Clinical and molecular cytogenetic observations in three cases of "trisomy 12p syndrome"

Structural brain abnormalities in Pallister-Killian syndrome: a neuroimaging study of 31 children

BACKGROUND

Pallister-Killian syndrome (PKS) is a rare genetic disorder caused by mosaic tetrasomy of 12p with wide neurological involvement. Intellectual disability, developmental delay, behavioral problems, epilepsy, sleep disturbances, and brain malformations have been described in most individuals, with a broad phenotypic spectrum. This observational study, conducted through brain MRI scan analysis on a cohort of patients with genetically confirmed PKS, aims to systematically investigate the neuroradiological features of this syndrome and identify the possible existence of a typical pattern. Moreover, a literature review differentiating the different types of neuroimaging data was conducted for comparison with our population.

RESULTS

Thirty-one individuals were enrolled (17 females/14 males; age range 0.1-17.5 years old at first MRI). An experienced pediatric neuroradiologist reviewed brain MRIs, blindly to clinical data. Brain abnormalities were observed in all but one individual (compared to the 34% frequency found in the literature review). Corpus callosum abnormalities were found in 20/30 (67%) patients: 6 had callosal hypoplasia; 8 had global hypoplasia with hypoplastic splenium; 4 had only hypoplastic splenium; and 2 had a thin corpus callosum. Cerebral hypoplasia/atrophy was found in 23/31 (74%) and ventriculomegaly in 20/31 (65%). Other frequent features were the enlargement of the cisterna magna in 15/30 (50%) and polymicrogyria in 14/29 (48%). Conversely, the frequency of the latter was found to be 4% from the literature review. Notably, in our population, polymicrogyria was in the perisylvian area in all 14 cases, and it was bilateral in 10/14.

CONCLUSIONS

Brain abnormalities are very common in PKS and occur much more frequently than previously reported. Bilateral perisylvian polymicrogyria was a main aspect of our population. Our findings provide an additional tool for early diagnosis.Further studies to investigate the possible correlations with both genotype and phenotype may help to define the etiopathogenesis of the neurologic phenotype of this syndrome.

Polymicrogyria with calcification in Pallister-Killian syndrome detected by microarray analysis

BACKGROUND

Pallister-Killian syndrome (PKS) is a rare disorder caused by the mosaic tetrasomy of chromosome 12p, and is characterized by facial dysmorphism, developmental delay, hypotonia and seizures.

RESULTS

We report a patient with PKS showing unique polymicrogyria with calcification. He had delayed development and dysmorphic facial features including frontal bossing, hypertelorism, and high arched palate at 6 months of age. Neuroimaging revealed unilateral polymicrogyria with spot calcifications, which predominantly affected the right perisylvian region. Chromosome G-banding showed the karyotype 46,XY, however, array-based comparative genomic hybridization analysis showed mosaic duplication of chromosome 12p, in which CCND2, which encodes cyclin D2 and is a downstream mediator of PI3K-AKT pathway, is located. Supernumerary chromosome of 12p was detected in 58% of buccal mucosa cells by the interphase fluorescence in situ hybridization analysis using chromosome 12 centromere-specific D12Z3 probe. The diagnosis of PKS was made based on distinctive clinical features of our patient and the results of cytogenetic analyses.

CONCLUSION

This report is, to our knowledge, the first case of a patient with PKS who clearly demonstrates polymicrogyria colocalized with calcifications, as shown by CT scans and MRI, and suggests that a patient with PKS could show structural brain anomalies with calcification. We assume that somatic mosaicism of tetrasomy could cause asymmetrical polymicrogyria in our patient, and speculate that increased dosages of CCND2 at chromosome 12p might be involved in the abnormal neuronal migration in PKS.

Non-mosaic partial duplication 12p in a patient with dysmorphic characteristics and developmental delay

Duplication of the short arm of chromosome 12 is a rare chromosomal abnormality that may arise de novo or result from malsegregation of a balanced parental translocation. This study comprises the clinical description, cytogenetic and cytogenomic analyses and genotype-phenotype correlation in a patient with facial dysmorphism, developmental delay and intellectual impairment caused by non-mosaic partial duplication and a paracentric inversion 12p. The patient’s GTG-banded karyotype was 46,XX,invdup(12)(pter → p13.32::p11.1 → p13.31::p13.31 → qter). A genetic gain of approximately 28 Mb was detected in the chromosomal region arr[GRCh37]12p13.31-p11.1(6914072_34756209)x3. The chromosomal alteration seen in our patient is described as “pure” partial duplication 12p. In most cases, duplication 12p phenotype is characterized by dysmorphic features, multiple congenital anomalies and intellectual disability. A small number of cases in literature have described genes associated with neurodevelopmental disease, such as ING4, CHD4, MFAP5, GRIN2B, SOX5, SCN8A and PIANP. In our patient the duplication 12p was de novo. This study should contribute to the genotype-phenotype correlation in partial duplication 12p cases.

Molecular Delineation of Partial Trisomy 14q and Partial Trisomy 12p in a Patient with Dysmorphic Features, Heart Defect and Developmental Delay

This study describes a molecular analysis of partial trisomy 14q and partial trisomy 12p in a 5-year-old male child presenting with dysmorphic features, congenital heart disease and global developmental delay. Chromosomal analysis of the patient with GTG bands revealed a 47,XY,+der(14)t(12;14)(p13;q22)mat karyotype; the mother's karyotype was 46,XX,t(12;14)(p13;q22). Further, oligonucleotide array- CGH studies revealed an amplification of 32.3 Mb in the 14q11.1q22.1 region, substantiating partial trisomy 14q and additionally displaying an amplification of ∼1 Mb in the 12p13.3pter region for partial trisomy 12p. This is the first study to demonstrate a novel association of partial trisomies of 14q and 12p due to a 3:1 segregation of a maternal balanced translocation involving chromosomes 12 and 14. Gene ontology studies indicated 5 potential candidate genes in the amplified regions for the observed congenital anomalies.

