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The severe mental retardation and speech deficits associated with 22q13 terminal deletions have been attributed in large part to haploinsufficiency of SHANK3, which maps to all 22q13 terminal deletions, although more proximal genes are assumed to have minor effects. We report two children with interstitial deletions of 22q13 and two copies of SHANK3, but clinical features similar to the terminal 22q13 deletion syndrome, including mental retardation and severe speech delay. Both these interstitial deletions are completely contained within the largest terminal deletion, but do not overlap with the nine smallest terminal deletions. These interstitial deletions indicate that haploinsufficiency for 22q13 genes other than SHANK3 can have major effects on cognitive and language development. However, the relatively mild speech problems and normal cognitive abilities of a parent who transmitted her identical interstitial deletion to her more severely affected son suggests that the phenotype associated with this region may be more variable than terminal deletions and therefore contribute to the relative lack of correlation between clinical severity and size of terminal deletions. The phenotypic similarity between the interstitial deletions and non-overlapping small terminal 22q13 deletions emphasizes the general nonspecificity of the clinical picture of the 22q13 deletion syndrome and the importance of molecular analysis for diagnosis.

22q11.2 microduplications of a 3-Mb region surrounded by low-copy repeats should be, theoretically, as frequent as the deletions of this region; however, few microduplications have been reported. We show that the phenotype of these patients with microduplications is extremely diverse, ranging from normal to behavioral abnormalities to multiple defects, only some of which are reminiscent of the 22q11.2 deletion syndrome. This diversity will make ascertainment difficult and will necessitate a rapid-screening method. We demonstrate the utility of four different screening methods. Although all the screening techniques give unique information, the efficiency of real-time polymerase chain reaction allowed the discovery of two 22q11.2 microduplications in a series of 275 females who tested negative for fragile X syndrome, thus widening the phenotypic diversity. Ascertainment of the fragile X-negative cohort was twice that of the cohort screened for the 22q11.2 deletion. We also report the first patient with a 22q11.2 triplication and show that this patient's mother carries a 22q11.2 microduplication. We strongly recommend that other family members of patients with 22q11.2 microduplications also be tested, since we found several phenotypically normal parents who were carriers of the chromosomal abnormality.

Methods: The 22q13 deletion syndrome (MIM 606232) is characterised by moderate to profound mental retardation, delay/absence of expressive speech, hypotonia, normal to accelerated growth, and mild dysmorphic features. We have determined the deletion size and parent of origin in 56 patients with this syndrome., Results: Similar to other terminal deletion syndromes, there was an overabundance of paternal deletions. The deletions vary widely in size, from 130 kb to over 9 Mb; however all 45 cases that could be specifically tested for the terminal region at the site of SHANK3 were deleted for this gene. The molecular structure of SHANK3 was further characterised. Comparison of clinical features to deletion size showed few correlations. Some measures of developmental assessment did correlate to deletion size; however, all patients showed some degree of mental retardation and severe delay or absence of expressive speech, regardless of deletion size., Conclusion: Our analysis therefore supports haploinsufficiency of the gene SHANK3, which codes for a structural protein of the postsynaptic density, as a major causative factor in the neurological symptoms of 22q13 deletion syndrome.

Pericentromeric regions of human chromosomes are preferential sites for the integration of duplicated DNA, or "duplicons", which often contain gene fragments. Although pericentromeric regions appear to be genomic junkyards, they could also be the birthplace of new genes with novel functions. We have characterized a chimeric transcription unit (cat eye syndrome critical region gene 7, CECR7) formed from three duplicons in the pericentromeric region of chromosome 22q. CECR7 exons show similarity to sequences on chromosomes 2, 5, 7, 10, 11, 12, 13, 14, 15, 16, 18, 19, 21, and elsewhere on 22. Based on polymerase chain reaction (PCR) analysis of CECR7 duplicon boundaries in various primate species, and the sequence divergence between the human duplicons and their putative ancestral human loci, CECR7 was probably formed before the separation of macaque and is therefore older than most previously reported pericentromeric duplicons. Expression of CECR7 was detected by RT-PCR in humans and gorilla fibroblasts, but not orangutan, suggesting that expression did not result immediately from the formation of this novel transcription unit, or that expression was silenced in orangutan following its formation.

