Genetic Findings as the Potential Basis of Personalized Pharmacotherapy in Phelan-McDermid Syndrome

Phelan-McDermid syndrome (PMS) is a genetic disorder often characterized by autism or autistic-like behavior. Most cases are associated with haploinsufficiency of the SHANK3 gene resulting from deletion of the gene at 22q13.3 or from a pathogenic variant in the gene. Treatment of PMS often targets SHANK3, yet deletion size varies from 9 Mb, potentially encompassing dozens of genes and disrupting regulatory elements altering gene expression, inferring the potential for multiple therapeutic targets. Repurposed drugs have been used in clinical trials investigating therapies for PMS: insulin-like growth factor 1 (IGF-1) for its effect on social and aberrant behaviors, intranasal insulin for improvements in cognitive and social ability, and lithium for reversing regression and stabilizing behavior. The pharmacogenomics of PMS is complicated by the CYP2D6 enzyme which metabolizes antidepressants and antipsychotics often used for treatment. The gene coding for CYP2D6 maps to 22q13.2 and is lost in individuals with deletions larger than 8 Mb. Because PMS has diverse neurological and medical symptoms, many concurrent medications may be prescribed, increasing the risk for adverse drug reactions. At present, there is no single best treatment for PMS. Approaches to therapy are necessarily complex and must target variable behavioral and physical symptoms of PMS.

State of the Science for Kidney Disorders in Phelan-McDermid Syndrome: UPK3A, FBLN1, WNT7B, and CELSR1 as Candidate Genes

Phelan-McDermid syndrome (PMS) is a neurodevelopmental disorder caused by chromosomal rearrangements affecting the 22q13.3 region or by SHANK3 pathogenic variants. The scientific literature suggests that up to 40% of individuals with PMS have kidney disorders, yet little research has been conducted on the renal system to assess candidate genes attributed to these disorders. Therefore, we first conducted a systematic review of the literature to identify kidney disorders in PMS and then pooled the data to create a cohort of individuals to identify candidate genes for renal disorders in PMS. We found 7 types of renal disorders reported: renal cysts, renal hypoplasia or agenesis, hydronephrosis, vesicoureteral reflux, kidney dysplasia, horseshoe kidneys, and pyelectasis. Association analysis from the pooled data from 152 individuals with PMS across 22 articles identified three genomic regions spanning chromosomal bands 22q13.31, 22q13.32, and 22q13.33, significantly associated with kidney disorders. We propose UPK3A, FBLN1, WNT7B, and CELSR1, located from 4.5 Mb to 5.5 Mb from the telomere, as candidate genes. Our findings support the hypothesis that genes included in this region may play a role in the pathogenesis of kidney disorders in PMS

Position effects of 22q13 rearrangements on candidate genes in Phelan-McDermid syndrome

Phelan-McDermid syndrome (PMS) is a multi-system disorder characterized by significant variability in clinical presentation. The genetic etiology is also variable with differing sizes of deletions in the chromosome 22q13 region and types of genetic abnormalities (e.g., terminal or interstitial deletions, translocations, ring chromosomes, or SHANK3 variants). Position effects have been shown to affect gene expression and function and play a role in the clinical presentation of various genetic conditions. This study employed a topologically associating domain (TAD) analysis approach to investigate position effects of chromosomal rearrangements on selected candidate genes mapped to 22q13 in 81 individuals with PMS. Data collected were correlated with clinical information from these individuals and with expression and metabolic profiles of lymphoblastoid cells from selected cases. The data confirmed TAD predictions for genes encompassed in the deletions and the clinical and molecular data indicated clear differences among individuals with different 22q13 deletion sizes. The results of the study indicate a positive correlation between deletion size and phenotype severity in PMS and provide evidence of the contribution of other genes to the clinical variability in this developmental disorder by reduced gene expression and altered metabolomics

The genomic landscape of balanced cytogenetic abnormalities associated with human congenital anomalies

Despite the clinical significance of balanced chromosomal abnormalities (BCAs), their characterization has largely been restricted to cytogenetic resolution. We explored the landscape of BCAs at nucleotide resolution in 273 subjects with a spectrum of congenital anomalies. Whole-genome sequencing revised 93% of karyotypes and demonstrated complexity that was cryptic to karyotyping in 21% of BCAs, highlighting the limitations of conventional cytogenetic approaches. At least 33.9% of BCAs resulted in gene disruption that likely contributed to the developmental phenotype, 5.2% were associated with pathogenic genomic imbalances, and 7.3% disrupted topologically associated domains (TADs) encompassing known syndromic loci. Remarkably, BCA breakpoints in eight subjects altered a single TAD encompassing MEF2C, a known driver of 5q14.3 microdeletion syndrome, resulting in decreased MEF2C expression. We propose that sequence-level resolution dramatically improves prediction of clinical outcomes for balanced rearrangements and provides insight into new pathogenic mechanisms, such as altered regulation due to changes in chromosome topology

Freezing, Thawing, and Packaging Cells for Transport

Cultured mammalian cells are used extensively in cell biology studies. It requires a number of special skills in order to be able to preserve the structure, function, behavior, and biology of the cells in culture. This video describes the basic skills required to freeze and store cells and how to recover frozen stocks

Phenotypic Variability in Phelan–McDermid Syndrome and Its Putative Link to Environmental Factors

Phelan–McDermid syndrome (PMS) is a multi-systemic disorder characterized by both genetic and phenotypic variability. Genetic abnormalities causing PMS span from pathogenic variants of the SHANK3 gene to chromosomal rearrangements affecting the 22q13 region and leading to the loss of up to over nine megabases. The clinical presentation of individuals with PMS includes intellectual disability, neonatal hypotonia, delayed or absent speech, developmental delay, and minor dysmorphic facial features. Several other features may present with differences in age of onset and/or severity: seizures, autism, regression, sleep disorders, gastrointestinal problems, renal disorders, dysplastic toenails, and disrupted thermoregulation. Among the causes of this phenotypic variability, the size of the 22q13 deletion has effects that may be influenced by environmental factors interacting with haploinsufficiency or hemizygous variants of certain genes. Another mechanism linking environmental factors and phenotypic variability in PMS involves the loss of one copy of genes like BRD1 or CYP2D6, located at 22q13 and involved in the regulation of genomic methylation or pharmacokinetics, which are also influenced by external agents, such as diet and drugs. Overall, several non-mutually exclusive genetic and epigenetic mechanisms interact with environmental factors and may contribute to the clinical variability observed in individuals with PMS. Characterization of such factors will help to better manage this disorder

Clinical utility gene card for: Deletion 22q13 syndrome

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