👪

Inheritance

1

X-linked recessive inheritance HP:0001419

L1 syndrome is inherited in an X-linked recessive manner. Affected individuals are usually hemizygous males; heterozygous female carriers are usually unaffected but may occasionally show (typically mild) manifestations, plausibly due to skewed X-inactivation.

X-linked recessive inheritance

Show evidence (2 references)

PMID:20301657 SUPPORT Human Clinical

"L1 syndrome is inherited in an X-linked manner."

GeneReviews establishes X-linked inheritance for L1 syndrome.

PMID:15662685 SUPPORT Human Clinical

"In this family, nine X-linked hydrocephalus and five female carriers were found in three generations"

A multigenerational pedigree with affected males and asymptomatic female carriers supports X-linked recessive transmission.

◆

Subtypes

4

X-linked hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS)

L1CAM hgnc:6470

The most severe end of the L1 spectrum. Affected males are born with severe congenital hydrocephalus due to stenosis of the aqueduct of Sylvius, adducted thumbs, and spasticity, with severe intellectual disability. Prenatal-onset hydrocephalus can lead to stillbirth or early infant death.

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"Males with HSAS are born with severe hydrocephalus, adducted thumbs, and spasticity; intellectual disability is severe."

GeneReviews defines the severe HSAS phenotype within the L1 spectrum.

MASA syndrome (mental retardation, aphasia, spastic paraplegia, adducted thumbs)

L1CAM hgnc:6470

A milder end of the L1 spectrum characterized by mental retardation (intellectual disability), aphasia (delayed speech), spastic paraplegia (shuffling gait), and adducted thumbs. MASA includes X-linked complicated hereditary spastic paraplegia type 1.

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"MASA (mental retardation ... aphasia ... spastic paraplegia ... adducted thumbs) syndrome including X-linked complicated hereditary spastic paraplegia type 1."

GeneReviews defines the MASA phenotype, which subsumes X-linked complicated hereditary spastic paraplegia type 1 (SPG1), within the L1 spectrum.

X-linked complicated hereditary spastic paraplegia type 1 (SPG1)

L1CAM hgnc:6470

The spastic paraplegia-predominant presentation of the L1 spectrum, in which progressive spasticity and gait disturbance from corticospinal tract involvement dominate the clinical picture. SPG1 falls within the MASA end of the spectrum.

Show evidence (1 reference)

PMID:11438988 SUPPORT Human Clinical

"L1 disease is a group of overlapping clinical phenotypes including X-linked hydrocephalus, MASA syndrome, spastic paraparesis type 1, and X-linked agenesis of corpus callosum."

The foundational review lists spastic paraparesis type 1 (SPG1) as one of the overlapping L1 phenotypes.

X-linked complicated corpus callosum agenesis

L1CAM hgnc:6470

A presentation in which agenesis or hypoplasia of the corpus callosum is a prominent feature, accompanied by variable spasticity, intellectual disability, and ventricular abnormalities.

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"X-linked complicated corpus callosum agenesis."

GeneReviews lists X-linked complicated corpus callosum agenesis as one of the L1 syndrome clinical phenotypes.

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Pathophysiology

4

Defective L1CAM Neural Cell Adhesion

Loss-of-function or hypomorphic variants in L1CAM impair the function of the L1 cell adhesion molecule, a single-pass transmembrane glycoprotein of the immunoglobulin superfamily expressed in neurons and Schwann cells. L1 is essential for nervous system development, mediating cell adhesion, signaling, and membrane trafficking. Mutations are distributed across the functional protein domains; the precise mechanisms by which they cause loss of L1 function are incompletely understood.

neuron CL:0000540 myelinating Schwann cell CL:0000218

L1CAM hgnc:6470 ⚠ ABNORMAL

cell adhesion GO:0007155 ↓ DECREASED nervous system development GO:0007399 ⚠ ABNORMAL myelination GO:0042552 ⚠ ABNORMAL

Downstream

Impaired Axon Guidance and Neurite Outgrowth Defective L1-mediated adhesion and signaling impairs axon guidance, neurite outgrowth, and neuronal migration during CNS development.

Show evidence (2 references)

PMID:11438988 SUPPORT Human Clinical

"The responsible gene, L1CAM, encodes the L1 protein which is a member of the immunoglobulin superfamily of neuronal cell adhesion molecules. The L1 protein is expressed in neurons and Schwann cells and seems to be essential for nervous system development and function."

Establishes L1CAM as the causal gene, its Ig-superfamily neural cell adhesion identity, and its expression in neurons and Schwann cells.

PMID:37569906 SUPPORT In Vitro

"The neural cell adhesion molecule L1 (also called L1CAM or CD171) functions not only in cell migration, but also in cell survival, differentiation, myelination, neurite outgrowth, and signaling during nervous system development and in adults."

Documents the breadth of L1 functions including myelination, cell survival, and differentiation, supporting myelination as an affected process in L1 dysfunction.

Impaired Axon Guidance and Neurite Outgrowth

L1 normally promotes neurite outgrowth, axon guidance/pathfinding, and neuronal migration. A 2023 mechanistic study showed that the L1-70 fragment binds LC3 (an autophagy-related protein) via an extracellular LC3-interacting region (LIR) motif in the fourth fibronectin type III domain, and that this interaction is required for L1-mediated neurite outgrowth and neuronal survival, linking L1CAM processing to autophagy-related machinery. Loss of L1 function therefore impairs the formation of major axon tracts.

neuron CL:0000540

axon guidance GO:0007411 ⚠ ABNORMAL neuron projection development GO:0031175 ↓ DECREASED neuron migration GO:0001764 ⚠ ABNORMAL

Downstream

Corticospinal Tract and Commissural Defects Failure of axon pathfinding and tract formation leads to maldevelopment of the corpus callosum and corticospinal tracts.

Aqueductal Stenosis and Hydrocephalus Abnormal neurodevelopment contributes to stenosis of the cerebral aqueduct and impaired CSF flow.

Show evidence (2 references)

PMID:37569906 SUPPORT In Vitro

"The disruption of the L1-LC3 interaction reduces L1-mediated neurite outgrowth and neuronal survival."

In vitro evidence that an L1CAM-dependent interaction is required for neurite outgrowth and neuronal survival, supporting impaired neurite outgrowth as a consequence of L1 dysfunction.

PMID:37569906 SUPPORT In Vitro

"L1-70 interacts with LC3 via the extracellular LIR motif in the fourth fibronectin type III domain"

Identifies the molecular L1-70/LC3 interaction underlying L1-dependent neurite outgrowth.

Corticospinal Tract and Commissural Defects

Defective axon guidance produces agenesis or hypoplasia of the corpus callosum and hypoplasia of the corticospinal tracts. These long-tract and midline commissural defects underlie the spastic paraplegia, gait disturbance, and contribute to intellectual disability in the L1 spectrum.

corpus callosum development GO:0022038 ⚠ ABNORMAL corticospinal tract morphogenesis GO:0021957 ⚠ ABNORMAL

corpus callosum UBERON:0002336 corticospinal tract UBERON:0002707

Show evidence (1 reference)

PMID:11438988 SUPPORT Human Clinical

"The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs."

Establishes corpus callosum and corticospinal tract defects as core neuroanatomic features of L1 disease.

Aqueductal Stenosis and Hydrocephalus

Stenosis of the aqueduct of Sylvius and impaired cerebrospinal fluid circulation produce ventriculomegaly and congenital hydrocephalus, the hallmark of HSAS/X-linked hydrocephalus. In severe cases this manifests prenatally and can be lethal; underlying brain malformations limit recovery even after neurosurgical CSF diversion.

cerebrospinal fluid circulation GO:0090660 ⚠ ABNORMAL

midbrain cerebral aqueduct UBERON:0002289

Show evidence (3 references)

PMID:34801143 SUPPORT Human Clinical

"Hydrocephalus, the abnormal accumulation and impaired circulation/clearance of cerebrospinal fluid, occurs as a common phenotypic feature of a diverse group of genetic syndromes."

A syndromic-hydrocephalus review (which discusses L1 syndrome) frames hydrocephalus as impaired CSF circulation/clearance.

PMID:30365056 SUPPORT Human Clinical

"The variants affect the highly conserved amino acids which are located in the key domains of the protein (the fourth Ig domain and second FnIII domain, respectively)."

Pathogenic L1CAM variants in conserved functional domains were identified in fetuses presenting with severe ventriculomegaly/hydrocephalus.

PMID:39135208 SUPPORT Human Clinical

"Approximately 5–15% of cases are associated with X-linked variations of L1CAM, known as L1 syndrome."

A congenital-hydrocephalus genetics review attributes 5-15% of aqueductal-stenosis (non-syndromic) congenital hydrocephalus to L1CAM (L1 syndrome), quantifying L1 syndrome as a leading cause of hydrocephalus from aqueductal stenosis.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

11

Musculoskeletal 1

Spastic paraplegia Spastic paraplegia HP:0001258

Course: PROGRESSIVE

Show evidence (1 reference)

PMID:11438988 SUPPORT Human Clinical

"The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs."

Spastic paraplegia is a core feature of the L1 spectrum.

Nervous System 6

Hydrocephalus Hydrocephalus HP:0000238

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"Males with HSAS are born with severe hydrocephalus, adducted thumbs, and spasticity; intellectual disability is severe."

GeneReviews documents severe congenital hydrocephalus in HSAS.

Ventriculomegaly Ventriculomegaly HP:0002119

Show evidence (1 reference)

PMID:32416898 SUPPORT Human Clinical

"We presented three fetuses with hydrocephalus and agenesis of the corpus callosum detected by ultrasound"

Fetal hydrocephalus/ventriculomegaly with corpus callosum agenesis was detected by ultrasound in L1CAM-mutation fetuses.

Agenesis of corpus callosum Agenesis of corpus callosum HP:0001274

Show evidence (1 reference)

PMID:32416898 SUPPORT Human Clinical

"We presented three fetuses with hydrocephalus and agenesis of the corpus callosum detected by ultrasound"

Agenesis of the corpus callosum was a presenting feature in L1CAM-mutation fetuses.

Hypoplasia of the corpus callosum Hypoplasia of the corpus callosum HP:0002079

Show evidence (1 reference)

PMID:11438988 SUPPORT Human Clinical

"The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs."

