Charcot–Marie–Tooth Disease Type 2B2 Due to Biallelic PNKP: Disease-Characteristics Report

Executive summary and curation conclusion

Charcot–Marie–Tooth disease type 2B2 (CMT2B2; ARCMT2B; OMIM 605589) is an exceptionally rare, autosomal-recessive, predominantly axonal sensorimotor neuropathy with variably associated cerebellar and oculomotor dysfunction. The definitive disease-specific evidence comes primarily from a large consanguineous Costa Rican family and five additional Costa Rican subjects. The original assignment to homozygous MED25 p.Ala335Val should be retained only as historical: reanalysis identified homozygous PNKP c.1549C>T (p.Gln517Ter) in the extended family and compound-heterozygous p.Gln517Ter/p.Thr408del in the five additional cases. These data support PNKP, not MED25, as the causal gene; the ClinGen CMT Gene Curation Expert Panel’s disputed classification of the MED25–CMT relationship is therefore concordant with the primary evidence. The principal paper was published online July 24, 2018 (PMID 30039206; DOI 10.1007/s10048-018-0555-7). (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

The defining clinical course is adult onset—approximately 28–42 years in the original family—followed by slowly progressive distal weakness and wasting, sensory loss, areflexia, gait impairment, and severe axonal sensorimotor abnormalities on nerve-conduction studies. Dysarthria, gait ataxia, oculomotor abnormalities, and mild cerebellar atrophy can accompany the neuropathy. Unlike severe PNKP-related microcephaly, seizures, and developmental delay (MCSZ), the reported CMT2B2 subjects did not have congenital microcephaly, seizures, or developmental delay. CMT2B2 is best curated as the adult-onset, neuropathy-predominant end of a continuous PNKP-related spectrum that also includes ataxia with oculomotor apraxia type 4 (AOA4) and MCSZ. (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 6-8, gatti2019fromcongenitalmicrocephaly pages 1-2)

Table: Compact knowledge-base table distinguishing PNKP-related CMT2B2 from the disputed MED25 attribution and summarizing its variants, phenotype, mechanism, allelic spectrum, diagnostics, treatment status, and evidence gaps.

1. Disease information

Definition

CMT2B2 is a hereditary motor and sensory neuropathy in which axonal loss, rather than primary demyelination, is the predominant peripheral-nerve lesion. Its distinctive syndromic extension is mild or variable cerebellar and oculomotor dysfunction. The label “CMT2B2” is historically locus- and pedigree-based; molecularly, the condition is a PNKP-related DNA-strand-break-repair disorder. (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 6-8)

Identifiers and synonyms

• OMIM: 605589, CMT2B2.
• MONDO: MONDO:0011570 was supplied in the request; this mapping should be checked against the current MONDO release before production ingestion.
• Synonyms: Charcot–Marie–Tooth disease type 2B2; CMT2B2; autosomal-recessive CMT type 2B; ARCMT2B; hereditary motor and sensory neuropathy, axonal, type 2B2; PNKP-related neuropathy-predominant disorder.
• Related but not synonymous: AOA4, OMIM 616267; MCSZ, OMIM 613402.
• ICD: There is no established subtype-specific ICD-10/ICD-11 code. A broader hereditary motor and sensory neuropathy/Charcot–Marie–Tooth code must be used, with the molecular diagnosis recorded separately.
• MeSH/SNOMED CT: Use the broader Charcot–Marie–Tooth disease or hereditary motor and sensory neuropathy concept plus PNKP and autosomal-recessive inheritance annotations.

This report summarizes aggregated disease-level evidence from published pedigrees and mechanistic experiments. It is not derived from an EHR or an individual clinical record.

Historical reassignment and authoritative interpretation

The original 19q13.3 locus was mapped in a large consanguineous Costa Rican family with autosomal-recessive axonal neuropathy, and homozygous MED25 p.Ala335Val was initially proposed as causal. Because no convincing independent MED25 CMT cases emerged, Leal and colleagues re-examined the family by exome sequencing. Their abstract states: “Using exome sequencing, we now identified a homozygous nonsense variant (p.Gln517ter) in the last exon of an adjacent gene, the polynucleotide kinase 3′-phosphatase (PNKP) gene.” Five additional subjects carrying one copy of the MED25 allele instead proved to have two PNKP alleles. This independent-genotype logic strongly favors PNKP and undermines MED25 causality. (leal2018thepolynucleotidekinase pages 1-2)

