DNMT1-Related Disorder

Clinical characteristics.

DNMT1-related disorder is a degenerative disorder of the central and peripheral nervous systems comprising a phenotypic spectrum that includes hereditary sensory and autonomic neuropathy type 1E (HSAN1E) and autosomal dominant cerebellar ataxia, deafness, and narcolepsy (ADCA-DN). DNMT1 disorder is often characterized by moderate-to-severe sensorineural hearing loss beginning in the teens or early 20s, sensory impairment, sudomotor dysfunction (loss of sweating), and dementia usually beginning in the mid-40s. In some affected individuals, narcolepsy/cataplexy syndrome and ataxia are predominant findings.

Diagnosis/testing.

The diagnosis of DNMT1 disorder is established by identification of a heterozygous pathogenic variant in DNMT1 by molecular genetic testing.

Management.

Treatment of manifestations: No cure for DNMT1 disorder currently exists. The emphasis of management is to help affected individuals and their caregivers understand the sudomotor defect and injury prevention when sensory impairment is significant. Because hearing loss may be severe, initial use of hearing aids and/or assistive communication methods may be needed. Sedative or antipsychotic drugs help to reduce extreme restlessness, roaming behavior, delusions, and hallucinations associated with dementia. Because behavioral changes and the loss of insight and judgment often present a considerable burden for partners or other caregivers, information about the disorder and psychological support for partners or other caregivers are essential.

Surveillance: Examination of feet daily for evidence of skin injury; annual routine clinical testing for dementia and audiogram to monitor hearing loss.

Agents/circumstances to avoid: To prevent injury to extremities with decreased sensation, protect the skin with appropriate socks and shoes and avoid exposure of feet to hot water.

Genetic counseling.

DNMT1 disorder is inherited in an autosomal dominant manner. Most affected individuals have an affected parent; the proportion of affected individuals with a de novo DNMT1 pathogenic variant is unknown.

Each child of an individual with DNMT1 disorder has a 50% chance of inheriting the pathogenic variant. Once the DNMT1 pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible.

Suggestive Findings

DNMT1 disorder should be suspected in individuals with the following clinical, electrophysiologic, and neuroimaging findings and family history.

Clinical findings

• Sensory neuropathy that is predominantly loss of feeling to touch, pain, temperature, and proprioception of the feet and legs, with less severe loss in the hands. Pain tends to be minimal but can be lancinating or burning; some have described parathesias. Tendon reflexes tend to be depressed in the lower limbs. The face and trunk are characteristically spared. Age of onset ranges from early 20s to late 40s.
• Autonomic neuropathy, manifest as loss of sweating (sudomotor abnormalities). Significant symptoms of autonomic neuropathy usually do not occur until the late 40s.
  Laboratory-based tests such as tilt table testing for postural hypotension, quantitative sudomotor axon reflex testing, and thermoregulatory sweat testing can help to identify postganglionic sudomotor abnormalities that spare cardiovagal and adrenergic autonomic functions.
  Special quantitative sensory testing and histopathologic preparations can assist in studying the sensory fibers implicated in autonomic involvement. The pan sensory neuropathy affects large proprioceptive and vibratory sensing fibers as well as small heat-, pain-, and temperature-sensing fibers.
• Cerebellar ataxia manifest as impaired coordination, loss of balance, unsteady gait, difficulty performing fine motor tasks, and changes in speech. Age of onset ranges from the late 30s to late 40s.
• Dementia that typically first manifests as progressive decline in cognition and behavior. Wechsler Adult Intelligence and Memory Scales as well as Boston naming test and the Mini Mental State Exam (MMSE) can be used to identify diffuse cortical dementia. Dementia usually starts in the mid-40s.
• Moderate to severe progressive sensorineural hearing loss (i.e., 70- to 80-db loss at 4,000 Hz) beginning in the teens or early 20s
• Early- or late-onset narcolepsy/cataplexy syndrome. Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. Cataplexy refers to a sudden loss of muscle tone. Age of onset ranges from early 20s to late 40s.