The foundational review lists agenesis or hypoplasia of the corpus callosum as a core feature.

Intellectual disability Intellectual disability HP:0001249

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"intellectual disability ranges from mild (IQ: 50-70) to moderate (IQ: 30-50)."

GeneReviews documents the range of intellectual disability in less severely affected males.

Aphasia Aphasia HP:0002381

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"MASA (mental retardation ... aphasia ... spastic paraplegia ... adducted thumbs) syndrome"

Aphasia (delayed speech) is one of the four components of the MASA acronym defined in GeneReviews.

Other 4

Aqueductal stenosis Aqueductal stenosis HP:0002410

Show evidence (1 reference)

PMID:30365056 SUPPORT Human Clinical

"Hydrocephalus due to aqueductal stenosis (HSAS; Online Mendelian Inheritance in Man #307000) is a rare X‑linked, recessively‑inherited disease characterized by severe hydrocephaly"

Defines HSAS as hydrocephalus due to aqueductal stenosis.

Adducted thumb Adducted thumb HP:0001181

Show evidence (1 reference)

PMID:11438988 SUPPORT Human Clinical

"The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs."

Adducted thumbs are listed among the characteristic features of L1 disease.

Shuffling gait Shuffling gait HP:0002362

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"spastic paraplegia shuffling gait adducted thumbs syndrome"

Shuffling gait (the spastic-paraplegia component) is part of the MASA acronym defined in GeneReviews.

Corticospinal tract hypoplasia Corticospinal tract hypoplasia HP:0007016

Show evidence (1 reference)

PMID:11438988 SUPPORT Human Clinical

"The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs."

Hypoplasia of the corticospinal tracts is listed among core L1 features.

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Genetic Associations

1

L1CAM (Loss-of-function and missense variants)

Gene: L1CAM hgnc:6470 relationship_type: CAUSATIVE variant_origin: GERMLINE

X-linked recessive inheritance

Show evidence (3 references)

PMID:11438988 SUPPORT Human Clinical

"Missense mutations in extracellular domains or mutations in cytoplasmic regions cause milder phenotypes than those leading to truncation in extracellular domains or to non-detectable L1 protein."

Establishes the genotype-phenotype correlation in L1CAM disease.

PMID:32416898 SUPPORT Human Clinical

"Its mutations result in L1 syndrome which is associated with brain malformation and nervous developmental delay."

Confirms L1CAM mutations as causal for L1 syndrome with brain malformation and developmental delay.

PMID:31572438 SUPPORT Human Clinical

"the mutation created a potential 5' splice site consensus sequence, which would result in an in-frame deletion of 72 bp from exon 5 and 24 amino acids of the L1CAM protein"

A silent (synonymous) L1CAM variant, c.453G>T (p.Gly151=), was shown by RT-PCR of patient cells to activate a cryptic 5' splice site producing an in-frame exon deletion, documenting splice disruption as a pathogenic mechanism even for silent coding variants.

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Medical Actions

4

Cerebrospinal Fluid Shunting

Action: cerebrospinal fluid shunting procedure Ontology label: surgical procedure MAXO:0000004

Shunting of cerebrospinal fluid (e.g., ventriculoperitoneal shunt; endoscopic third ventriculostomy in selected cases) is performed as needed to reduce intracranial pressure in hydrocephalus. Neurodevelopmental outcome in severe cases may remain poor despite CSF diversion because of underlying brain malformation.

Target Phenotypes: Hydrocephalus HP:0000238

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"Shunting of the cerebrospinal fluid should be performed as needed to reduce intracranial pressure."

GeneReviews recommends CSF shunting for hydrocephalus management.

Genetic Counseling

Action: Genetic Counseling NCIT:C15240

Genetic counseling for families with a known L1CAM variant, including heterozygote (carrier) detection. Once the L1CAM pathogenic variant is identified, prenatal testing and preimplantation genetic testing are possible.

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"Once the L1CAM pathogenic variant has been identified in an affected family member, heterozygote detection, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible."

GeneReviews supports genetic counseling, carrier detection, prenatal and preimplantation testing.

Prenatal Genetic Testing

Action: prenatal genetic testing MAXO:0000529

Prenatal molecular testing for an L1CAM pathogenic variant in a pregnancy at increased risk, using DNA from chorionic villus sampling or amniocentesis.

Show evidence (1 reference)

PMID:20301657 SUPPORT Human Clinical

"prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible."

GeneReviews supports prenatal genetic testing once the familial variant is known.

Supportive and Rehabilitative Care

Action: supportive care MAXO:0000950

Multidisciplinary supportive management with pediatrics, child neurology, neurosurgery, rehabilitation, and clinical genetics. Individualized educational programming for developmental delay/intellectual disability; standard treatment for spasticity; a splint may help reduce thumb adduction (surgery is not generally indicated). There is no disease-modifying or curative therapy for L1 syndrome.

Show evidence (2 references)

PMID:20301657 SUPPORT Human Clinical

"It is best to involve a multidisciplinary team with expertise in pediatrics, child neurology, neurosurgery, rehabilitation, and clinical genetics."

GeneReviews recommends multidisciplinary supportive and rehabilitative management.

PMID:11438988 SUPPORT Human Clinical

"At present, there is no therapy for the prevention or cure of patients' neurological disabilities."

Confirms the absence of curative/disease-modifying therapy.

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Experimental Models

2

L1-201 (D201) point-mutant mouse

A mouse model of L1 syndrome carrying a mutation at aspartic acid position 201 in the extracellular domain of L1. Male L1-201 mutants show significantly worse learning and memory after experimental traumatic brain injury, modeling extracellular-domain L1CAM variant consequences.

Show evidence (1 reference)

PMID:38474289 SUPPORT Model Organism

"we utilized a novel mouse model of L1 syndrome with a mutation at aspartic acid position 201 in the extracellular domain of L1 (L1-201)."

Describes the L1-201 mouse as a model of L1 syndrome with an extracellular-domain mutation.

L1 third-FNIII-domain dibasic-motif mutant mouse

Mice with disruption of the dibasic RK/KR sequence at position 858-863 in the third fibronectin type III domain of L1 (an extracellular-domain mutation) show enhanced hippocampal neuronal cell death, increased astrogliosis, and behavioral alterations, modeling the more severe extracellular-domain variant phenotype.

Show evidence (2 references)

PMID:37238646 SUPPORT Model Organism

"Mutant mice display higher numbers of caspase 3-positive neurons, a reduced number of principle neurons in the hippocampus, and an enhanced number of glial cells."

Demonstrates neuronal cell death and astrogliosis from an extracellular-domain L1 mutation in mice.

PMID:37238646 SUPPORT Model Organism

"mutations in the extracellular domain were shown to cause a severe phenotype more often than mutations in the intracellular domain."

Supports the genotype-phenotype correlation (extracellular > intracellular severity) in a model context.

{ }

Source YAML

click to show

name: L1 Syndrome
creation_date: "2026-06-15T00:00:00Z"
category: Mendelian
disease_term:
  preferred_term: L1 syndrome
  term:
    id: MONDO:0017140
    label: L1 syndrome
description: >-
  L1 syndrome is an X-linked recessive neurodevelopmental disorder caused by
  pathogenic variants in L1CAM (Xq28), which encodes the L1 neural cell adhesion
  molecule. It comprises a phenotypic spectrum historically described as
  overlapping clinical entities: X-linked hydrocephalus with stenosis of the
  aqueduct of Sylvius (HSAS), MASA syndrome (which subsumes X-linked complicated
  hereditary spastic paraplegia type 1, SPG1), and X-linked complicated corpus
  callosum agenesis. The acronym CRASH (corpus callosum hypoplasia, retardation/
  intellectual disability, adducted thumbs, spastic paraplegia, hydrocephalus)
  is also used for the broad spectrum. Cardinal features include congenital
  hydrocephalus/ventriculomegaly (often with aqueductal stenosis), agenesis or
  hypoplasia of the corpus callosum, spasticity/spastic paraplegia, intellectual
  disability, and adducted thumbs. Severity ranges from prenatal-onset, often
  lethal hydrocephalus to milder, survivable motor and cognitive phenotypes, and
  all phenotypes can co-occur within a single family.

references:
- reference: PMID:20301657
  title: "L1 Syndrome."
  tags:
  - GeneReviews
- reference: PMID:11438988
  title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."

synonyms:
- HSAS
- MASA syndrome
- CRASH syndrome
- X-linked hydrocephalus
- Spastic paraplegia type 1
- SPG1
- L1CAM syndrome
- L1 disease

inheritance:
- name: X-linked recessive inheritance
  inheritance_term:
    preferred_term: X-linked recessive inheritance
    term:
      id: HP:0001419
      label: X-linked recessive inheritance
  description: >-
    L1 syndrome is inherited in an X-linked recessive manner. Affected
    individuals are usually hemizygous males; heterozygous female carriers are
    usually unaffected but may occasionally show (typically mild) manifestations,
    plausibly due to skewed X-inactivation.
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      L1 syndrome is inherited in an X-linked manner.
    explanation: >-
      GeneReviews establishes X-linked inheritance for L1 syndrome.
  - reference: PMID:15662685
    reference_title: "A novel L1CAM mutation with L1 spectrum disorders."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      In this family, nine X-linked hydrocephalus and five female carriers were found in three generations
    explanation: >-
      A multigenerational pedigree with affected males and asymptomatic female
      carriers supports X-linked recessive transmission.