2. Etiology

Causal factors

The primary cause is germline biallelic damaging variation in PNKP. In the extended family, p.Gln517Ter was homozygous; in five additional cases, p.Gln517Ter occurred in trans with the in-frame deletion p.Thr408del. Both genotypes are consistent with partial loss of PNKP function. The disease is not infectious, toxic, immune-mediated, or environmentally acquired. (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 4-6)

Genetic risk

Having two pathogenic or likely pathogenic PNKP alleles is the necessary established risk factor. Consanguinity increased the probability of homozygosity in the original family. A first-degree family history compatible with recessive inheritance raises diagnostic probability, but absence of such history does not exclude compound heterozygosity. The MED25 p.Ala335Val allele is not an independently supported risk factor for CMT2B2 and should not be used for predictive testing by itself. (leal2018thepolynucleotidekinase pages 1-2)

Variant nomenclature should be transcript-verified before clinical loading because historical papers may use differing transcript conventions. The reported forms are:

• PNKP c.1549C>T, p.Gln517Ter/p.Gln517* — nonsense, last exon.
• PNKP c.1221_1223del, p.Thr408del — in-frame three-base deletion.

Population frequencies, Costa Rican carrier frequencies, and ancestry-stratified frequencies were not established in the retrieved disease-specific literature. No modifier gene, protective allele, epigenetic risk state, or reproducible susceptibility locus has been demonstrated.

Environmental, protective, and gene–environment factors

No environmental exposure has been shown to cause or protect against CMT2B2. Because reactive oxygen species generate substrates repaired by PNKP, oxidative burden is mechanistically relevant, but no human study shows that smoking, diet, occupation, radiation, alcohol, or exercise modifies penetrance or progression. Avoidance of neurotoxic medications and excessive alcohol is prudent in hereditary neuropathy care, but it is tertiary risk reduction rather than proven CMT2B2-specific prevention. The same distinction applies to exercise: appropriately dosed activity may preserve function, but it does not correct PNKP deficiency.

3. Phenotypes

Core peripheral phenotype

The original family had onset at approximately 28–42 years; additional subjects generally developed polyneuropathy in the third decade. Initial manifestations included gait disturbance, falls, and postural instability. Progression produced distal weakness and atrophy in feet, calves, and hands; absent or impaired tendon reflexes; severe loss of vibration and position sense; claw hands; and, in some cases, pes cavus or hammertoes. Nerve-conduction studies showed absent or markedly reduced sensory responses and low or absent compound muscle action potentials. Modest motor-conduction slowing was interpreted as secondary to severe axonal loss rather than evidence of a primary demyelinating neuropathy. (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

Suggested HPO concepts include adult onset, progressive peripheral neuropathy, axonal sensorimotor polyneuropathy, distal muscle weakness, distal muscle atrophy, areflexia, impaired proprioception, reduced vibration sense, gait disturbance, pes cavus, hammertoes, claw hand, reduced CMAP amplitude, and absent sensory nerve action potentials.

Cerebellar and oculomotor phenotype

Slurred speech/dysarthria was prominent in the additionally characterized cases. Wide-based or mildly ataxic gait, cerebellar dysfunction, and variable oculomotor abnormalities were reported; two listed subjects had oculomotor apraxia. MRI could show mild cerebellar atrophy without brainstem or cerebral white-matter abnormalities. Candidate HPO concepts are cerebellar ataxia, dysarthria, oculomotor apraxia, abnormal ocular movement, postural instability, and cerebellar atrophy. (leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

Severity, progression, and frequency limitations

Expression was variable. One additional subject became wheelchair-dependent after five years, while another remained ambulatory with mild gait ataxia. Frequencies calculated from this tiny, ascertained series would not be valid population estimates. Accordingly, findings such as dysarthria “in all listed additional cases” should be stored as case-series observations, not universal penetrance. (leal2018thepolynucleotidekinase pages 4-6)

Negated and overlapping features

The Costa Rican CMT2B2 patients lacked microcephaly, seizures, developmental delay, cognitive impairment, and dystonia. These are important negated phenotypes for the reported cohort, not absolute exclusion criteria for every future neuropathy-predominant PNKP case. Broader PNKP cohorts demonstrate overlap: early MCSZ can later acquire neuropathy and ataxia, and adult disease can emphasize polyneuropathy and cerebellar signs. (leal2018thepolynucleotidekinase pages 1-2, gatti2019fromcongenitalmicrocephaly pages 1-2, gatti2019fromcongenitalmicrocephaly pages 2-3)

Quality of life

No CMT2B2-specific EQ-5D, SF-36, PROMIS, CMT Health Index, or disease-burden study was identified. Nevertheless, the documented falls, hand and foot weakness, sensory loss, speech impairment, orthopedic deformity, and wheelchair dependence indicate substantial effects on mobility, activities of daily living, communication, and independence. Quantitative utility values should be marked unavailable.

