17q12 Recurrent Deletions and Duplications: Description of a Case Series with Neuropsychiatric Phenotype

Syndromic neurodevelopmental disorders are usually investigated through genetics technologies, within which array comparative genomic hybridization (Array-CGH) is still considered the first-tier clinical diagnostic test. Among recurrent syndromic imbalances, 17q12 deletions and duplications are characterized by neurodevelopmental disorders associated with visceral developmental disorders, although expressive variability is common. Here we describe a case series of 12 patients with 17q12 chromosomal imbalances, in order to expand the phenotypic characterization of these recurrent syndromes whose diagnosis is often underestimated, especially if only mild traits are present. Gene content and genotype-phenotype correlations have been discussed, with special regard to neuropsychiatric features, whose impact often requires etiologic analysis.


Background
Neurodevelopmental disorders could be considered either idiopathic or syndromic, depending on whether the neuropsychic conditions are isolated or associated with the involvement of malformations [1,2].
The recurrence of 17q12 genomic imbalances depends on a susceptible region flanked by segmental duplications, namely low copy repeats (LCRs), prone to nonallelic homologous recombination (NAHR) [10]. The critical region associated with these recurrent syndromic conditions is sized at about 1.4 Mb, and includes 17 refseq genes [8].
Here we describe a large series of patients with 17q12 chromosomal imbalances in order to deepen the highly variable clinical presentation and to expand the phenotypic characterization of these recurrent syndromes, whose diagnosis is often underestimated,

Results
The age of patients ranged from 3 years old to 17 years old. We have found six patients harboring 17q12 microdeletion, whose size ranged from 1.32 Mb to 1.73 Mb, and six patients with 17q12 microduplication, whose size ranged from 0.92 to 1.73 Mb. Four were females and eight were males.
Three pairs of patients had the same genomic imbalances (Patients 4 and 5, Patients 9 and 10, and Patients 11 and 12, respectively), with perfect overlap between the breakpoints, besides Patients 1 and 2 who were siblings and inherited the same 17q12 deletion from their father. Patients 7 and 8 had the same imbalance size, although the former carried a microdeletion and the latter a microduplication. Only Patient 1 had an additional imbalance which involved the 6q22.31 region.
Genetic and neuropsychiatric features of the 12 patients have been summarized in Table 1a (Demographic distribution and genetic findings) and Table 1b (Patients' phenotypic characterization).

