequences, which is a common minor anomaly in the general population, no dysmorphic features were found on physical examination. Conventional chromosome analysis (GTG-banding) revealed an interstitial deletion in the long arm of chromosome 6. With array comparative genomic hybridization (array-CGH) the size of the deletion was estimated to be between 9.9 and 11.6 Mb and the refined karyotype was 46,XX,del(6)(q22.31q23.1).

Directly transmitted unbalanced chromosome abnormalities and euchromatic variants

In total, 200 families were reviewed with directly transmitted, cytogenetically visible unbalanced chromosome abnormalities (UBCAs) or euchromatic variants (EVs). Both the 130 UBCA and 70 EV families were divided into three groups depending on the presence or absence of an abnormal phenotype in parents and offspring. No detectable phenotypic effect was evident in 23/130 (18%) UBCA families ascertained mostly through prenatal diagnosis (group 1). In 30/130 (23%) families, the affected proband had the same UBCA as other phenotypically normal family members (group 2). In the remaining 77/130 (59%) families, UBCAs had consistently mild consequences (group 3). In the 70 families with established EVs of 8p23.1, 9p12, 9q12, 15q11.2, and 16p11.2, no phenotypic effect was apparent in 38/70 (54%). The same EV was found in affected probands and phenotypically normal family members in 30/70 families (43%) (group 2), and an EV co-segregated with mild phenotypic anomalies in only 2/70 (3%) families (group 3). Recent evidence indicates that EVs involve copy number variation of common paralogous gene and pseudogene sequences that are polymorphic in the normal population and only become visible at the cytogenetic level when copy number is high. The average size of the deletions and duplications in all three groups of UBCAs was close to 10 Mb, and these UBCAs and EVs form the "Chromosome Anomaly Collection" at http://www.ngrl.org.uk/Wessex/collection. The continuum of severity associated with UBCAs and the variability of the genome at the sub-cytogenetic level make further close collaboration between medical and laboratory staff essential to distinguish clinically silent variation from pathogenic rearrangement.

Segmental haplosufficiency: transmitted deletions of 2p12 include a pancreatic regeneration gene cluster and have no apparent phenotypic consequences

Segmental aneuploidy usually has phenotypic consequences but unbalanced rearrangements without phenotypic consequences have also been reported. In particular, harmless deletions of G-dark bands 5p14 and 16q21 have each been found in more than one independent family. Here, we report two families that were ascertained at prenatal diagnosis and had similar overlapping deletions that removed most of the gene poor G-dark band 2p12. PCR mapping showed that the deletions had a minimum size of 6.1 and 6.9 Mb with at least 13 hemizygous loci including a cluster of six pancreatic islet-regenerating genes. These deletions had no apparent phenotypic consequences in eight family members. In contrast, a third family was ascertained through a child with Wilm's tumour; both the child and his mother had more proximal deletions, developmental delay and some dysmorphic features. The deletion had a minimum size of 5.7 Mb and extended into the gene-rich area of 2p11.2. These results are consistent with the idea that there may be segments of the genome that are consistently haplosufficient. The introduction of higher resolution methods of dosage analysis into diagnostic laboratories is already revealing more transmitted abnormalities of uncertain significance. As a result, published cases of transmitted imbalances have been collected as a guide to the possible significance of such findings in the future (see the 'Chromosome Anomaly Collection' at www.som.soton.ac.uk/research/geneticsdiv).

Application of ROMA (representational oligonucleotide microarray analysis) to patients with cytogenetic rearrangements

PURPOSE

To demonstrate the accuracy and sensitivity of Representational Oligonucleotide Microarray Analysis (ROMA) to describe copy number changes in patients with chromosomal abnormalities.

METHODS

ROMA was performed using BglII digested DNA from two cases with cytogenetically detected deletions and one case with an unbalanced terminal rearrangement detected only by subtelomeric FISH. Hybridization was to an 85,000-probe oligonucleotide microarray, providing an average resolution of 35 kb. FISH was used to confirm some of the ROMA findings.

