Two cousins with partial trisomy 12q and monosomy 12p recombinants of a familial pericentric inversion of the chromosome 12

Partial Monosomy 4p and Trisomy 12q due to a t(4;12)(p16.3;q24.31) Familial Translocation in Two Cousins

Wolf-Hirschhorn syndrome (WHS) is caused by a distal 4p monosomy usually involving the region of the WHSC1 and WHSC2 genes. About 40-45% of WHS patients show an unbalanced translocation leading to both 4p monosomy and partial trisomy of another chromosome arm. In this case report, we describe 2 female cousins (P1 and P2) with a derivative chromosome leading to a 4p16.3pter deletion and 12q24.31qter duplication. Conventional karyotyping and genomic analyses showed that they both had the same rearrangement derived from a balanced parental translocation involving chromosomes 4 and 12, t(4;12)(p16.3;q24.31). The rearrangements occurred between 4p16.3pter and 12q24.31qter detected by array-CGH analysis, with a 2.7-Mb loss at 4p and a large 12.4-Mb gain at 12q. Both affected patients shared global developmental delay and craniofacial dysmorphisms with some distinct phenotypic findings associated with both WHS and 12qter trisomy. P2 was more severely impaired than P1, and she showed severe intellectual disability, seizures, midface hypoplasia, unilateral microtia, and deafness which were absent in P1. Previous studies of distal 4p monosomies have found phenotypic variability in WHS which does not correlate with haploinsufficiency of specific genes. Features of 12q trisomies are diverse with developmental and growth delay, intellectual disability, behavioral problems, and facial abnormalities. Collectively, our analysis of the literature of 3 similar translocations involving 4p and 12q, together with the clinical features of the affected cousins in this familial translocation, permits an evaluation of genes closely linked to WHSC1 and WHSC2 in the context of WHS and the genes involved in 12q trisomy.

Subtelomeric chromosomal rearrangements in a large cohort of unexplained intellectually disabled individuals in Indonesia: A clinical and molecular study

CONTEXT

Unbalanced subtelomeric chromosomal rearrangements are often associated with intellectual disability (ID) and malformation syndromes. The prevalence of such rearrangements has been reported to be 5-9% in ID populations.

AIMS

To study the prevalence of subtelomeric rearrangements in the Indonesian ID population.

MATERIALS AND METHODS

We tested 436 subjects with unexplained ID using multiplex ligation dependent probe amplification (MLPA) using the specific designed sets of probes to detect human subtelomeric chromosomal imbalances (SALSA P070 and P036D). If necessary, abnormal findings were confirmed by other MLPA probe kits, fluorescent in situ hybridization or Single Nucleotide Polymorphism array.

RESULTS

A subtelomeric aberration was identified in 3.7% of patients (16/436). Details on subtelomeric aberrations and confirmation analyses are discussed.

CONCLUSION

This is the first study describing the presence of subtelomeric rearrangements in individuals with ID in Indonesia. Furthermore, it shows that also in Indonesia such abnormalities are a prime cause of ID and that in developing countries with limited diagnostic services such as Indonesia, it is important and feasible to uncover the genetic etiology in a significant number of cases with ID.

Clinical delineation of a patient with trisomy 12q23q24

Trisomies of 12q23q24 have been described rarely in literature. Only a few case-reports have been published so far almost exclusively reporting on neonates or young infants. We present a 16-year-old patient with a trisomy of 12q23.3q24.3. Full phenotypic evaluation at this age comprised: severe growth retardation, developmental delay, intellectual disability and characteristic facial dysmorphisms. Initially, in the proband an insertion was cytogenetically mapped at chromosome 16: der(16)dir ins(16; 12)(q12.1; q24.11q24.31). The mother appeared carrier of a balanced insertion. Subsequent SNP-array analysis in the proband revealed a 16.3 Mb gain of 12q23.3 → 12q24.31. The clinical and molecular findings in this patient are compared with previous literature on cases with overlapping isolated 12q trisomies. The common phenotype observed consists of severe growth retardation, intellectual disability and characteristic facial features with hypertelorism, flat nasal bridge, down-turned mouth and poorly lobulated/low set ears. In addition, pediatric follow up into adolescence showed feeding difficulties requiring gastric tube feeding, recurrent otitis media, progressive contractures of joints and genito-renal problems, speech, communication and behavioral problems. These symptoms should be taken into account in the care and management of children with this condition.