4. Genetic and molecular information

Causal gene and protein

PNKP encodes polynucleotide kinase 3′-phosphatase, a bifunctional DNA-end-processing enzyme. It contains an N-terminal forkhead-associated interaction domain and catalytic phosphatase and kinase regions. PNKP operates in XRCC1-associated single-strand-break/base-excision repair and XRCC4–LIG4-associated nonhomologous end joining. (weinfeld2011tidyinguploose pages 5-7, weinfeld2011tidyinguploose pages 4-5, dumitrache2017polynucleotidekinasephosphatase(pnkp) pages 1-2)

Variant interpretation

The reported variants are constitutional/germline, not somatic. p.Gln517Ter truncates a conserved C-terminal region. Structural modeling in the disease report predicted disruption of kinase/phosphatase-domain orientation and the ADP-binding region, providing a plausible reduction-of-function mechanism. p.Thr408del is an in-frame deletion previously observed in recessive ataxia and contributes to disease when paired with p.Gln517Ter. (leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

For clinical curation, classification should be performed independently under current ACMG/AMP specifications using the laboratory’s selected transcript, validated population frequency, segregation, phase, and any available functional evidence. “Pathogenic” should not be inferred solely from this report’s wording without that transcript-level review.

Other molecular categories

No reproducible CMT2B2 modifier genes, methylation signature, chromatin biomarker, large structural rearrangement, somatic mosaicism, or germline mosaicism have been reported. The disease does not involve aneuploidy, repeat expansion, mitochondrial-genome variation, or a recurrent cytogenetic rearrangement. PNKP may participate in mitochondrial DNA repair, but a CMT2B2-specific mitochondrial molecular signature has not been established. (gatti2019fromcongenitalmicrocephaly pages 1-2, hulmakova2025theroleof pages 32-35)

5. Environmental information

No toxin, pollutant, radiation exposure, occupation, diet, infection, smoking behavior, or alcohol exposure has been causally associated with CMT2B2. Reactive oxygen species and ionizing radiation generate DNA termini that PNKP normally processes, establishing biochemical substrate relevance—not a demonstrated epidemiologic exposure effect. There is no zoonotic or transmissible agent.

6. Mechanism and pathophysiology

Ordered causal chain

1. Biallelic p.Gln517Ter or p.Gln517Ter/p.Thr408del variation leads to reduced or structurally impaired PNKP function. Variant-specific structural impairment is supported by modeling; exact residual activity in patient neurons remains incompletely measured. (leal2018thepolynucleotidekinase pages 6-8)
2. Reduced PNKP leads to inefficient conversion of obstructive DNA 3′-phosphate and 5′-hydroxyl termini into ligatable 3′-OH and 5′-phosphate ends. This end-processing function is demonstrated biochemically for PNKP. (weinfeld2011tidyinguploose pages 5-7, weinfeld2011tidyinguploose pages 4-5)
3. Defective end processing leads to delayed single-strand-break/base-excision repair and, potentially, selected double-strand-break repair by NHEJ. Patient fibroblast literature more consistently demonstrates SSBR impairment; the extent of DSBR impairment varies by allele and assay. (hulmakova2025theroleof pages 32-35, jiang2022mutationsofthe pages 13-13)
4. Persistent strand-break intermediates lead to transcriptional obstruction, PARP-related stress, genome instability, or cell dysfunction. These consequences are supported across PNKP and related strand-break-repair models but are not fully demonstrated in CMT2B2 patient axons. (jiang2022mutationsofthe pages 12-13, dumitrache2017polynucleotidekinasephosphatase(pnkp) pages 1-2)
5. Accumulated DNA-repair stress is inferred to preferentially injure long-lived, metabolically active peripheral neurons and cerebellar circuits. Neuronal susceptibility is biologically supported by high oxidative metabolism, longevity, and transcriptional activity; selective involvement of particular axons remains unresolved. (dumitrache2017polynucleotidekinasephosphatase(pnkp) pages 1-2)
6. Peripheral axonal dysfunction and degeneration lead to reduced CMAP/SNAP amplitudes, distal weakness, atrophy, sensory loss, and areflexia. This clinicophysiologic link is demonstrated in the human cohort. (leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)
7. A parallel cerebellar/oculomotor branch leads to dysarthria, gait ataxia, oculomotor abnormalities, and mild cerebellar atrophy. The clinical branch is demonstrated; its cellular mechanism is inferred from general PNKP neurobiology. (leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