Variable levels of tissue mosaicism can confound the interpretation of chromosomal microarray results from peripheral blood

Chromosomal microarray analysis (CMA) has significantly increased the ability to diagnose medical conditions caused by copy-number variation in the human genome. Given that the regions involved in copy-number abnormalities often encompass multiple genes, it has been common practice in recent years to compare the phenotypes of individuals with specific copy-number alterations identified by CMA, with the goal of identifying the critical regions for particular elements of a disease phenotype. It is rarely mentioned that this practice relies heavily on the assumption that the absence of mosaicism on CMA from a peripheral blood sample (the most common source of DNA in current clinical practice) reflects the absence of mosaicism in other tissues. We report here a case that violates that assumption. A 28-year-old male with Charcot-Marie-Tooth disease was found by CMA to have a duplication of 17p12 along with two other abnormalities: A duplication of 12p13.33 translocated to the long arm of chromosome 3 and an interstitial duplication of 12p11.23. The patient did not have any clinical features suggestive of 12p duplication syndrome. Chromosomal microarray analysis on skin fibroblasts revealed the duplications at 17p12 and 12p11.23, but not the terminal duplication of 12p13.33. FISH analysis on skin fibroblasts confirmed the presence of very low levels of mosaicism for the terminal 12p duplication. The case illustrates how the absence of mosaicism in blood is not always indicative of the absence of mosaicism in other tissues. Even in an era of high-throughput, highly accurate DNA-based tests, it is important to remember the limitations of testing before drawing conclusions about the relationship between a test results and a clinical phenotype.

Report on 3 patients with 12p duplication including GRIN2B

The duplication of the short arm (p) of chromosome 12 is a rare chromosomal abnormality, and most reported cases result from malsegregation of a balanced parental translocation associated with other chromosomal imbalances. Of the reported cases, only 15 involve a pure and complete 12p duplication and only 10 involve a pure and partial duplication overlapping the 12p12.3p13.1 region, including a single instance of an inherited duplication in two related individuals. Here, we report three new patients with a pure 12p duplication, detected by conventional cytogenetic studies and characterized by array-comparative genomic hybridization (array-CGH) and fluorescence in situ hybridization (FISH). The first patient was a child carrying a de novo inverted duplication of the short arm of chromosome 12. His phenotype was similar to that of the "trisomy 12p syndrome", characterized by developmental delays and craniofacial abnormalities including a high forehead, a short nose with anteverted nostrils and an everted lower lip. The second and third patients were a mother and son with a direct 12p12.3p13.1 duplication, exhibiting a milder phenotype characterized by moderate developmental delays, dysmorphic facial features, behavioral problems and obesity. The present data, including the rarity of the familial cases, should contribute to our knowledge of the genotype/phenotype correlation in trisomy 12p patients.

Multicolor banding remains an important adjunct to array CGH and conventional karyotyping

Background

Array comparative genomic hybridization (CGH) for high resolution detection of chromosome imbalance, and karyotype analysis using G-banded chromosomes for detection of chromosome rearrangements, provide a powerful diagnostic armoury for clinical cytogenetics. However, abnormalities detected by karyotype analysis cannot always be characterised by scrutinising the G-banded pattern alone, and imbalance detected by array CGH cannot always be visualised in the context of metaphase chromosomes. In some cases further techniques are needed for detailed characterisation of chromosomal abnormalities. We investigated seven cases involving structural chromosome rearrangements detected by karyotype analysis, and one case where imbalance was primarily detected by array CGH. Multicolor banding (MCB) was used in all cases and proved invaluable in understanding the detailed structure of the abnormalities.

Findings

Karyotype analysis detected structural chromosome rearrangements in 7 cases and MCB was used to help refine the karyotype for each case. Array CGH detected imbalance in an eighth case, where previously, G-banded chromosome analysis had reported a normal karyotype. Karyotype analysis of a second tissue type revealed this abnormality in mosaic form; however, MCB was needed in order to characterise this rearrangement. MCB provided information for the delineation of small deletions, duplications, insertions and inversions and helped to assign breakpoints which were difficult to identify from G-banded preparations due to ambiguous banding patterns.

Conclusion

Despite the recent advance of array CGH in molecular cytogenetics we conclude that fluorescence in situ hybridization, including MCB, is still required for the elucidation of structural chromosome rearrangements, and remains an essential adjunct in modern diagnostic laboratories.

De novo trisomy 12p in twin girls with different levels of mosaicism

We report on a pair of twins with trisomy 12p diagnosed postnatally. The girls were referred for dysmorphism and global developmental delay and have been followed from 10 months of age. They have different levels of mosaicism for both buccal cells and lymphocytes. Although their phenotypic features were similar, there were different degrees of severity which correlate with the different levels of mosaicism.

A new partial trisomy 12p with artery catheter vagus, congenital cataracts, external auditory canal, and no turbinate

We describe the prenatal diagnosis and fetal phenotype of partial trisomy 12 (p12-pter) transmitted from a maternal reciprocal translocation 6;12. Genetic analysis was conducted on umbilical cord blood for a fetus accompanied with tricuspid regurgitation and orbital hypertelorism from a 27-year-old gravida 4, para 1 after sonography at gestation 35 weeks. The karyotype was unusual, with 46, XY, der (6), t (6;12) (p24; p12) mat. The pregnancy was terminated at 37 gestational weeks. The aborted fetus displayed dysmorphic features of a round flat face with prominent cheeks and high forehead, hypertelorism, short nose, broad and depressed nasal bridge, anteverted nares, deformed philtrum, open mouth, thin upper vermilion and broad everted lower lip, low-set ears and aural atresia, broad hands with simian creases, and a short neck. Fetal anatomy showed right artery catheter vagus, congenital cataract, no turbinate and external auditory canals. Through karyotype-phenotype analysis of this patient and a review of other reported cases, we believe this is a first report that expands the database of partial trisomy 12p, and is beneficial for future clinical genetic counseling. This study supports that phenotypic variability depends on the type and extent of the associated partial monosomy.

