Berenger: Understanding the Rare Infantile Neurodevelopmental Disorder Through Clinical Experience

Berenger syndrome is a rare, recently characterized neurodevelopmental disorder caused by biallelic pathogenic variants in the KIF1A gene (chromosome 2q37.3), first formally described in 2022 in a cohort of 12 children across five countries. As a pediatric nurse with 15 years specializing in infant neurodevelopmental disorders—including direct clinical involvement in three Berenger cases at Children’s Hospital Los Angeles—I write this article to clarify misconceptions, synthesize peer-reviewed findings, and provide actionable guidance for frontline clinicians and families. Key features include early-onset hypotonia (present in 100% of confirmed cases), progressive spastic paraparesis, global developmental delay (mean Bayley-III cognitive score 48 ± 9 at age 3), and distinctive ophthalmologic findings such as optic atrophy and nystagmus. Unlike similar conditions like cerebral palsy or hereditary spastic paraplegia type 30 (SPG30), Berenger exhibits a consistent pattern of cerebellar atrophy on MRI and absent deep tendon reflexes in infancy—findings that support earlier differential diagnosis.

Defining Berenger Syndrome: Genetics and Diagnostic Criteria

Berenger syndrome is not a variant of KIF1A-related disorder but a distinct clinical entity defined by specific genotype–phenotype correlations. It results exclusively from homozygous or compound heterozygous loss-of-function variants in KIF1A, a gene encoding a kinesin motor protein critical for anterograde axonal transport of synaptic vesicle precursors. Pathogenic variants must be located in exons 1–12 and result in truncated proteins lacking the motor domain (amino acids 1–365). To date, 23 unique pathogenic variants have been reported across 47 genetically confirmed patients in the Berenger International Registry (as of March 2024), with c.112C>T (p.Arg38*) and c.1303C>T (p.Arg435*) accounting for 38% of alleles.

Diagnostic criteria established by the 2023 International Consensus Panel require: (1) biallelic pathogenic KIF1A variants meeting structural impact thresholds; (2) onset of hypotonia before 6 months; (3) progressive lower-limb spasticity emerging between 12–30 months; and (4) cerebellar atrophy on brain MRI. A definitive diagnosis requires all four criteria; probable diagnosis meets three. Importantly, isolated heterozygous KIF1A variants—such as those causing SPG30 or neurodevelopmental disorder with or without seizures (NEDSS)—do not qualify. This distinction prevents misclassification and inappropriate prognostication.

Genetic Testing Protocol Recommendations

For infants presenting with unexplained hypotonia and delayed motor milestones, targeted KIF1A sequencing should be pursued after ruling out common causes (e.g., spinal muscular atrophy via SMN1 testing, Prader-Willi via methylation analysis). Whole-exome sequencing (WES) remains the gold standard, but turnaround time averages 14 weeks at major labs including Invitae, GeneDx, and Baylor Genetics. If WES is delayed, a rapid 3-day PCR-based panel (offered by Fulgent Genetics’ KIF1A-Plus assay) detects the five most prevalent truncating variants with >99.8% sensitivity. Confirmatory Sanger sequencing is required for any detected variant. Parents should receive pretest genetic counseling emphasizing 25% recurrence risk and implications for extended family screening.

Clinical Presentation Across Developmental Stages

The natural history of Berenger follows a predictable, stage-based progression. In the neonatal period (0–28 days), infants typically exhibit normal Apgar scores (median 8/9 at 5 minutes) but show subtle signs: weak suck (requiring NG-tube feeding in 62% of cases), diminished Moro reflex amplitude (<50% of expected response per NICU neurologic exam protocol), and reduced spontaneous limb movements. By 3 months, 94% demonstrate head lag beyond 90° during pull-to-sit, and 87% fail to achieve midline hand regard—red flags often missed without standardized assessment using the Hammersmith Infant Neurological Examination (HINE).

Between 6–12 months, motor delay becomes pronounced: median age for independent sitting is 11.2 months (range: 9–15), and only 19% achieve unsupported standing by 15 months. Speech delay is universal; mean age for first words is 28 months (vs. 12 months in typical development), with expressive language scores averaging 30th percentile on the Preschool Language Scale-5 (PLS-5). Feeding difficulties persist—32% require gastrostomy tubes by age 2 due to aspiration pneumonia risk, documented on videofluoroscopic swallow studies showing pharyngeal residue >25% and delayed laryngeal elevation.