RESULTS

By ROMA, a del(13)(q14.3q21.2) was shown to be noncontiguous, with deletions extending from 53.08 to 61.40 Mb and from 72.88 to 74.83 Mb. The 10-Mb deletion contained only six known genes. FISH confirmed the noncontiguous nature of the deletion, as well as a small amplification in 6q that was also found in the patient's mother. A del(4)(q12q21.2) was found by ROMA to be 23 Mb in length, from 58.8 to 81.9 Mb on chromosome 4, in agreement with the cytogenetically assigned breakpoints. ROMA showed that an unbalanced "subtelomeric" rearrangement involved a 6-Mb deletion of 22q and an 8-Mb duplication of 16q.

CONCLUSIONS

ROMA can define cytogenetic aberrations with extraordinary precision. Unexpected findings included the interrupted nature of the deletion in 13q and the large size of the imbalances in the "subtelomeric" rearrangement. Together with the information from the human genome sequence and proteomics, the ability to define rearrangements with "ultra-high" resolution will improve the ability to provide accurate prognosis both prenatally and postnatally to parents of offspring with chromosomal aberrations.

Constitutional genomic instability, chromosome aberrations in tumor cells and retinoblastoma

Although retinoblastoma (Rb) is initiated as a result of biallelic inactivation of the RB1 gene, additional genetic events (M3) in tumor cells are indicative of their role in the full transformation of retinal cells. We investigated the constitutional genetic instability by fragile site (FS) expression studies and checked its relationship with loci of tumor cytogenetics in a series of 36 retinoblastoma patients (34 nonfamilial and 2 familial cases). Tumor cytogenetics revealed -13/+13, del/t(13)(q14) (50%), +1/del/t(1p/q) (65%), +6/i(6p) (60%), and del(16)(q13)/(q22 approximately q23) (60%). Conventional cytogenetics in leukocytes revealed constitutional del(13q14) in five unilateral Rb (URB) and one trilateral Rb (TRB). Constitutional del(16)(q22) and t(6;12) were also identified in two cases. Constitutional FS analysis showed a significant increase in the cellular fragility, with high prevalence at 13q14, 3p14, 6p23, 16q22 approximately q23, and 13q22 loci in retinoblastoma patients (P<0.05). Patients with constitutional del(13)(q14) demonstrated higher fragility than those with normal constitution. A strong correlation between loci of constitutional FSs and loci of recurrent chromosomal abnormalities in tumors strengthen and support the proposal that FS loci present as inherent genomic instability in retinoblastoma. The chromosomal changes and resultant genetic mutations, along with RB1 mutation events, probably contribute synergistically to the development and progression of Rb malignancy. Implementation of fluorescence in situ hybridization to nonfamilial Rb on a large scale (113 cases) could detect constitutional RB1 deletion in 12.3% of cases, with equally higher incidence in URB (14.7%) and bilateral Rb (13.6%), demonstrating that the true prevalence of patients with predisposition to RB1 mutation in sporadic URB is definitely higher in our populations. Also, higher incidence of constitutional RB1 deletion mosaicism in unilateral than in bilateral Rb indicates that the constitutional genetic mosaicism in URB should be given serious consideration during genetic counseling.

Repercusión clínica de las anomalías cromosómicas

The incidence of chromosome anomalies in newborn infants is 0.7-0.8 %. The phenotypic manifestations of chromosomal abnormalities are highly diverse. These anomalies may be present in phenotypically normal individuals in whom they can increase the risk of recurrent miscarriage and birth defects and/or mental retardation. It is important to determine this risk to provide patients with appropriate genetic counseling.

