Clinical characteristics.

ANKRD17-related neurodevelopmental syndrome is characterized by developmental delay – particularly affecting speech – and variable intellectual disability. Additional features include autism spectrum disorder, attention-deficit/hyperactivity disorder, ophthalmologic abnormalities (strabismus and refractive errors), growth deficiency, feeding difficulties, recurrent infections, gait and/or balance disturbances, and epilepsy. Characteristic craniofacial features include triangular face shape, high anterior hairline, deep-set and/or almond-shaped eyes with periorbital fullness, low-set ears, thick nasal alae and flared nostrils, full cheeks, and thin vermilion of the upper lip. Less common but distinctive features include cleft palate with Pierre Robin sequence, renal agenesis, and scoliosis.

Diagnosis/testing.

The diagnosis of ANKRD17-related neurodevelopmental syndrome is established in a proband with a heterozygous pathogenic variant in ANKRD17 identified by molecular genetic testing.

Management.

Treatment of manifestations: Developmental and educational support; standard treatments for seizures, behavioral findings, ophthalmologic involvement, genitourinary anomalies, and spasticity; feeding therapy with gastrostomy tube placement as needed for persistent feeding issues; routine immunizations; referral to immunologist for those with recurrent infections; family support and care coordination as needed.

Surveillance: Assess developmental progress, educational needs, seizures, changes in tone, movement disorders, growth, nutrition, feeding, and family needs at each visit; assess behavioral and musculoskeletal manifestations annually or as needed.

Pregnancy management: The teratogenic risk to the fetus associated with the use of anti-seizure medication during pregnancy depends on the type of anti-seizure medication used, the dose, and the gestational age of the fetus.

Genetic counseling.

ANKRD17-related neurodevelopmental syndrome is an autosomal dominant disorder typically caused by a de novo pathogenic variant. If the ANKRD17 pathogenic variant identified in the proband is not identified in either parent, the risk to sibs is low but greater than that of the general population because of the possibility of parental germline mosaicism. Once the ANKRD17 pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible.

Suggestive Findings

ANKRD17-related neurodevelopmental syndrome should be considered in individuals with the following clinical findings.

Clinical findings

• Developmental delay particularly affecting speech
• Intellectual disability of variable severity
• Neurodevelopmental and behavioral disorders including autism spectrum disorder and attention-deficit/hyperactivity disorder
• Ophthalmologic abnormalities (refractive errors and strabismus)
• Growth deficiency (postnatal short stature and poor weight gain) accompanied by feeding difficulties
• Recurrent infections without identified immune deficiency
• Gait and/or balance disturbances
• Epilepsy, most commonly focal seizures with secondary generalization
• Dysmorphic craniofacial features (triangular face shape, high anterior hairline, deep-set and/or almond-shaped eyes with periorbital fullness, low-set ears, thick nasal alae and flared nostrils, full cheeks, thin vermilion of the upper lip, Pierre Robin sequence)
• Genitourinary anomalies including unilateral renal agenesis

Establishing the Diagnosis

The diagnosis of ANKRD17-related neurodevelopmental syndrome is established in a proband with suggestive findings and a heterozygous pathogenic (or likely pathogenic) variant in ANKRD17 identified by molecular genetic testing (see Table 1).

Note: (1) Per ACMG/AMP variant interpretation guidelines, the terms "pathogenic variant" and "likely pathogenic variant" are synonymous in a clinical setting, meaning that both are considered diagnostic, and both can be used for clinical decision making [Richards et al 2015]. Reference to "pathogenic variant" in this section is understood to include any likely pathogenic variant. (2) Identification of a heterozygous ANKRD17 variant of uncertain significance does not establish or rule out the diagnosis.

Molecular genetic testing in a child with developmental delay or an older individual with intellectual disability may begin with comprehensive genomic testing (exome sequencing, genome sequencing) and/or chromosomal microarray analysis (CMA). Other options include use of a multigene panel. Note: Because many of the features of this disorder are nonspecific and overlap with a range of neurodevelopmental disorders, single-gene testing (sequence analysis of ANKRD17, followed by gene-targeted deletion/duplication analysis) is rarely useful and typically NOT recommended.

