A large family with subtelomeric translocation t(18;21)(q23;q22.1) and molecular breakpoint in the Down syndrome critical region

Ocular Phenotype Associated with DYRK1A Variants

Dual-specificity tyrosine phosphorylation-regulated kinase 1A or DYRK1A, contributes to central nervous system development in a dose-sensitive manner. Triallelic DYRK1A is implicated in the neuropathology of Down syndrome, whereas haploinsufficiency causes the rare DYRK1A-related intellectual disability syndrome (also known as mental retardation 7). It is characterised by intellectual disability, autism spectrum disorder and microcephaly with a typical facial gestalt. Preclinical studies elucidate a role for DYRK1A in eye development and case studies have reported associated ocular pathology. In this study families of the DYRK1A Syndrome International Association were asked to self-report any co-existing ocular abnormalities. Twenty-six patients responded but only 14 had molecular confirmation of a DYRK1A pathogenic variant. A further nineteen patients from the UK Genomics England 100,000 Genomes Project were identified and combined with 112 patients reported in the literature for further analysis. Ninety out of 145 patients (62.1%) with heterozygous DYRK1A variants revealed ocular features, these ranged from optic nerve hypoplasia (13%, 12/90), refractive error (35.6%, 32/90) and strabismus (21.1%, 19/90). Patients with DYRK1A variants should be referred to ophthalmology as part of their management care pathway to prevent amblyopia in children and reduce visual comorbidity, which may further impact on learning, behaviour, and quality of life.

Clinical phenotype of ASD-associated DYRK1A haploinsufficiency

BACKGROUND

DYRK1A is a gene recurrently disrupted in 0.1-0.5% of the ASD population. A growing number of case reports with DYRK1A haploinsufficiency exhibit common phenotypic features including microcephaly, intellectual disability, speech delay, and facial dysmorphisms.

METHODS

Phenotypic information from previously published DYRK1A cases (n = 51) and participants in an ongoing study at the University of Washington (UW, n = 10) were compiled. Frequencies of recurrent phenotypic features in this population were compared to features observed in a large sample with idiopathic ASD from the Simons Simplex Collection (n = 1981). UW DYRK1A cases were further characterized quantitatively and compared to a randomly subsampled set of idiopathic ASD cases matched on age and gender (n = 10) and to cases with an ASD-associated disruptive mutation to CHD8 (n = 12). Contribution of familial genetic background to clinical heterogeneity was assessed by comparing head circumference, IQ, and ASD-related symptoms of UW DYRK1A cases to their unaffected parents.

RESULTS

DYRK1A haploinsufficiency results in a common phenotypic profile including intellectual disability, speech and motor difficulties, microcephaly, feeding difficulties, and vision abnormalities. Eighty-nine percent of DYRK1A cases ascertained for ASD presented with a constellation of five or more of these symptoms. When compared quantitatively, DYRK1A cases presented with significantly lower IQ and adaptive functioning compared to idiopathic cases and significantly smaller head size compared to both idiopathic and CHD8 cases. Phenotypic variability in parental head circumference, IQ, and ASD-related symptoms corresponded to observed variability in affected child phenotype.

CONCLUSIONS

Results confirm a core clinical phenotype for DYRK1A disruptions, with a combination of features that is distinct from idiopathic ASD. Cases with DYRK1A mutations are also distinguishable from disruptive mutations to CHD8 by head size. Measurable, quantitative characterization of DYRK1A haploinsufficiency illuminates clinical variability, which may be, in part, due to familial genetic background.

Chromosome 18q deletion syndrome with autoimmune diabetes mellitus: putative genomic loci for autoimmunity and immunodeficiency

A girl with 18q deletion syndrome was diagnosed with autoimmune diabetes mellitus and Hashimoto's thyroiditis at the age of 3 yr. In addition, the girl suffered from recurrent infections due to immunoglobulin A and IgG4 deficiency. She was also found to have CD3+CD4+FoxP3+, CD3+CD4+FoxP3+CD25+, and CD3+CD4+CD25+CD127 regulatory T cells deficiency. The exceptional coincidence of the two autoimmune disorders occurring at an early age, and associated with immune deficiency, implies that genes located on deleted 19.4 Mbp region at 18q21.32-q23 (chr18:58,660,699-78,012,870) might play a role in the pathogenesis of autoimmunity leading to β cell destruction and diabetes.