Discussion
17q12 deletion and duplication syndromes determine an increased risk for neurodevelopmental and neuropsychiatric disorders, such as developmental delay, ID (mild to severe), ASD, psychotic disorder, anxiety, and bipolar disorder [8,9]. They have also been related to visceral and endocrine anomalies, these being the implicated organs likely sensitive to dosage changes of genes located in the 17q12 chromosomal region. However, the prevalence of specific features (i.e., kidney involvement and facial dysmorphisms) in patients with deletions, compared with others (i.e., more severe esophageal defects) in patients with duplications, suggests an organ-specific susceptibility to higher or lower gene dosage [8,9]. In addition, patients with 17q12 duplication display a wide phenotypic spectrum due to reduced penetrance and variable expressivity, ranging from relevant cognitive impairment to asymptomatic carriers. Consequently, the prevalence of this genomic imbalance is expected to be underestimated [13], and more frequently inherited in respect to 17q12 deletion [9].
Microcephaly has been more often associated with 17q12 duplication [13], while macrocephaly has been associated with the reciprocal chromosomal imbalance [8]. In our cohort of patients nobody had altered occipito-frontal circumference.
Non-specific brain anomalies have been reported in 17q12 genomic imbalances. These include ventricular dilatation, mild cerebellar atrophy, abnormal signal intensity of subcortical white matter, atrophy of the hippocampus [9], cortical malformations [13], and thinning/agenesia of the corpus callosum [8]. In our patients, brain MRIs were substantially normal, independently from the range of clinical severity. Only Patient 3 showed aspecific peritrigonal white matter anomalies. This evidence may confirm that ultrastructural and functional anomalies, which are determined by the dysregulations of key molecules, underlie neurodevelopmental disorders even without detectable brain structure abnormalities [14,15].
Reduced weight at birth and intrauterine growth retardation were noticed in some of our patients. Abnormal prenatal evidences have been reported in patients with genomic imbalance, significantly with 17q12 deletions [16].
By analyzing the critical 17q12 region gene content, HNF1B may be responsible for the majority of features related to 17q12 microdeletion/microduplication syndromes, including neurodevelopmental disorders, this gene being widely distributed [17]. In particular, this gene confers the acronym RCAD (renal cysts and diabetes) to the 17q12 deletion syndrome, being responsible for the combination of kidney dysfunction and maturity-onset diabetes of the young (MODY5) [9]. Kidney alterations were present in two patients, although abdominal ultrasounds were executed only in five patients. No patient had diabetes, yet it is not possible to exclude its future manifestation, since the studied cohort is only composed of youngsters.
LHX1 is involved in neuronal differentiation, axon migration, and in cerebellum development [18,19], thus it may concur with ASD and with other neurodevelopmental disorders described in these recurrent syndromes [14,20,21].
Recently, Gametogenetin Binding Protein 2 (GGNBP2) has been included among ASD candidate genes and reported in the Autism Informatics Portal AUTDB (http://autism. mindspec.org/autdb (accessed on 10 October 2021), although at the time of writing it has not been associated with any Mendelian disease [22]. Interestingly, this gene is co-expressed with other autism-and brain-enriched genes such as MECP2 [22], suggesting a role in pathways implicated in the ASD pathology.
We could also hypothesize that SYNRG, a gene involved in Golgi trafficking and, in particular, in inwardly rectifying K+ channels (e.g., Kir4.1) export, may concur with ASD [23], and even be associated with epilepsy [24].
TADA2A acts as a transcriptional activator, managing histone acetylation and chromatin organization. Therefore, it may regulate gene expression in critical development phases [25]. On the other hand, AATF inhibits the histone deacetylase HDAC1 and activates cell cycle progression [25]. Both genes may thus influence neurodevelopment. Patient 1 had the most severe picture, considering both his neuropsychiatric profile and multiorgan involvement. Besides 17q12 microdeletion inherited from his father and shared with his sister, he carried an additional 6q22.31 duplication inherited from his mother. This duplication encompassed TBC1D32 without a definite pathogenic role, although this gene is involved in cell cycle and consequently in early development, particularly in sonic hedgehog signaling. It has been related to ciliopathies and is a brain-enriched coding gene [26]. Therefore, we cannot exclude the possibility that this double hit may concur to aggravate the composite picture of Patient 1, as described in other cases [27]. Another hypothesis regards incomplete penetrance and variable expressivity of 17q12 genomic imbalances, reported in many dominant mechanisms [28]. Indeed, his peculiar ocular picture could be attributable to 17q12 deletion, since eye abnormalities, such as strabismus and horizontal nystagmus, are included within its features [9]. Furthermore, his paroxysmal movement disorder may show the contribution of at least two genes included in the 17q12 region, namely the aforementioned SYNRG and MYO19. The former may alter calcium ion binding by regulating the clathrin-mediated vesicular traffic and concurring to cause channelopathy [29] in a similar way to what has been described in relation to Kir channels [23]. The latter is a mitochondrial gene implied in cytokinesis and in reactive oxygen species (ROS) distribution [30], and could resemble other genes' functionality, such as myofibrillogenesis regulator 1, itself associated with paroxysmal movement disorders [31].