An intellectual disability or autism spectrum disorder multigene panel that includes ANKRD17 and other genes of interest (see Differential Diagnosis) may be considered to identify the genetic cause of the condition in a person with a nondiagnostic CMA while limiting identification of variants of uncertain significance and pathogenic variants in genes that do not explain the underlying phenotype. Note: (1) The genes included in the panel and the diagnostic sensitivity of the testing used for each gene vary by laboratory and are likely to change over time. (2) Some multigene panels may include genes not associated with the condition discussed in this GeneReview. Of note, given that ANKRD17-related neurodevelopmental syndrome is rare and relatively recently described, some panels for intellectual disability may not include this gene. (3) In some laboratories, panel options may include a custom laboratory-designed panel and/or custom phenotype-focused exome analysis that includes genes specified by the clinician. (4) Methods used in a panel may include sequence analysis, deletion/duplication analysis, and/or other non-sequencing-based tests.

For an introduction to multigene panels click here. More detailed information for clinicians ordering genetic tests can be found here.

Comprehensive genomic testing does not require the clinician to determine which gene(s) are likely involved. Exome sequencing is most commonly used and yields results similar to an intellectual disability multigene panel with the additional advantage that exome sequencing includes genes recently identified as causing intellectual disability whereas some multigene panels may not. Genome sequencing is also possible.

For an introduction to comprehensive genomic testing click here. More detailed information for clinicians ordering genomic testing can be found here.

Clinical Description

The most common clinical manifestations of ANKRD17-related neurodevelopmental syndrome are developmental delay – particularly affecting speech – and variable intellectual disability. Characteristic facial features have been described but may be subtle. Additional features include ophthalmologic abnormalities, growth deficiency, feeding difficulties, gait and/or balance disturbances, epilepsy, and behavioral findings. Recurrent infections, particularly bacterial and involving the respiratory tract, have been reported. Nonspecific brain MRI findings have been reported in half of individuals. Less common but distinctive features include cleft palate with Pierre Robin sequence, renal agenesis, and scoliosis.

To date, 33 individuals with a pathogenic variant in ANKRD17 have been reported [Chopra et al 2021]. The following description of the phenotypic features associated with this condition is based on this report.

Developmental delay (DD) and intellectual disability (ID). Most individuals with ANKRD17-related neurodevelopmental syndrome present with DD and/or ID. Development and cognitive abilities are variable, with disability ranging from borderline to severe. Normal cognition has been reported in two individuals, one of whom had a history of speech delay that improved with therapy and another with autism spectrum disorder.

The domain of speech is particularly affected in this disorder. Speech delay has been reported in nearly all individuals with ANKRD17-related neurodevelopmental syndrome, including those with intellectual abilities in the normal range. Most individuals eventually acquire words or short sentences with speech therapy, but a significant proportion remain nonverbal and rely on other means of communication.

Motor delay is also common, with an average age of walking of two years (range: 9 months to 4 years).

The trajectory of fine motor and social development is not completely understood at this time.

Developmental regression has been reported in one individual; however, this was thought to be secondary to poorly controlled epilepsy.

Other neurodevelopmental features

• Gait and balance abnormalities have been described in some individuals, in particular a wide-based or ataxic gait. No correlation between gait and neuroimaging abnormalities has been found.
• A subset of individuals manifest abnormalities in tone, including both hypotonia (typically truncal) and hypertonia with or without spasticity (typically distal).

Epilepsy has been reported in approximately one third of individuals with ANKRD17-related neurodevelopmental syndrome. Age of onset ranges from infancy to early adolescence. Individuals with infantile-onset epilepsy tend to have more frequent seizures than those with childhood- or adolescent-onset epilepsy. Abnormal EEG in the absence of epilepsy has also been described.