has_subtypes:
- name: HSAS
  display_name: X-linked hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS)
  description: >-
    The most severe end of the L1 spectrum. Affected males are born with severe
    congenital hydrocephalus due to stenosis of the aqueduct of Sylvius, adducted
    thumbs, and spasticity, with severe intellectual disability. Prenatal-onset
    hydrocephalus can lead to stillbirth or early infant death.
  genes:
  - preferred_term: L1CAM
    term:
      id: hgnc:6470
      label: L1CAM
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Males with HSAS are born with severe hydrocephalus, adducted thumbs, and spasticity; intellectual disability is severe.
    explanation: >-
      GeneReviews defines the severe HSAS phenotype within the L1 spectrum.
- name: MASA
  display_name: MASA syndrome (mental retardation, aphasia, spastic paraplegia, adducted thumbs)
  description: >-
    A milder end of the L1 spectrum characterized by mental retardation
    (intellectual disability), aphasia (delayed speech), spastic paraplegia
    (shuffling gait), and adducted thumbs. MASA includes X-linked complicated
    hereditary spastic paraplegia type 1.
  genes:
  - preferred_term: L1CAM
    term:
      id: hgnc:6470
      label: L1CAM
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MASA (mental retardation ... aphasia ... spastic paraplegia ... adducted thumbs) syndrome including X-linked complicated hereditary spastic paraplegia type 1.
    explanation: >-
      GeneReviews defines the MASA phenotype, which subsumes X-linked complicated
      hereditary spastic paraplegia type 1 (SPG1), within the L1 spectrum.
- name: SPG1
  display_name: X-linked complicated hereditary spastic paraplegia type 1 (SPG1)
  description: >-
    The spastic paraplegia-predominant presentation of the L1 spectrum, in which
    progressive spasticity and gait disturbance from corticospinal tract
    involvement dominate the clinical picture. SPG1 falls within the MASA end of
    the spectrum.
  genes:
  - preferred_term: L1CAM
    term:
      id: hgnc:6470
      label: L1CAM
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      L1 disease is a group of overlapping clinical phenotypes including X-linked hydrocephalus, MASA syndrome, spastic paraparesis type 1, and X-linked agenesis of corpus callosum.
    explanation: >-
      The foundational review lists spastic paraparesis type 1 (SPG1) as one of
      the overlapping L1 phenotypes.
- name: X-linked ACC
  display_name: X-linked complicated corpus callosum agenesis
  description: >-
    A presentation in which agenesis or hypoplasia of the corpus callosum is a
    prominent feature, accompanied by variable spasticity, intellectual
    disability, and ventricular abnormalities.
  genes:
  - preferred_term: L1CAM
    term:
      id: hgnc:6470
      label: L1CAM
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      X-linked complicated corpus callosum agenesis.
    explanation: >-
      GeneReviews lists X-linked complicated corpus callosum agenesis as one of
      the L1 syndrome clinical phenotypes.

prevalence:
- population: Live male births (HSAS / X-linked hydrocephalus)
  measure_type: BIRTH_PREVALENCE
  prevalence_class: BAND_1_9_PER_100000
  rate_per_100000: 3.333333
  percentage: ~1 in 30,000 live male births
  notes: >-
    HSAS (X-linked hydrocephalus) is described as the most common inherited form
    of hydrocephalus.
  evidence:
  - reference: PMID:31572438
    reference_title: "A Novel Silent Mutation in the L1CAM Gene Causing Fetal Hydrocephalus Detected by Whole-Exome Sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      X-linked hydrocephalus (XLH), a genetic disorder, has an incidence of 1/30,000 male births. The great proportion of XLH is ascribed to loss-of-function mutations of L1 cell adhesion molecule gene (L1CAM)
    explanation: >-
      Reports the 1/30,000 male-birth incidence of L1CAM-related X-linked
      hydrocephalus, the most common inherited form of hydrocephalus.
  - reference: PMID:30365056
    reference_title: "Two novel pathogenic variants of L1CAM gene in two fetuses with isolated X‑linked hydrocephaly: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hydrocephalus due to aqueductal stenosis (HSAS; Online Mendelian Inheritance in Man #307000) is a rare X‑linked, recessively‑inherited disease characterized by severe hydrocephaly
    explanation: >-
      This case report frames HSAS as a rare X-linked recessive disease.
- population: Congenital hydrocephalus (overall global)
  measure_type: BIRTH_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 200.0
  percentage: ~1 in 500 births (congenital hydrocephalus overall)
  notes: >-
    L1CAM is one of the small set of confirmed human congenital-hydrocephalus
    genes; genetics may contribute to up to 40% of congenital hydrocephalus but a
    precise genetic etiology is identified in fewer than 5% of cases.
  evidence:
  - reference: PMID:39135208
    reference_title: "Congenital hydrocephalus: a review of recent advances in genetic etiology and molecular mechanisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The global prevalence rate for congenital hydrocephalus (CH) is approximately one out of every five hundred births
    explanation: >-
      Provides the epidemiologic framing for congenital hydrocephalus, within
      which L1CAM is a confirmed causal gene.

pathophysiology:
- name: Defective L1CAM Neural Cell Adhesion
  description: >-
    Loss-of-function or hypomorphic variants in L1CAM impair the function of the
    L1 cell adhesion molecule, a single-pass transmembrane glycoprotein of the
    immunoglobulin superfamily expressed in neurons and Schwann cells. L1 is
    essential for nervous system development, mediating cell adhesion, signaling,
    and membrane trafficking. Mutations are distributed across the functional
    protein domains; the precise mechanisms by which they cause loss of L1
    function are incompletely understood.
  gene:
    preferred_term: L1CAM
    description: L1 cell adhesion molecule, an Ig-superfamily neuronal cell adhesion molecule.
    modifier: ABNORMAL
    term:
      id: hgnc:6470
      label: L1CAM
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  - preferred_term: myelinating Schwann cell
    term:
      id: CL:0000218
      label: myelinating Schwann cell
  biological_processes:
  - preferred_term: cell adhesion
    term:
      id: GO:0007155
      label: cell adhesion
    modifier: DECREASED
  - preferred_term: nervous system development
    term:
      id: GO:0007399
      label: nervous system development
    modifier: ABNORMAL
  - preferred_term: myelination
    term:
      id: GO:0042552
      label: myelination
    modifier: ABNORMAL
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The responsible gene, L1CAM, encodes the L1 protein which is a member of the immunoglobulin superfamily of neuronal cell adhesion molecules. The L1 protein is expressed in neurons and Schwann cells and seems to be essential for nervous system development and function.
    explanation: >-
      Establishes L1CAM as the causal gene, its Ig-superfamily neural cell
      adhesion identity, and its expression in neurons and Schwann cells.
  - reference: PMID:37569906
    reference_title: "Interaction of L1CAM with LC3 Is Required for L1-Dependent Neurite Outgrowth and Neuronal Survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The neural cell adhesion molecule L1 (also called L1CAM or CD171) functions not only in cell migration, but also in cell survival, differentiation, myelination, neurite outgrowth, and signaling during nervous system development and in adults.
    explanation: >-
      Documents the breadth of L1 functions including myelination, cell
      survival, and differentiation, supporting myelination as an affected
      process in L1 dysfunction.
  downstream:
  - target: Impaired Axon Guidance and Neurite Outgrowth
    causal_link_type: DIRECT
    description: >-
      Defective L1-mediated adhesion and signaling impairs axon guidance,
      neurite outgrowth, and neuronal migration during CNS development.

- name: Impaired Axon Guidance and Neurite Outgrowth
  description: >-
    L1 normally promotes neurite outgrowth, axon guidance/pathfinding, and
    neuronal migration. A 2023 mechanistic study showed that the L1-70 fragment
    binds LC3 (an autophagy-related protein) via an extracellular LC3-interacting
    region (LIR) motif in the fourth fibronectin type III domain, and that this
    interaction is required for L1-mediated neurite outgrowth and neuronal
    survival, linking L1CAM processing to autophagy-related machinery. Loss of L1
    function therefore impairs the formation of major axon tracts.
  cell_types:
  - preferred_term: neuron
    term:
      id: CL:0000540
      label: neuron
  biological_processes:
  - preferred_term: axon guidance
    term:
      id: GO:0007411
      label: axon guidance
    modifier: ABNORMAL
  - preferred_term: neuron projection development
    term:
      id: GO:0031175
      label: neuron projection development
    modifier: DECREASED
  - preferred_term: neuron migration
    term:
      id: GO:0001764
      label: neuron migration
    modifier: ABNORMAL
  evidence:
  - reference: PMID:37569906
    reference_title: "Interaction of L1CAM with LC3 Is Required for L1-Dependent Neurite Outgrowth and Neuronal Survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      The disruption of the L1-LC3 interaction reduces L1-mediated neurite outgrowth and neuronal survival.
    explanation: >-
      In vitro evidence that an L1CAM-dependent interaction is required for
      neurite outgrowth and neuronal survival, supporting impaired neurite
      outgrowth as a consequence of L1 dysfunction.
  - reference: PMID:37569906
    reference_title: "Interaction of L1CAM with LC3 Is Required for L1-Dependent Neurite Outgrowth and Neuronal Survival."
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: >-
      L1-70 interacts with LC3 via the extracellular LIR motif in the fourth fibronectin type III domain
    explanation: >-
      Identifies the molecular L1-70/LC3 interaction underlying L1-dependent
      neurite outgrowth.
  downstream:
  - target: Corticospinal Tract and Commissural Defects
    causal_link_type: DIRECT
    description: >-
      Failure of axon pathfinding and tract formation leads to maldevelopment of
      the corpus callosum and corticospinal tracts.
  - target: Aqueductal Stenosis and Hydrocephalus
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    description: >-
      Abnormal neurodevelopment contributes to stenosis of the cerebral aqueduct
      and impaired CSF flow.

- name: Corticospinal Tract and Commissural Defects
  description: >-
    Defective axon guidance produces agenesis or hypoplasia of the corpus
    callosum and hypoplasia of the corticospinal tracts. These long-tract and
    midline commissural defects underlie the spastic paraplegia, gait
    disturbance, and contribute to intellectual disability in the L1 spectrum.
  locations:
  - preferred_term: corpus callosum
    term:
      id: UBERON:0002336
      label: corpus callosum
  - preferred_term: corticospinal tract
    term:
      id: UBERON:0002707
      label: corticospinal tract
  biological_processes:
  - preferred_term: corpus callosum development
    term:
      id: GO:0022038
      label: corpus callosum development
    modifier: ABNORMAL
  - preferred_term: corticospinal tract morphogenesis
    term:
      id: GO:0021957
      label: corticospinal tract morphogenesis
    modifier: ABNORMAL
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs.
    explanation: >-
      Establishes corpus callosum and corticospinal tract defects as core
      neuroanatomic features of L1 disease.