A fourteen years follow-up of a case of partial trisomy 12q and monosomy 12p recombinants of a familial pericentric inversion of chromosome 12: Clinical, cytogenetic and molecular observations

Partial trisomy 12q and monosomy 12p lead to multiple malformation syndromes. Only four cases were previously reported with the association of these two aneusomies resulting from a familial pericentric inversion of chromosome 12. We report on the clinical, cytogenetic and molecular findings in a boy with an unbalanced karyotype which resulted from a familial pericentric inversion of chromosome 12. The patient was evaluated at birth and followed up until 14 years of age. He showed severe mental retardation, seizures, and dysmorphic features related both to a trisomy 12q and a monosomy 12p. Chromosome breakpoint BAC-FISH mapping revealed that the rec(12) chromosome had a terminal deletion of a 6.7Mb region extending from 12pter to 12p13.31 and a duplicated region of 19.8Mb extending from 12qter to 12q24.13. The findings from the case reported here emphasize the occurrence of some consistent clinical features and illustrate the deficiencies associated with the recombinants from the inversion inv(12)(p13.31q24.13)mat.

Moyamoya syndrome in a child with trisomy 12p syndrome

A female, 2 years and 7 months of age, was admitted to the hospital with stupor and nystagmus following projectile vomiting. She had been prenatally diagnosed with trisomy 12p with a familial pericentric inversion of chromosome 12 originating from her mother. She manifested developmental delay and some dysmorphic features of the face and limbs compatible with the clinical features of trisomy 12p. Four-vessel cerebral angiography revealed severe stenosis and occlusion of the supraclinoid portion of the right and left internal carotid arteries with numerous collateral vessels in the vicinity of the occlusion. These features are consistent with moyamoya syndrome. This report presents the first case of moyamoya syndrome with trisomy 12p with a familial pericentric inversion of chromosome 12.

A novel 2.3 Mb microduplication of 12q24.21q24.23 detected by genome-wide tiling-path resolution array comparative genomic hybridization in a girl with syndromic mental retardation

We report on a female patient with severe mental retardation, dysmorphic features, deafness, spasticity, and behavioural problems in whom a 2.3 Mb duplication of 12q24.21q24.23 was detected by genome-wide tiling-path resolution array-based comparative genomic hybridization. Mental retardation, microcephaly, short stature, recurrent infections, hypotonia and facial features, such as hypertelorism, epicanthal folds, and a broad nasal bridge, were also described in patients with larger duplications overlapping the 12q24.21q24.23 region. The duplicated region contains 16 genes, of which several genes, such as thyroid hormone receptor associated protein 2, replication factor C5 and nitric oxide synthase 1, are expressed in the brain and/or are involved in embryogenesis. The current case shows that microduplications might be a more frequent cause of mental retardation and human malformation than previously appreciated.

Prenatal findings and molecular cytogenetic analyses of partial trisomy 12q (12q24.32→qter) and partial monosomy 21q (21q22.2→qter)

OBJECTIVES

To present the prenatal findings and molecular cytogenetic analyses of partial trisomy 12q and partial monosomy 21q, and a review of the literature.

METHODS

Amniocentesis was performed at 23 gestational weeks in a 33-year-old woman because of abnormal sonographic findings. Amniocentesis revealed a derivative chromosome 21, or der(21), with a deletion on the region of 21q22.2 and an addendum of a small chromosomal segment of unknown origin. The maternal karyotype was subsequently found to be 46,XX,t(12;21)(q24.32;q22.2). Level II ultrasound showed microcephaly, micrognathia, a ventricular septal defect, and rocker-bottom feet. The pregnancy was terminated. A malformed infant was delivered without the phenotype of holoprosencephaly (HPE). Fluorescence in situ hybridization (FISH) and polymorphic DNA markers were used to investigate the involved chromosomal segments.