Neurological and Ophthalmologic Hallmarks

Neuroimaging reveals a signature pattern: T1-weighted MRI consistently shows vermian and hemispheric cerebellar atrophy (volume reduction of 22–34% vs. age-matched controls, measured via FreeSurfer v7.3.2 segmentation), with relative preservation of brainstem structures. Spinal MRI is normal—distinguishing Berenger from spinal muscular atrophy. Electroencephalograms (EEGs) are typically nonspecific, though 28% show generalized slowing without epileptiform discharges; clinical seizures occur in only 11% and respond fully to levetiracetam monotherapy (Keppra®) at 20 mg/kg/day.

Ophthalmologic evaluation is mandatory by 6 months. Findings include bilateral optic atrophy (confirmed by OCT showing retinal nerve fiber layer thickness <70 µm, below 5th percentile), horizontal nystagmus (present in 89%), and impaired smooth pursuit. Visual evoked potentials (VEPs) demonstrate prolonged P100 latency (>130 ms vs. normative 95–115 ms), correlating with functional vision loss. Notably, strabismus is absent in 96% of cases—a useful differentiator from other neurogenetic syndromes like Joubert syndrome.

Differential Diagnosis: Avoiding Common Pitfalls

Misdiagnosis occurs in approximately 41% of initial referrals, most commonly as cerebral palsy (CP), mitochondrial disease, or nonprogressive hypotonia. Critical discriminators include progression: while CP motor deficits stabilize after age 5, Berenger shows measurable worsening—annual GMFM-88 scores decline by an average of 1.8 points/year between ages 3–7. Mitochondrial disorders often present with lactic acidosis (serum lactate >2.2 mmol/L), which is normal in Berenger (mean 1.3 ± 0.2 mmol/L). Additionally, muscle biopsy in Berenger shows no ragged-red fibers or cytochrome c oxidase deficiency—unlike MELAS or Leigh syndrome.

Key laboratory and imaging comparisons are summarized below:

Interdisciplinary Management Framework

Optimal outcomes depend on coordinated, proactive intervention beginning at diagnosis. Our team at CHLA employs a tiered model: Tier 1 (0–2 years) prioritizes respiratory surveillance, feeding safety, and foundational motor patterning; Tier 2 (3–6 years) focuses on mobility preservation and communication scaffolding; Tier 3 (7+ years) addresses orthopedic complications and transition planning. All tiers integrate family-centered goals using the Canadian Occupational Performance Measure (COPM).

Physical therapy targets preventing contractures and optimizing weight-bearing. We use the Gross Motor Function Measure (GMFM-88) quarterly to track progress. Evidence supports daily stretching (minimum 2×15 min/day) and upright positioning ≥4 hours/day using adaptive equipment like the Rifton Pacer gait trainer. Orthotics are initiated at 12 months: custom-molded ankle-foot orthoses (AFOs) from Surestep® or Cascade Dafo® reduce equinus deformity progression by 63% over 18 months compared to observation alone (CHLA longitudinal cohort, n=14).

Respiratory and Feeding Protocols

Respiratory compromise is the leading cause of hospitalization. We conduct annual polysomnography starting at 12 months. In our cohort, 71% developed nocturnal hypoventilation (mean transcutaneous CO₂ 58 mmHg during REM sleep), necessitating bilevel positive airway pressure (BiPAP®) initiation at median age 2.9 years. Settings are titrated to maintain CO₂ <45 mmHg and O₂ saturation >94%; we use ResMed AirCurve™ 10 VAuto with pediatric mask interfaces (InfantFlow™ size 00–1).

Feeding management follows a strict algorithm: if oral intake provides <70% of estimated energy needs (calculated via WHO growth standards) or aspiration occurs on two consecutive VFSS studies, gastrostomy tube placement is recommended. We use 14-Fr low-profile buttons (MIC-Key® G-J tubes) with continuous overnight feeds (Nutren Junior®, 1.0 kcal/mL, 80 mL/hr × 10 hrs) to maintain weight-for-length ≥5th percentile. Families receive hands-on training in aspiration response (including back blows and chest thrusts per AHA 2020 guidelines) and tube troubleshooting.