- name: Aqueductal Stenosis and Hydrocephalus
  description: >-
    Stenosis of the aqueduct of Sylvius and impaired cerebrospinal fluid
    circulation produce ventriculomegaly and congenital hydrocephalus, the
    hallmark of HSAS/X-linked hydrocephalus. In severe cases this manifests
    prenatally and can be lethal; underlying brain malformations limit recovery
    even after neurosurgical CSF diversion.
  locations:
  - preferred_term: midbrain cerebral aqueduct
    term:
      id: UBERON:0002289
      label: midbrain cerebral aqueduct
  biological_processes:
  - preferred_term: cerebrospinal fluid circulation
    term:
      id: GO:0090660
      label: cerebrospinal fluid circulation
    modifier: ABNORMAL
  evidence:
  - reference: PMID:34801143
    reference_title: "Syndromic Hydrocephalus."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hydrocephalus, the abnormal accumulation and impaired circulation/clearance of cerebrospinal fluid, occurs as a common phenotypic feature of a diverse group of genetic syndromes.
    explanation: >-
      A syndromic-hydrocephalus review (which discusses L1 syndrome) frames
      hydrocephalus as impaired CSF circulation/clearance.
  - reference: PMID:30365056
    reference_title: "Two novel pathogenic variants of L1CAM gene in two fetuses with isolated X‑linked hydrocephaly: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The variants affect the highly conserved amino acids which are located in the key domains of the protein (the fourth Ig domain and second FnIII domain, respectively).
    explanation: >-
      Pathogenic L1CAM variants in conserved functional domains were identified
      in fetuses presenting with severe ventriculomegaly/hydrocephalus.
  - reference: PMID:39135208
    reference_title: "Congenital hydrocephalus: a review of recent advances in genetic etiology and molecular mechanisms."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Approximately 5–15% of cases are associated with X-linked variations of L1CAM, known as L1 syndrome.
    explanation: >-
      A congenital-hydrocephalus genetics review attributes 5-15% of
      aqueductal-stenosis (non-syndromic) congenital hydrocephalus to L1CAM
      (L1 syndrome), quantifying L1 syndrome as a leading cause of hydrocephalus
      from aqueductal stenosis.

phenotypes:
- category: Phenotypic abnormality
  name: Hydrocephalus
  description: >-
    Congenital, often prenatal-onset hydrocephalus is the hallmark of the severe
    (HSAS) end of the L1 spectrum.
  phenotype_term:
    preferred_term: Hydrocephalus
    term:
      id: HP:0000238
      label: Hydrocephalus
  subtype: HSAS
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Males with HSAS are born with severe hydrocephalus, adducted thumbs, and spasticity; intellectual disability is severe.
    explanation: >-
      GeneReviews documents severe congenital hydrocephalus in HSAS.
- category: Phenotypic abnormality
  name: Ventriculomegaly
  description: >-
    Enlargement of the cerebral ventricles, frequently detected by prenatal
    ultrasound or fetal MRI.
  phenotype_term:
    preferred_term: Ventriculomegaly
    term:
      id: HP:0002119
      label: Ventriculomegaly
  evidence:
  - reference: PMID:32416898
    reference_title: "L1CAM mutations in three fetuses diagnosed by medical exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We presented three fetuses with hydrocephalus and agenesis of the corpus callosum detected by ultrasound
    explanation: >-
      Fetal hydrocephalus/ventriculomegaly with corpus callosum agenesis was
      detected by ultrasound in L1CAM-mutation fetuses.
- category: Phenotypic abnormality
  name: Aqueductal stenosis
  description: >-
    Stenosis of the aqueduct of Sylvius is the classic structural cause of
    obstructive hydrocephalus in HSAS.
  phenotype_term:
    preferred_term: Aqueductal stenosis
    term:
      id: HP:0002410
      label: Aqueductal stenosis
  subtype: HSAS
  evidence:
  - reference: PMID:30365056
    reference_title: "Two novel pathogenic variants of L1CAM gene in two fetuses with isolated X‑linked hydrocephaly: A case report."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Hydrocephalus due to aqueductal stenosis (HSAS; Online Mendelian Inheritance in Man #307000) is a rare X‑linked, recessively‑inherited disease characterized by severe hydrocephaly
    explanation: >-
      Defines HSAS as hydrocephalus due to aqueductal stenosis.
- category: Phenotypic abnormality
  name: Agenesis of corpus callosum
  description: >-
    Complete absence of the corpus callosum, part of the CRASH/L1 spectrum; may
    be complete or partial and is often detected prenatally.
  phenotype_term:
    preferred_term: Agenesis of corpus callosum
    term:
      id: HP:0001274
      label: Agenesis of corpus callosum
  subtype: X-linked ACC
  evidence:
  - reference: PMID:32416898
    reference_title: "L1CAM mutations in three fetuses diagnosed by medical exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      We presented three fetuses with hydrocephalus and agenesis of the corpus callosum detected by ultrasound
    explanation: >-
      Agenesis of the corpus callosum was a presenting feature in L1CAM-mutation
      fetuses.
- category: Phenotypic abnormality
  name: Hypoplasia of the corpus callosum
  description: >-
    Underdevelopment of the corpus callosum (the "C" in CRASH), part of the L1
    neuroanatomic spectrum.
  phenotype_term:
    preferred_term: Hypoplasia of the corpus callosum
    term:
      id: HP:0002079
      label: Hypoplasia of the corpus callosum
  subtype: X-linked ACC
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs.
    explanation: >-
      The foundational review lists agenesis or hypoplasia of the corpus
      callosum as a core feature.
- category: Phenotypic abnormality
  name: Adducted thumb
  description: >-
    Adducted (clasped) thumbs are a characteristic, though not universal, feature
    of L1 syndrome; reported in approximately 45% of cases in foundational
    literature.
  phenotype_term:
    preferred_term: Adducted thumb
    term:
      id: HP:0001181
      label: Adducted thumb
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs.
    explanation: >-
      Adducted thumbs are listed among the characteristic features of L1 disease.
- category: Phenotypic abnormality
  name: Spastic paraplegia
  description: >-
    Spasticity and spastic paraplegia, prominent in the MASA/SPG1 end of the
    spectrum, reflect corticospinal tract involvement.
  phenotype_term:
    preferred_term: Spastic paraplegia
    term:
      id: HP:0001258
      label: Spastic paraplegia
    clinical_course: PROGRESSIVE
  subtype: SPG1
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs.
    explanation: >-
      Spastic paraplegia is a core feature of the L1 spectrum.
- category: Phenotypic abnormality
  name: Intellectual disability
  description: >-
    Intellectual disability is common across the spectrum, ranging from mild
    (IQ 50-70) to moderate (IQ 30-50) in less severely affected males, and severe
    in HSAS.
  phenotype_term:
    preferred_term: Intellectual disability
    term:
      id: HP:0001249
      label: Intellectual disability
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      intellectual disability ranges from mild (IQ: 50-70) to moderate (IQ: 30-50).
    explanation: >-
      GeneReviews documents the range of intellectual disability in less
      severely affected males.
- category: Phenotypic abnormality
  name: Aphasia
  description: >-
    Aphasia (delayed/impaired speech), the "A" in MASA, occurs in the milder
    surviving phenotypes.
  phenotype_term:
    preferred_term: Aphasia
    term:
      id: HP:0002381
      label: Aphasia
  subtype: MASA
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      MASA (mental retardation ... aphasia ... spastic paraplegia ... adducted thumbs) syndrome
    explanation: >-
      Aphasia (delayed speech) is one of the four components of the MASA acronym
      defined in GeneReviews.
- category: Phenotypic abnormality
  name: Shuffling gait
  description: >-
    Shuffling gait, part of the MASA acronym, reflects corticospinal tract
    dysfunction/spastic paraparesis.
  phenotype_term:
    preferred_term: Shuffling gait
    term:
      id: HP:0002362
      label: Shuffling gait
  subtype: MASA
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      spastic paraplegia shuffling gait adducted thumbs syndrome
    explanation: >-
      Shuffling gait (the spastic-paraplegia component) is part of the MASA
      acronym defined in GeneReviews.
- category: Phenotypic abnormality
  name: Corticospinal tract hypoplasia
  description: >-
    Hypoplasia of the corticospinal tracts is part of the core neuroanatomic
    spectrum and likely underlies spastic paraplegia and spastic gait.
  phenotype_term:
    preferred_term: Corticospinal tract hypoplasia
    term:
      id: HP:0007016
      label: Corticospinal tract hypoplasia
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      The patients are characterized by hydrocephalus, agenesis or hypoplasia of corpus callosum and corticospinal tracts, mental retardation, spastic paraplegia, and adducted thumbs.
    explanation: >-
      Hypoplasia of the corticospinal tracts is listed among core L1 features.

genetic:
- name: L1CAM
  gene_term:
    preferred_term: L1CAM
    term:
      id: hgnc:6470
      label: L1CAM
  association: Loss-of-function and missense variants
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  inheritance:
  - name: X-linked recessive inheritance
    inheritance_term:
      preferred_term: X-linked recessive inheritance
      term:
        id: HP:0001419
        label: X-linked recessive inheritance
  notes: >-
    More than 280 distinct L1CAM variants have been reported, approximately 50%
    missense, with many "private" to individual families. Variant types include
    missense, nonsense, frameshift, splice-altering, and structural variants/CNVs.
    Even synonymous (silent) coding variants can be pathogenic when they activate
    a cryptic splice site and cause in-frame exon deletion, so silent variants
    detected on exome sequencing should not be dismissed. A genotype-phenotype
    trend exists: truncating variants (especially extracellular-domain
    truncations producing absent/non-detectable protein) are associated with
    severe phenotypes and higher infant mortality, whereas missense and
    cytoplasmic-domain variants tend to produce milder phenotypes.
  evidence:
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Missense mutations in extracellular domains or mutations in cytoplasmic regions cause milder phenotypes than those leading to truncation in extracellular domains or to non-detectable L1 protein.
    explanation: >-
      Establishes the genotype-phenotype correlation in L1CAM disease.
  - reference: PMID:32416898
    reference_title: "L1CAM mutations in three fetuses diagnosed by medical exome sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Its mutations result in L1 syndrome which is associated with brain malformation and nervous developmental delay.
    explanation: >-
      Confirms L1CAM mutations as causal for L1 syndrome with brain malformation
      and developmental delay.
  - reference: PMID:31572438
    reference_title: "A Novel Silent Mutation in the L1CAM Gene Causing Fetal Hydrocephalus Detected by Whole-Exome Sequencing."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      the mutation created a potential 5' splice site consensus sequence, which would result in an in-frame deletion of 72 bp from exon 5 and 24 amino acids of the L1CAM protein
    explanation: >-
      A silent (synonymous) L1CAM variant, c.453G>T (p.Gly151=), was shown by
      RT-PCR of patient cells to activate a cryptic 5' splice site producing an
      in-frame exon deletion, documenting splice disruption as a pathogenic
      mechanism even for silent coding variants.