In Patients 7 and 8, the genomic imbalances were perfectly overlapping, although reciprocal (i.e., the former had a deletion and the latter a duplication). Their dimension was broader than the others described in our sample, and they included four genes encoding chemokines, such as CCL1L1, CCL3L3, CCL4L1, and CCL4L2, besides the genes of the 17q12 critical region. Differing from the majority of the other patients, who presented ASD and intellectual disability, their clinical picture was characterized by ADHD, anxiety, and mood disorder, associated with cognitive impairment. Recent studies have also emphasized the role of neuroinflammation in these neurodevelopmental and psychiatric disorders [32][33][34].
Furthermore, Patient 7 had a cryptogenic cholangiopathy which may be related to 17q12 microdeletion, since elevated hepatic transaminase enzyme levels, cholestasis, liver abnormalities involving choledochal, and bile duct cysts have been reported [9]. We cannot exclude the possibility that chemokines involvement in this broader deletion may have also contributed to this hepatic disorder, which often has an inflammatory origin [35]. Patients 9 and 10 had an overlapping 17q12 deletion and a similar clinical picture, both presenting with high-functioning ASD and receptive-expressive language disorder.
Interestingly, Patients 11 and 12, who presented a smaller duplication outside and upstream to the critical 17q12 duplication syndrome, met the diagnostic criteria for ASD similar to patients with 17q12 duplication syndrome, although different genes are involved. A fascinating hypothesis regards the immunologic imbalance, which has been related to ASD, deriving from these CNVs which shared the same distal breakpoints and the same gene content, even though the proximal breakpoints were different. Specifically, cytokine and chemokine profiles alteration, which is derived from CCL2 [36], CCL7, and CCL11 [37] imbalance in our patients, may provoke this neurodevelopmental disorder. Furthermore, ASIC2 has been linked with gut microbiome modulation [38], which is nowadays considered responsible for many psychiatric disturbances, including ASD, since it may contribute to inflammation via the gut-brain axis [39]. Autistic regression has recently been related to neuroinflammation [40], as occurred in Patient 11, who had a cessation of language development and a regression of relational abilities after a respiratory infection, and each subsequent inflammatory episode connoted similar functional consequences. ASIC2 is also involved in neurotransmission [41]. Neural adhesion and immunologic functions may also be influenced by TMEM132E [42], which has been associated with panic disorder, while other TMEM family members have been related to high-functioning autism [43].
In the light of this evidence, we may hypothesize as to their implication in human pathology, although both duplications are reported to be frequent in the DGV.
A confirmation of 17q12 recurrent CNVs' strong association with neurodevelopmental disorders has been recently highlighted considering brain-enriched coding and long noncoding (lnc) RNA genes [44]. In particular, authors reported two patients: the former carried a duplication sizing 40 Mb not involving brain-enriched genes but encompassing five lncRNAs; the latter carried a deletion sizing 1.410 Mb involving four brain-enriched genes and five lncRNAs. They shared the same proximal breakpoints. In the Decipher databases no patients have been reported with CNVs overlapping with the duplication, while several patients have been reported with the same deletion, many of whom present ID, one presenting with intrauterine growth retardation (IUGR) and hyperechogenic kidneys, and one presenting with diabetes. In our series of patients, ten had proximal breakpoints downstream to those presented in [44], although the brain-enriched coding and lncRNA genes are the same (respectively, four and five, Table 2, [44]). IUGR was present in one patient with deletion and in another with duplication. The other two patients carrying smaller CNVs upstream to the critical region presented two brain-enriched coding and three lnc RNA genes ( Table 2). While the role of brain-enriched coding genes is sufficiently known in 17q12 imbalances as described above, understanding epigenetic regulation due to lncRNAs during cell differentiation and development is continuously ongoing. LncRNAs are involved in epigenetic reprogramming during cell growth and development by acting as chromatin, transcriptional, post-transcriptional, and post-translational regulators [45]. For this reason, lncRNAs dysregulation is related to several neurodevelopmental disorders, since they interfere with synaptic transport/signaling and long-term potentiation and depression [45]. In our series, three pairs of patients displayed overlapping genomic imbalances and also shared overlapping phenotypes; therefore, genotype-phenotype correlations may appear to be more easily interpreted. Furthermore, as evidenced by Patients 7 and 8, 17q12 deletions and duplications could provoke similar neurodevelopmental disorders, although congenital malformations are more frequent in the former [8].
One limitation of our study regards the lack of functional studies which could permit one to better understand gene expression, also regulated by lncRNAs. Furthermore, prediction and prioritization of bioinformatic studies may help in predicting transcript sequence features and performing functional characterization of the candidate genes and lncRNAs [46].

Conclusions
Syndromic neurodevelopmental disorders are conditions characterized by the cooccurrence of phenotypic-behavioral anomalies associated with dysmorphic or malformative pictures. Based on the prevalence of the neuropsychiatric or pediatric impact, they usually draw the attention of a specialist who should vet each feature of the child, and examine in depth the biological, functional, and genetic aspects to increase the probability of reaching an etiological diagnosis.
The knowledge evolution about recurrent genomic imbalances and their gene content, with special regard to candidate genes in neurodevelopmental disorders and brain-enriched genes, will allow one to progressively clarify the genotype expression.