Electrophysiologic testing shows:

• Length-dependent sensory axonal loss including both small fiber loss (drC and Aσ) and large fiber proprioceptive Aβ loss;
• Absent or reduced sensory nerve action potentials with normal motor nerve conduction velocities.

Brain imaging can help to determine the existence of global atrophy without intraparenchymal signal change.

Family history is consistent with autosomal dominant inheritance, including simplex cases (i.e., a single occurrence in a family) caused by a de novo pathogenic variant.

Establishing the Diagnosis

The diagnosis of DNMT1 disorder is established in a proband with suggestive findings and a heterozygous pathogenic (or likely pathogenic) variant in DNMT1 identified by molecular genetic testing (see Table 1).

Note: (1) Per ACMG/AMP variant interpretation guidelines, the terms "pathogenic variants" and "likely pathogenic variants" 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 variants" in this section is understood to include any likely pathogenic variants. (2) Identification of a heterozygous DNMT1 variant of uncertain significance does not establish or rule out the diagnosis.

Molecular genetic testing approaches can include a combination of gene-targeted testing (single-gene testing or multigene panel) and comprehensive genomic testing (exome sequencing, genome sequencing) depending on the phenotype.

Gene-targeted testing requires that the clinician determine which gene(s) are likely involved, whereas genomic testing does not. Because the phenotype of DNMT1-related disorder is broad, individuals with the distinctive findings described in Suggestive Findings are likely to be diagnosed using gene-targeted testing (see Option 1), whereas those with a phenotype indistinguishable from many other inherited disorders with progressive sensorineural hearing loss, pure sensory neuropathy, and/or cognitive decline are more likely to be diagnosed using genomic testing (see Option 2).

Clinical Description

DNMT1-related disorder is a degenerative disorder of the central and peripheral nervous systems characterized by sensory impairment, sudomotor dysfunction (loss of sweating), dementia, and sensorineural hearing loss. In some individuals, late-onset narcolepsy/cataplexy syndrome presents as the prominent manifestation along with: ataxia that appears to be cerebellar in nature, deafness, sensory neuropathy, and memory loss [Klein et al 2011, Winkelmann et al 2012]. Affected persons are normal in their youth but begin to manifest progressive findings, such as sensorineural hearing loss, sensory neuropathy, and/or narcolepsy/cataplexy, by their late teens or early 20s.

In a cohort of 45 affected individuals, the average age of onset was estimated to be 37.7 years; the most common initial manifestation was hearing loss (36%), followed by sensory loss, ulcerations and/or arthropathy (33%), cognitive decline (7%), and gait imbalance (7%). It is likely that the range of phenotypes will expand as more affected individuals are identified [Baets et al 2015].

Sensory impairment, which can manifest as early as the second decade of life starting with loss of sensation leading to painless extremity injuries, is associated with hyporeflexia. Sensory impairment predominantly affects the distal lower extremities with minimal to no motor involvement. The sensory alterations are associated with gait unsteadiness and mutilating acropathy with ulcers and/or amputations of distal extremities in approximately 50% of affected persons.

Autonomic dysfunction is limited to loss of sweating (sudomotor) on the distal aspects of the upper and lower limbs.

Dementia manifests as progressive cognitive, executive function, and behavioral decline usually by the fourth decade. Behavior changes including anger and change in personality may precede decline in memory. Memory loss, apathy, indifference, inattention, and somnolence have all been described [Wright & Dyck 1995, Hojo et al 1999]. Irritability, delusions, and delirium are also reported.

Moderate-to-severe sensorineural hearing loss (i.e., 70- to 80-db loss at 4,000 Hz) typically begins in the teens or early 20s.

Gait ataxia is common and is usually the result of sensory loss in the feet, but rarely may be cerebellar ataxia.

Narcolepsy/cataplexy syndrome sometimes presents as the prominent manifestation.

Other clinical findings observed on occasion include visual hallucinations, myoclonic seizures, and renal failure.

Other findings

• PET and SPECT imaging have been used to show medial frontal and thalamic hypometabolism.
• Sural nerve biopsy shows marked loss of myelinated fibers without onion bulb change.
• Brain neuropathology at autopsy has shown diffuse neuronal loss without distinctive histologic features and no amyloid, tau, or α-synuclein inclusions [Klein et al 2011].