Single-strand-break repair in detail

Oxidative damage, base-excision intermediates, and trapped topoisomerase-I lesions can leave 3′-phosphate, 3′-phosphoglycolate, or 5′-OH termini that cannot be directly ligated. PARP1 or PARP2 senses damaged chromatin and promotes recruitment of XRCC1. XRCC1 acts as a scaffold for PNKP, DNA polymerase β, and DNA ligase III. PNKP removes 3′ phosphate and phosphorylates 5′ hydroxyl; polymerase fills the gap and LIG3 seals the strand. XRCC1 can stimulate PNKP turnover by displacing it from processed products. Evidence also supports lesion-dependent alternative recruitment orders in which PNKP or APE1 engages an end before stable XRCC1 accumulation; neither model should be treated as universally exclusive. (weinfeld2011tidyinguploose pages 4-5, hulmakova2025theroleof pages 20-23)

A concise functional quotation from the mechanistic literature is that PNKP participates in both “XRCC1-based single-strand break/base-excision repair” and NHEJ. The neurologic relevance arises because unrepaired oxidative SSBs can block transcription in nondividing neurons. (dumitrache2017polynucleotidekinasephosphatase(pnkp) pages 1-2)

Double-strand-break repair

In NHEJ, PNKP binds the CK2-phosphorylated XRCC4 tail through its FHA domain, processes abnormal DNA ends, and facilitates subsequent ligation by DNA ligase IV. PNKP kinase activity supplies 5′ phosphate, while its phosphatase activity can remove 3′ phosphate. However, lack of immunodeficiency in most PNKP-affected people implies that V(D)J-associated end joining is sufficiently preserved by residual function or redundant processing. This helps explain why PNKP disease is neurologically prominent rather than a classic radiosensitive immunodeficiency. (hulmakova2025theroleof pages 32-35, weinfeld2011tidyinguploose pages 5-7)

Allelic spectrum: CMT2B2, AOA4, and MCSZ

• CMT2B2: adult-onset, neuropathy-predominant; slowly progressive axonal sensorimotor neuropathy with mild/variable ataxia, dysarthria, oculomotor signs, and cerebellar atrophy; no microcephaly, seizures, or developmental delay in the Costa Rican cohort. (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 6-8)
• AOA4: generally childhood-to-young-adult progressive cerebellar ataxia with oculomotor apraxia and axonal polyneuropathy. It is a neurodegenerative PNKP phenotype rather than a wholly separate pathway.
• MCSZ: typically congenital microcephaly, early often intractable seizures, developmental delay, and progressive cerebellar atrophy; neuropathy and ataxia may appear later. More than 40 affected individuals had been summarized by 2019, supporting a continuum from congenital neurodevelopmental disease to adult-onset neurodegeneration. (gatti2019fromcongenitalmicrocephaly pages 1-2, gatti2019fromcongenitalmicrocephaly pages 2-3)

The 2018 authors explicitly concluded that the Costa Rican presentation represented a milder “allelic effect.” Current evidence supports a residual-function continuum but not a deterministic rule linking one domain or activity to one phenotype. The same or nearby alleles can occur across overlapping syndromes; genetic background and unknown modifiers probably contribute. (leal2018thepolynucleotidekinase pages 1-2, gatti2019fromcongenitalmicrocephaly pages 1-2, hulmakova2025theroleof pages 32-35)

Molecular profiling and recent developments

No CMT2B2-specific transcriptomic, proteomic, metabolomic, lipidomic, single-cell, spatial-transcriptomic, CRISPR-screen, or integrated multi-omics dataset was identified. Recent work has nevertheless refined the wider PNKP field:

• A 2023 functional study of an AOA4 mutation linked defective DNA-end processing and oxidative-damage responses to neurodegeneration, strengthening the residual-function model, although it did not study the Costa Rican alleles directly.
• A 2024 MCSZ study reported novel variants associated with reduced SSBR, providing contemporary functional confirmation that impaired PNKP repair remains central to the allelic spectrum.
• A 2024 study identified cell-cycle-dependent regulation of PNKP in DNA replication and Okazaki-fragment maturation, expanding PNKP biology beyond canonical strand-break repair; relevance to adult peripheral axons is presently uncertain. (hulmakova2025theroleof pages 32-35, hulmakova2025theroleof pages 38-41)

Suggested GO terms include DNA 3′-phosphatase activity, polynucleotide 5′-hydroxyl-kinase activity, DNA single-strand-break repair, base-excision repair, nonhomologous end joining, cellular response to oxidative stress, DNA-damage response, and maintenance of genome stability. Suggested cell types are peripheral sensory neuron, lower motor neuron, cerebellar Purkinje cell, and Schwann cell; neuronal involvement is primary, whereas a primary Schwann-cell defect is not demonstrated.

7. Anatomical structures affected

The primary system is the peripheral nervous system, particularly long motor and sensory axons of distal limbs. Secondary structures include distal skeletal muscle, which undergoes neurogenic wasting, and feet/hands, which develop imbalance-related deformity. Cerebellar and oculomotor pathways are variably involved. Findings are usually bilateral and length-dependent rather than focal or unilateral. (leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

Candidate anatomical annotations include peripheral nerve, spinal nerve, motor neuron axon, sensory neuron axon, skeletal muscle of limb, hand, foot, cerebellum, and ocular motor system. Candidate UBERON concepts should be identifier-validated locally. At the subcellular level, relevant compartments are nucleus, chromatin, DNA-repair complex, and possibly mitochondrion; only the nuclear strand-break-repair role is firmly linked to CMT2B2.

8. Temporal development

CMT2B2 onset is chronic and insidious, usually in adulthood in the known Costa Rican cases. Early disease consists of gait disturbance, falls, and distal sensorimotor symptoms. Intermediate disease adds progressive weakness, wasting, proprioceptive loss, dysarthria, and ataxia. Advanced disease may require a wheelchair, although progression is variable. No episodic attacks, relapses, or spontaneous remissions were reported. The disorder is lifelong and progressive. (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

There is no validated staging system, annualized progression rate, or proven therapeutic window. Earlier identification is nevertheless clinically useful before fixed contractures, recurrent falls, or severe deconditioning emerge.

9. Inheritance and population

Inheritance is autosomal recessive. For two carrier parents, each pregnancy has a 25% probability of an affected child, 50% probability of an unaffected carrier, and 25% probability of inheriting neither familial allele. Both sexes are expected to be affected equally. Anticipation is not expected. Penetrance appears high among reported biallelic adults, but the denominator is too small and ascertained to claim complete penetrance. Expressivity is variable. (leal2018thepolynucleotidekinase pages 1-2, leal2018thepolynucleotidekinase pages 4-6)

Consanguinity was central to discovery of the homozygous extended family. The recurrence of p.Gln517Ter and p.Thr408del among Costa Rican cases suggests population enrichment or shared ancestry, but formal haplotype/founder analysis and carrier-frequency data are unavailable. No prevalence per 100,000, incidence, sex ratio, or global geographic distribution can be calculated. The known disease-specific evidence is geographically concentrated in Costa Rica; broader PNKP disease has been reported internationally, but it cannot be used as CMT2B2 epidemiology.

10. Diagnostics

Clinical and electrophysiologic assessment

Evaluation should include detailed pedigree and consanguinity history; neurologic examination of distal power, atrophy, reflexes, proprioception, gait, speech, cerebellar function, and eye movements; and nerve-conduction studies/EMG. The expected electrophysiologic pattern is severe axonal sensorimotor polyneuropathy with low or absent SNAPs and CMAPs. Brain MRI is indicated when ataxia, dysarthria, or oculomotor findings are present and may show mild cerebellar atrophy. (leal2018thepolynucleotidekinase pages 6-8, leal2018thepolynucleotidekinase pages 4-6)