The 22q11 region is involved in chromosomal rearrangements that lead to altered gene dosage, resulting in genomic disorders that are characterized by mental retardation and/or congenital malformations. Three such disorders-cat-eye syndrome (CES), der(22) syndrome, and velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS)-are associated with four, three, and one dose, respectively, of parts of 22q11. The critical region for CES lies centromeric to the deletion region of VCFS/DGS, although, in some cases, the extra material in CES extends across the VCFS/DGS region. The der(22) syndrome region overlaps both the CES region and the VCFS/DGS region. Molecular approaches have revealed a set of common chromosome breakpoints that are shared between the three disorders, implicating specific mechanisms that cause these rearrangements. Most VCFS/DGS and CES rearrangements are likely to occur by homologous recombination events between blocks of low-copy repeats (e.g., LCR22), whereas nonhomologous recombination mechanisms lead to the constitutional t(11;22) translocation. Meiotic nondisjunction events in carriers of the t(11;22) translocation can then lead to offspring with der(22) syndrome. The molecular basis of the clinical phenotype of these genomic disorders has also begun to be addressed. Analysis of both the genomic sequence for the 22q11 interval and the orthologous regions in the mouse has identified >24 genes that are shared between VCFS/DGS and der(22) syndrome and has identified 14 putative genes that are shared between CES and der(22) syndrome. The ability to manipulate the mouse genome aids in the identification of candidate genes in these three syndromes. Research on genomic disorders on 22q11 will continue to expand our knowledge of the mechanisms of chromosomal rearrangements and the molecular basis of their phenotypic consequences.

We have sequenced a 1.1-Mb region of human chromosome 22q containing the dosage-sensitive gene(s) responsible for cat eye syndrome (CES) as well as the 450-kb homologous region on mouse chromosome 6. Fourteen putative genes were identified within or adjacent to the human CES critical region (CESCR), including three known genes (IL-17R, ATP6E, and BID) and nine novel genes, based on EST identity. Two putative genes (CECR3 and CECR9) were identified, in the absence of EST hits, by comparing segments of human and mouse genomic sequence around two solitary amplified exons, thus showing the utility of comparative genomic sequence analysis in identifying transcripts. Of the 14 genes, 10 were confirmed to be present in the mouse genomic sequence in the same order and orientation as in human. Absent from the mouse region of conserved synteny are CECR1, a promising CES candidate gene from the center of the contig, neighboring CECR4, and CECR7 and CECR8, which are located in the gene-poor proximal 400 kb of the contig. This latter proximal region, located approximately 1 Mb from the centromere, shows abundant duplicated gene fragments typical of pericentromeric DNA. The margin of this region also delineates the boundary of conserved synteny between the CESCR and mouse chromosome 6. Because the proximal CESCR appears abundant in duplicated segments and, therefore, is likely to be gene poor, we consider the putative genes identified in the distal CESCR to represent the majority of candidate genes for involvement in CES.

Cat eye syndrome (CES) is a developmental disorder with multiple organ involvement, associated with the duplication of a 2-Mb region of 22q11.2. Using exon trapping and genomic sequence analysis, we have isolated and characterized a gene, CECR1, that maps to this critical region. The protein encoded by CECR1 is similar to previously identified novel growth factors: IDGF from Sarcophaga peregrina (flesh fly) and MDGF from Aplysia californica (sea hare). The CECR1 gene is alternatively spliced and expressed in numerous tissues, with most abundant expression in human adult heart, lung, lymphoblasts, and placenta as well as fetal lung, liver, and kidney. In situ hybridization of a human embryo shows specific expression in the outflow tract and atrium of the developing heart, the VII/VIII cranial nerve ganglion, and the notochord. The location of this gene in the CES critical region and its embryonic expression suggest that the overexpression of CECR1 may be responsible for at least some features of CES, particularly the heart defects., (Copyright 2000 Academic Press.)

