Meiotic chromosome segregation in human t(11;22)(q23;q11) carriers: a theoretical consideration

The t(11;22)(q23;q11) translocation is the most frequently encountered familial reciprocal translocation in humans. In the majority of reported cases ascertainment has been through the birth of a child with the chromosomal constitution 47,XX,+der(22) or 47,XY,+der(22), i.e., tertiary trisomy. Previous segregation analysis of familial cases showed a number of interesting features. Thus, euploid unbalanced genotypes resulting from adjacent segregation are absent in the progeny, and only tertiary trisomic offspring are recovered. To explain this unusual progeny output we present here a model for the meiotic behavior of this translocation in the carriers based on an analysis of cytogenetic data of progeny of carriers. This model predicts the formation of a chain trivalent with chromosome order 11-der(11)-22 during prophase I and its predominant alternate orientation at metaphase I.     

Unbalanced karyotype due to adjacent 1 segregation of t(11;22)(q23.3;q13.2).

The 11q;22q translocations, whatever the breakpoints may be, are of particular interest because of their propensity to 3:1 segregation of the chromosomes at meiosis I. Until now, no unbalanced karyotype resulting from 2:2 adjacent segregation was published among offspring of 11q;22q translocation carriers. The authors report the case of an unbalanced karyotype due to adjacent 1 segregation of a maternal translocation (11;22)(q23.3;q13.2). The proband's karyotype was 46,XX,-22,+der(22)(11;22)(q23.3;q13.2)mat. This finding demonstrates that adjacent 1 segregation is possible in t(11;22) with breakpoints at 11q23 and 22q13, and can lead to birth of viable infants.     

31 cases with oculoauriculovertebral dysplasia (Goldenhar syndrome): clinical, neuroradiologic, audiologic and cytogenetic findings

Goldenhar syndrome (GS) or oculoauriculovertebral dysplasia (OAVD) is characterized by pre-auricular skin tags, microtia, facial asymmetry, ocular abnormalities and vertebral anomalies of different size and shape. The phenotypical findings of this syndrome are variable due to heterogenous aetiology. For that reason, the physician sometimes faces difficulty when making a definite diagnosis of OAVD. We reviewed the clinical and laboratory findings of 31 patients (15 boys and 16 girls) aged from 1 day to 16 years with the clinical diagnosis of GS. The characteristic features were pre-auricular skin tags (90%), microtia (52%), hemifacial microsomia (77%) and epibulbar dermoids (39%). Vertebral anomalies were noted in 70% of the patients. Cardiac malformations were found in 39% while a genitourinary anomaly was noted in 23% and various central nervous system malformations in 47%. There were 3 pregnancies following an intracytoplasmic sperm injection (ICSI) technique among the 31 patients. Two patients with GS came from the same family. Their relatives had hydrocephaly, myelomeningocele and neural tube defects. It is known that some chromosomal aberrations are seen in GS. We performed chromosome analysis of 29 patients. Among these cases, only one patient with severe mental and motor retardation had a 47,XX,+der(22)t(11,22)(q23; q11 karyotype due to a maternal balanced translocation t(11;22)(q23;q11). This translocation was demonstrated in her sister, brother and maternal uncle. Additionally CATCH 22 analysis in 13 cases with OAVD with a CATCH 22 phenotype revealed no deletion. OAVD patients present with different morphologic features and systemic manifestations. A multidisciplinary approach should be undertaken by departments such as pediatric cardiology, audiology, ophthalmology and plastic surgery when evaluating patients with OAVD. Chromosome analysis should be performed in every patient with Goldenhar syndrome.     

The unbalanced offspring of the male carriers of the 11q;22q translocation: nondisjunction at meiosis II in a balanced spermatocyte

Summary Carriers of the standard translocation t(11;22) (q23.3;q11.2) produce only one type of unbalanced offspring, a tertiary trisomy resulting into the karyotype 47,XX or XY, +der(22)t(11;22)(q23.3;q11.2), usually derived from the mother. The exception is one single patient 47,XY,t(11;22)(q23.3;q11.2),+der(22)t(11;22) (q23.3;q11.2)pat. We report a second case with the same karyotype, also of paternal origin. Thus, the rare unbalanced offspring of a carrier father (only 5 cases known) may receive a supernumerary der(22), as a consequence of tertiary trisomy, but also as a consequence of nondisjunction at meiosis II of a balanced spermatocyte.     