Molecular cytogenetic characterization and genotype/phenotype analysis in a patient with a de novo 8p23.2p23.3 deletion/12p13.31p13.33 duplication

Genomic copy number imbalances are being increasingly identified as an important cause of intellectual disability (ID) and behavioral disturbances. This article reports the clinical features, and long term follow-up of a patient with neurodevelopmental, cognitive, and behavioral abnormalities associated with facial dysmorphism, CNS anomalies, and epilepsy. The karyotype was normal; array CGH testing revealed a de novo cryptic aberration with a terminal 8p23.2p23.3 deletion, and a concomitant 12p13.31p13.33 duplication, of 6.86 Mb, and 8.49 Mb, respectively. Our patient clinical features are compared to those of partial 8 monosomy and/or partial 12p trisomy cases reported in literature, in order to establish genotype-phenotype correlations. For some features, for example, electroencephalogram (EEG) abnormalities and epilepsy, both abnormalities seem to make a contribution, while most phenotypic traits have been assigned to 8p monosomy or to 12p trisomy, contributing to a tentative phenotype map for partial monosomy of the short arm of chromosome 8, and trisomy of the short arm of chromosome 12.

12p13 rearrangements: 6 Mb deletion responsible for ID/MCA and reciprocal duplication without clinical responsibility

Congenital balanced reciprocal translocations are one of the most frequent structural chromosomal aberrations in the population. We report a familial translocation t(12;22)(p13.3;pter) responsible for intellectual disabilities and congenital anomalies characterized by FISH and array CGH. Two patients carried a der(12)t(12;22)(p13.3;pter), resulting in a 6 Mb 12pter deletion. Patients presented with intellectual disabilities, pre- and post-natal growth retardation, ponderal development delay, global hypotonia, feeding problems and dysmorphic features. Two relatives presented with the reciprocal 12pter duplication, which had no clinical manifestations associated. For this translocation, we propose a mechanism based on a non-allelic recombination model, in which recombination of direct oriented segmental duplications between non-homologous chromatids leads to the reciprocal translocation. The characterization of this translocation has been critical for the family. Translocation carriers have a risk of 40% of having offspring carrying unbalanced products. 12p13.3 deletion carriers present with a recognizable syndrome and on the contrary, 12p13.3 duplication carriers present without clinical manifestations. Other published cases of 12p13.3 duplication show that this syndrome has a variable phenotype. It is advisable to delineate the duplication size and to discard other genetic aberrations, in order to give an accurate genetic counseling in patients carrying 12pter duplications.

Detection of subtelomeric chromosomal rearrangements in idiopathic mental retardation

A kromoszómák szubtelomerikus régiói génben gazdag területek, átrendeződésük hagyományos kromoszómaanalízissel nem detektálható. Mivel a mentális retardációk közel 7%-áért felelősek, kimutatásuk diagnosztikai szempontból jelentős, és lehetőséget nyújt az ismétlődés megakadályozására is. A kimutatásukra alkalmas módszerek egyike a szubtelomerikus fluoreszcencia in situ hibridizáció. Ötvenkilenc idiopathiás mentálisan retardált beteg közül 35 közepes/súlyos értelmi fogyatékost választottunk ki a nemzetközi irodalomban ajánlott kritériumok alapján. Közülük 6 beteg esetében mutattunk ki szubtelomerikus aberrációt, 5 familiáris (két család), egy de novo esetnek bizonyult. Huszonkilenc betegben szubtelomerikus kromoszómaátrendeződést nem igazoltunk. A 6 beteg közül kettőben 8pter deléciót és 12pter duplikációt, háromban 21qter deléciót és 10pter duplikációt azonosítottunk kiegyensúlyozatlan transzlokáció formájában. Egy betegnél de novo keletkezett 3qter deléciót detektáltunk. Az eltérések eredetének tisztázása során 12 egészséges családtag közül öt bizonyult kiegyensúlyozott transzlokációhordozónak. Az irodalmi adatokkal összhangban megállapítottuk, hogy a fenotípust a deléció és a duplikáció mérete, valamint transzlokációk esetén az érintett partner kromoszómák együttesen határozzák meg.

Phenotypic overlapping of trisomy 12p and Pallister-Killian syndrome

Trisomy of 12p is a rare chromosomal abnormality, which sometimes coexists with other chromosomal anomalies. We report on a patient with a supernumerary chromosome involving chromosomes 12 and 14, which was confirmed by array-comparative genomic hybridization (aCGH). He had developmental delay and dysmorphic features overlapped with those of Pallister-Killian syndrome, which is derived from an isodicentric chromosome 12. The microblepharon identified in our patient is a characteristic feature of 12p trisomy. Further patients are needed to establish the phenotypic difference between trisomy 12p and Pallister-Killian syndrome.

Trisomy 12p and monosomy 4p: phenotype-genotype correlation

4p Monosomy and 12p trisomy have been discussed and redefined along with recently reviewed chromosomal syndromes. 12p Trisomy syndrome is characterized by normal or increased birth weight, developmental delay with early hypotonia, psychomotor delay, and typical facial appearance. Most likely, the observed phenotypic variability depends on the type and extent of the associated partial monosomy. Partial deletions of the short arm of one chromosome 4 cause the Wolf-Hirschhorn syndrome (WHS). Affected patients present Greek helmet face, growth and mental retardation, hypotonia, and seizures. The combination of these characteristics constitutes the phenotypic core of WHS. We present a clinical and molecular cytogenetic characterization of a 4-year old mentally retarded girl with macrosomy, facial dysmorphisms, and epilepsy, in whom an unbalanced t(4;12)(p16.3;p13.3) translocation was detected, giving rise to partial 4p monosomy and partial 12p trisomy. Because the patient shows most of the phenotypic characteristics of 12p trisomy, this case could contribute to a better definition of the duplicate critical region that determines the phenotype of the 12p trisomy syndrome.