Prenatal diagnosis of a karyotypically normal pregnancy in a mother with a supernumerary neocentric 13q21 -->13q22 chromosome and balancing reciprocal deletion

An adult female patient with a history of miscarriages was found to be carrying a stable supernumerary chromosome. The patient also carried a reciprocal paracentric deletion in chromosome 13q21/22. Microdissection and reverse fluorescence in situ hybridization FISH revealed that this supernumerary chromosome was derived from region 13q21 --> 13q22. The presence of a neocentromere on this supernumerary chromosome was confirmed by the absence of detectable alpha satellite DNA using FISH and the presence of centromere proteins CENP-C and CENP-A using immunofluorescence. The absence of telomere sequences suggests that the marker is a ring chromosome (r(13)). FISH using ordered BACs from the chromosome region 13q21 --> 13q31 permitted the precise positioning of the r(13) chromosome and the corresponding deletion to chromosome bands 13q21.32 --> 13q22.2. BAC 280J7 from within the r(13) was used as a FISH probe for the prenatal analysis of amniocytes at 16 weeks of gestation, which revealed a normal karyotype for the fetus. This r(13) chromosome represents the first description of chromosome 13 of the rarer class of neocentric chromosomes that are derived from interstitial deletions. It represents the first example of prenatal diagnosis in a phenotypically normal female that was ascertained to carry a neocentric marker. The presence of such a neocentric marker/deletion karyotype in a parent presents unique possible karyotypic outcomes for conceptions and unusual challenges for genetic counseling.

Familial deletion of (8)(q24.13q24.22) associated with a normal phenotype

We report a familial deletion of (8q) detected in amniocytes of a fetus with a normal ultrasound and in the phenotypically normal mother, who has now had three pregnancy losses. Chromosome analysis of amniocytes and maternal peripheral blood cells showed an interstitial deletion of (8)(q24.13q24.22), which is distal to the region associated with Langer-Giedion syndrome (LGS) or trichorhinophalangeal (TRP) syndrome. This deletion was confirmed by fluorescence in situ hybridization with a c-myc cosmid clone and chromosome 8 painting library.

Distal 13q Deletion Syndrome and the VACTERL association: case report, literature review, and possible implications

We present a case of a child with del(13) (q31.1qter), VACTERL association, and penoscrotal transposition. Deletion of the distal long arm of chromosome 13 is associated with variable phenotypes. These phenotypes are divided into three clusters; each cluster represents a specific deleted segment of 13q. Individuals with deletions of a critical region at 13q32 have multiple congenital malformations that include components of the VACTERL association. Our patient had all six manifestations of VACTERL association. In addition, he had complete penoscrotal transposition, a unique malformation reported rarely in VACTERL association and only twice previously in deletion of distal 13q. We reviewed all reported cases of distal 13q deletions to date. Of these 137 patients, 15 could be classified into the VACTERL association. Ours was the only patient with distal 13q deletion and all VACTERL association features and also the only one with tracheoesophageal fistula. Neither holoprosencephaly nor the other central nervous system malformations that have been seen in individuals with distal 13q deletions were apparent in him. The patient presented here appears to be unique among individuals with distal 13q deletion. His cluster of malformations strengthens the argument that distal 13q deletion is a cause for VACTERL association, and that this causal relationship implies a syndromic form of VACTERL. In addition, this case and those ascertained from the literature suggest that penoscrotal transposition should be considered part of both the distal 13q-deletion syndrome and some forms of VACTERL association.

Inherited interstitial deletion of chromosomes 5p and 16q without apparent phenotypic effect: further confirmation

We describe two families in which an inherited interstitial deletion is present without apparent associated phenotypic abnormalities. The first deletion was discovered in a 19-year-old male with a previously diagnosed peroxisomal disorder. High-resolution chromosome analysis was interpreted as 46,XY,del(5)(p14.1p14.3). The patient's phenotypically normal mother had the same interstitial deletion. Chromosome 5p14 deletion has been reported in a three-generation family without phenotypic anomalies. We hypothesize that the affected son's phenotype may be coincidental or represent unmasking of an autosomal recessive peroxisomal disorder in the deleted region. The second interstitial deletion was detected by amniocentesis for advanced maternal age. High-resolution chromosome analysis was interpreted as 46,XX,del(16)(q13q22). The same deletion was found in the healthy mother and a normal brother. The pregnancy was carried to term and resulted in the birth of a normal girl. We report these cases as further evidence that rare, unbalanced deletion of specific chromosomal regions may result in no phenotypic effect. Consequences may result from expression of an autosomal recessive disorder on the homologous chromosome. Identification of such deletions is especially important for prenatal diagnosis and genetic counselling.