Duplication of a segment of the long arm of human chromosome 3 (3q26.3-q27) results in a syndrome characterized by multiple congenital abnormalities and neurological anomalies in some patients. We have identified a novel gene (KCNMB3) that maps to this region. KCNMB3 has significant sequence similarity to the regulatory subunit of the large-conductance calcium-activated potassium channel. Due to the significance of potassium channels in neuronal functions, the overexpression of this gene may play a role in the abnormal neurological functions seen in some of these patients. A related sequence corresponding to the second and third exons of this gene resides in the pericentromeric region of 22q11, where a number of other unprocessed pseudogenes are known to map., (Copyright 1999 Academic Press.)

Two closely related genes have been identified at 2q13 and 22q13.3. These genes show similarity to members of the RAB family of small GTPases. RABL2A and RABL2B differ by three conservative amino acid changes over a total of 228 residues. Both are expressed in all tissues tested. Northern analysis showed that a 2.5-kb transcript is expressed in all tissues tested while a 1.4-kb transcript is specifically expressed only in muscle. The size difference between these two transcripts is the result of differential splicing of an intron within the 3' UTR. RABL2B is located within the subtelomeric region of 22q13.3. RABL2A maps to 2q13, the site of an ancestral telomere fusion event, suggesting that it also may be a subtelomeric gene., (Copyright 1999 Academic Press.)

We have constructed a 1.5-Mb contig spanning the distal half of the critical region for cat eye syndrome on human chromosome 22 from D22S543 to D22S181. The contig consists of 20 P1 artificial chromosome (PAC) clones and 11 bacterial artificial chromosome (BAC) clones screened from 2 BAC and 2 PAC libraries. Continuous overlap between the clones was confirmed using vectorette PCR and riboprobes. Despite the instability of this region in a previous YAC contig, only 1 BAC showed a minor instability and then in only one isolation. This contig is now providing the basis for genomic sequencing and gene identification in the cat eye syndrome critical region., (Copyright 1999 Academic Press.)

A patient with several features consistent with duplication of 22q11.2 (cat eye syndrome or CES) was found to be mosaic for a dicentric double ring chromosome 22 on postnatal karyotyping of peripheral blood. The initial karyotype was 46,XX,r(22)(p12q13) [46]/46,XX,dic r(22)(p12q13; p12q13)[4]. The amount of material duplicated in the dic r(22) was determined to include and extend beyond the CES critical region into 22q13.3. However, karyotyping of lymphocytes and fibroblasts, at 27 and 13 months of age respectively, showed no dic r(22) present in any of the cells examined. We suggest that the CES features in this patient, and potentially in other ring cases with CES phenotypic features, might result from a high level of mosaicism for a dic r(22) during early fetal development. Usually this unstable dic r(22) is subsequently lost from most cells.

Cat eye syndrome (CES) is associated with a duplication of a segment of human chromosome 22q11.2. Only one gene, ATP6E, has been previously mapped to this duplicated region. We now report the mapping of the human homologue of the apoptotic agonist Bid to human chromosome 22 near locus D22S57 in the CES region. Dosage analysis demonstrated that BID is located just distal to the CES region critical for the majority of malformations associated with the syndrome (CESCR), as previously defined by a single patient with an unusual supernumerary chromosome. However, BID remains a good candidate for involvement in CES-related mental impairment, and its overexpression may subtly add to the phenotype of CES patients. Our mapping of murine Bid confirms that the synteny of the CESCR and the 22q11 deletion syndrome critical region immediately telomeric on human chromosome 22 is not conserved in mice. Bid and adjacent gene Atp6e were found to map to mousechromosome 6, while the region homologous to the DGSCR is known to map to mouse chromosome 16., (Copyright 1998 Academic Press.)