The most common seizure type is focal seizures with secondary generalization. Other seizure types include Lennox-Gastaut epilepsy, tonic seizures with head deviation, myoclonic epilepsy, tonic-clonic epilepsy, and absence seizures. Efficacy of anti-seizure medications is variable, with refractory epilepsy in a minority of individuals.

Neurobehavioral/psychiatric manifestations. Autism spectrum disorder is present in some affected individuals. Stereotypic movements, particularly of the hands, have also been reported. Four individuals have been reported to have attention-deficit/hyperactivity disorder. Anxiety and depression have been reported in a single affected adult.

Ophthalmologic abnormalities were reported in more than half of affected individuals. Abnormalities were generally minor and included refractive errors and strabismus. Bilateral optic nerve hypoplasia was also reported in one individual.

Growth and feeding. Neonatal growth parameters are normal in most individuals. Postnatal growth deficiency (defined as height and/or weight equal to or greater than two standard deviations below the mean for age and sex) and/or failure to thrive have been reported in almost half of individuals. This is often accompanied by feeding difficulties, which may necessitate enteral tube feeding. The basis of these difficulties may be poor progression to solids, reduced appetite, and/or food aversions.

Microcephaly and, less commonly, macrocephaly have also been observed in affected individuals.

Recurrent infections have been reported in approximately one third of affected individuals. Infections are usually bacterial, but recurrent viral infections have also been reported. The most common sites of infection are the lower respiratory system and middle ear. One individual had a history of Pseudomonas and methicillin-resistant Staphylococcal aureus (MRSA) infection on his toes. Immunology assessments have not identified immunodeficiencies in any affected individuals.

Craniofacial features. Individuals with ANKRD17-related neurodevelopmental syndrome present with characteristic facial features, which may be subtle and only evident to a trained dysmorphologist. These include a triangular face shape, high anterior hairline, deep-set and/or almond-shaped eyes with periorbital fullness, low-set ears, thick nasal alae and flared nostrils, full cheeks, and a thin vermilion of the upper lip (Figure 1). Microcephaly (7/31 individuals), macrocephaly (4/31 individuals), and normal head size have all been reported. Cleft palate with Pierre Robin sequence was reported in two individuals, and unilateral cleft lip and palate was reported in one individual.

Figure 1.

Dysmorphic facial features of ANKRD17-related neurodevelopmental syndrome. Physical characteristics include a triangular face (I1, 4, 5, 6, 9, 15, 22, 30, 31, and 33), high anterior hairline (I1-10, 12, 15, 18, 25, 29, 30, 31, 32, and 33), deep-set (I2, (more...)

Musculoskeletal features

• Joint hypermobility has been reported in one third of affected individuals. In most individuals, hypermobility was generalized.
• Minor digital anomalies have been described, including brachydactyly, fifth digit clinodactyly, and prominent fingertip pads.
• Scoliosis has been reported in three individuals.

Genitourinary anomalies have been described in 15% of individuals. Unilateral renal agenesis has been described in three individuals. More minor genitourinary anomalies include crossed fused renal ectopia, urethral stricture, and cryptorchidism.

Pigmentary anomalies, including hypopigmented skin and hair, progressive vitiligo, hyperpigmented patches with overlying freckles, and café au lait macules have been described in a minority of individuals.

Brain MRI abnormalities were reported in almost half of individuals who had imaging records. Findings were generally nonspecific and included decreased white matter volume, thinning of the corpus callosum, optic nerve hypoplasia, focal hyperintensities, right temporal sclerosis, and dilated Virchow-Robin spaces. Periventricular nodular heterotopia was reported in a single affected individual. Thus far, no correlation between MRI abnormalities and abnormal neurologic examination or epilepsy has been demonstrated.