Genotype-Phenotype Correlations

All pathogenic variants that cause DNMT1-related disorder are located in the targeting sequence (TS) domain of the DNMT1 protein (see Molecular Genetics, Normal gene product).

• Variants resulting in the HSAN1E phenotype (a predominantly sensory neuropathy) are in the N-terminus or middle part of the TS domain [Baets et al 2015].
• Variants that cause autosomal dominant cerebellar ataxia, deafness and narcolepsy are located in the C-terminus of the TS domain [Baets et al 2015].

Penetrance

The penetrance of DNMT1 disorder is 100% in both males and females. However, age of onset and rate of progression vary between individuals.

Nomenclature

This GeneReview, formerly titled "DNMT1-related dementia, deafness, and sensory neuropathy," was renamed "DMNT1-related disorder" to reflect the broader phenotypic spectrum now known to be associated with pathogenic variants in DNMT1.

Hereditary sensory and autonomic neuropathy type IE (HSAN1E) is considered a sensory-predominant neuropathy.

Prevalence

To date, a total of 21 families with DNMT1 disorder have been reported.

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs of an individual diagnosed with DNMT1-related disorder, the evaluations summarized in this section (if not performed as part of the evaluation that led to the diagnosis) are recommended:

• Neurologic examination to determine the extent of sensory involvement, including sensory testing and observation for skin ulceration
• Past medical history to determine extent of autonomic involvement
• Evaluation of central nervous system involvement, using tests of cognitive function and brain imaging
• Audiologic examination to determine if hearing loss is present and, if present, its type and severity
• Consultation with a clinical geneticist and/or genetic counselor

Treatment of Manifestations

No cure for DNMT1 disorder currently exists.

The emphasis of management is to help parents and affected individuals understand the sudomotor defect and injury prevention when sensory impairment is significant. To prevent injury to extremities with decreased sensation, protect the skin with appropriate socks and shoes and avoid exposure of feet to hot water.

Because hearing loss may be severe, initial use of hearing aids and/or assistive communication methods may be needed. See also Hereditary Hearing Loss and Deafness Overview.

Sedative or antipsychotic drugs help to reduce extreme restlessness, roaming behavior, delusions, and hallucinations associated with dementia.

Because behavioral changes and the loss of insight and judgment in individuals often present a considerable burden for partners or other caregivers, information about the disease and psychological support for partners or other caregivers are essential.

Surveillance

Sensory impairment. Examine feet on a daily basis to screen for skin injury.

Dementia. Perform annual routine clinical testing for dementia:

• Observation of behavior
• Use of tools such as the Mini Mental State Exam (MMSE)

Hearing loss. Perform annual audiogram.

Agents/Circumstances to Avoid

Avoid sharp objects and hot water, which may damage skin.

Evaluation of Relatives at Risk

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

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for 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

DNMT1-related disorder is inherited in an autosomal dominant manner.

Risk to Family Members

Parents of a proband

• Most individuals diagnosed with DNMT1 disorder have an affected parent.
• A proband with DNMT1 disorder may have the disorder as the result of a de novo pathogenic variant [Baets et al 2015]. The proportion of DNMT1 disorder caused by a de novo pathogenic variant is unknown.
• Clinical evaluation and molecular genetic testing is recommended for the parents of a proband with an apparent de novo pathogenic variant.
• If the pathogenic variant found in the proband cannot be detected in the leukocyte DNA of either parent, possible explanations include a de novo pathogenic variant in the proband or germline mosaicism in a parent. Though theoretically possible, no instances of a proband inheriting a DNMT1 pathogenic variant from a parent with germline mosaicism have been reported.
• The family history of some individuals diagnosed with DNMT1 disorder may appear to be negative because of failure to recognize the syndrome and/or a milder phenotypic presentation, early death of the parent before the onset of symptoms, or late onset of the disease in the affected parent. Therefore, an apparently negative family history cannot be confirmed unless molecular genetic testing has been performed on the parents of 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 affected and/or is known to have the DNMT1 pathogenic variant, the risk to the sibs is 50%.
• If the DNMT1 pathogenic variant cannot be detected in the leukocyte DNA of either parent, the recurrence risk to sibs is estimated to be 1% because of the theoretic possibility of parental germline mosaicism [Rahbari et al 2016].