The supernumerary cat eye syndrome (CES) chromosome is dicentric, containing two copies of 22pter-->q11.2. We have found that the duplication breakpoints are clustered in two intervals. The more proximal, most common interval is the 450-650 kb region between D22S427 and D22S36, which corresponds to the proximal deletion breakpoint interval found in the 22q11 deletion syndrome (DiGeorge/velocardiofacial syndrome). The more distal duplication breakpoint interval falls between CRKL and D22S112, which overlaps with the common distal deletion interval of the 22q11 deletion syndrome. We have therefore classified CES chromosomes into two types based on the location of the two breakpoints required to generate them. The smaller type I CES chromosomes are symmetrical, with both breakpoints located within the proximal interval. The larger type II CES chromosomes are either asymmetrical, with one breakpoint located in each of the two intervals, or symmetrical, with both breakpoints located in the distal interval. The co-localization of the breakpoints of these different syndromes, plus the presence of low-copy repeats adjacent to each interval, suggests the existence of several specific regions of chromosomal instability in 22q11.2 which are involved in the production of both deletions and duplications. Since the phenotype associated with the larger duplication does not appear to be more severe than that of the smaller duplication, determination of the type of CES chromosome does not currently have prognostic value.

Two unrelated patients with cryptic subtelomeric deletions of 22q13.3 were identified using FISH with the commercially available Oncor probe, D22S39. Proband 1 was found to have a derivative chromosome 22 resulting from the unbalanced segregation of a t(1;22)(q44;q13.32) in her mother. Additional FISH analysis of proband 1 and her mother placed the breakpoint on chromosome 22 in this family proximal to D22S55 and D22S39 and distal to D22S45. We have mapped D22S39 to within 170 kb of D22S21 using pulsed field gel electrophoresis. D22S21 is genetically mapped between D22S55 and D22S45. These data indicate that the deletion in proband 1 is smaller than in eight of nine reported del(22)(q13.3) patients. Probands 1 and 2 share features of hypotonia, developmental delay, and expressive language delay, also seen in previously reported del(22)(q13.3) patients, although proband 1 appears to be more mildly affected. Proband 1 is also trisomic for the region 1q44-->qter. This very small duplication has been previously reported only once and the patient had idiopathic mental retardation. This is the first report where 22q13.3 terminal deletion patients have been identified through the use of FISH, and the first report of a deletion of this region occurring because of missegregation of a parental balanced cryptic translocation. We feel that investigation of the frequency of del(22)(q13.3) in the idiopathic mentally retarded population is warranted and may be aided by the ability to use a commercially available probe (D22S39), which is already currently in use in a large number of cytogenetic laboratories.

The smallest region of deletion overlap in the patients we have studied defines a DIGeorge syndrome/velocardiofacial syndrome (DGS/VCFS) minimal critical region (MDGCR) of approximately 250 kb within 22q11. A de novo constitutional balanced translocation has been identified within the MDGCR. The patient has some features which have been reported in individuals with DGS/VCFS, including: facial dysmorphia, mental retardation, long slender digits and genital anomalies. We have cloned the breakpoint of his translocation and shown that it interrupts the clathrin heavy chain-like gene (CLTCL) within the MDGCR. The breakpoint of the translocation partner is in a repeated region telomeric to the rDNA cluster on chromosome 21p. Therefore, it is unlikely that the patient's findings are caused by interruption of sequences on 21p. The chromosome 22 breakpoint disrupts the 3' coding region of the CLTCL gene and leads to a truncated transcript, strongly suggesting a role for this gene in the features found in this patient. Further, the patient's partial DGS/VCFS phenotype suggests that additional features of DGS/VCFS may be attributed to other genes in the MDGCR. Thus, haploinsufficiency for more than one gene in the MDGCR may be etiologic for DGS/VCFS.

We have analyzed a recently described 22q13.3 microdeletion in a child with some overlapping features of the cytologically visible 22q13.3 deletion syndrome. Patient NT, who shows mild mental retardation and delay of expressive speech, was previously found to have a paternal microdeletion in the subtelomeric region of 22q. In order to characterize this abnormality further, we have constructed a cosmid/P1 contig covering the terminal 150 kb of 22q, which encompasses the 130-kb microdeletion. The microdeletion breakpoint is within the VNTR locus D22S163. The cloning of the breakpoint sequence revealed that the broken chromosome end was healed by the addition of telomeric repeats, indicating that the microdeletion is terminal. This is the first cloned terminal deletion breakpoint on a human chromosome other than 16p. The cosmid/P1 contig was mapped by pulsed-field gel electrophoresis analysis to within 120 kb of the arylsulfatase A gene, which places the contig in relation to genetic and physical maps of the chromosome. The acrosin gene maps within the microdeletion, approximately 70 kb from the telomere. With the distal end of chromosome 22q cloned, it is now possible to isolate genes that may be involved in the overlapping phenotype of this microdeletion and 22q13.3 deletion syndrome.