RESULTS

FISH study showed the absence of the signal of 21q subtelomeric probe and the presence of the signal of 12q subtelomeric probe in the der(21). The fetal karyotype was 46,XY,der(21) t(12;21)(q24.32;q22.2)mat. Genetic marker analysis showed a deletion at 21q22.2 and a breakpoint between D21S156 (present) and D21S1245 (absent). The deleted segment was measured about 4.5 Mb encompassing the HPE critical region.

CONCLUSIONS

Molecular genetic analyses help in determining the prenatally detected unbalanced cryptic translocation as well as parental balanced subtle translocation. A duplication of 12q24.32-->qter and a deletion of 21q22.2-->qter may be associated with prenatal sonographic findings of microcephaly, borderline ventriculomegaly and cerebellar hypoplasia, micrognathia, a ventricular septal defect, and rocker-bottom feet. Haploinsufficiency of the HPE critical region at 21q22.3 may not cause an HPE phenotype.

De novo pure 12q22q24.33 duplication: First report of a case with mental retardation, ADHD, and Dandy-Walker malformation

We present a patient with a de novo 12q nonmosaic pure duplication characterized by multiple minor anomalies and Dandy-Walker malformation. A neurological and behavioral assessment revealed psychomotor retardation and attention deficit/hyperactivity disorder (ADHD), with neurobehavioral abnormalities (auto- and heteroaggressive behavior). Fluoxetine therapy in this case markedly improved the neurobehavioral profile, with a decreased level of aggression. To define the extension of the duplicated region, we performed FISH analyses by using YAC probes. The analyses revealed a tandem duplication of the 12q22q24.33 region, with the proximal breakpoint located between 96.5 and 97.6 cM and the distal one between 154 and 161 cM. This is the first case of pure de novo duplication involving the 12q22q24.33 region. To better define the clinical phenotype associated with 12q partial duplication, we compared our case with the four patients with similar pure duplications previously described.

Sperm studies in heterozygote inversion carriers: a review

The risk of producing unbalanced gametes in heterozygous inversion carriers mostly depends on the occurrence of recombination events within the inverted segment. Recombination determines the possibility of producing chromosomes with duplications/deficiencies (pericentric inversions) or with duplications/deficiencies which furthermore appear as dicentric and acentric fragments (paracentric inversions). In this work, a general description of the close relationship between the occurrence of crossovers in pericentric and paracentric inversions and the final segregation outcome is presented. After this introduction, a compilation of inversion segregation data and interchromosomal effect results from previously published sperm studies have been reviewed. Segregation results indicate a great heterogeneity in the percentage of unbalanced gametes, from 0 to 37.38%. The size of the inverted segments and their proportion in the chromosome are two parameters closely related with the incidence of recombination (P < 0.0001; using a quadratic model and Pearson's correlation test). These results suggest that the production of a significant level of unbalanced gametes would require a minimum inversion size of 100 Mbp and the inversion of at least 50% of the chromosome. Interchromosomal effects are seldom observed in chromosomal inversions. Finally, implications of the meiotic behavior of the inversions in the progeny of the carriers and the incorporation of sperm FISH segregation analysis for reproductive genetic counseling are discussed.

Detailed clinical description of four patients with 1.3 and 2.1 Mb chromosome imbalances derived from a familial t(12;17)(q24.33;q25.3)

We describe a family carrying a submicroscopic reciprocal translocation involving 12qter and 17qter detected by subtelomeric FISH analysis. Four family members inherited unbalanced variants-two cases inherited the derivative chromosome 12 and the other two the derivative chromosome 17. The two individuals with the derivative chromosome 17 showed a distinct phenotype with mild mental retardation in combination with multiple minor malformations, while the phenotype in the cases with the derivative chromosome 12 was milder and only partly concordant. Detailed FISH analysis using 19 BAC clones covering the distal part of chromosome 12q and 17q estimated the imbalances to 2.1 and 1.3 Mb, respectively. The clinical and cytogenetic findings of the two different genotypes are reported and discussed. This family illustrates that small chromosome imbalances can be detected in individuals with mild phenotype and normal, or near-normal, cognitive functions.