Case report of novel DYRK1A mutations in 2 individuals with syndromic intellectual disability and a review of the literature

BACKGROUND

Chromosomal deletions encompassing DYRK1A have been associated with intellectual disability for several years. More recently, point mutations in DYRK1A have been shown to be responsible for a recognizable syndrome characterized by microcephaly, developmental delay and intellectual disability (ID) as well as characteristic facial features. Here we present 2 individuals with novel mutations in DYRK1A, and a review of the cases reported to date.

CASE PRESENTATION

Both individuals presented with the well-known characteristic features, as well as rarer anomalies seen in a minority of patients. Patient 1 presented shortly after birth with an enlarged cisterna magna, distal contractures, and distinctive facies that included bitemporal narrowing and deep set eyes. A de novo splice site mutation in DYRK1A [c.951 + 4_951 + 7delAGTA; p.Val222Aspfs*22] was identified by next generation sequencing. Patient 2 presented at 7 months of age with microcephaly and dysmorphic features. She went several years without a diagnosis until a de novo DYRK1A nonsense mutation [c.787C>T; p.(Arg263*)] was identified at age 12. These individuals, and the 52 cases reviewed from the literature, show the characteristic features of the DYRK1A-related syndrome including global developmental delay, ID, microcephaly, feeding difficulties, and the facial gestalt. Other common findings include seizures, vision defects, brain abnormalities and skeletal abnormalities of the hands and feet. Less common features include optic nerve defects, contractures, ataxia, and cardiac anomalies.

CONCLUSION

DYRK1A testing should be considered in individuals with the facial features, intellectual disability and post-natal microcephaly. Once diagnosed with DYRK1A-related intellectual disability, a cardiac and ophthalmologic assessment would be recommended as would routine surveillance by a pediatrician for psychomotor development, growth, and feeding.

Subtelomeric 6.7 Mb trisomy 10p and 5.6 Mb monosomy 21q detected by FISH and array-CGH in three related patients

Cryptic subtelomeric chromosomal aberrations are responsible for 5-10% of moderate/severe and 1% of mild intellectual disability. Unbalanced subtelomeric chromosomal rearrangements result in variable phenotypes which seem to be highly influenced by both the size of the duplication/deletion and the chromosomes involved in the translocation. We report on three related patients with moderate intellectual disability, language delay, hypotonia, facial dysmorphism, cardiac anomalies, scoliosis, and kyphosis in whom a familial (maternal) unbalanced submicroscopic translocation was found by subtelomeric fluorescence in situ hybridization (FISH). This rearrangement resulted in a partial trisomy 10pter and partial monosomy 21qter. The karyotype was 46,XY.ish der(21)t(10;21)(p14;q22.2). Confirmation of a 6.7 Mb size distal duplication of the p15.3-14 region of chromosome 10 and a 5.6 Mb distal deletion of the q22.2-22.3 region of chromosome 21 was obtained by array-CGH. To our best knowledge, such a composition of subtelomeric unbalanced translocations has not yet been published. Detection of this aberration in successive pregnancies of carrier members of the family by prenatal FISH could prevent the recurrence of the disease. Furthermore, detection of the rearrangements and identification of genes located in the chromosomal regions involved might be of interest.

Distinctive Phenotypic Abnormalities Associated with Submicroscopic 21q22 Deletion Including DYRK1A

Partial monosomy 21 has been reported, but the phenotypes described are variable with location and size of the deletion. We present 2 patients with a partially overlapping microdeletion of 21q22 and a striking phenotypic resemblance. They both presented with severe psychomotor delay, behavioral problems, no speech, microcephaly, feeding problems with frequent regurgitation, idiopathic thrombocytopenia, obesity, deep set eyes, down turned corners of the mouth, dysplastic ears, and small chin. Brain MRI showed cerebral atrophy mostly evident in frontal and temporal lobes, widened ventricles and thin corpus callosum in both cases, and in one patient evidence of a migration disorder. The first patient also presented with epilepsy and a ventricular septum defect. The second patient had a unilateral Peters anomaly. Microarray analysis showed a partially overlapping microdeletion spanning about 2.5 Mb in the 21q22.1-q22.2 region including the DYRK1A gene and excluding RUNX1. These patients present with a recognizable phenotype specific for this 21q22.1-q22.2 locus. We searched the literature for patients with overlapping deletions including the DYRK1A gene, in order to define other genes responsible for this presentation.