Cat eye syndrome (CES) is typically associated with a supernumerary bisatellited marker chromosome derived from human chromosome 22pter to 22q11.2. The region of 22q duplicated in the typical CES marker chromosome extends between the centromere and locus D22S36. We have constructed a long-range restriction map of this region using pulsed-field gel electrophoresis and probes to 10 loci (11 probes). The map covers -3.6 Mb. We have also used 15 loci to construct a yeast artificial chromosome contig, which encompasses about half of the region critical to the production of the CES phenotype (centromere to D22S57). Thus, the CES critical region has been mapped and a substantial portion of it cloned in preparation for the isolation of genes in this region.

Cat eye syndrome (CES) is typically associated with a supernumerary bisatellited marker chromosome (inv dup 22pter-22q11.2) resulting in four copies of this region. We describe an individual showing the inheritance of a minute supernumerary double ring chromosome 22, which resulted in expression of all cardinal features of CES. The size of the ring was determined by DNA dosage analysis and FISH analysis for five loci mapping to 22q11.2. The probes to the loci D22S9, D22S43, and ATP6E were present in four copies, whereas D22S57 and D22S181 were present in two copies. This finding further delineates the distal boundary of the critical region of CES, with ATP6E being the most distal duplicated locus identified. The phenotypically normal father and grandfather of the patient each had a small supernumerary ring chromosome and demonstrated three copies for the loci D22S9, D22S43, and ATP6E. Although three copies of this region have been reported in other cases with CES features, it is possible that the presence of four copies leads to greater susceptibility.

Cat eye syndrome (CES) is associated with a supernumerary bisatellited marker chromosome which is derived from duplicated regions of 22pter-22q11.2. In this study we have used dosage and RFLP analyses on 10 CES patients with marker chromosomes, by using probes to five loci mapped to 22q11.2. The sequences recognized by the probes D22S9, D22S43, and D22S57 are in four copies in all patients, but the sequences at the more distal loci, D22S36 and D22S75, are duplicated only in some individuals. D22S36 is present in three copies in some individuals, and D22S75 is present in two copies in the majority of cases. Only three individuals have a duplication of the most distal locus examined (D22S75), and these individuals have the largest marker chromosomes identified in this study. From the dosage analysis it was found that the marker chromosomes are variable in size and can be asymmetric in nature. There is no obvious correlation between the severity of the phenotype and the size of the duplication. The distal boundary of the CES critical region (D22S36) is proximal to that of DiGeorge syndrome, a contiguous-gene-deletion syndrome of 22q11.2.

We have studied seven patients who have chromosome 22q13.3 deletions as revealed by high-resolution cytogenetic analysis. Clinical evaluation of the patients revealed a common phenotype that includes generalized developmental delay, normal or accelerated growth, hypotonia, severe delays in expressive speech, and mild facial dysmorphic features. Dosage analysis using a series of genetically mapped probes showed that the proximal breakpoints of the deletions varied over approximately 13.8 cM, between loci D22S92 and D22S94. The most distally mapped locus, arylsulfatase A (ARSA), was deleted in all seven patients. Therefore, the smallest region of overlap (critical region) extends between locus D22S94 and a region distal to ARSA, a distance of > 25.5 cM.

As part of a general effort to identify new genes mapping to disease-associated regions of human chromosome 22, we have isolated heterogeneous nuclear RNA from somatic cell hybrids selected for their chromosome 22 content. Inter-Alu PCR amplification yielded a series of human DNA fragments which all detected evolutionarily-conserved sequences. The centromere-most gene fragment candidate, XEN61, was shown to lie centromeric to the chromosome 22 breakpoint in the X/22-33-11TG somatic cell hybrid. This region, which is still devoid of characterized genes, overlaps with the critical region for the cat eye syndrome (CES), a developmental disorder associated with chromosomal duplication within 22pter-q11.2. Gene dosage analysis performed on DNA from six CES patients consistently revealed the presence of four copies of XEN61. A fetal brain cDNA clone, 61EW, was identified with XEN61 and entirely sequenced. The deduced protein is the E subunit of vacuolar H(+)-ATPase. This 31 KDa component of a proton pump is essential in eukaryotic cells as it both controls acidification of the vacuolar system and provides it with its main protonmotive force. RT-PCR experiments using oligonucleotides designed from the 61EW cDNA sequence indicated that the corresponding messenger is widely transcribed.