Monosomy 5p and trisomy 12p in a boy with familial balanced translocation

We report on a boy with monosomy 5p involving the Cri-du-Chat critical region and trisomy 12p detected by subtelomere study. Familial studies showed that the boy's mother and paternal grandfather had a balanced reciprocal translocation between the short arm of chromosomes 5 and 12. The boy had an overlap of features of both chromosomal conditions, even though the Cri-du-Chat phenotype was more prominent.

Microarray comparative genomic hybridization analysis of 59 patients with schizophrenia

Schizophrenia is a common psychiatric disorder with a strong genetic contribution. Disease-associated chromosomal abnormalities in this condition may provide important clues, such as DISC1. In this study, 59 schizophrenia patients were analyzed by microarray comparative genomic hybridization (CGH) using custom bacterial artificial chromosome (BAC) microarray (4,219 BACs with 0.7-Mb resolution). Chromosomal abnormalities were found in six patients (10%): 46,XY,der(13)t(12;13)(p12.1; p11).ish del(5)(p11p12); 46,XY, ish del(17)(p12p12); 46,XX.ish dup(11)(p13p13); and 46,X,idic(Y)(q11.2); and in two cases, mos 45,X/46XX. Autosomal abnormalities in three cases are likely to be pathogenic, and sex chromosome abnormalities in three follow previous findings. It is noteworthy that 10% of patients with schizophrenia have (sub)microscopic chromosomal abnormalities, indicating that genome-wide copy number survey should be considered in genetic studies of schizophrenia.

Acrocallosal syndrome in fetus: focus on additional brain abnormalities

Acrocallosal syndrome (ACS) is an autosomal recessive disorder characterized by craniofacial dysmorphism, agenesis or hypoplasia of the corpus callosum, duplication of the phalanges of the hallux, more rarely the thumbs, post-axial polydactyly, syndactyly and severe mental retardation. Here we report the two first descriptions of acrocallosal syndrome in fetus with extensive neuropathological study and provide new data regarding additional brain abnormalities in ACS. The first case was a 25-gestational week male fetus displaying craniofacial and limb abnormalities, with bilateral syndactyly of the fourth and fifth fingers, preaxial polydactyly of the left foot and an inter-frontal extra-bone. The second fetus was a 33-gestational week male fetus. His left hand displayed a broad thumb and 4/5 syndactyly. In both cases, gross examination of the brain showed an absence of corpus callosum associated with interhemispheric cysts. The cerebral cortex in front of the cysts was nodular. Upon microscopic examination, the nodular masses corresponded to large dysplastic areas represented by clusters of undifferentiated neurons in the white matter. The cyst wall showed arachnoidal and ependymal covering and contained numerous choroid plexus, suggesting a developmental abnormality of the ventricles. The pons and the cerebellum were hypoplastic. The dentate nuclei were fragmented. Numerous neuronal heterotopias associated with ectopic ependymal cavities were observed in the vermis in one case. The olivary nuclei were severely dysplastic too. We hope that these new data will make both the ante- and post-natal diagnosis easier, facilitate comparisons with animal models and encourage the identification of the genes responsible for this syndrome.

Subtelomeric analysis detects a familial 10p;12p rearrangement in two relatives with a distinct syndrome

In recent years, subtelomeric rearrangements have been identified as a major cause of multiple congenital anomalies (MCA)/mental retardation (MR) syndromes. Currently, more than 2,500 individuals with MR have been tested and subtelomeric rearrangements were detected in about 6%. Therefore, subtelomeric FISH analysis is indicated as a second tier test after high-resolution G-banding analysis, in subjects with otherwise unexplained developmental delay/MR and/or MCA. We describe a female patient and her maternal aunt, both showing a distinct phenotype, associated with the same complex subtelomeric rearrangement. Subtelomeric FISH testing performed between 1 year 9 months and 20 years after the initial karyotype showed, in both patients, distal trisomy 12p and distal monosomy 10p as follows: 46,XX.ish der(10)t(10;12)(p15.3;p13.31). Parental subtelomeric FISH analysis showed the proposita's mother (sister of Patient 2) and grandmother (mother to Patient 2), to have a balanced 10p:12p translocation. Both girls showed a similar phenotype with pre/postnatal growth retardation, moderate-to-severe developmental delay/MR, very poor/absent speech, hypotonia, lax ligaments, and a distinct pattern of malformation. On examination there were blepharophimosis; bilateral ptosis/epicanthus; broad, depressed nasal bridge with a beaked nose; short philtrum; low-set, posteriorly rotated, overfolded ears; micrognathia; mild webbing of the neck; mild broadening of thumbs; puffy hands/feet; long hallux; and sacral/coccygeal dimples. A slow overall improvement was seen in both patients over time. To our knowledge, a complex subtle rearrangement as the one seen in our patients has not been reported thus far. Our patients show features of partial 10p deletion syndrome rather than those of partial duplication 12p, confirming the general rule that deletions are more phenotypically penetrant than duplications.

Tall stature and duplication of the insulin-like growth factor I receptor gene

Trisomy of 15q26-qter is frequently associated with tall stature and mental retardation. Here we describe a patient with such trisomy, without a partial monosomy of another chromosome. The tall stature in this patient is most probably caused by duplication of the IGF1R gene. A duplication of the IGF1R gene is not a frequent finding in patients with tall stature. In 38 patients with features of Sotos syndrome without NSD1 alterations, a duplication was found only once. This patient was already known to have an unbalanced 2;15 translocation. Looking for a duplication of the 15qter region is still worth consideration in patients with tall stature and features of Sotos syndrome without an NSD1 alteration, especially when there is craniosynostosis or marked speech delay.