treatments:
- name: Cerebrospinal Fluid Shunting
  description: >-
    Shunting of cerebrospinal fluid (e.g., ventriculoperitoneal shunt;
    endoscopic third ventriculostomy in selected cases) is performed as needed to
    reduce intracranial pressure in hydrocephalus. Neurodevelopmental outcome in
    severe cases may remain poor despite CSF diversion because of underlying
    brain malformation.
  treatment_term:
    preferred_term: cerebrospinal fluid shunting procedure
    term:
      id: MAXO:0000004
      label: surgical procedure
  therapeutic_modality: SURGERY
  target_phenotypes:
  - preferred_term: Hydrocephalus
    term:
      id: HP:0000238
      label: Hydrocephalus
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Shunting of the cerebrospinal fluid should be performed as needed to reduce intracranial pressure.
    explanation: >-
      GeneReviews recommends CSF shunting for hydrocephalus management.
- name: Genetic Counseling
  description: >-
    Genetic counseling for families with a known L1CAM variant, including
    heterozygote (carrier) detection. Once the L1CAM pathogenic variant is
    identified, prenatal testing and preimplantation genetic testing are possible.
  treatment_term:
    preferred_term: Genetic Counseling
    term:
      id: NCIT:C15240
      label: Genetic Counseling
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      Once the L1CAM pathogenic variant has been identified in an affected family member, heterozygote detection, prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible.
    explanation: >-
      GeneReviews supports genetic counseling, carrier detection, prenatal and
      preimplantation testing.
- name: Prenatal Genetic Testing
  description: >-
    Prenatal molecular testing for an L1CAM pathogenic variant in a pregnancy at
    increased risk, using DNA from chorionic villus sampling or amniocentesis.
  treatment_term:
    preferred_term: prenatal genetic testing
    term:
      id: MAXO:0000529
      label: prenatal genetic testing
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      prenatal testing for a pregnancy at increased risk, and preimplantation genetic testing are possible.
    explanation: >-
      GeneReviews supports prenatal genetic testing once the familial variant is
      known.
- name: Supportive and Rehabilitative Care
  description: >-
    Multidisciplinary supportive management with pediatrics, child neurology,
    neurosurgery, rehabilitation, and clinical genetics. Individualized
    educational programming for developmental delay/intellectual disability;
    standard treatment for spasticity; a splint may help reduce thumb adduction
    (surgery is not generally indicated). There is no disease-modifying or
    curative therapy for L1 syndrome.
  treatment_term:
    preferred_term: supportive care
    term:
      id: MAXO:0000950
      label: supportive care
  evidence:
  - reference: PMID:20301657
    reference_title: "L1 Syndrome."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      It is best to involve a multidisciplinary team with expertise in pediatrics, child neurology, neurosurgery, rehabilitation, and clinical genetics.
    explanation: >-
      GeneReviews recommends multidisciplinary supportive and rehabilitative
      management.
  - reference: PMID:11438988
    reference_title: "Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: >-
      At present, there is no therapy for the prevention or cure of patients' neurological disabilities.
    explanation: >-
      Confirms the absence of curative/disease-modifying therapy.

experimental_models:
- name: L1-201 (D201) point-mutant mouse
  description: >-
    A mouse model of L1 syndrome carrying a mutation at aspartic acid position 201
    in the extracellular domain of L1. Male L1-201 mutants show significantly
    worse learning and memory after experimental traumatic brain injury, modeling
    extracellular-domain L1CAM variant consequences.
  evidence:
  - reference: PMID:38474289
    reference_title: "Single Nucleotide Polymorphism in Cell Adhesion Molecule L1 Affects Learning and Memory in a Mouse Model of Traumatic Brain Injury."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      we utilized a novel mouse model of L1 syndrome with a mutation at aspartic acid position 201 in the extracellular domain of L1 (L1-201).
    explanation: >-
      Describes the L1-201 mouse as a model of L1 syndrome with an
      extracellular-domain mutation.
- name: L1 third-FNIII-domain dibasic-motif mutant mouse
  description: >-
    Mice with disruption of the dibasic RK/KR sequence at position 858-863 in the
    third fibronectin type III domain of L1 (an extracellular-domain mutation)
    show enhanced hippocampal neuronal cell death, increased astrogliosis, and
    behavioral alterations, modeling the more severe extracellular-domain variant
    phenotype.
  evidence:
  - reference: PMID:37238646
    reference_title: "Mice Mutated in the Third Fibronectin Domain of L1 Show Enhanced Hippocampal Neuronal Cell Death, Astrogliosis and Alterations in Behavior."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      Mutant mice display higher numbers of caspase 3-positive neurons, a reduced number of principle neurons in the hippocampus, and an enhanced number of glial cells.
    explanation: >-
      Demonstrates neuronal cell death and astrogliosis from an
      extracellular-domain L1 mutation in mice.
  - reference: PMID:37238646
    reference_title: "Mice Mutated in the Third Fibronectin Domain of L1 Show Enhanced Hippocampal Neuronal Cell Death, Astrogliosis and Alterations in Behavior."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: >-
      mutations in the extracellular domain were shown to cause a severe phenotype more often than mutations in the intracellular domain.
    explanation: >-
      Supports the genotype-phenotype correlation (extracellular > intracellular
      severity) in a model context.

📚

References & Deep Research

References

2

PMID:20301657

L1 Syndrome.

No top-level findings curated for this source.

PMID:11438988

Genetic and clinical aspects of X-linked hydrocephalus (L1 disease): Mutations in the L1CAM gene.

No top-level findings curated for this source.

Deep Research

1

Falcon ▸

L1 Syndrome (L1CAM-related disorder) — Disease Characteristics Research Report

Edison Scientific Literature 33 citations 2026-06-15T23:56:45.575394

L1 Syndrome (L1CAM-related disorder) — Disease Characteristics Research Report

Executive summary

L1 syndrome is an X-linked recessive neurodevelopmental disorder caused by pathogenic variants in L1CAM (Xq28), encompassing a phenotypic spectrum historically described as X-linked hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS), MASA syndrome, SPG1 (X-linked spastic paraplegia type 1), and CRASH syndrome. Cardinal features include congenital hydrocephalus/ventriculomegaly (often with aqueductal stenosis), corpus callosum agenesis/hypoplasia, spasticity/spastic paraplegia, intellectual disability, and (in ~45%) adducted thumbs. Disease severity ranges from prenatal-onset lethal hydrocephalus to milder, survivable motor/cognitive phenotypes. (weller2001geneticandclinical pages 1-2)

Two 2023–2024 advances particularly relevant to mechanism and translational framing are: (i) a mechanistic connection between L1 processing and autophagy machinery via LC3 binding, required for L1-dependent neurite outgrowth and neuronal survival (loers2023interactionofl1cam pages 14-16, loers2023interactionofl1cam pages 2-4); and (ii) a 2024 synthesis of congenital hydrocephalus genetics that places L1CAM among the small set of confirmed human congenital-hydrocephalus genes and categorizes mechanisms (neurodevelopment, cilia/CSF flow, etc.), including a summary figure (liu2024congenitalhydrocephalusa pages 1-3, liu2024congenitalhydrocephalusa media 5d669376).

Target disease

Disease name: L1 syndrome
Category: Mendelian
MONDO ID: MONDO:0017140 (OpenTargets Search: L1 syndrome-L1CAM)

1. Disease Information

1.1 Definition and overview

L1 syndrome (also termed “L1 disease” in foundational literature) is a group of overlapping X-linked phenotypes caused by L1CAM mutations and classically including HSAS, MASA, SPG1, and X-linked agenesis of the corpus callosum; the broad clinical spectrum is often referred to as CRASH syndrome (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 1-2).

1.2 Key identifiers and synonyms

MONDO: MONDO:0017140 (OpenTargets Search: L1 syndrome-L1CAM)
Gene/OMIM note: L1CAM is noted as OMIM 308840 in a prenatal-exome case series (li2020l1cammutationsin pages 1-3).
Spectrum terms/synonyms used clinically: HSAS, MASA, CRASH, SPG1, X-linked ACC (li2020l1cammutationsin pages 1-3, silan2005anovell1cam pages 1-2, weller2001geneticandclinical pages 1-2).

1.3 Evidence type

The knowledge base–relevant information is drawn from: - Aggregated disease-level resources and curated databases (e.g., Open Targets disease mapping to MONDO) (OpenTargets Search: L1 syndrome-L1CAM) - Human clinical genetics reviews and case reports (prenatal and postnatal) (weller2001geneticandclinical pages 1-2, ochando2016prenataldiagnosisof pages 2-3, li2020l1cammutationsin pages 1-3) - Model organism and mechanistic experimental studies (mouse/in vitro) (loers2023interactionofl1cam pages 14-16, jiang2024singlenucleotidepolymorphism pages 1-2).

URL examples: - Weller & Gärtner 2001 (Human Mutation; 2001-07; DOI URL): https://doi.org/10.1002/humu.1144 (weller2001geneticandclinical pages 1-2) - Liu et al. 2024 (Military Medical Research; 2024-08; DOI URL): https://doi.org/10.1186/s40779-024-00560-5 (liu2024congenitalhydrocephalusa pages 1-3)

2. Etiology

2.1 Disease causal factors

Primary cause: pathogenic germline variation in L1CAM (Xq28), an Ig-superfamily neuronal cell adhesion molecule required for nervous system development and multiple neurodevelopmental processes (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 1-2).

Inheritance: typically X-linked recessive; affected individuals are usually hemizygous males, while heterozygous females are often asymptomatic but can occasionally show manifestations, plausibly due to skewed X-inactivation (silan2005anovell1cam pages 2-3).

2.2 Risk factors

For a Mendelian disease, the major risk factor is carrier status in the mother and familial history of affected males; prenatal case reports emphasize recurrence in pedigrees and the role of targeted L1CAM analysis (ochando2016prenataldiagnosisof pages 2-3, ochando2016prenataldiagnosisof pages 1-2).