Other associated features

• Cardiovascular features. Two individuals were reported to have prominent venous patterns on the forehead and torso, one of whom was reported to be hypermobile. Congenital heart defects including patent foramen ovale, dysplastic aortic valve, and ventricular septal defect have been reported.
• Endocrine features. Hypoglycemia and hypothyroidism have each been reported in a single individual. Spontaneous vertebral fractures with hypercalciuria have been reported.
• Hearing loss. One individual with bilateral sensorineural hearing loss and another with conductive hearing loss have been reported.

Prognosis. Based on current data, there is no evidence that life span is limited by this condition, as several adults have been reported. Data on possible progression of behavior abnormalities or neurologic findings are still limited. Since many adults with disabilities have not undergone advanced genomic evaluation, it is likely that adults with this condition are underrecognized and underreported.

Genotype-Phenotype Correlations

No genotype-phenotype correlations have been identified. Individuals with pathogenic missense variants are clinically indistinguishable from those with truncating variants.

Penetrance

Based on current literature, penetrance is believed to be complete with variable expressivity.

Nomenclature

The title of this GeneReview, ANKRD17-related neurodevelopmental syndrome, is based on the dyadic naming approach proposed by Biesecker et al [2021] to delineate mendelian genetic disorders.

Prevalence

The prevalence of this rare genetic disorder is unknown. To date, 33 individuals with ANRKD17-related neurodevelopmental syndrome have been reported and well characterized [Chopra et al 2021], and the authors are aware of a further 14 individuals who are affected.

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with ANKRD17-related neurodevelopmental syndrome, the evaluations summarized in Table 3 (if not performed as part of the evaluation that led to diagnosis) are recommended.

Treatment of Manifestations

There is no cure for ANKRD17-related neurodevelopmental syndrome. Supportive care to improve quality of life, maximize function, and reduce complications is recommended. This can include multidisciplinary care by specialists in neurology, speech therapy, physical therapy, occupational therapy, ophthalmology, mental health, and clinical genetics (see Table 4).

Surveillance

Evaluation of Relatives at Risk

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Pregnancy Management

To date, there has been one affected individual in the literature who had a pregnancy [Chopra et al 2021]. In general, women with epilepsy or a seizure disorder of any cause are at greater risk for mortality during pregnancy than pregnant women without a seizure disorder; use of anti-seizure medication during pregnancy reduces this risk. However, exposure to anti-seizure medication may increase the risk for adverse fetal outcome (depending on the drug used, the dose, and the stage of pregnancy at which medication is taken). Nevertheless, the risk of an adverse outcome to the fetus from anti-seizure medication exposure is often less than that associated with exposure to an untreated maternal seizure disorder. Therefore, use of anti-seizure medication to treat a maternal seizure disorder during pregnancy is typically recommended. Discussion of the risks and benefits of using a given anti-seizure medication during pregnancy should ideally take place prior to conception. Transitioning to a lower-risk medication prior to pregnancy may be possible [Sarma et al 2016].

See MotherToBaby for further information on medication use during pregnancy.

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Mode of Inheritance

ANKRD17-related neurodevelopmental syndrome is an autosomal dominant disorder typically caused by a de novo pathogenic variant.

Risk to Family Members

Parents of a proband

• Most probands reported to date with ANKRD17-related neurodevelopmental syndrome whose parents have undergone molecular genetic testing have the disorder as a result of a de novo ANKRD17 pathogenic variant.
• Rarely, individuals diagnosed with ANKRD17-related neurodevelopmental syndrome inherited an ANKRD17 pathogenic variant from a parent.
  • In one family, a heterozygous mother with borderline intellectual disability, anxiety, depression, and short stature transmitted an ANKRD17 pathogenic variant to an affected child [Chopra et al 2021].
  • Transmission of an ANKRD17 pathogenic variant from an unaffected father with somatic and germline mosaicism to an affected child has also been reported [Chopra et al 2021].
• Molecular genetic testing is recommended for the parents of the proband regardless of family history to confirm parental genetic status and to allow reliable recurrence risk counseling.
• If the pathogenic variant identified in the proband is not identified in either parent and parental identity testing has confirmed biological maternity and paternity, the following possibilities should be considered:
  • The proband has a de novo pathogenic variant.
  • The proband inherited a pathogenic variant from a parent with germline (or somatic and germline) mosaicism.* Note: Testing of parental leukocyte DNA may not detect all instances of somatic mosaicism and will not detect a pathogenic variant that is present in the germ cells only.
    * A parent with somatic and germline mosaicism for an ANKRD17 pathogenic variant may have very subtle clinical features.
• The family history of some individuals diagnosed with ANKRD17-related neurodevelopmental syndrome may appear to be negative because of failure to recognize the disorder in heterozygous family members with subtle clinical features. Therefore, parental molecular genetic testing is recommended to demonstrate that neither parent is heterozygous for the ANKRD17 pathogenic variant identified in the proband.