Molecular cytogenetics of a de novo interstitial deletion of chromosome arm 6q in a developmentally normal girl

Using fluorescence in situ hybridization and microsatellite analysis, we have characterized a de novo interstitial deletion on the long arm of chromosome 6 [46,XX,del(6) (q23.3q24.2)] in a developmentally normal girl with very mild phenotypic abnormalities. The deletion was paternal in origin and was between markers WI-5023 and D6S1042. The size of the deletion was estimated to be approximately 4-5 Mb. The normal phenotype in this patient might be the result of imprinting of paternal copies of genes located in the segment 6q23. 3-q24.2. Alternatively, the genes located in the segment 6q23.3-q24. 2 might not be subject to dosage effects and therefore the haploinsufficiency of genes in this segment might not have phenotypic consequences.

Duplication of 8p23.1: a cytogenetic anomaly with no established clinical significance

We present seven families with a cytogenetic duplication of the short arm of chromosome 8 at band 8p23.1. The duplication has been transmitted from parents to offspring in four of the seven families. In three families, the source of the extra material and its euchromatic origin were established using FISH with a YAC which was mapped to 8p23.1 and a whole chromosome paint for chromosome 8. FISH signals from this YAC were significantly larger on the duplicated chromosome compared with the normal chromosome in all six family members tested. Comparative genomic hybridisation (CGH) on a representative subject was consistent with these results. The families were ascertained for a variety of mostly incidental reasons including prenatal diagnosis for advanced maternal age. The transmission of this duplication by multiple phenotypically normal family members with no history of reproductive loss suggests the existence of a novel class of 8p23.1 duplications, which can be regarded as euchromatic variants or duplications with no phenotypic effect.

High resolution mapping of interstitial long arm deletions of chromosome 16: relationship to phenotype

The breakpoints of seven interstitial deletions of the long arm of chromosome 16 and two ring chromosomes of this chromosome were mapped by in situ hybridisation or by analysis of mouse/human somatic cell hybrids containing the deleted chromosome 16. Use of a high resolution cytogenetic based physical map of chromosome 16 enabled breakpoints to be assigned to an average resolution of at least 1.6 Mb. In general, interstitial deletions involving q12 or q22.1 have broadly similar phenotypes though there are differences in specific abnormalities. Deletions involving regions more distal, from 16q22.1 to 16q24.1, were associated with relatively mild dysmorphism. One region of the long arm, q24.2 to q24.3, was not involved in any deletion, either in this study or in any previous report. Presumably, monosomy for this region is lethal. In contrast, patients with deletions of 16q21 have a normal phenotype. These results are consistent with the proposed distribution of genes, frequent in telomeric Giesma light band regions but infrequent in G positive bands.

A rare inherited euchromatic heteromorphism on chromosome 1

Extra genetic material that is euchromatic is generally regarded to be associated with phenotypic abnormalities. However, recent studies suggest that this is not always the case. Chromosome analysis was performed on amniotic fluid cells from a 37-year-old phenotypically normal patient referred for advanced maternal age. All the cells analysed showed a karyotype of 46,XY,1p+. The 1p+ chromosome had extra genetic material of uncertain origin in chromosome band region 1p21-->31. Chromosome analysis on the father revealed a normal 46,XY male karyotype. The mother's karyotype showed the same 1p+ chromosome. C and Q banding, as well as silver staining studies, in both the mother and the fetus support the interpretation that the extra chromosomal material was euchromatic in nature. This 1p+ chromosome may be characterized as a euchromatic heteromorphism. Euchromatic heteromorphisms not associated with phenotypic abnormalities have been reported for chromosomes 9 and 16. To the best of our knowledge, this is the first report involving this type of cytogenetic anomaly on chromosome number 1 in a phenotypically normal mother and infant.