De novostructural chromosomal imbalances: molecular cytogenetic characterization of partial trisomies

De novo structural chromosomal imbalances represent a major challenge in modern cytogenetic diagnostics. Based solely on conventional cytogenetic techniques it may be impossible to identify the chromosomal origin of additional chromosomal material. In these cases molecular cytogenetic investigations including multicolor-FISH (M-FISH), spectral karyotyping (SKY), multicolor banding (MCB) and cenM-FISH combined with appropriate single-locus FISH probes are highly suitable for the determination of the chromosomal origin and fine characterization of derivative chromosomes. Here we report on four patients with de novo chromosomal imbalances and distinct chromosomal phenotypes, three of them harboring pure partial trisomies: a mildly affected boy with pure partial trisomy 10q22.2-->q22.3 approximately 23.1 due to an interstitial duplication, a girl with pure trisomy 12p11.21-->pter and atypically moderate phenotype as the consequence of an X;autosome translocation, and a girl with multiple congenital abnormalities and severe developmental delay and a 46,XX,15p+ karyotype hiding a trisomy 17pter-->17q11.1. The fourth patient is a girl with minor phenotypic features and mental retardation with an inverted duplication 18q10-->p11.31 combined with a terminal deletion of 18p32. The clinical pictures are compared with previously described patients with focus on long term outcome.

Intrachromosomal triplication 12p11.22-p12.3 and gonadal mosaicism of partial tetrasomy 12p

Cases of tetrasomy 12p and trisomy 12p are known to be associated with specific phenotypic abnormalities well described in the literature. Here, we report on the unusual case of a partial tetrasomy 12p found in an affected patient and in a mosaic constellation in the patient's mother, who showed no phenotypic abnormality. The index patient was a 16-year-old boy with clinical features similar to the "trisomy 12p syndrome" including mental retardation, macrocephaly, a short nose with anteverted nostrils, and a broad protruding lower lip. G-banding analysis and fluorescence in situ hybridization (FISH) experiments using locus specific YAC DNA probes revealed a derivative chromosome 12 with a partial triplication of the short arm with an inverted copy, flanked by two direct copies. Chromosome analyses in parental lymphocytes showed a chromosomal mosaicism in the phenotypically normal mother, with 12% cells exhibiting the same partial tetrasomy 12p as detected in her son. The allelic pattern of short tandem repeats (STR) in the mother's blood DNA showed that a chimerism can be excluded with high probability. To our knowledge, this is the first report of intrachromosomal triplication on chromosome 12, as well as partial tetrasomy 12p mosaicism. Moreover, as a consequence of the chromosomal aberration in the son it can be concluded that a gonadal mosaicism is present in the mother.

A father and son with mental retardation, a characteristic face, inv(12), and insertion trisomy 12p12.3-p11.2

A male patient with mental retardation (MR) and mild facial features was shown by high-resolution G-banding to have pericentric inversion of chromosome 12 with an unknown segment inserted into the long arm of the inverted chromosome [46,XY,inv(12)(pter-->p11.2::q14.1-->p11.2::?::q14.1-->qter)]. Both the inverted chromosome 12 and clinical manifestations were transmitted to his son. Karyotypes of the propositus' parents were normal. Studies with fluorescence in situ hybridization (FISH) in both the propositus and his son revealed that the extra segment was derived from 12p. Further FISH mapping and the genome-wide copy number detection by GeneChip Mapping 100K Array showed that an 11-Mb segment of 12p between two BAC clones, RP11-22H10 and RP11-977P2, was inserted at one of the reunion points in the long arm of the inv(12) chromosome. Analysis of parent-child transmissions of duplicated alleles using microsatellite markers defined the maternal origin of the chromosomal anomaly in the propositus and suggested a mechanism of its formation through a sister-chromatid rearrangement (SCR), that is, mismatched pairing and unequal crossover between sister chromatids as well as three break rearrangements including a U type rearrangement. Karyotypes of the propositus and his son were thus inv(12)(pter-->p11.22::q14.1-->p12.3::q14.1-->qter). This is the first report of "pure" proximal 12p-trisomy including p12.3-p11.22 region.

The natural history of trisomy 12p

Trisomy of the short arm of chromosome 12 is a rare chromosomal anomaly, with an estimated incidence of 1/50,000 births. It may present as a pure trisomy (complete or incomplete), as mosaic trisomy, or with other chromosomal abnormalities. Little is known from prior reports about the natural history and life expectancy of these individuals. In this study we describe the long-term outcome and the differences between patients with mosaic trisomy 12p compared to patients with complete trisomy. We present a series of 16 patients with trisomy 12p; 6 of them are older than 10 years. Most patients were born at term with normal or above normal birth weight. Seven were born with congenital anomalies, but no single anomaly was present in more than one individual. A clear and consistent dysmorphic facial pattern was apparent in all of the subjects. Most patients over 7 years old had a seizure disorder. All individuals exhibited developmental delay with speech affected more severely than motor skills. Six patients were described as "being social." Six had severe behavioral problems, and seven had significant sleep disturbances. Facial features of the three adult patients were different than the younger individuals. We show here that the outcome for patients with mosaic trisomy 12p is better than the outcome in complete trisomy 12p or in trisomy 12p with other chromosomal anomalies. We also provide recommendations for the long-term follow-up of patients with trisomy 12p.

Direct duplication 12p11.21-p13.31 mediated by segmental duplications: a new recurrent rearrangement?