Sibs of a proband. The risk to the sibs of the proband depends on the genetic status of the proband's parents:

• If a parent of the proband is known to have the ANKRD17 pathogenic variant identified in the proband, the risk to the sibs of inheriting the variant is 50%.
• If the ANKRD17 pathogenic variant identified in the proband cannot be detected in the leukocyte DNA of either parent, the recurrence risk to sibs is slightly greater than that of the general population because of the possibility of germline mosaicism in a parent.
• If the parents have not been tested for the ANKRD17 pathogenic variant but are clinically unaffected, the risk to the sibs of a proband appears to be low but still increased over that of the general population because of the possibility of variable expressivity resulting in a mild, unrecognized phenotype in a heterozygous parent and the possibility of parental germline mosaicism.

Offspring of a proband. Each child of an individual with ANKRD17-related neurodevelopmental syndrome has a 50% chance of inheriting the pathogenic variant.

Other family members. The risk to other family members depends on the status of the proband's parents: if a parent has the ANKRD17 pathogenic variant, the parent's family members may be at risk.

Related Genetic Counseling Issues

Family planning

• The optimal time for determination of genetic risk and discussion of the availability of prenatal/preimplantation genetic testing is before pregnancy.
• It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to parents of affected individuals.

Prenatal Testing and Preimplantation Genetic Testing

Once the ANKRD17 pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible.

Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing. While most centers would consider use of prenatal testing to be a personal decision, discussion of these issues may be helpful.

Molecular Pathogenesis

Ankyrin repeat domain-containing protein 17 (ANKRD17) belongs to a group of proteins characterized by the presence of the ankyrin repeat motif [Li et al 2006]. These repeats are typically organized into linear arrays and serve as protein-protein interaction surfaces. A range of functions for this gene have been proposed:

• There is in vitro evidence for the role of ANKRD17 in cell cycle progression through cyclin E/CDK2 [Deng et al 2009].
• A role for ANKRD17 in antibacterial and antiviral immunity has also been proposed, via the NOD1/NOD2 [Menning & Kufer 2013] and RIG-I-like receptor-mediated pathway [Wang et al 2012].

The precise mechanism by which ANKRD17 loss of function leads to the neurodevelopmental phenotype is unknown.

Mechanism of disease causation. The mutational spectrum of ANKRD17-related neurodevelopmental syndrome and the intolerance of this gene to loss of function in the general population (gnomAD pLI score = 1) is highly suggestive of haploinsufficiency as the underlying disease mechanism. Most missense variants in ANKRD17 are believed to disrupt the stability of ankyrin repeats.

ANKRD17-specific laboratory technical considerations. The ANKRD17 gene contains two clusters of ankyrin repeats. Most pathogenic missense variants identified thus far are located in these clusters. Missense variants outside of the ankyrin repeat domain require careful interpretation.

Author Notes

Maya Chopra web page

Rosamund Stone Zander Translational Neuroscience Center web page

Acknowledgments

The authors acknowledge the patients, families, and clinicians who have contributed to the understanding of this disorder.

Revision History

• 22 December 2022 (sw) Review posted live
• 17 October 2022 (mc) Original submission

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