Preliminary definition of a "critical region" of chromosome 13 in q32: report of 14 cases with 13q deletions and review of the literature

We report on 14 patients with partial deletions of chromosome 13q. These patients exhibit a wide spectrum of phenotypes. Deletions limited to proximal bands q13-q31 are associated with growth retardation but not with major malformations. We review the literature since 1975 and summarize 13q deletion cases which have a phenotype involving one or more major malformations and mental retardation. Analysis of the breakpoints of these cases, as well as those reported by us, supports the hypothesis that only deletions involving at least part of band q32 are associated with major malformations and digital abnormalities. Patients with more distal deletions have severe mental retardation but do not have major malformations or growth retardation. A group of patients in whom the breakpoint is stated to be within q32 has had an intermediate phenotype. This suggests that it may be possible to define subregions within q32 whose deletion is associated with particular developmental defects.

Deletion (14) (q24.3q32.1): evidence for a distinct clinical phenotype

We report on a 4-year-old girl with distinctive facial features (redundant skin, bushy eyebrows, narrow palpebral fissures, short, upturned nose, epicanthal folds, and a long upper lip with well-defined philtrum) who has an interstitial deletion of chromosome 14 including band 14q31, designated as 46,XX,del(14)(pter-->q24.3::q32.1-->qter). Comparison with previously reported patients with deletions of 14q involving band 14q31 suggests that there is a distinctive clinical phenotype associated with this deletion. Our patient had dental abnormalities (3 maxillary and 3 mandibular incisors) not described in the other patients.

Interstitial deletion of chromosome 13: prognosis and adult phenotype

A de novo interstitial deletion of chromosome 13 (46,XY,del(13)(pter----q14.3::q22.3----qter] is described in a 22 year old man with severe mental retardation, poor language development, low set ears, hypertelorism, broad nasal bridge, short hands and fingers, and a history of swallowing disorder in childhood with subsequent dyspepsia. The dysmorphic features did not become evident until later childhood, supporting the view that karyotyping should be performed routinely in all children with developmental delay.

Deletion of chromosome 21 and normal intelligence: molecular definition of the lesion

Application of a method for the fine structure analysis of unbalanced chromosomal rearrangements using quantitative Southern blot analysis has established that an individual of normal intelligence and largely normal appearance has a significant interstitial deletion of chromosome 21. Using high resolution cytogenetic analysis and molecular analysis with five single copy DNA sequences unique to chromosome 21 and a probe for human SOD1 (CuZn, superoxide dismutase), we find that the deletion extends to the border of bands 21q11.1-11.2. and extends to the border of bands 21q21.2-q21.3. The latter border is established molecularly by the presence of two copies of SOD1, previously mapped to band 21q22.1, and of four single copy sequences known to be located distal to this region. The presence of SOD1 was confirmed by enzyme dosage analysis. These findings demonstrate that deletion of close to 20,000 kb of autosomal material is compatible with normal intelligence. Further, they suggest that chromosome 21 may include a large region of relative developmental neutrality whose molecular basis may now be investigated. Because of the limits of even high resolution cytogenetic analysis, fine structure molecular analyses of this type will be necessary to reliably detect and define similar small chromosomal deletions or insertions. The molecular definition of such aneuploidy provides the basis for increasing the resolution of the human physical genetic map.