Serum alpha-fetoprotein, albumin, and cholesterol may be abnormal elsewhere in the PNKP spectrum, particularly AOA4/MCSZ, but no laboratory analyte is a validated CMT2B2 biomarker. A broader nine-patient PNKP cohort found increasing alpha-fetoprotein and progressive cerebellar atrophy across the spectrum; these findings should be considered supportive, not subtype-defining. (garrelfs2020eurresearchinformation pages 1-3)

Genetic-testing strategy

1. Use a hereditary neuropathy panel that includes PNKP and genes for axonal CMT, or a combined neuropathy/ataxia panel when cerebellar signs are present.
2. If negative or the phenotype is atypical, perform trio/family WES or WGS. Exome reanalysis was decisive in correcting the original CMT2B2 assignment. (leal2018thepolynucleotidekinase pages 1-2)
3. Confirm candidate variants by an orthogonal method where required, establish phase and segregation, and review copy-number calling because a sequence-only assay may miss exon-level deletions.
4. Do not diagnose CMT2B2 from MED25 p.Ala335Val alone.

Single-gene PNKP testing is efficient when the familial variants are known. CMA, karyotype, FISH, mitochondrial DNA analysis, and repeat-expansion testing are not first-line for a classic familial case, although they may be used in unresolved differential diagnosis. RNA sequencing may clarify a suspected splice variant but is not a routine validated CMT2B2 assay.

Differential diagnosis

Important alternatives include other axonal CMT genes; AOA1/APTX, AOA2/SETX, and AOA4/PNKP; spinocerebellar ataxia with axonal neuropathy; Friedreich ataxia; POLG-related disease; RFC1 biallelic expansion disease; mitochondrial neuropathies; and acquired toxic, metabolic, inflammatory, or nutritional neuropathy. Adult neuropathy plus dysarthria/oculomotor findings and recessive inheritance should elevate PNKP.

Screening

Population and newborn screening are not indicated because prevalence, carrier frequency, and early intervention benefit are unknown. Cascade testing of adult relatives and targeted carrier testing of reproductive partners are appropriate after molecular confirmation.

11. Outcomes and prognosis

No disease-specific survival curve, mortality rate, life-expectancy estimate, or 5-/10-year outcome is available. The principal morbidity is progressive motor and sensory disability, falls, deformity, loss of ambulation, and communication difficulty. At least one patient became wheelchair-dependent rapidly, whereas another retained mobility with mild ataxia, demonstrating substantial prognostic variability. (leal2018thepolynucleotidekinase pages 4-6)

Respiratory failure, cardiomyopathy, immunodeficiency, and systemic organ failure are not established defining complications. A broader PNKP cohort found no consistent immunodeficiency or cancer predisposition; isolated malignancies should not be interpreted as a proven syndrome-level risk. (garrelfs2020eurresearchinformation pages 1-3)

No validated prognostic biomarker exists. Baseline motor function, rate of decline, electrophysiologic axonal loss, falls, contractures, and cerebellar involvement are reasonable clinical monitoring variables but not validated prediction models.

12. Treatment

There is no approved disease-modifying therapy, PNKP replacement, gene therapy, RNA therapy, or genome-editing treatment for CMT2B2. No relevant disease-specific interventional trial was identified in the ClinicalTrials.gov search; therefore, response rates and molecular-treatment adverse-event data do not exist.

Current real-world management is multidisciplinary and supportive:

• physical therapy, stretching, balance and gait training, and individualized low-to-moderate intensity conditioning;
• occupational therapy and adaptive strategies for hand weakness;
• ankle–foot orthoses, custom footwear, canes, walkers, or wheelchairs;
• fall prevention and home-safety assessment;
• orthopedic review for progressive cavovarus deformity, contracture, or tendon imbalance, with surgery considered individually;
• standard neuropathic-pain treatment where needed;
• speech-language therapy for dysarthria and swallowing assessment if symptoms emerge;
• neurologic surveillance for ataxia, eye-movement dysfunction, and functional decline.

Candidate NCIT intervention concepts are physical therapy, occupational therapy, orthotic device, assistive device, exercise therapy, pain management, speech therapy, genetic counseling, and orthopedic surgery. These interventions may preserve independence or address complications, but there are no CMT2B2-specific controlled outcome estimates.

13. Prevention

Primary prevention through lifestyle or vaccination is not applicable to a Mendelian recessive disorder. Reproductive prevention options include genetic counseling, carrier testing of relatives and partners, prenatal diagnosis, and preimplantation genetic testing for a known familial genotype. Secondary prevention consists of molecular diagnosis before substantial disability and anticipatory assessment of gait, falls, deformity, and cerebellar symptoms. Tertiary prevention includes orthoses, exercise, contracture prevention, safe mobility, pain treatment, and avoidance of unnecessary neurotoxic exposure. There is no prophylactic drug.