A long-range restriction map of the region between the immunoglobulin lambda locus and the Ewing sarcoma breakpoint has been constructed using the rare-cutting enzymes NotI, NruI, AscI, and BsiWI. The map spans approximately 11,000 kb and represents about one-fifth of the long arm of chromosome 22. Thirty-nine markers, including seven NotI junction clones as well as numerous genes and anonymous sequences, were mapped to the region with a somatic cell hybrid panel. These probes were then used to produce the map. The seven NotI junction clones each identified a possible CpG island. The breakpoints of the RAJ5 hybrid and the Ewing sarcoma t(11;22) were also localized in the resulting map. This physical map will be useful in studying chromosomal rearrangements in the region, as well as providing the details to examine the fidelity of the YAC and cosmid contigs currently under construction. Comparisons of this physical map to genetic and radiation hybrid maps are discussed.

The human immunoglobulin lambda-like (IGLL) genes, which are homologous to the human immunoglobulin lambda (IGL) light chain genes, are expressed only in pre-B cells and are involved in B cell development. Three IGLL genes, 14.1, 16.1, and 16.2 are present in humans as opposed to one, lambda 5 (Igll), found in the mouse. To precisely map the location of the human IGLL genes in relation to each other and to the human IGL gene locus, at 22q11.1-2, a somatic cell hybrid panel and pulsed field gel electrophoresis (PFGE) were used. Hybridization with a lambda-like gene-specific DNA probe to somatic cell hybrids revealed that these genes reside on 22q11.2 between the breakpoint cluster region (BCR) and the Ewing sarcoma breakpoint at 22q12 and that gene 16.1 was located distal to genes 14.1 and 16.2. Gene 14.1 was found by PFGE to be proximal to 16.2 by at least 30 kilobases (kb). A 210 kb Not I fragment containing genes 14.1 and 16.2 is adjacent to a 400 kb Not I fragment containing the BCR locus, which is just distal to the IGL-C (IGL constant region) genes. We have determined that the IGLL genes 14.1 and 16.2 are approximately 670 kb and 690 to 830 kb distal, respectively, to the 3'-most IGL-C gene in the IGL gene locus, IGL-C7. We thus show the first physical linkage of the IGL and the IGLL genes, 14.1 and 16.2. We discuss the relevance of methylation patterns and CpG islands to expression, and the evolutionary significance of the IGLL gene duplications. Consistent with the GenBank nomenclature, these human IGLL genes will be referred to as IGLL1 (14.1), IGLL2 (16.2), and IGLL3 (16.1), reflecting their position on chromosome 22, as established by this report.

We report on a 3-year-old boy with a terminal deletion of 22q. The activity of alpha-N-acetylgalactosaminidase was normal while arylsulfatase A activity was reduced. Molecular analysis demonstrated the lack of paternal alleles of D22S45 and D22S55.

We constructed a genetic linkage map of the entire long arm of human chromosome 22 with 30 polymorphic markers, defining 22 loci. The map consists of a continuous linkage group 110 cM long, when male and female recombination fractions are combined; average distance between the loci is 5.2 cM. All loci were placed on the map with high support against alternative orders (odds in excess of 1000:1). The order of loci presented in our map is in full agreement with that of the previous linkage maps of chromosome 22 and with the physical assignment of markers. Two markers included in this map, KI-831 (D22S212) and pEFZ31 (D22S32), allowed us to better define the region of the (11;22) translocation breakpoint specific for Ewing sarcoma. Ten additional polymorphic markers were placed on the 22-loci map with odds lower than 1000:1 against alternative locations. In total, we have introduced 29 new markers on the linkage map of chromosome 22.