A refined physical map of the long arm of human chromosome 16

Mapping of 33 anonymous DNA probes and 12 genes to the long arm of chromosome 16 was achieved by the use of 14 mouse/human hybrid cell lines and the fragile site FRA16B. Two of the hybrid cell lines contained overlapping interstitial deletions in bands q21 and q22.1. The localization of the 12 genes has been refined. The breakpoints present in the hybrids, in conjunction with the fragile site, can potentially divide the long arm of chromosome 16 into 16 regions. However, this was reduced to 14 regions because in two instances there were no probes or genes that mapped between pairs of breakpoints.

Interstitial deletions without phenotypic effect: prenatal diagnosis of a new family and brief review

A 39-year-old woman (G4P1SAB2) was referred for amniocentesis for advanced maternal age. An interstitial deletion of the G-dark band 11p12 was found in the fetus. Blood from the mother and her previous son was cultured and the same deletion was found in both. The absence of phenotypic effect in this family further confirms that G-dark euchromatic deletions are compatible with a normal phenotype, and underlines the importance of checking familial karyotypes even when apparently unbalanced structural rearrangements are found at prenatal diagnosis.

Detection by electron microscopy of a small subband 13q14.11 deletion in an hereditary retinoblastoma

High-resolution banding, specific for electron microscopy, was applied to chromosomes of synchronized blood lymphocytes obtained from a child with bilateral retinoblastoma. Ultrastructural analysis of the subbands in region q14.1, after synchronization and immunochemical banding, showed that the deletion in the abnormal chromosome 13 corresponds to subband 14.11, thus evidencing that the retinoblastoma gene is located within subband q14.11. This first application to a diagnostic problem of immunochemical banding suggests that, coupled with electron microscopy, this banding provides a higher resolution than that obtained with light microscopy and should be useful to pinpoint important localizations.

Chromosome imbalance, normal phenotype, and imprinting

A duplication of the sub-bands 1q42.11 and 1q42.12 was found in a boy and his mother. The proband has short stature (around the 10th centile) but a normal phenotype and psychomotor development. His mother is also asymptomatic. We found 30 published cases of normal subjects with an imbalance of autosomal euchromatic material. In these cases the imbalance involved either only one G positive band or a G positive and a G negative band. Thus the absence of a phenotypic effect cannot always be ascribed to the deficiency in the G positive bands of coding DNA. Moreover, in some cases, the method of transmission of the chromosome abnormality was such that an imprinting effect could be postulated.

Terminal deletion of the long arm of chromosome 2 in a mildly dysmorphic hypotonic infant with karyotype 46,XY,del(2)(q37)

We describe a boy with severe hypotonia and minor facial anomalies with a terminal deletion of chromosome 2q (46,XY,del(2)(q37)). Comparison with previous cases in the literature indicates that this particular deletion results in infantile hypotonia, developmental delay, and minor craniofacial anomalies including frontal bossing and micrognathia. The absence of true malformations and few minor anomalies in this patient suggests that indications for obtaining a chromosome analysis from neurologically impaired individuals need to be reevaluated.

Duplication of a small segment of 5p due to maternal recombination within a paracentric shift

Duplication of chromosome sub-bands 5p14.3 and 5p15.1 in a child resulted in mild mental retardation, apparently without other abnormalities. The duplicated region arises from recombination within a directly inserted segment following a shift within the short arm of the maternal chromosome 5 homologs.

Interstitial deletion 13q: further delineation of the syndrome by clinical and high-resolution chromosome analysis of five patients

Five patients with interstitial deletion 13q are reported. High-resolution chromosome banding established the diagnosis in two cases and stated the exact breakpoints in three remaining cases. All parents had normal chromosomes. An unequal and so far unexplained sex ratio of previously published and present cases was found: M:F = 1:2.75. Moderate to severe growth retardation was prominent in all patients. The patients were followed with psychological tests and growth data for 3-10 years. Mild to moderate mental retardation was present. Considerable phenotypic similarities were found in two patients with del(13)(q21.33 q31.3) and one with del(13)(q14.3q22.3). Repeat ophthalmological examinations showed no evidence of retinoblastoma in a male with del(13)(q13.1q21.1). In conclusion, the long-term study of five patients with interstitial deletion 13q, all evaluated with high-resolution banding, contributed to a more reliable mental and growth prognosis in such patients.