2.3 Protective factors and gene–environment interaction

No protective genetic variants or environmental protective factors were identified in the retrieved evidence. L1 syndrome is not typically conceptualized as gene–environment driven; however, severity may be modulated by variant class/domain and potentially genetic background (model systems show allele/background dependence for hydrocephalus phenotypes) (congiu2023micemutatedin pages 16-17).

3. Phenotypes

3.1 Core phenotype spectrum (clinical)

Commonly described features across the L1 spectrum include: - Hydrocephalus/ventriculomegaly, often congenital and sometimes prenatal-onset (weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4) - Agenesis/hypoplasia of the corpus callosum (weller2001geneticandclinical pages 1-2, ochando2016prenataldiagnosisof pages 2-3) - Spastic paraplegia/spasticity with gait disturbance (weller2001geneticandclinical pages 1-2, gasser2010efnsguidelineson pages 8-9) - Intellectual disability/developmental delay (weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4) - Adducted thumbs (~45% in a foundational review) (weller2001geneticandclinical pages 1-2) - MASA-associated features including aphasia/speech impairment and shuffling gait (li2020l1cammutationsin pages 1-3, gasser2010efnsguidelineson pages 8-9)

3.2 Prenatal imaging phenotypes

Prenatal ultrasound and fetal MRI findings reported in L1CAM-related disease include severe ventriculomegaly/hydrocephalus, third ventricle dilation, and corpus callosum agenesis; absent cavum septum pellucidum has been described in affected fetuses (li2020l1cammutationsin pages 3-4, ochando2016prenataldiagnosisof pages 1-2).

3.3 HPO mapping

A structured HPO mapping is provided below.

Phenotype	Suggested HPO term(s)	Onset / frequency / notes	Evidence sources
Hydrocephalus / ventriculomegaly	HP:0000238 Hydrocephalus; HP:0002119 Ventriculomegaly	Often prenatal or congenital; may begin in utero and range from severe fetal hydrocephalus to milder ventricular enlargement; core hallmark of L1 syndrome/HSAS (weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4, li2020l1cammutationsin pages 1-3)	(weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4, li2020l1cammutationsin pages 1-3)
Aqueductal stenosis	HP:0002620 Stenosis of the cerebral aqueduct	Classic feature of HSAS/X-linked hydrocephalus; commonly inferred from prenatal/postnatal neuroimaging and disease definition (weller2001geneticandclinical pages 1-2, varagur2022syndromichydrocephalus. pages 1-3, varagur2022syndromichydrocephalus. pages 19-23)	(weller2001geneticandclinical pages 1-2, varagur2022syndromichydrocephalus. pages 1-3, varagur2022syndromichydrocephalus. pages 19-23)
Corpus callosum agenesis / hypoplasia	HP:0001274 Agenesis of the corpus callosum; HP:0002079 Hypoplasia of the corpus callosum	Frequently detected prenatally or congenitally; part of CRASH/L1 spectrum; may be complete or partial (weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4, ochando2016prenataldiagnosisof pages 2-3, li2020l1cammutationsin pages 1-3)	(weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4, ochando2016prenataldiagnosisof pages 2-3, li2020l1cammutationsin pages 1-3)
Adducted thumbs	HP:0001182 Adducted thumb	Characteristic but not universal; reported in ~45% of cases in a foundational review; can sometimes be detected prenatally (weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4)	(weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4)
Spastic paraplegia / spasticity	HP:0001258 Spasticity; HP:0007021 Spastic paraplegia	Usually childhood-onset in SPG1/MASA end of spectrum; chronic motor disability affecting gait and mobility; severity variable (weller2001geneticandclinical pages 1-2, gasser2010efnsguidelineson pages 8-9, kutlubaeva2024hereditaryspasticparaplegias pages 1-2)	(weller2001geneticandclinical pages 1-2, gasser2010efnsguidelineson pages 8-9, kutlubaeva2024hereditaryspasticparaplegias pages 1-2)
Intellectual disability / developmental delay	HP:0001249 Intellectual disability; HP:0001263 Global developmental delay	Common across the spectrum; severity ranges from mild learning impairment to severe developmental disability (weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4, silan2005anovell1cam pages 1-2)	(weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 3-4, silan2005anovell1cam pages 1-2)
Aphasia / speech impairment	HP:0002381 Aphasia; HP:0002167 Delayed speech and language development	Included in MASA acronym; speech/language impairment may be part of milder surviving phenotypes (li2020l1cammutationsin pages 1-3, gasser2010efnsguidelineson pages 8-9)	(li2020l1cammutationsin pages 1-3, gasser2010efnsguidelineson pages 8-9)
Shuffling gait / gait abnormality	HP:0002362 Shuffling gait; HP:0001288 Gait disturbance	Included in MASA acronym; usually reflects corticospinal tract dysfunction/spastic paraparesis with childhood onset or progressive mobility limitation (li2020l1cammutationsin pages 1-3, gasser2010efnsguidelineson pages 8-9, awuah2024hereditaryspasticparaplegia pages 1-2)	(li2020l1cammutationsin pages 1-3, gasser2010efnsguidelineson pages 8-9, awuah2024hereditaryspasticparaplegia pages 1-2)
White matter abnormalities / hypomyelination	HP:0002500 Abnormal cerebral white matter morphology; HP:0003429 Hypomyelination	Reported as reduced white matter / hypomyelination in L1 spectrum and model data; may contribute to motor/cognitive dysfunction (silan2005anovell1cam pages 1-2, varagur2022syndromichydrocephalus. pages 1-3, awuah2024hereditaryspasticparaplegia pages 8-10)	(silan2005anovell1cam pages 1-2, varagur2022syndromichydrocephalus. pages 1-3, awuah2024hereditaryspasticparaplegia pages 8-10)
Corticospinal tract hypoplasia	HP:0031887 Corticospinal tract hypoplasia	Described as part of the core neuroanatomic spectrum and likely underlies spastic paraplegia/spastic gait (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 1-2)	(weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 1-2)
Macrocephaly	HP:0000256 Macrocephaly	May accompany ventriculomegaly/hydrocephalus, especially in affected males; secondary to CSF accumulation rather than a universal primary trait (silan2005anovell1cam pages 1-2)	(silan2005anovell1cam pages 1-2)
Dilated third ventricle (prenatal ultrasound/MRI finding)	HP:0003370 Enlarged third ventricle	Prenatal imaging clue; reported with severe fetal hydrocephalus/ventriculomegaly and corpus callosum anomalies (li2020l1cammutationsin pages 3-4, ochando2016prenataldiagnosisof pages 1-2, silan2005anovell1cam pages 2-3)	(li2020l1cammutationsin pages 3-4, ochando2016prenataldiagnosisof pages 1-2, silan2005anovell1cam pages 2-3)
Absent cavum septum pellucidum (prenatal imaging finding)	HP:0012113 Absent septum pellucidum	Prenatal imaging clue that may accompany corpus callosum agenesis and ventriculomegaly in affected male fetuses (ochando2016prenataldiagnosisof pages 2-3, ochando2016prenataldiagnosisof pages 1-2)	(ochando2016prenataldiagnosisof pages 2-3, ochando2016prenataldiagnosisof pages 1-2)

Table: This table maps the principal clinical and prenatal imaging features of L1 syndrome to suggested HPO terms, with brief notes on onset and frequency where available. It is useful for structured phenotype annotation in a disease knowledge base.

3.4 Quality of life impact

Direct QoL instruments specific to L1 syndrome were not found in the retrieved primary sources. However, L1 syndrome includes SPG1/MASA phenotypes within the hereditary spastic paraplegia (HSP) spectrum. A 2024 review of HSP emphasizes that HSP “does not reduce a person’s lifespan” but “significantly impairs their quality of life as they age,” reflecting progressive mobility impairment (awuah2024hereditaryspasticparaplegia pages 1-2). This provides indirect but clinically relevant framing for QoL in L1CAM-related spastic paraplegia phenotypes.

4. Genetic / Molecular Information

4.1 Causal gene

L1CAM encodes a ~1275 aa single-pass transmembrane glycoprotein with six Ig-like domains and five FNIII domains and a conserved cytoplasmic tail that includes the ankyrin-binding FIGQY motif (weller2001geneticandclinical pages 1-2).

4.2 Pathogenic variant spectrum

Key points supported by clinical genetics sources: - Reported >280 distinct L1CAM mutations, ~50% missense; many are “private” to individual families (xie2018twonovelpathogenic pages 1-2). - Variant types include missense, nonsense, frameshift, splice-altering variants, and structural variants/CNVs (xie2018twonovelpathogenic pages 1-2, weller2001geneticandclinical pages 10-11).

4.3 Genotype–phenotype correlations (current understanding)

A consistent trend across the clinical literature is: - Truncating variants (especially extracellular-domain truncations leading to absent/non-detectable protein) are associated with severe phenotypes including severe hydrocephalus and higher infant mortality (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 2-3). - Missense variants and cytoplasmic-domain variants often produce milder phenotypes than extracellular truncations (weller2001geneticandclinical pages 1-2, xie2018twonovelpathogenic pages 1-2). - A practical classification framework (Classes I–IV) dividing extracellular truncating vs extracellular missense vs cytoplasmic vs splicing-related groups is described in fetal hydrocephalus case literature (xie2018twonovelpathogenic pages 1-2).

4.4 Allele frequency and constraint notes

A genetics study in another phenotype context (childhood-onset psychosis) reports L1CAM is highly constrained (e.g., pLI=1) and uses gnomAD rarity thresholds for candidate variants; while not L1-syndrome–specific, it underscores strong selective constraint on L1CAM (sato2020hemizygousmutationsin pages 1-6).

4.5 Modifier genes / epigenetics / chromosomal abnormalities

No definitive modifier genes or disease-specific epigenetic signatures were identified in retrieved sources. Some reports acknowledge phenotypic variability within families and across variants, implying possible modifying factors (silan2005anovell1cam pages 2-3).

5. Environmental Information

No established environmental, lifestyle, or infectious causal contributors were identified in the retrieved evidence. L1 syndrome is primarily genetic (X-linked, L1CAM pathogenic variants) (weller2001geneticandclinical pages 1-2).