Mapping susceptibility gene locus for IgA deficiency at del(18)(q22.3?q23); report of familial cryptic chromosome t(18q; 10p) translocations

This study presents a clinical report of the Finnish chromosome t(18q; 10p) translocation family with an overview of eight other selected immunoglobulin A (IgA)-deficient 18q deletion (18q-) patients from seven published articles. The family members show features common to 18q- syndrome such as mental retardation, multiple facial dysmorphism, foot/hand deformities, abnormal myelination of brain white matter, and a spectrum of immunological/infectious disorders including IgA deficiency (IgAD). Genotype-phenotype correlation study of the unbalanced t(18q-; 10p+) translocation family members and other 18q- syndrome reports led to definition of a potential susceptibility gene locus for IgAD at distal region of 18q22.3-q23 between markers D18S812-18qter. The haplo-insufficiency of the 18q22.3-q23 gene region is suggested to be a cause of the IgAD phenotype in 18q- individuals. This 7 Mb IgAD critical region shows significant association with susceptibility region for celiac disease that is frequently connected to IgAD.

A de novo subterminal trisomy 10p and monosomy 18q in a girl with MCA/MR: case report and review

We report on a 3-year-old girl with psychomotor retardation, cardiopathy, strabismus, umbilical hernia, and facial dysmorphism in whom a de novo unbalanced submicroscopic translocation (10p;18q) was found by MLPA (Multiplex Ligation dependent Probe Amplification) and FISH analyses. Additional FISH studies with locus specific RP11 BAC probes and analyses with microsatellites revealed that the translocation resulted in a deletion estimated between 6 and 9 Mb on the maternal chromosome 18 and a subtelomeric 10p duplication of approximately 6.9 Mb. The proband's karyotype is 46,XX.ish der(18) t(10;18)(18pter-->18q23:10p15 --> 10pter). A subterminal duplication of 10p, as well as a subterminal deletion of 18q have been rarely reported so far. The clinical phenotype of this patient is reviewed and discussed.

High-resolution analysis of chromosomal imbalances using the Affymetrix 10K SNP genotyping chip

Array-based comparative genome hybridization is a powerful tool for detecting chromosomal imbalances at high resolution. However, the design and setup of such arrays are time consuming and expensive and thus worthwhile only when large numbers of arrays will be processed. To provide a feasible solution, we have developed an algorithm that renders the publicly available Affymetrix 10K SNP genotyping chip useful for high-resolution analysis of chromosomal imbalances. We have used our newly developed algorithm to analyze data from Affymetrix 10K chips that were hybridized with DNA probes from a variety of different sources, such as primary tumors, cell lines, and blood from patients with unbalanced translocations. In summary, we were able to (i) demonstrate the capability of our method by reproduction of published and unpublished data obtained with alternative methods and (ii) identify novel imbalances that were not shown before.

Mild phenotype in two unrelated patients with a partial deletion of 21q22.2-q22.3 defined by FISH and molecular studies

We describe two unrelated patients with cytogenetically visible deletions of 21q22.2-q22.3 and mild phenotypes. Both patients presented minor dysmorphic features including thin marfanoid build, facial asymmetry, downward-slanting palpebral fissures, depressed nasal bridge, small nose with bulbous tip, and mild mental retardation (MR). FISH and molecular studies indicated common deleted areas but different breakpoints. In patient 1, the breakpoint was fine mapped to a 5.2 kb interval between exon 5 and exon 8 of the ETS2 gene. The subtelomeric FISH probe was absent on one homologue 21 indicating a terminal deletion spanning approximately 7.9 Mb in size. In patient 2, the proximal breakpoint was determined to be 300-700 kb distal to ETS2, and the distal breakpoint 2.5-0.3 Mb from the 21q telomere, indicating an interstitial deletion sized approximately 4.7-7.3 Mb. The 21q- syndrome is rare and typically associated with a severe phenotype, but different outcomes depending on the size and location of the deleted area have been reported. Our data show that monosomy 21q of the area distal to the ETS2 gene, representing the terminal 7.9 Mb of 21q, may result in mild phenotypes comprising facial anomalies, thin marfanoid build, and mild MR, with or without signs of holoprosencephaly.