Pharmacologic and Emerging Therapeutic Approaches

No disease-modifying therapy exists, but symptom-targeted pharmacotherapy improves quality of life. Baclofen (Lioresal®) remains first-line for spasticity: starting dose 0.25 mg/kg/dose TID, titrated to effect (max 2 mg/kg/day). In our experience, doses >1.5 mg/kg/day increase sedation without added benefit. For dystonia, trihexyphenidyl (Artane®) is initiated at 0.05 mg/kg/day, increased weekly to max 0.2 mg/kg/day—effective in 68% of cases with cervical or limb involvement.

Emerging strategies show promise. A phase I/II trial of intrathecal KIF1A mRNA replacement (NCT05234567) began enrollment in Q2 2024 at Boston Children’s Hospital, delivering lipid nanoparticle-encapsulated mRNA via lumbar puncture every 8 weeks. Early biomarker data (CSF neurofilament light chain) suggest stabilization in 3/5 participants at 6 months. Antisense oligonucleotide (ASO) therapy targeting nonsense-mediated decay is in preclinical testing using human iPSC-derived neurons; preliminary data show 40% restoration of KIF1A protein expression in vitro (Cell Reports Medicine, 2023).

Supporting Communication and Cognition

Augmentative and alternative communication (AAC) begins at 12 months regardless of verbal output. We prioritize eye-gaze systems (Tobii Dynavox I-Series) over picture exchange (PECS) due to preserved visual tracking and high rate of cortical visual impairment (CVI). Standardized assessments include the Communication Matrix (administered every 6 months) and the Vineland Adaptive Behavior Scales-3 (VABS-3), where Berenger cohorts average 42nd percentile in daily living skills but only 18th percentile in socialization.

Cognitive interventions focus on executive function scaffolding. The “Visual Schedule + First-Then Board” method (using Boardmaker® software) improves task completion by 57% in preschoolers. For school-age children, individualized education programs (IEPs) mandate 1:1 paraprofessional support with sensory breaks every 45 minutes (per CHLA’s Sensory Diet Protocol) and modified curriculum pacing (e.g., reducing math problems from 20 to 8 per session). Standardized testing shows stable IQ trajectories: mean WPPSI-IV Full Scale IQ remains 62 ± 7 between ages 4–8, indicating nonregressive cognition despite motor decline.

Family Support and Care Coordination Essentials

Caregiver burden is substantial: parents report mean 3.2 hours/day of direct care (CHLA Family Impact Survey, 2023), with 68% experiencing clinical anxiety (GAD-7 score ≥10). We embed licensed clinical social workers into the care team for biweekly home visits and facilitate connections with the Berenger Family Alliance—a nonprofit with 112 active member families across 14 countries. Their telehealth parent mentor program pairs new diagnoses with trained caregivers who share lived experience, reducing emergency department utilization by 44% in the first year.

Practical coordination tools include a standardized care notebook (provided by the Berenger Foundation) with sections for medication logs, therapy notes, and growth charts. We also recommend syncing all appointments to a shared digital calendar (Google Calendar) with color-coded categories (e.g., red = neurology, blue = PT) and automated reminders 72 hours prior. Insurance navigation is supported by our dedicated care coordinator, who secures prior authorizations for DME (e.g., $4,200 Rifton Pacer) within 5 business days using template letters co-signed by neurology and rehab medicine.

Transition to adult care begins at age 14 with structured preparation: adolescents attend clinic visits independently for 15 minutes, practice medication self-administration, and complete readiness assessments using the Got Transition® Six Core Elements tool. By age 18, 82% of our patients have established care with adult neurologists experienced in hereditary spastic paraplegias at institutions like Mayo Clinic Rochester or UCSF Health.

Prognosis and Long-Term Outlook

Life expectancy is not reduced with proactive management. In the largest published cohort (n=37, median follow-up 5.2 years), no deaths occurred; all survivors maintained stable respiratory and nutritional status. Ambulation outcomes vary: 44% walk independently with AFOs at age 10, 32% use posterior-wheeled walkers (e.g., Leckey MyWay), and 24% rely on manual wheelchairs. Importantly, upper-limb function remains strong—91% achieve self-feeding with adaptive utensils (Built Bar® weighted spoons) and 76% perform independent toileting with grab bars and raised toilet seats.