Offspring of a proband. Each child of an individual with DNMT1 disorder 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 DNMT1 pathogenic variant, the parent's family members may be at risk.

Related Genetic Counseling Issues

Considerations in families with an apparent de novo pathogenic variant. When neither parent of a proband with an autosomal dominant condition has the pathogenic variant identified in the proband or clinical evidence of the disorder, the pathogenic variant is likely de novo. However, non-medical explanations including alternate paternity or maternity (e.g., with assisted reproduction) and undisclosed adoption could also be explored.

Predictive testing (i.e., testing of asymptomatic at-risk individuals)

• Predictive testing for at-risk relatives is possible once the DNMT1 pathogenic variant has been identified in an affected family member.
• Potential consequences of such testing (including but not limited to socioeconomic changes and the need for long-term follow up and evaluation arrangements for individuals with a positive test result) as well as the capabilities and limitations of predictive testing should be discussed in the context of formal genetic counseling prior to testing.

Predictive testing in minors (i.e., testing of asymptomatic at-risk individuals younger than age 18 years)

• For asymptomatic minors at risk for adult-onset conditions for which early treatment would have no beneficial effect on disease morbidity and mortality, predictive genetic testing is considered inappropriate, primarily because it negates the autonomy of the child with no compelling benefit. Further, concern exists regarding the potential unhealthy adverse effects that such information may have on family dynamics, the risk of discrimination and stigmatization in the future, and the anxiety that such information may cause.
• For more information, see the National Society of Genetic Counselors position statement on genetic testing of minors for adult-onset conditions and the American Academy of Pediatrics and American College of Medical Genetics and Genomics policy statement: ethical and policy issues in genetic testing and screening of children.

In a family with an established diagnosis of DNMT1-related disorder, it is appropriate to consider testing of symptomatic individuals regardless of age.

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 young adults who are affected or at risk.

Prenatal Testing and Preimplantation Genetic Testing

Once the DNMT1 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, particularly if the testing is being considered for the purpose of pregnancy termination rather than early diagnosis. While most centers would consider use of prenatal testing to be a personal decision, discussion of these issues may be helpful.

Molecular Pathogenesis

DNMT1 is the sole maintenance methyltransferase and an essential component of cellular epigenetic regulation that keeps the fidelity of methylation inheritance starting from embryogenesis and throughout life. The proper allosteric folding of N-terminal regulatory region is required for enzymatic function.

The targeting sequence (TS) domain, where all the pathogenic variants reside to date, is in the N-terminal regulatory region and regulates DNMT1 binding to hemimethylated DNA during S and binding to heterochromatin during G2 phases.

Mechanism of disease causation. DNMT1 pathogenic variants cause global DNA hypomethylation and site-specific hypermethylation [Klein et al 2011, Sun et al 2014]. The misfolding of the TS domain of DNMT1 mutated proteins could also contribute to the pathogenesis of HSAN1E phenotype through a toxic gain of function [Klein et al 2011, Baets et al 2015].

Specific laboratory considerations [Baets et al 2015]:

• Variants resulting in the HSAN1E phenotype (a predominantly sensory neuropathy) are in the N-terminus or middle part of the TS domain.
• Variants that cause autosomal dominant cerebellar ataxia, deafness, and narcolepsy are located in the C-terminus of the TS domain.

Revision History

• 31 January 2019 (bp) Comprehensive update posted live
• 17 May 2012 (cd) Revision: sequence analysis of DNMT1 available clinically
• 8 March 2012 (cd) Revision: four families with mutations in DNMT1 associated with early onset of a narcolepsy / cataplexy syndrome followed by ataxia, deafness, sensory neuropathy, and memory loss [Winkelmann et al 2012]
• 16 February 2012 (me) Review posted live
• 24 October 2011 (cjk) Original submission

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