6. Mechanism / Pathophysiology

6.1 Causal chain (high-level)

L1CAM pathogenic variants → impaired cell adhesion/signaling/trafficking and impaired neurite outgrowth/axon guidance/migration and CNS tract development → neuroanatomic malformations (aqueductal stenosis, ventriculomegaly/hydrocephalus, corpus callosum/corticospinal tract abnormalities) → developmental delay/intellectual disability and motor syndrome (spastic paraplegia/gait disturbance), plus associated features (e.g., adducted thumbs). (weller2001geneticandclinical pages 1-2)

6.2 2023 mechanistic advance: L1–LC3 (autophagy-related) coupling

A 2023 mechanistic study reports that the L1-70 fragment binds LC3 via an extracellular LIR motif in the fourth FNIII domain, and that this interaction is required for L1-mediated neurite outgrowth and neuronal survival (loers2023interactionofl1cam pages 14-16, loers2023interactionofl1cam pages 2-4). This creates a mechanistic bridge between L1CAM processing and autophagy/mitophagy-related pathways.

Direct abstract-supported quote (from abstract text captured): the study states that “L1-70 interacts with LC3 via the extracellular LIR motif in the fourth fibronectin type III domain” and that “the disruption of the L1-LC3 interaction reduces L1-mediated neurite outgrowth and neuronal survival” (loers2023interactionofl1cam pages 1-2).

6.3 2024 congenital hydrocephalus genetics synthesis

A 2024 congenital hydrocephalus review provides epidemiologic framing and pathway categories (cilia movement, neurogenesis/apoptosis, etc.), and explicitly lists L1CAM among the limited number of genes currently associated with congenital hydrocephalus in humans (liu2024congenitalhydrocephalusa pages 1-3).

Direct abstract-supported quote: “The global prevalence rate for congenital hydrocephalus (CH) is approximately one out of every five hundred births” and genetic influences may be involved in “up to 40%” of cases, but the etiology has been pinpointed in “fewer than 5%” of human instances (liu2024congenitalhydrocephalusa pages 1-3).

A key figure from this review summarizes L1CAM within genetic and mechanistic groupings: - Figure shows L1CAM listed under “nervous system growth/development” among CH genetic causes (liu2024congenitalhydrocephalusa media 5d669376).

6.4 Anatomy and cell types implicated

Primary anatomic substrates include: - Brain ventricles and CSF pathways (ventriculomegaly/hydrocephalus; aqueduct) (weller2001geneticandclinical pages 1-2, varagur2022syndromichydrocephalus. pages 1-3) - Corpus callosum and corticospinal tracts (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 1-2)

Suggested ontology mappings: - UBERON: UBERON:0000955 (brain); UBERON:0002285 (corpus callosum); UBERON:0004686 (cerebral aqueduct); UBERON:0002288 (lateral ventricle) (anatomy inferred from phenotypes) (weller2001geneticandclinical pages 1-2, varagur2022syndromichydrocephalus. pages 1-3). - CL (cell types): CL:0000540 (neuron); CL:0000129 (glial cell); CL:0000127 (astrocyte); Schwann cell involvement noted for L1 expression (CL:0000218) (weller2001geneticandclinical pages 1-2). - GO biological processes (examples): neuron migration, axon guidance, neurite outgrowth, cell–cell adhesion, myelination, regulation of autophagy/mitophagy (supported conceptually by L1 functions and L1–LC3 evidence) (weller2001geneticandclinical pages 1-2, loers2023interactionofl1cam pages 14-16).

6.5 Molecular profiling / omics

No disease-specific multi-omics signatures (transcriptomic/proteomic/metabolomic) in patients were found in the retrieved sources.

7. Anatomical Structures Affected

Primary systems: CNS (ventricular system/CSF flow, midline structures, long tracts) (weller2001geneticandclinical pages 1-2)
Structures: aqueduct of Sylvius, ventricles (hydrocephalus), corpus callosum, corticospinal tracts (weller2001geneticandclinical pages 1-2, varagur2022syndromichydrocephalus. pages 19-23)
Peripheral/other: adducted thumbs reflect limb/hand posture abnormalities (weller2001geneticandclinical pages 1-2).

8. Temporal Development

Onset: commonly prenatal/congenital for severe HSAS; prenatal imaging may detect ventriculomegaly and ACC in the second trimester (ochando2016prenataldiagnosisof pages 1-2, li2020l1cammutationsin pages 3-4).
Course: severe prenatal hydrocephalus can lead to stillbirth/early infant death; milder variants may survive with chronic neurodevelopmental disability (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 1-2).

9. Inheritance and Population

9.1 Inheritance pattern

X-linked recessive (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 2-3).

9.2 Epidemiology (statistics)

HSAS frequency: ~1 in 30,000 live male births (silan2005anovell1cam pages 1-2, xie2018twonovelpathogenic pages 1-2).
Contribution to congenital hydrocephalus: L1CAM mutations estimated up to ~25% of isolated male congenital hydrocephalus in classic review literature (weller2001geneticandclinical pages 1-2).
Proportion of congenital hydrocephalus that is X-linked hydrocephalus: ~5% (varagur2022syndromichydrocephalus. pages 1-3).
Congenital hydrocephalus overall: ~1/500 births globally; genetics may contribute to up to 40% but <5% of cases are genetically solved (liu2024congenitalhydrocephalusa pages 1-3).

10. Diagnostics

10.1 Clinical/imaging

Prenatal ultrasound: ventriculomegaly/hydrocephalus, third ventricle dilation, corpus callosum agenesis; adducted thumbs can sometimes be detected (li2020l1cammutationsin pages 3-4, silan2005anovell1cam pages 2-3).
Fetal MRI can complement ultrasound for ventriculomegaly and callosal anomalies (ochando2016prenataldiagnosisof pages 2-3).
Postnatal MRI is used to assess hydrocephalus/aqueductal stenosis and associated malformations (varagur2022syndromichydrocephalus. pages 19-23).

10.2 Genetic testing approaches (real-world)

If L1 syndrome is suspected (e.g., male fetus with hydrocephalus + other signs) and karyotype is normal, targeted L1CAM sequencing is used in practice (ochando2016prenataldiagnosisof pages 1-2).
Medical exome sequencing has been used for fetuses with ultrasound abnormalities to identify L1CAM variants, using ACMG/AMP interpretation; reported detection rates vary strongly by family history (15.7% sporadic vs 74.2% with ≥2 affected relatives) (li2020l1cammutationsin pages 3-4).

10.3 Differential diagnosis (prenatal hydrocephalus)

Differential diagnoses noted in prenatal L1CAM hydrocephalus work include Chiari II malformation, other aqueductal stenosis/gliosis, intrauterine infection, hemorrhage, fetal alcohol syndrome, and chromosomal abnormalities (trisomy 13/18, triploidy) (ochando2016prenataldiagnosisof pages 2-3).

11. Outcome / Prognosis

Spectrum: ranges from severe prenatal-onset hydrocephalus with stillbirth/early infant death to milder ventricular enlargement compatible with longer survival (weller2001geneticandclinical pages 1-2).
Severe cases: can have poor neurodevelopmental outcomes even after neurosurgical CSF diversion (e.g., ventriculostomy) because of underlying brain malformations (silan2005anovell1cam pages 1-2).
Motor disability/QoL: in L1CAM-related spastic paraplegia phenotypes, progressive spasticity and gait impairment can substantially impair QoL; HSP literature suggests lifespan may be preserved in many forms but disability can be significant (awuah2024hereditaryspasticparaplegia pages 1-2, gasser2010efnsguidelineson pages 8-9).

12. Treatment

12.1 Surgical/interventional management (hydrocephalus)

Syndromic hydrocephalus management commonly includes ventriculoperitoneal shunting; ETV ± CPC is used in some settings but efficacy is variable in young infants (varagur2022syndromichydrocephalus. pages 1-3, varagur2022syndromichydrocephalus. pages 19-23).
Case literature includes endoscopic ventriculostomy in a severe L1CAM family case (silan2005anovell1cam pages 1-2).

Suggested MAXO terms (examples): - MAXO:0000058 (cerebrospinal fluid shunting procedure; ventriculoperitoneal shunt) — concept mapped to VP shunt use (varagur2022syndromichydrocephalus. pages 19-23) - MAXO:0000756 (endoscopic third ventriculostomy) — concept mapped to ETV (varagur2022syndromichydrocephalus. pages 19-23)

12.2 Pharmacotherapy / disease-modifying therapies

No disease-modifying pharmacotherapy is established for L1 syndrome in the retrieved sources; foundational and prenatal reports emphasize lack of curative therapy and the role of genetic counseling (silan2005anovell1cam pages 1-2, weller2001geneticandclinical pages 1-2).

12.3 Experimental/advanced therapeutics

Mouse/in vitro work describes L1 mimetics and multiple L1-based strategies in CNS injury contexts (e.g., L1 peptides, function-triggering antibodies, recombinant domains), but these are not clinical L1 syndrome therapies in the retrieved evidence (jiang2024singlenucleotidepolymorphism pages 1-2).

13. Prevention

Primary prevention is genetic: - Genetic counseling and carrier testing in families with known L1CAM variants (varagur2022syndromichydrocephalus. pages 1-3). - Prenatal diagnosis using DNA from chorionic villus sampling or amniocentesis with targeted mutation analysis is emphasized; preimplantation genetic diagnosis/testing is also described as possible (silan2005anovell1cam pages 2-3, ochando2016prenataldiagnosisof pages 2-3).

Suggested MAXO terms (examples): - MAXO:0000079 (genetic counseling) - MAXO:0001002 (prenatal genetic testing) - MAXO:0001184 (preimplantation genetic testing)

14. Other Species / Natural Disease

No naturally occurring veterinary analogs were identified in the retrieved evidence.

15. Model Organisms

Mouse and in vitro models provide substantial mechanistic support: - L1/858–863 knock-in mouse: mutation of a dibasic motif in FNIII domain disrupts cleavage sites and is associated with hippocampal neuronal death, astrogliosis and behavioral alterations (congiu2023micemutatedin pages 1-2, congiu2023micemutatedin pages 2-4). - L1-201 (D201) point-mutant mouse: used as an L1 syndrome model; males show worse learning/memory after experimental TBI; in vitro L1 mimetics normalized neuritogenesis and survival deficits and Schwann-cell process formation (jiang2024singlenucleotidepolymorphism pages 1-2). - L1 deficiency/other alleles: multiple mouse perturbations show axon guidance and tract defects and variable ventriculomegaly/hydrocephalus depending on allele and genetic background (congiu2023micemutatedin pages 16-17). - Mechanistic in vitro assays: ELISA/immunoprecipitation/proximity ligation and neurite outgrowth assays demonstrate L1–LC3 coupling required for neurite outgrowth and neuronal survival (loers2023interactionofl1cam pages 2-4, loers2023interactionofl1cam pages 1-2).

