The ADNP syndrome, also known as Helsmoortel-Van der Aa syndrome (HVDAS), is an autosomal dominant neurodevelopmental disorder caused by heterozygous truncating variants abolishing the homeobox and/or HP1 domains of ADNP. Rare missense changes in the ADNP gene are usually variants of uncertain significance or reclassified as (likely) benign because they are inherited from an unaffected parent, and a causative role was documented for only three of them. We report a 24-year-old Italian woman presenting with intellectual disability, visual and severe speech impairment, microcephaly, truncal obesity, and hirsutism. Behavioral disturbance was significant and included fragmented sleep, self- and hetero-aggression, outbursts of anger, and verbal and physical violence crises. Additional unusual findings were hyperandrogenism and secondary amenorrhea. Next-generation sequencing showed the novel de novo missense variant c.2405C>T, p.(Ser802Phe) affecting the DNA-binding homeodomain of ADNP. In silico analysis revealed this variant is located in a genomic region highly intolerant to missense changes, and several tools predicted a deleterious effect on protein function. Counterintuitively to the known molecular pathogenesis for ADNP syndrome, calculation of the binding free energy and dissociation constant of the p.(Ser802Phe) missense substitution suggested a stronger ADNP-DNA interaction, thus opening the path to the hypothesis of a gain-of-function effect. This clinical report expands genotype-phenotype variability and correlations in ADNP syndrome. ADNP-related Helsmoortel-Van der Aa syndrome (also referred to as Helsmoortel-Van der Aa syndrome [HVDAS]) is characterized by hypotonia, speech and motor delay, mild-to-severe intellectual disability, and characteristic facial features (prominent forehead, high anterior hairline, wide and depressed nasal bridge, and short nose with full, upturned nasal tip). Features of autism spectrum disorder are common (stereotypic behavior, impaired social interaction). Other common findings include additional behavioral problems, sleep disturbance, structural brain abnormalities, feeding issues, gastrointestinal problems, visual dysfunction (hypermetropia, strabismus, cortical visual impairment), musculoskeletal anomalies, recurrent infections, endocrine issues including short stature and thyroid and/or growth hormone deficiencies, cardiac anomalies, hearing loss, seizures, and urinary tract anomalies. The diagnosis of ADNP-related HVDAS is established by identification of a heterozygous ADNP pathogenic variant by molecular genetic testing. Treatment of manifestations: Treatment is symptomatic and can include: speech, occupational, and physical therapy; specialized learning programs depending on individual needs; treatment of neuropsychiatric features; nutritional support as needed; standard treatment of gastrointestinal, ophthalmologic, and musculoskeletal issues, recurrent infections, endocrine and cardiac findings, hearing loss, seizures, and urinary tract anomalies; family and social support. Surveillance: At each visit monitor developmental progress, educational needs, behavioral issues, occupational and physical therapy needs, growth and nutrition, gastrointestinal issues, infection frequency, endocrine issues, seizures, urinary tract infections, and family needs; annual vision and hearing assessment. ADNP-related HVDAS is an autosomal dominant disorder. Most probands whose parents have undergone molecular genetic testing have the disorder as the result of a de novo ADNP pathogenic variant. In two families reported to date, probands diagnosed with ADNP-related HVDAS inherited a pathogenic variant from an unaffected parent. Once the ADNP pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible.

Background: Helsmoortel-Van der Aa syndrome (HVDAS) is a rare multisystemic neurodevelopmental disorder caused by pathogenic variants in the Activity-Dependent Neuroprotective Homeobox Protein (ADNP) gene. Since the extensive clinical description of a cohort of 78 affected individuals in 2019, numerous reports described additional cases affected by the condition. However, no systematic synthesis of the clinical and molecular spectrum of these additional individuals has been conducted to date. Methods: In accordance with the PRISMA 2020 guidelines, we performed a systematic review of all publications describing individuals with genetically confirmed HVDAS. Clinical characteristics, comorbidities, and developmental milestones were systematically extracted to illustrate novel or underrecognized manifestations. Results: A total of 105 individuals reported across 34 publications were included. Of these, 66 were clinically and genetically evaluated, and 39 were analyzed only at the genetic level. Our analysis refines the phenotypic spectrum of HVDAS, including developmental delay, visual anomalies, and congenital heart defects. The additional literature also allows us to characterize in more detail the ophthalmological abnormalities, gait disturbances, and the cognitive profile of HVDAS. Advances in ADNP methylation profiling further enhance diagnostic precision and variant interpretation in this evolving neurodevelopmental syndrome. Conclusions: This systematic review provides a comprehensive synthesis of the clinical, genetic, and epigenetic landscape of HVDAS. It underscores the multisystemic nature of the disorder and the need for multidisciplinary management. The expanding phenotypic heterogeneity likely reflects both improved clinical recognition of the more subtle features and the tendency to prioritize publication of more complex or severely affected cases.