14. Other species and natural disease

No well-established naturally occurring veterinary disease equivalent to human p.Gln517Ter/p.Thr408del CMT2B2 was identified. There is no breed association, zoonotic potential, transmission, or cross-species infectious susceptibility. PNKP orthologs and DNA-end-processing functions are evolutionarily conserved, which supports comparative modeling, but database-specific NCBI Gene, Taxon, and VBO identifiers should be verified before knowledge-base insertion.

15. Model organisms and experimental systems

Complete PNKP loss is embryonically lethal in mice. Conditional neural deletion demonstrated that PNKP is required for neurogenesis and genome stability through multiple DNA-repair pathways, strongly supporting nervous-system dependence on PNKP. These models reproduce severe neurodevelopmental consequences more closely than adult-onset CMT2B2 and should not be described as exact CMT2B2 models. (hulmakova2025theroleof pages 32-35, jiang2022mutationsofthe pages 13-13)

Cellular systems include PNKP-deficient or complemented human cell lines, patient fibroblasts, DNA-end-processing assays, clonogenic genotoxic-sensitivity assays, and structural/biochemical reconstitution. These demonstrate impaired repair, persistent abnormal ends, and sensitivity to oxidative, radiomimetic, or topoisomerase-associated damage. Their limitations are the absence of long axons, neuron–glia interactions, and organismal aging. (weinfeld2011tidyinguploose pages 4-5, jiang2022mutationsofthe pages 13-13, jiang2022mutationsofthe pages 12-13)

No validated knock-in mouse, zebrafish, Drosophila, organoid, or patient-derived motor/sensory-neuron model carrying exactly p.Gln517Ter alone or p.Gln517Ter/p.Thr408del was identified in the evidence reviewed through 2024. Developing isogenic iPSC-derived peripheral sensory and motor neurons with these genotypes is a high-priority research need.

Evidence quality and knowledge gaps

The PNKP reassignment is convincing because it integrates exome discovery, recessive segregation, two genotypic configurations, multiple subjects, biological plausibility, and a coherent allelic spectrum. However, nearly every quantitative disease-characteristic field remains limited by the small, geographically concentrated cohort. Prevalence, penetrance, carrier frequency, longitudinal progression, survival, quality-of-life scores, biomarkers, modifiers, treatment outcomes, and environmental interactions are unknown. Mechanistic evidence is strong for PNKP generally but only partly allele- and cell-type-specific for CMT2B2. Thus, the knowledge-base entry should clearly separate demonstrated human CMT2B2 observations, broader human PNKP-spectrum evidence, experimental PNKP mechanism, and inferred selective axonal pathophysiology.

References

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4. (gatti2019fromcongenitalmicrocephaly pages 1-2): Marta Gatti, Stefania Magri, Lorenzo Nanetti, Elisa Sarto, Daniela Di Bella, Ettore Salsano, Chiara Pantaleoni, Caterina Mariotti, and Franco Taroni. From congenital microcephaly to adult onset cerebellar ataxia: distinct and overlapping phenotypes in patients with pnkp gene mutations. American Journal of Medical Genetics Part A, 179:2277-2283, Aug 2019. URL: https://doi.org/10.1002/ajmg.a.61339, doi:10.1002/ajmg.a.61339. This article has 29 citations.

5. (weinfeld2011tidyinguploose pages 5-7): Michael Weinfeld, Rajam S. Mani, Ismail Abdou, R. Daniel Aceytuno, and J.N. Mark Glover. Tidying up loose ends: the role of polynucleotide kinase/phosphatase in dna strand break repair. Trends in biochemical sciences, 36 5:262-71, May 2011. URL: https://doi.org/10.1016/j.tibs.2011.01.006, doi:10.1016/j.tibs.2011.01.006. This article has 247 citations and is from a domain leading peer-reviewed journal.

6. (weinfeld2011tidyinguploose pages 4-5): Michael Weinfeld, Rajam S. Mani, Ismail Abdou, R. Daniel Aceytuno, and J.N. Mark Glover. Tidying up loose ends: the role of polynucleotide kinase/phosphatase in dna strand break repair. Trends in biochemical sciences, 36 5:262-71, May 2011. URL: https://doi.org/10.1016/j.tibs.2011.01.006, doi:10.1016/j.tibs.2011.01.006. This article has 247 citations and is from a domain leading peer-reviewed journal.