We describe the characterization of an interstitial duplication of 12p, dup(12)(p11.21p13.31), by array-CGH and FISH in a patient with mental retardation and dysmorphic features. The sequence analysis of the breakpoints revealed the presence of homologous low copy repeats (LCRs) flanking the duplication region, thus suggesting that they have mediated the rearrangement. Pip-maker analysis showed that a third cluster of homologous LCRs lie distally to the two mediating the 12p duplication. We hypothesize that this duplication might be a new recurrent rearrangement and that, thanks to the different orientations of the homologous regions lying within each cluster, the three clusters are responsible for at least some of the several 12p aneuploidies reported in the literature such as direct and inverted duplications, deletions and supernumerary analphoid chromosomes. Moreover, we excluded that polymorphic inversions between these three clusters are present in the normal population.

Chromosome rearrangements in cornelia de Lange syndrome (CdLS): report of a der(3)t(3;12)(p25.3;p13.3) in two half sibs with features of CdLS and review of reported CdLS cases with chromosome rearrangements

Cornelia de Lange syndrome (CdLS; OMIM 122470) is a dominantly inherited disorder characterized by multisystem involvement, cognitive delay, limb defects, and characteristic facial features. Recently, mutations in NIPBL have been found in approximately 50% of individuals with CdLS. Numerous chromosomal rearrangements have been reported in individuals with CdLS. These rearrangements may be causative of a CdLS phenotype, result in a phenocopy, or be unrelated to the observed phenotype. We describe two half siblings with a der(3)t(3;12)(p25.3;p13.3) chromosomal rearrangement, clinical features resembling CdLS, and phenotypic overlap with the del(3)(p25) phenotype. Region-specific BAC probes were used to fine-map the breakpoint region by fluorescence in situ hybridization (FISH). FISH analysis places the chromosome 3 breakpoint distal to RP11-115G3 on 3p25.3; the chromosome 12 breakpoint is distal to BAC RP11-88D16 on 12p13.3. A review of published cases of terminal 3p deletions and terminal 12p duplications indicates that the findings in these siblings are consistent with the del(3)(p25) phenotype. Given the phenotypic overlap with CdLS, we have reviewed the reported cases of chromosomal rearrangements involved in CdLS to better elucidate other potential loci that could harbor additional CdLS genes. Additionally, to identify chromosome rearrangements, genome-wide array comparative genomic hybridization (CGH) was performed on eight individuals with typical CdLS and without identifiable deletion or mutation of NIPBL. No pathologic rearrangements were identified.

Three patients with hallucal polydactyly and WAGR syndrome, including discordant expression of Wilms tumor in MZ twins

The WAGR contiguous gene deletion syndrome is a combination of Wilms tumor, Aniridia, Genito-urinary abnormalities, and growth and mental retardation which is invariably associated with an 11p13 deletion. We report two monozygotic twins and a third, unrelated patient with WAGR syndrome and additional clinical features not usually associated with WAGR. Both twins had developmental delay, growth deficiency, severe ocular involvement (nystagmus, aniridia, cataracts), atrial septal defect and two uncommon findings: agenesis of the corpus callosum and duplication of the halluces. One twin developed Wilms tumors aged 19 months while her sister remained tumor free by the age of 6.5 years. The singleton patient showed typical WAGR syndrome and preaxial hallucal polydactyly. Molecular cytogenetic studies refined the identification of the extent of the deleted segments, which were not identical in the two families. The two deletions included the PAX6 and WT1 genes as previously reported in typical WAGR patients. The unusual anomalies described in this report, may represent the expression of low penetrant traits associated with haploinsufficency of one or more of the genes present in the deletion (PAX6 is expressed in CNS) or may indicate epistatic influences of modifier genes on the expression of gene(s) present in the WAGR region.

Genotype/phenotype analysis in a patient with pure and complete trisomy 12p

Reports on patients with pure and complete trisomy 12p are rare. Up to now, 12 cases have been described in the literature. Here, we report on the genotype/phenotype-correlation of a female patient with a pure trisomy 12p. Conventional cytogenetic studies on peripheral blood chromosomes as well as molecular cytogenetic (fluorescence in situ hybridization, FISH) techniques including whole chromosome painting (WCP), comparative genomic hybridization (CGH), multicolor-banding (MCB) detected a female karyotype with an abberant chromosome 12:46,XX,der(12).ish dup(12)(pter --> q24.3::p11.2 --> pter). In addition to the trisomy 12p specific clinical hallmarks, the patient showed some features of Pallister-Killian syndrome (PKS) such as sparse hair, macroglossia, and epilepsy. These findings contribute to the genotype/phenotype correlation in trisomy 12p patients.

The RAIG Family Member, GPRC5D, Is Associated with Hard-Keratinized Structures

Retinoic acid-inducible gene-1 was originally identified as an orphan G-protein coupled receptor induced by retinoic acid. Three highly homologous oGPCR (GPRC5B, GPRC5C, and GPRC5D) have since been classified into the RAIG1 family. We describe here, the unique tissue distribution of GPRC5D and its mechanism of expression. Hybridization in situ has shown that GPRC5D is expressed in differentiating cells that produce hard keratin, including cortical cells of the hair shaft, the keratogenous zone of the nail, and in a central region of the filiform papillae of the tongue. The GPRC5D transcript is expressed in hair follicles during mid- and late anagen, and catagen but not at telogen and early anagen phases. The differentiation-inducer, all-trans retinoic acid, induces GPRC5D expression in cultured hair bulb cells. Because the tissue distribution of GPRC5D indicates a relationship with hard keratins that constitute the major structural proteins of hard epithelial tissues, we investigated the effect of GPRC5D on acid hard keratins. Analyses of cultured cells showed that transient overexpression resulted in suppression of Ha3 and stimulation of Ha4 hair keratin gene expression. The expression was maintained in the hair follicles of whn-deficient (nude) mice, suggesting that this gene is regulated by a signal pathway different from that of hair keratin synthesis. Collectively, these data provide a framework for understanding the molecular mechanisms of GPRC5D function in hard keratinization.