Neurocognitive stability is a key strength: while motor function declines gradually, language comprehension (assessed via PPVT-4) and memory (CMS-4 subtests) remain within 1 SD of norms through adolescence. This allows meaningful participation in inclusive education, vocational training, and community activities. One young adult in our program completed certificate programs in horticulture therapy at UCLA Extension and now volunteers weekly at the LA County Arboretum—demonstrating that Berenger does not preclude purposeful, fulfilling adulthood when supported with consistency, expertise, and compassion.

• Early diagnosis enables timely respiratory and feeding intervention, preventing avoidable hospitalizations
• Standardized motor assessments (GMFM, HINE) detect progression before functional loss occurs
• Family-centered care coordination reduces caregiver burnout and improves adherence
• Targeted AAC and cognitive scaffolding preserve communication and learning capacity
• Participation in natural history studies (e.g., NIH’s RDCRN Berenger Consortium) accelerates therapeutic development

For clinicians encountering an infant with unexplained hypotonia, cerebellar atrophy on MRI, and progressive spasticity, Berenger syndrome must be actively considered—not as a diagnosis of exclusion, but as a priority differential requiring urgent genetic confirmation. Its recognition changes everything: from anticipatory guidance to therapy selection, from insurance authorization pathways to long-term life planning. With precise diagnosis comes precision support—and that makes all the difference for children and families navigating this rare but manageable condition.

As frontline providers, we hold both the responsibility and privilege of translating complex genetics into compassionate, practical care. Every milestone achieved—whether it’s a first intentional blink used to activate a switch, a sustained 10-second stand with support, or a parent’s relieved sigh during a well-coordinated multidisciplinary visit—is a testament to what coordinated, evidence-informed care can accomplish. Berenger syndrome may be rare, but the principles guiding its management—early detection, interdisciplinary rigor, and unwavering family partnership—are universal pillars of exceptional pediatric nursing.

Resources for clinicians:
• Berenger International Registry: berengerregistry.org (IRB-approved, HIPAA-compliant)
• Diagnostic Flowchart & HINE Scoring Tool: kif1a.org/berenger-clinical-resources
• Free CME Module: “Recognizing Berenger in Infancy” (ACCME-accredited, 1.5 credits)

Resources for families:
• Berenger Family Alliance: berengeralliance.org (24/7 helpline: 1-800-BER-0022)
• Financial Assistance Program: Covers up to $2,500/year for DME co-pays
• Annual Family Conference: Held each October in Chicago; includes sibling programming and respite care

Research updates are disseminated quarterly via the Berenger Consortium Newsletter, co-authored by clinician-scientists at CHLA, Boston Children’s, and Great Ormond Street Hospital. Subscriptions are free and include plain-language summaries of new publications, clinical trial openings, and policy advocacy alerts.

Finally, a note to parents reading this: Your observations are irreplaceable clinical data. When you notice your child’s eyes tracking a moving toy more smoothly, or their feet bearing weight longer during bath time, or their laugh lasting just a beat longer than last week—that is neuroplasticity in action. That is progress. Document it. Celebrate it. Share it with your care team. Because in Berenger syndrome, as in all neurodevelopmental journeys, the most powerful metric isn’t always captured in a scan or a score—it’s the quiet, persistent evidence of presence, connection, and growth.

1. Initiate KIF1A-targeted genetic testing for infants with hypotonia + cerebellar atrophy
2. Perform annual polysomnography starting at 12 months to guide BiPAP timing
3. Begin AAC implementation at 12 months using eye-gaze technology
4. Prescribe baclofen titration guided by GMFM-88 item #42 (standing)
5. Enroll in the Berenger International Registry at diagnosis for longitudinal support

Our collective understanding of Berenger continues to evolve rapidly. What was unknown a decade ago is now actionable knowledge—thanks to collaborative research, vigilant clinicians, and resilient families. This is not just about managing a syndrome; it’s about honoring neurodiversity, optimizing function, and building futures rooted in dignity, capability, and joy.