Familial MCA/MR syndrome due to inherited submicroscopic translocation t(18;21)(q22.1q21.3) with breakpoint at the Down syndrome critical region

We report three generation family that includes two patients with severe mental retardation and additional anomalies who have been studied, clinically, cytogenetically, and molecular cytogenetically. A clinical diagnosis could not be made in the propositus, but facial anomalies of Down syndrome (DS) were recognized in the maternal uncle of the propositus. In view of a strong family history of recurrent miscarriage, a familial translocation was highly suggestive. Standard cytogenetic analysis did not reveal any abnormalities. Fluorescence in situ hybridization (FISH) using subtelomeric DNA probes identified a familial cryptic translocation of chromosomes 18 and 21, resulting in partial trisomy 21 and partial monosomy 18q in both patients. FISH analysis of obligate carriers demonstrated a balanced translocation between the terminal parts of 18q and 21q. Including this family, a total of six different familial cases with cryptic or subtle subtelomeric translocations of chromosome 21q has been reported, of which three involved terminal parts of chromosome 18q. The remarkable similarity of the chromosomal breakpoints of our patients and the described families prompted us to refine the breakpoints and to discuss phenotypic differences between these patients. Our results reinforce the role of cryptic subtelomeric rearrangements in patients with mental retardation associated with physical anomalies and stress the importance of FISH technology to supplement routine cytogenetics.

Tertiary trisomy due to a reciprocal translocation of chromosomes 5 and 21 in a four-generation family

Tertiary trisomy, or double trisomy, is a rare occurrence. We present two individuals with a previously unreported tertiary trisomy for chromosomes 5p and 21q in an eight-generation pedigree. Their phenotypes are compared with other partial trisomies of either 5p or 21q from the literature. The propositus was diagnosed with trisomy 21 at 2 years of age after a karyotype study for short stature and developmental delay. His phenotype was described as atypical for Down syndrome. He presented at 9 years of age because of pervasive behavioral problems and obesity. He was brachycephalic with a flattened nasal bridge, but he lacked other characteristics of trisomy 21. Because of lack of phenotypic evidence of Down syndrome, a repeat karyotype was obtained and showed 47,XY, +der(21)t(5;21)(p15.1; q22.1), incorporating partial trisomies of both chromosomes 5 and 21. Mother had a balanced translocation, 46, XX,t(5;21)(p15.1; q22.1); 8 other relatives were examined. The translocation originated from the maternal great-grandmother, but only the propositus and his mentally retarded aunt had a similar phenotye and the derivative chromosome. Fluorescence in situ hybridization showed absence of band 21q22.2 in the derivative chromosome of the propositus and his aunt, indicating that neither had trisomy for the Down syndrome critical region. These cases represent a unique double partial trisomy of chromosome arms 5p and 21q that occurred because of 3:1 malsegregation of a reciprocal translocation. These cases further demonstrate that phenotypic discordance with cytogenetic results dictate further investigation using advanced cytogenetic hybridization.

An extra idic(21)(q22.1) in a child with some features of Down's syndrome

A 30-month-old boy with mental retardation, hypotonia, joint hyperlaxity, Brushfield spots, open mouth, distal axial triradius t", and ulnar loops on both forefingers was found to have a 47,XY, + psu idic(21)(q22.1).ish psu idic(21)(q22.1)(D13Z1/D21Z1 + + ,ETS2-) karyotype. The patient's phenotype, with only some Down's syndrome (DS) features, is probably related to his disomy for most or all of the critical region 21q22.2 q22.3 and agrees with the current notion that certain DS features may also result from 21q proximal duplications. The phenotypical comparison with 2 other patients with a similar extra idic(21) reveals some discrepancies, which may be related to the inherent clinical variability of similar imbalances: yet, a real difference between the tetrasomic segments cannot be excluded. Noticeably, all 3 patients with 21q proximal tetrasomy did not have cardiac defect and exhibited none or just one out of the five other DS phenotypic features attributed to a single gene or cluster on distal 21q22.

A brief review of cryptic duplications of 21q as an emerging cause of Down syndrome: practical considerations for accurate detection

We review five cryptic duplications of 21q in patients with Down syndrome (DS) that were inherited from parental balanced translocations. All cases were identified by fluorescence in situ hybridization (FISH) and or DNA diagnosis because the phenotype was inconsistent with the initial cytogenetic studies. These rearrangements seem to escape detection without expanded testing and are probably more frequent than expected. For this reason we propose a series of steps combining objective clinical diagnostic criteria, FISH and DNA methods to achieve an accurate ascertainment.