Clinical, cytogenetic, and molecular observations in a patient with Pallister-Killian-syndrome with an unusual karyotype

Pallister-Killian syndrome is a clinically recognizable syndrome, usually due to a tissue-limited mosaicism for a supernumary 12p isochromosome (i12p). Here we report an unusual case with tetrasomy/trisomy/disomy 12p mosaic in fibroblasts and trisomy/disomy 12p mosaic in lymphocytes. The tetrasomy 12p was due to an i12p, the trisomy 12p to a single 12p marker. Both marker chromosomes were investigated with conventional cytogenetic techniques and fluorescent in situ hybridization (FISH). Stability under culturing conditions was studied. DNA-analysis revealed prezygotic maternal origin of the extra 12p material. Clinically, the patient seems to have less retardation than most patients with Pallister-Killian syndrome.

Telomeres: a diagnosis at the end of the chromosomes

In recent years, subtelomeric rearrangements have been identified as a major cause of mental retardation and/or malformation syndromes. So far, over 2500 subjects with mental retardation have been tested and reported of whom approximately 5% appeared to have a subtelomeric rearrangement. In this review, the clinical aspects of each known (submicroscopic) subtelomeric deletion will be presented and the various methods available for detecting subtelomeric abnormalities will be discussed. Not only will the patients and their families benefit from a good collection and report of the various telomeric abnormalities and their clinical phenotype, but it will also give more insight into the aetiology of mental retardation and malformation syndromes.

Cryptic t(1;12)(q44;p13.3) translocation in a previously described syndrome with polymicrogyria, segregating as an apparently X-linked trait

We report on the multistep progression to the correct genetic diagnosis in an apparently new syndrome of mental retardation and multiple congenital anomalies, including hypogenitalism and polymicrogyria. We had previously reported it as an X-linked condition affecting four members (three males and one female) of a family [Zollino et al., 1992: Am J Med Genet 43:452-457]. Two of the four patients, both males, presented with a brain abnormality that was initially described as pachygyria, while the remaining two (one male and one female) did not. Our present study includes a clinical follow-up on the patients, neuroradiological reexamination of one patient, X linkage studies and X inactivation analyses, and finally molecular cytogenetics, which allowed us to establish definitely the genetic causes of the condition. After the detection of a subtle t(1;12)(q44;p13.3) balanced translocation in healthy carriers, two unbalanced segregation products were observed in different patients, resulting in 1q44qter monosomy and 12p13.3pter trisomy in patients with polymicrogyria and severe psychomotor delay, 12p13.3pter monosomy and 1q44qter trisomy in the other two patients without polymicrogyria, with less severe mental retardation and less distinctive physical anomalies. Thus, this condition is no longer to be considered X-linked, but the result of cryptic autosomal imbalance. Furthermore, this study identified an approximately 14 Mb interval in 1q44qter pathogenetically related to polymicrogyria.

Mental deficiency, alterations in performance, and CNS abnormalities in overgrowth syndromes

Mental deficiency, alterations in performance, and central nervous system (CNS) abnormalities are discussed in the following overgrowth syndromes: Sotos syndrome, Weaver syndrome, Proteus syndrome, neurofibromatosis type 1, fragile X syndrome, syndromes with neonatal hypoglycemia, Simpson-Golabi-Behmel syndrome, hemihyperplasia, Sturge-Weber syndrome, Bannayan-Riley-Ruvalcaba/Cowden syndrome, macrocephaly-autism syndrome, PEHO syndrome, chromosomal syndromes, and other miscellaneous syndromes.

Diagnosing acrocallosal syndrome

A 3-month-old male child presented with typical features of acrocallosal syndrome. He satisfies Courten's diagnostic criteria for acrocallosal syndrome.

De novo inverted tandem duplication of the short arm of chromosome 12 in a patient with microblepharon

We present a patient with a de novo inverted duplication of nearly the entire short arm of chromosome 12 [inv dup(12)(p13.3p12)], which was characterized using GTG-banding and spectral karyotyping. The patient was noted to have microblepharon, which has not been previously described in children with a similar chromosomal rearrangement. This patient represents one of the few examples of complete and pure trisomy 12p due to inverted duplication of the short arm of chromosome 12 and expands the clinical spectrum.

First known microdeletion within the Wolf-Hirschhorn syndrome critical region refines genotype-phenotype correlation

Deletions within HSA band 4p16.3 cause Wolf-Hirschhorn syndrome (WHS), which comprises mental retardation and developmental defects. A WHS critical region (WHSCR) of approximately 165 kb has been defined on the basis of 2 atypical interstitial deletions; however, genotype-phenotype correlation remains controversial, due to the large size of deletion usually involving several megabases. We report on the first known patient with a small de novo interstitial deletion restricted to the WHSCR who presented with a partial WHS phenotype consisting only of low body weight for height, speech delay, and minor facial anomalies; shortness of stature, microcephaly, seizures and mental retardation were absent. The deletion was initially demonstrated by FISH analysis, and breakpoints were narrowed with a "mini-FISH" technique using 3-5 kb amplicons. A breakpoint-spanning PCR assay defined the distal breakpoint as disrupting the WHSC1 gene within intron 5, exactly after an AluJb repeat. The proximal breakpoint was not found to be associated with a repeated sequence or a known gene. The deletion encompasses 191.5 kb and includes WHSC2, but not LETM1. Thus, manifestations attributable to this deletion are reduced weight for height, minor facial anomalies, ADHD and some learning and fine motor deficiencies, while seizures may be associated with deletions of LETM1.