De novo variants in the Activity-Dependent Neuroprotective Protein (ADNP) gene cause the autistic Helsmoortel-Van der Aa syndrome with patients showing mild to disastrous phenotypes impacting brain functioning, behavior, and organ functions. In this respect, two treatment strategies have been proposed to alleviate symptoms in patients with this syndrome: (1) the ADNP-derived octapeptide investigational drug NAP (davunetide), which enhances ADNP's ability to target cytoskeletal deficits, and (2) subnarcotic levels of ketamine, which are suggested to increase endogenous ADNP mRNA levels. Here, we focus on the perspective of ketamine and investigated the transcriptomic response of low-dose and high-dose ketamine applications at different time points, experimentally controlled by the non-toxic drug NAP, in lymphoblastoid cell lines obtained from individuals with Helsmoortel-Van der Aa syndrome. Transcriptome profiling was performed at baseline conditions, followed by dose (low or high) and time (40 min or 4 h)-dependent ketamine application in patient and control lymphoblastoid cell lines. We showed that ketamine affected ADNP expression levels in a dose- and time-dependent manner with only toxic ketamine concentrations increasing ADNP protein levels. Ketamine application also triggered a transcriptomic response with profound gene expression alterations centered around processes such as immune response-regulating signaling pathways and cell fate commitment at low-dose ketamine, together with organelle assembly and cytoskeletal dysregulation at high doses. A parallel control experiment with NAP under the same experimental conditions did not induce detectable gene expression differences in patient-derived cell lines. The ketamine-induced cytoskeletal alterations were functionally studied using immunoblotting, showing a disturbed expression of α-tubulin, β-actin, and to a minor extent microtubule-associated protein EB3 in patient-derived lymphoblastoid cells. Ketamine upregulates wild-type ADNP transcript and protein levels in a dose- and time-dependent manner in patient-derived lymphoblastoid cell lines from individuals with Helsmoortel-Van der Aa syndrome, while inducing a transcriptomic response that affects key processes including immune system signaling and cytoskeletal organization.

The Helsmoortel-Van der Aa syndrome is an autosomal-dominant neurodevelopment disorder caused by heterozygous de novo variants in the Activity-Dependent Neuroprotective Protein (ADNP) gene, characterized by autism, intellectual disability, dysmorphic facial features, and deficits in multiple organ systems. ADNP is a zinc finger DNA-binding protein that primarily interacts with chromatin remodelers regulating embryonic development, while also associating with components of the cytoskeleton, thereby regulating autophagy and microtubule dynamics during development. In this study, we investigated these nucleocytoskeletal alterations explaining neurodevelopmental delay in a child with Helsmoortel-Van der Aa syndrome who had an unaffected dizygotic twin brother. We performed a genome-wide methylation array on PBMCs from dizygotic twins, showing a predominant CpG hypomethylation episignature. Enrichment analysis of methylated genes revealed significant pathway changes in actin filament organization, Wnt signaling, embryonic development, heart development, and the immune system. In addition, transcriptome sequencing substantiated the affected pathways regulating nuclear and cytoskeletal filamentous alterations associated with autism and neurodevelopmental delay. Brain magnetic resonance imaging showed a mild generalized prominence of the subarachnoid space overlying both hemispheres, revealing intricate patterns of neurodevelopmental delay. We report the first molecular study performed on dizygotic twins of which one was diagnosed with Helsmoortel-Van der Aa syndrome, revealing Wnt signaling and filamentous cytoskeletal alterations as a potential drug targets for therapy. Indications for neurodegeneration, following these cytoskeletal perturbations, have been observed in cellular and murine models for the Helsmoortel-Van der Aa syndrome. However, clinical evidence remains unclear due to the young age of patients, limiting long-term studies on the aging brain. Further longitudinal imaging studies combined with histopathological autopsy sections are required to study the impact of an ADNP variant in the brain as patients come to age.