Partial trisomy of 13(pter→q12) due to 47,XY,+der(13),t(13;22)(q12;q13)mat

Summary A 36-month-old boy presented with short stature, short neck, shield-shaped chest, and mental retardation. Chromosome analysis showed trisomy for the short arm and the proximal portion of the long arm of chromosome 13 [47,XY,+der(13),t(13;22)(q12;q13)mat]. The patient's mother has a balanced translocation between the long arms of chromosomes 13 and 22 [46,XX,t(13;22)(q12;q13)]. The patient's neutrophils showed an elevated number of nuclear projections and his fetal hemoglobin level was undetectable.     

Tertiary trisomy (22q11q),47,+der(22),t(11;22)

Summary We describe a case of tertiary trisomy (22q11q) 47,XX,+der(22),(22pter22q13: : 11q2511qter) in a child with mental retardation, cleft palate, and congenital heart disease resulting from 3: 1 meiotic nondisjunction in a maternal (11;22) translocation carrier. The clinical findings in previously reported cases are reviewed and compared with the features of reported patients with partial trisomy 11q and trisomy 22 syndromes. Half of the ten reported families had additional balanced translocation carriers who may have an increased risk of having a liveborn child with an MCA/MR syndrome, although none have been reported to date.     

Partial trisomies 13 and 22 due to nondisjunction of a maternal reciprocal translocation,t(13;22)(q22;q11)

Summary A family is reported in which the propositus has an extra G-like chromosome with an unusual G-banding pattern. Cytogenetic family studies showed that the mother is a carrier of a balanced reciprocal translocation t(13;22), which does not affect the size and morphology of the chromosomes involved. The propositus has a 47,XY,+der(22),t(13;22)(q22;q11) karyotype and is therefore partially trisomic for the distal third of the long arm of chromosome 13 and for a very small part of chromosome 22. The clinical findings are presented and compared with those of other reported cases of partial trisomies 13 and 22.     

Confirmation of regional assignment of nucleoside phosphorylase (NP) on chromosome 14 by gene dosage studies

Summary Gene dosage studies yielded results consistent with assignment of the locus for nucleoside phosphorylase to band 14q13. The red blood cells from a patient with the karyotype 47,XX,+der(14),t(8;14)(8qter8q24: :14q2114pter)pat had enzyme activity 50% higher than red cells from 47 normal controls, two trisomies involving chromosomes other than 14, and five balanced translocations involving chromosome 14. On the other hand, the red cells of a case with a karyotype 45,XX,-14,-22,+der(22),t(14;22)(14qter14q11 or 14q12::22p1122qter)mat and a case with a karyotype 47,XX, +der(14),t(14;16)(14pter14q11::16q2416qter)mat had normal activity.     

Emanuel syndrome due to unusual segregation of paternal origin

Emanuel syndrome is an inherited chromosomal abnormality resulting from 3:1 meiotic segregation from parental balanced translocation carrier t(11;22)(q23;q11), mostly of maternal origin. It is characterized by mental retardation, microcephaly, preauricular tag or sinus, ear anomalies, cleft or high arched palate, micrognathia, congenital heart diseases, kidney abnormalities, structural brain anomalies and genital anomalies in male. Here in, we describe a female patient with supernumerary der(22) syndrome (Emanuel syndrome) due to balanced translocation carrier father t(11;22) (q23;q11). She was mentally and physically disabled and had most of the craniofacial dysmorphism of this syndrome. Our patient had cleft palate, maldeveloped corpus callosum and hind brain with normal internal organs. Additionally, arachnodactyly, hyperextensibility of hand joints, abnormal deep palmar and finger creases, extra finger creases and bilateral talipus were evident and not previously described with this syndrome. Cytogenetic analysis and FISH documented that the patient had both translocation chromosomes plus an additional copy of der(22) with karyotyping: 47,XX,t(11; 22)(q23;q11),+der(22)t(11;22)(q23;q11). We postulated that this rare chromosomal complement can arise from; 2:2 segregation in the first meiotic division of the balanced translocation father followed by non-disjunction at meiosis II in the balanced spermatocyte.     