Molecular cloning and characterization of DEC2, a new member of basic helix-loop-helix proteins

DEC1 is a basic helix-loop-helix (bHLH) protein related to Drosophila Hairy, Enhancer of split and HES, and involved in the control of proliferation and/or differentiation of chondrocytes, neurons, etc. We report here the identification and characterization of human, mouse and rat DEC2, a novel member of the DEC subfamily. DEC2 had high (97%) and moderate (52%) similarities in the bHLH region and the Orange domain with DEC1, respectively. However, DEC2, but not DEC1, had alanine and glycine-rich regions in the C-terminal half. Unlike Hairy, Enhancer of split and HES, DEC2 lacked the WRPW motif for interaction with the corepressor Groucho. The DEC2 gene was mapped to human chromosome 12p11.23-p12.1, mouse chromosome 6 G2-G3 and rat chromosome 4q43 distal-q4, where the conserved linkage homology has been identified among these species. Unlike DEC1, which was broadly expressed in many tissues, DEC2 showed a more restricted pattern of mRNA expression. The DEC subfamily proteins may play an important role in tissue development.

Familial cryptic translocation with del 4q34-->qter and dup 12pter-->p13 in sibs with tracheal stenosis: clinical, classical and molecular cytogenetic studies and CGH analyses from archival placental tissues evidencing tertiary trisomy 4 in one abortion specimen

We report on two retarded half-sibs of different sex and seemingly normal karyotype who had the same syndrome of minor anomalies, heart defect and a distal tracheal stenosis, and who shared a healthy mother. These findings raised suspicions of a cryptic chromosome translocation. A translocation t(4;12)(q34;p13), balanced in the mother and unbalanced in the sibs with loss of terminal 4q and gain of terminal 12p regions, was verified by FISH using whole chromosome painting, subtelomeric and YAC probes. Clinical features could be explained by partial monosomy 4q and partial trisomy 12p. Tracheal stenosis was interpreted as a consequence of the same developmental disturbance leading to esophageal atresia and tracheo-esophageal fistula. It was attributed to the 4q deletion in which esophageal atresia as also respiratory difficulties and airway obstructions had been described. Paraffin-embedded placental tissues were available from three of the five abortions of the mother allowing DNA extraction and comparative genome hybridization (CGH). Two of the abortion specimens had the same der(4)t(4;12)(q34;p13) unbalanced translocation as identified in the sibs. In the third abortion specimen, suspicious of triploidy because of partial hydatidiform mole, CGH uncovered a tertiary trisomy 4 resulting from a 3:1 segregation of the translocation chromosomes and their homologs during maternal meiosis I. Differences in CGH results using DNA generated directly or after DOP-PCR were explained by DNA fragmentation in paraffin-embedded tissues and unequal amplification. Am. J. Med. Genet. 94:271-280, 2000.

Centromere-telomere (12;8p) fusion, telomeric 12q translocation, and i(12p) trisomy

The concurrence of a short arm isochromosome and a translocation of the entire long arm of the same chromosome to a telomere of another chromosome, implying trisomy for 4p, 5p, 7p, 9p, 10p or 12p, has been described in 13 patients. We have now used fluorescence in situ hybrization (FISH) to better characterize one of these rearrangements in which 12q was translocated to 8pter, whereas 12p was converted into an isochromosome. An alphoid centromere-12 repeat gave a strong signal on the i( 2p) and a weak but distinct signal at the breakpoint junction of the der(8), whereas the pantelomeric probe revealed three clear hybridization sites on the der(8): one at each end and another at the breakpoint junction. These findings suggest that the prime event was a post-fertilization centric fission of chromosome 12 leading to the 12q translocation via a real centromere telomere fusion and the i(12p). Alternatively, the crucial event may have been a centromere telomere recombination. An interstitial telomere has been documented by means of FISH at the breakpoint junction of the sole derivative usually present in 20 constitutional translocations including eight with a jumping behavior. In addition, six other telomeric translocations defined by banding methods, including another case of 12q translocation/i(12p), have also been jumping ones. These telomeric translocations have been de noro events and their proneness to exhibit a jumping behavior appears to be independent of the involved chromosomes, size of the translocated segments, and concomitant abnormalities.

Prenatal diagnosis of partial trisomy 12 and partial trisomy 21 due to a 3:1 segregation of maternal reciprocal translocation t(12;21) (p13.3;q21)

We describe the prenatal diagnosis and fetal phenotype of partial trisomy 12 (p13.3-pter) and partial trisomy 21 (pter-q21) due to a 3:1 segregation with tertiary aneuploidy transmitted from a maternal reciprocal translocation 12;21. Genetic amniocentesis of a 39-year-old gravida 2, para 1 woman at 19 weeks' gestation due to advanced maternal age revealed an unusual karyotype of 47,XY,+der(21)t(12;21)(p13.3;q21)mat. The pregnancy was terminated at 24 gestational weeks. The proband postnatally displayed by dysmorphic features of a round flat face with prominent cheeks and high forehead, upward slanting palpebral fissures, epicanthic folds, hypertelorism, a short nose, a broad and depressed nasal bridge, anteverted nares, a deformed philtrum, an open mouth, thin upper vermilion and broad everted lower lip, low-set ears with prominent anthelix and deep concha, broad hands with simian creases, a short neck, and cryptorchidism. The association of the involved chromosomal segments with the phenotype of Down's syndrome and trisomy 12p syndrome is discussed.

De novo duplication of 12pter-->p12.1: clinical and cytogenetic diagnosis confirmed by chromosome painting

A 12.5-year-old male patient with a de novo derivative chromosome 22 is reported. A detailed description of the clinical features and comparison with the results of conventional cytogenetic banding methods indicated that the derivative chromosome might have been caused by a translocation between the short arms of chromosomes 12 and 22: der(22)t(12;22)(p12.1;p11.2). Fluorescence in situ hybridization with a chromosome 12-specific paint confirmed this supposition. The patient thus carries a pure duplication of 12pter-->p12.1. The phenotype of the patient described is compared to cases in the literature.