Thirty-five new, unique, DNA probes have been isolated and each has been assigned to one of five regions on chromosome 22. The distribution of probes along the chromosome is what would be expected based on the estimated size of each region with the exception of the short arm (22p). RFLP analysis was performed using 13 different restriction enzymes and over 50% of the probes were found to have useful polymorphisms. Probes mapping to 22q11 were further characterized by pulsed-field gel analysis and it has been possible to link several on large restriction fragments. These 35 new probes will be useful reagents for producing genetic and physical maps of chromosome 22.

Two individuals, a boy and girl, with a clinical diagnosis of cat eye syndrome had an extra bisatellited chromosome. In the girl, the diagnosis was made on the basis of coloboma of the right iris, right preauricular pit, and imperforate anus; in the boy, bilateral colobomata of the iris, down-slanting palpebral fissures, right preauricular skin tag, and right preauricular pit. Multiple staining techniques were used to characterize the extra chromosomes. With G-banding the extra chromosome usually appeared monocentric with two major G-positive bands, but with satellites on both ends; with C-banding, two C-band positive regions were evident, indicating that the chromosomes were likely dicentric. Silver staining demonstrated the presence of NORs near each end; Q-banding showed satellites on each end, differing in brightness and size. The chromosomes of the parents were normal; comparisons of Q-band heteromorphisms of the acrocentric chromosomes of the parents with those of the extra chromosome showed in each case one short arm/satellite region of the extra chromosome identical in appearance to one chromosome 22 of the mother and the other end of the extra bisatellited chromosome identical to the short arm/satellite of the mother's second chromosome 22. This extra chromosome, then, is the result of a maternal meiotic error in each case. In situ hybridization studies using the chromosome 22-derived probe p22/34, which identifies locus D22S9, showed 16% of the cells from the female patient to have silver grains on the proximal long arm of the normal chromosome 22 and 14% on the extra chromosome, while 10% of cells from the male had grains on the normal chromosomes 22 and an equal number on the extra chromosome, confirming the chromosome 22 origin of the extra chromosome in these patients.

We constructed a library in lambda L47.1 with DNA isolated from flow-sorted human chromosome 22. Over 50% of the recombinants contained the same highly repetitive sequence. When this sequence was used to probe Southern blots of EcoRI-digested genomic DNA, a ladder of bands with increments of about 170 bp was observed. This sequence comigrates with satellite III in Ag+/Cs2SO4 gradients and may account for at least part of the 170 bp Hae III ladder seen in isolated satellite III DNA. Partial sequence analysis revealed homology to the 171 bp monomeric repeat unit of alpha-R1-DNA and the X specific alpha-satellite consensus sequence. After low stringency in situ hybridization, silver grains were found over the centromeres of a number of chromosomes. Under high stringency conditions, however, the labeling was concentrated over the centromeric region of chromosome 22. This localization was confirmed using DNA from a panel of human/hamster cell lines which showed that the homologous 2.1 and 2.8 kb EcoR1 restriction fragments were chromosome 22 specific. These clones therefore contain chromosome 22 derived alpha-satellite sequences analogous to other chromosome-specific satellite sequences described previously.

Human chromosome band 22q11 is involved in numerous chromosomal rearrangements. A long-range molecular map of this region would allow the more precise localization of the various breakpoints of these rearrangements. Toward this goal we have constructed a genomic DNA library that allows the isolation of DNA clones that are directly adjacent to NotI sites. NotI was chosen because it is a restriction enzyme that digests infrequently in the human genome. The genomic DNA used in this library was from a human/hamster hybrid cell line that has a chromosome 22 as the only visible human chromosome. Two clones were isolated and mapped to different regions of 22q11 using a somatic cell hybrid mapping panel. A long-range restriction map flanking the NotI site of each of these two clones was produced using NotI and other infrequently cutting enzymes. Both NotI sites analyzed were located in HTF islands, regions often associated with the 5' end of genes. Thus, the NotI map of 22q11 may also aid in the cloning of undiscovered genes, giving a starting point for the study of duplication/deficiency syndromes of the region.