Supernumerary chromosome der(22)t(11;22): Emanuel syndrome associates with novel features

Emanuel syndrome results from +der(22)t(11q23;22q11). Cleft palate, ear anomalies, heart defects, genital anomalies, hypotonia, and mental retardation are the main features of the syndrome. We report a nine-year-old boy with the t(11;22)(q23;q11) chromosome, transmitted in an unbalanced fashion from his mother, and originated in the maternal grandmother's meiosis. In addition to mental retardation, hypotonia, craniofacial anomalies, and cryptorchidism, he has novel findings such as, joint hyperextensibility, left liver lobe agenesis, left sided malposition of the gallbladder and pancreas hypoplasia. This is the first report associating these features with Emanuel syndrome.     

De novo (11;13) translocation

Summary The clinical features and cytogenetic Giemsa banding studies of a case of partial trisomy 4p [47,XX,+der(21), der(4), der(21), t(4p 21p;4q 21q) mat] are presented. This aberration resulted from a reciprocal translocation rcq(4p 21p; 4q 21q) found in the mother.     

Der(22) syndrome and velo-cardio-facial syndrome/DiGeorge syndrome share a 1.5-Mb region of overlap on chromosome 22q11

Derivative 22 (der[22]) syndrome is a rare disorder associated with multiple congenital anomalies, including profound mental retardation, preauricular skin tags or pits, and conotruncal heart defects. It can occur in offspring of carriers of the constitutional t(11;22)(q23;q11) translocation, owing to a 3:1 meiotic malsegregation event resulting in partial trisomy of chromosomes 11 and 22. The trisomic region on chromosome 22 overlaps the region hemizygously deleted in another congenital anomaly disorder, velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS). Most patients with VCFS/DGS have a similar 3-Mb deletion, whereas some have a nested distal deletion endpoint resulting in a 1.5-Mb deletion, and a few rare patients have unique deletions. To define the interval on 22q11 containing the t(11;22) breakpoint, haplotype analysis and FISH mapping were performed for five patients with der(22) syndrome. Analysis of all the patients was consistent with 3:1 meiotic malsegregation in the t(11;22) carrier parent. FISH-mapping studies showed that the t(11;22) breakpoint occurred in the same interval as the 1.5-Mb distal deletion breakpoint for VCFS. The deletion breakpoint of one VCFS patient with an unbalanced t(18;22) translocation also occurred in the same region. Hamster-human somatic hybrid cell lines from a patient with der(22) syndrome and a patient with VCFS showed that the breakpoints occurred in an interval containing low-copy repeats, distal to RANBP1 and proximal to ZNF74. The presence of low-copy repetitive sequences may confer susceptibility to chromosome rearrangements. A 1.5-Mb region of overlap on 22q11 in both syndromes suggests the presence of dosage-dependent genes in this interval.     

Meiotic studies of a human male carrier of the common translocation, t(11;22), suggests postzygotic selection rather than preferential 3:1 MI segregation as the cause of liveborn offspring with an unbalanced translocation

The t(11;22)(q23;q11) translocation is the only non-Robertsonian rearrangement for which there are a large number of unrelated families, apparently with the same breakpoints. These families most often have been ascertained through an abnormal child with the karyotype 47,XX or XY, +der(22) t(11;22)(q23;q11). To explain the high incidence of 3:1 segregants, rarely seen in offspring of carriers of other reciprocal translocations, a number of theoretical models have been suggested. We have used both electron microscope analysis of the synaptonemal complex (SC) and dual-color FISH to investigate the meiotic chromosome behavior in a male carrier of the translocation who has the karyotype 46,XY, t(11;22)(q23;q11). Chromosome synapsis, first-meiotic chiasma configuration, and segregation behavior of this translocation have been analyzed directly. Examination of SCs by electron microscopy showed pachytene-cross formation in 49/50 nuclei. Approximately 50% (26/50) revealed a classical fully synapsed quadrivalent. A proportion of these (10/26), however, showed some central asymmetry, suggesting heterologous synapsis. The remaining cells appeared to have incomplete synapsis. FISH analysis showed only quadrivalents in all 100 metaphase I nuclei. The chiasma frequency was increased within the interstitial segments, in comparison with the same region in normal bivalents. All types of segregation category were found in metaphase II nuclei. There was no indication of preferential 3:1 anaphase I segregation. We conclude that the +der(22) constitution in offspring of carriers of t(11;22)(q23;q11) is not likely to be due to meiotic 3:1 segregation being especially common. Rather, the +der(22) constitution is more likely to be the result of postzygotic selection against other unbalanced karyotypes.     