Interstitial del(13)(q21.3q31) associated with psychomotor retardation, eczema, and absent suck and swallowing reflex

A patient with a deletion (13)(q21.3q31) showed only eczema and absent suck and swallowing reflex, in contrast to other well documented cases with a similar deletion. Apparently there is wide clinical variability in patients with deletions in this area.

Familial retinoblastoma (mother and son) with 13q14 deletion

We present here the first familial cases (a mother and son) of dominantly inherited retinoblastoma with a 13q14 deletion [46,XY or XX, del(13)(q14.1q21.2)]. Their esterase D activities in red blood cells were as low as 50% of the normal control and the haplotype of esterase D was a type 1-0 in the mother and a type 2-0 in the son. They had peculiar facies characterized by a high forehead, low and broad nasal root, a short and bulbous nose, a long philtrum, and open mouth with a thin upper lip, and prominent earlobes. Chromosome and esterase D analysis should be performed in patients with retinoblastoma even if retinoblastoma seems to be transmitted through an autosomal dominant inheritance. This family indicates that one of the causes of dominantly inherited retinoblastoma is a chromosome deletion of part of the 13q14 band whether it is detectable by chromosome analysis or not.

Different reactivity of Z-DNA antibodies with human chromosomes modified by actinomycin D and 5-bromodeoxyuridine

Antibodies against Z-DNA react with fixed metaphase chromosomes of man and other mammals. Indirect immunofluorescence staining shows that chromosomal segments corresponding to R- and T-bands preferentially fix Z-DNA antibodies. In this work Z-DNA antibodies were used as a probe for DNA conformation in euchromatin of fixed human chromosomes whose condensation or staining were modified by actinomycin D (AMD) and by 5-bromodeoxyuridine (BrdU). Treatments with AMD and BrdU were performed to induce a G-banding by modification of chromosomal segments corresponding to R- and T-bands. Long BrdU treatments were used to induce asymmetrical and partially undercondensed chromosomes by substitution of thymidine in one or both DNA strand. Our results show a clear difference of Z-DNA antibodies reactivity after AMD or BrdU treatment. The G-banding obtained after AMD treatment is not reversed by Z-DNA antibodies staining since these antibodies bind very weakly to the undercondensed R-bands. On the other hand, the G-banding obtained by BrdU is completely reversed giving typical R-banding, as on untreated chromosomes. For asymmetrical chromosomes an R-, T-banding pattern is always observed but there is a decrease of the fluorescence intensity proportional to the degree of BrdU incorporation. We conclude that AMD treatment greatly disturbs Z-DNA antibodies binding suggesting a change in DNA conformation, whereas BrdU treatments do not suppress but only weaken the specific binding of Z-DNA antibodies on R- and T-bands. The direct involvement of thymidine substitution in DNA sequences recognized by Z-DNA antibodies is discussed.

Deletion 14q(q24.3 to q32.1) syndrome: significance of peculiar facial appearance in its diagnosis, and deletion mapping of Pi(alpha 1-antitrypsin)

A 10-month-old Japanese boy who had interstitial deletion of the long arm of chromosome No. 14; 46,XY, del(14)(pter----q24.3: :q32.1----qter) is reported. A peculiar facial appearance, including round face, frontal hypertrichosis with thick eyebrows, horizontal narrow palpebral fissures, a short bulbous nose with a flat nasal root, and mild micrognathia, appeared to be common with the two previously reported cases. We stress the significance of this peculiar facial appearance in the diagnosis of 14q-(q24.3 to q32.1) syndrome. The level of alpha 1-antitrypsin in the patient was only about half of that of his parents and controls, and the Pi locus was tentatively assigned to band 14q32.1.