7. (dumitrache2017polynucleotidekinasephosphatase(pnkp) pages 1-2): Lavinia C. Dumitrache and Peter J. McKinnon. Polynucleotide kinase-phosphatase (pnkp) mutations and neurologic disease. Mechanisms of Ageing and Development, 161:121-129, Jan 2017. URL: https://doi.org/10.1016/j.mad.2016.04.009, doi:10.1016/j.mad.2016.04.009. This article has 95 citations and is from a peer-reviewed journal.

8. (hulmakova2025theroleof pages 20-23): A Hulmáková. The role of polynucleotide kinase/phosphatase in dna strand break repair and its implications in human diseases. Unknown journal, 2025.

9. (jiang2022mutationsofthe pages 13-13): Bingcheng Jiang, Cameron Murray, Bonnie L. Cole, J. N. Mark Glover, Gordon K. Chan, Jean Deschenes, Rajam S. Mani, Sudip Subedi, John D. Nerva, Anthony C. Wang, Christina M. Lockwood, Heather C. Mefford, Sarah E. S. Leary, Jeffery G. Ojemann, Michael Weinfeld, and Chibawanye I. Ene. Mutations of the dna repair gene pnkp in a patient with microcephaly, seizures, and developmental delay (mcsz) presenting with a high-grade brain tumor. Scientific Reports, Mar 2022. URL: https://doi.org/10.1038/s41598-022-09097-w, doi:10.1038/s41598-022-09097-w. This article has 17 citations and is from a peer-reviewed journal.

10. (garrelfs2020eurresearchinformation pages 1-3): MR Garrelfs, S Takada, EJ Kamsteeg, and S Pegge. Eur research information portal. Unknown journal, 2020.

11. (gatti2019fromcongenitalmicrocephaly pages 2-3): Marta Gatti, Stefania Magri, Lorenzo Nanetti, Elisa Sarto, Daniela Di Bella, Ettore Salsano, Chiara Pantaleoni, Caterina Mariotti, and Franco Taroni. From congenital microcephaly to adult onset cerebellar ataxia: distinct and overlapping phenotypes in patients with pnkp gene mutations. American Journal of Medical Genetics Part A, 179:2277-2283, Aug 2019. URL: https://doi.org/10.1002/ajmg.a.61339, doi:10.1002/ajmg.a.61339. This article has 29 citations.

12. (hulmakova2025theroleof pages 32-35): A Hulmáková. The role of polynucleotide kinase/phosphatase in dna strand break repair and its implications in human diseases. Unknown journal, 2025.

13. (jiang2022mutationsofthe pages 12-13): Bingcheng Jiang, Cameron Murray, Bonnie L. Cole, J. N. Mark Glover, Gordon K. Chan, Jean Deschenes, Rajam S. Mani, Sudip Subedi, John D. Nerva, Anthony C. Wang, Christina M. Lockwood, Heather C. Mefford, Sarah E. S. Leary, Jeffery G. Ojemann, Michael Weinfeld, and Chibawanye I. Ene. Mutations of the dna repair gene pnkp in a patient with microcephaly, seizures, and developmental delay (mcsz) presenting with a high-grade brain tumor. Scientific Reports, Mar 2022. URL: https://doi.org/10.1038/s41598-022-09097-w, doi:10.1038/s41598-022-09097-w. This article has 17 citations and is from a peer-reviewed journal.

14. (hulmakova2025theroleof pages 38-41): A Hulmáková. The role of polynucleotide kinase/phosphatase in dna strand break repair and its implications in human diseases. Unknown journal, 2025.

Artifacts

• Edison artifact artifact-00

Reference Validation

Checked with linkml-reference-validator 0.2.1.

All extracted references resolved successfully.

Term Validation

Checked with linkml-term-validator 0.4.5, through the ols: adapter.

Terms the report names something else

These identifiers resolve, so nothing about them looks wrong, and the ontology calls them something unrelated to what the report calls them. That usually means the identifier is not the one the sentence needs:

• MONDO:0011570 (3 mentions) - the report calls it "if available"; MONDO calls it Charcot-Marie-Tooth disease type 2B2