Familial unbalanced translocation t(8;15)(p23.3;q11) with uniparental disomy in Angelman syndrome

A 29-year-old male with Angelman syndrome and an unbalanced reciprocal translocation, 45,XY,-8,-15,+der(8),t(8;15)(p23.3;q11)pat, was evaluated with DNA studies. These showed the underlying mechanism to be paternal uniparental disomy. This is the second case reported of Angelman syndrome that has resulted from a familial unbalanced reciprocal translocation.     

19q distal trisomy due to a de novo (19;22)(q13.2;p11) translocation

A 2 4/12-year-old girl whith a de novo 46,XX,-22 + der(22), t(19;22)(q13.2;p11) karyotype is described. From this and other eight similar cases previously published, a typical phenotype in distal 19q trisomy is concluded.     

47,XY,+der(11;22)(q23;q12) following balanced translocation t(11;22)(q23;q12)mat

Summary Report of a supernumerary extra chromosome der(11;22)(q23; q12) resulting from a balanced translocation in the mother. The propositus suffers from mental deficiency, deafness and extreme muscular weakness and exhibits cleft palate, a labial lymphangioma and an atrial septum defect. Since the features of partial trisomy 11q23 frequently associated with a translocation t(11q;22q) bear similarities with the cases of so called trisomy 22 one might conjecture that some of these observations are in fact products of translocations including partial 11q.     

Double partial trisomy of 6p23-pter and 9pter-q21.2 in a neonate resulting from 4:2 meiotic segregation of a maternal complex t(6;7;9)(p23;p15;q21.2) translocation

We report, a newborn presenting multiple congenital abnormalities with karyotype; 47,XY,der(7)t(6;7)(pter-p23::p15-->qter),+der(9)t(7;9)(pter-->p15::q21.2--> pter)t(6;7;9)(p23;p15;q21.2)mat[20]. The mother and her phenotypically normal daughter were carriers of a complex chromosomal rearrangement with karyotypes; 46,XX,t(6;7;9)(p23;p15;q21.2)[20]. Paternal chromosomes were normal. In our case the extra derivative chromosome was the result of a 4:2 segregation of the chromosomes involved in translocation during oogenesis. Double partial trisomy in newborns resulting from 4:2 segregation is a rare event, and double partial trisomies of the 6p23-pter and trisomy 9pter-q22 regions have not reported to date.     

Partial trisomy 11q and familial translocation 11--22 (author's transl)]

By heat denaturation, a reciprocal translocation was found in the mother of two malformed sibs. In her 46,XX,t(11 ;22)(q23 ;q11) caryotype, the rearranged elements exhibit no change of length. The 2 sibs are trisomic for the distal part of the long arm of chromosome 11.     

Six cases of partial duplication-deficiency 21 syndrome: 21(dupq22delp23) due to maternal pericentric inversion: inv(21)(p12;q22). A family study

Six probands, apparently not related, with a minimal phenotype of Down's syndrome were investigated between 1970 and 1984 in our laboratory. We found in all of them an identical chromosomal abnormality 46,XX or XY,-21,+ der21(dupq22delp23). The der 21 was due to aneusomie de recombinaison, each mother having an abnormal chromosome 21: inv(21)(p12;q22). The fathers' caryotypes were normal. All parents were young and healthy. Pedigrees were established in order to find a relationship between these families. Four of our probands could be related. Familial investigations are still in progress for the last two cases; the ancestors being born in the same small geographical area (within 50 km2) we think that we shall be able to establish a relationship with the others families.