Key knowledge-base summary table

Category	Key points (concise)	Evidence/notes
Disease identifier	L1 syndrome; MONDO:0017140	Open Targets disease mapping links L1 syndrome to MONDO_0017140 and L1CAM as the principal associated target (OpenTargets Search: L1 syndrome-L1CAM)
Core synonyms / spectrum terms	Overlapping L1CAM-related phenotypes include X-linked hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS), MASA syndrome, CRASH syndrome (corpus callosum hypoplasia, retardation/intellectual disability, adducted thumbs, spastic paraplegia, hydrocephalus), SPG1 (spastic paraplegia type 1), and X-linked agenesis/partial agenesis of the corpus callosum (ACC)	Synonym set and spectrum terminology are consistently described across foundational reviews and case reports (weller2001geneticandclinical pages 1-2, xie2018twonovelpathogenic pages 1-2, li2020l1cammutationsin pages 1-3, silan2005anovell1cam pages 1-2)
Causal gene	L1CAM (L1 cell adhesion molecule), Xq28; neural cell-adhesion glycoprotein important for CNS development	L1CAM is the established causal gene for L1 syndrome and related allelic disorders (OpenTargets Search: L1 syndrome-L1CAM, weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 1-3)
Inheritance	X-linked recessive; affected individuals are usually hemizygous males; female carriers are often asymptomatic but can occasionally manifest disease with skewed/non-random X-inactivation	Human clinical literature describes typical X-linked transmission and occasional manifesting females (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 2-3, li2020l1cammutationsin pages 3-4)
Hallmark phenotypes	Major recurrent features: congenital hydrocephalus/ventriculomegaly (often aqueductal stenosis), adducted thumbs, spasticity/spastic paraplegia, agenesis/hypoplasia of corpus callosum, intellectual disability/developmental delay, gait and speech problems; severity ranges from fetal-lethal hydrocephalus to milder neurodevelopmental disease	Core phenotype spectrum summarized in reviews and prenatal/fetal case series (weller2001geneticandclinical pages 1-2, xie2018twonovelpathogenic pages 1-2, li2020l1cammutationsin pages 3-4, li2020l1cammutationsin pages 1-3)
Onset / course	Often prenatal or congenital for severe HSAS; hydrocephalus may start in utero; milder presentations may survive into childhood/adulthood with chronic motor/cognitive disability	Natural-history pattern described in foundational review and fetal studies (weller2001geneticandclinical pages 1-2, li2020l1cammutationsin pages 1-3, xie2018twonovelpathogenic pages 1-2)
Key epidemiology: L1 syndrome / HSAS	~1 in 30,000 live male births; described as the most common inherited form of hydrocephalus	Reported in multiple L1CAM-focused papers (silan2005anovell1cam pages 1-2, xie2018twonovelpathogenic pages 1-2, li2020l1cammutationsin pages 3-4)
Key epidemiology: contribution to congenital hydrocephalus	Up to ~25% of isolated male congenital hydrocephalus may be attributable to an X-chromosomal gene mutation in classic literature on L1 disease	Foundational review gives this estimate in the context of L1 disease/X-linked hydrocephalus (weller2001geneticandclinical pages 1-2)
Broader congenital hydrocephalus epidemiology	Congenital hydrocephalus (CH) affects ~1/500 births globally; genetic factors may contribute up to 40% of cases, but a precise genetic etiology has been pinpointed in <5% of human cases	Recent CH review provides current epidemiologic framing and highlights limited solved fraction despite substantial genetic contribution (liu2024congenitalhydrocephalusa pages 1-3)
Variant spectrum	Broad spectrum with >280 reported L1CAM variants; about ~50% missense; many are private/family-specific; variant types include missense, nonsense, frameshift, splice-site, CNVs, and whole-gene deletions	Mutation spectrum summarized in case literature/reviews; CNVs are also recognized in HSP-related genes including L1CAM (xie2018twonovelpathogenic pages 1-2, weller2001geneticandclinical pages 9-10)
Genotype–phenotype correlation	General trend: missense variants in extracellular or cytoplasmic regions often produce milder phenotypes, whereas truncating / loss-of-function variants, especially in extracellular domains or with absent protein, are associated with more severe disease including severe hydrocephalus and higher infant mortality	Recurrent genotype–phenotype trend across classic and later reports (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 2-3, li2020l1cammutationsin pages 3-4, xie2018twonovelpathogenic pages 1-2)
Mutation classes	Proposed functional classes: Class I extracellular frameshift/nonsense → loss of function, severe; Class II extracellular missense → partial function, variable severity; Class III cytoplasmic variants → signaling defects, usually milder; Class IV extracellular variants associated with aberrant splicing, phenotype less clearly defined	Practical classification summarized in fetal hydrocephalus report/review (xie2018twonovelpathogenic pages 1-2)
2023 mechanistic advance	L1–LC3 interaction: the L1-70 fragment binds LC3 via an extracellular LIR motif in the 4th FNIII domain; disrupting this interaction impairs L1-dependent neurite outgrowth and neuronal survival, linking L1CAM to autophagy/mitophagy-related machinery	Direct mechanistic evidence from 2023 study; important for understanding downstream neuronal vulnerability in L1CAM dysfunction (loers2023interactionofl1cam pages 14-16, loers2023interactionofl1cam pages 1-2, loers2023interactionofl1cam pages 16-17, loers2023interactionofl1cam pages 2-4)
2023-2024 broader mechanism context	L1CAM biology supports cell migration, neurite outgrowth, neuronal survival, myelination, synaptic plasticity; congenital hydrocephalus pathways highlighted in 2024 review include nervous system growth/development, cilia synthesis/movement, ion channels/transport, Reissner’s fiber synthesis, cell apoptosis, and neurogenesis	Recent CH review places L1CAM among the limited confirmed CH genes and Figure 2 summarizes pathway groupings; recent mouse work also supports consequences of extracellular-domain mutations for neuronal death/behavior (liu2024congenitalhydrocephalusa pages 1-3, liu2024congenitalhydrocephalusa media 5d669376, congiu2023micemutatedin pages 20-21, jiang2024singlenucleotidepolymorphism pages 1-2)
Diagnostic/KB note	Evidence here is drawn from aggregated disease-level resources and published human case series/reviews, with mechanistic support from mouse/in vitro studies; useful for phenotype, mechanism, and inheritance fields in a knowledge base	Human clinical, review, and model-organism evidence are all represented in the cited contexts (OpenTargets Search: L1 syndrome-L1CAM, weller2001geneticandclinical pages 1-2, liu2024congenitalhydrocephalusa pages 1-3, loers2023interactionofl1cam pages 14-16)

Table: This table summarizes high-yield knowledge base facts for L1 syndrome, including identifiers, synonyms, inheritance, hallmark phenotypes, epidemiology, genotype-phenotype patterns, and recent mechanistic advances. It is useful as a concise evidence-backed overview of L1CAM-related disease.

Visual evidence (recent review)

Figure evidence supporting L1CAM as a congenital hydrocephalus gene and mechanism category: - A 2024 review figure summarizes genetic causes/pathways of congenital hydrocephalus and includes L1CAM under nervous system growth/development (liu2024congenitalhydrocephalusa media 5d669376).

Notes on limitations of this report

Disease identifiers beyond MONDO (e.g., Orphanet IDs, ICD-10/ICD-11, MeSH IDs) were not directly retrievable in the current tool context; key synonym/phenotype mapping is nonetheless supported by primary and review literature (weller2001geneticandclinical pages 1-2, silan2005anovell1cam pages 1-2).
Many 2023–2024 L1 syndrome clinical reports and some systematic reviews were not obtainable in full text via the current retrieval; consequently, some sections (e.g., formal diagnostic criteria, detailed prevalence by region, standardized QoL metrics) remain qualitative. (liu2024congenitalhydrocephalusa pages 1-3, weller2001geneticandclinical pages 1-2)

References

(weller2001geneticandclinical pages 1-2): Sabine Weller and Jutta Gärtner. Genetic and clinical aspects of x‐linked hydrocephalus (l1 disease): mutations in the l1cam gene. Human Mutation, 18:1-12, Jul 2001. URL: https://doi.org/10.1002/humu.1144, doi:10.1002/humu.1144. This article has 241 citations and is from a domain leading peer-reviewed journal.
(loers2023interactionofl1cam pages 14-16): Gabriele Loers, Ralf Kleene, Viviana Granato, Ute Bork, and Melitta Schachner. Interaction of l1cam with lc3 is required for l1-dependent neurite outgrowth and neuronal survival. International Journal of Molecular Sciences, 24:12531, Aug 2023. URL: https://doi.org/10.3390/ijms241512531, doi:10.3390/ijms241512531. This article has 9 citations.
(loers2023interactionofl1cam pages 2-4): Gabriele Loers, Ralf Kleene, Viviana Granato, Ute Bork, and Melitta Schachner. Interaction of l1cam with lc3 is required for l1-dependent neurite outgrowth and neuronal survival. International Journal of Molecular Sciences, 24:12531, Aug 2023. URL: https://doi.org/10.3390/ijms241512531, doi:10.3390/ijms241512531. This article has 9 citations.
(liu2024congenitalhydrocephalusa pages 1-3): Xiu-Yun Liu, Xin Song, Marek Czosnyka, Chiara Robba, Zofia Czosnyka, Jennifer Lee Summers, Hui-Jie Yu, Guo-Yi Gao, Peter Smielewski, Fang Guo, Mei-Jun Pang, and Dong Ming. Congenital hydrocephalus: a review of recent advances in genetic etiology and molecular mechanisms. Military Medical Research, Aug 2024. URL: https://doi.org/10.1186/s40779-024-00560-5, doi:10.1186/s40779-024-00560-5. This article has 16 citations and is from a peer-reviewed journal.
(liu2024congenitalhydrocephalusa media 5d669376): Xiu-Yun Liu, Xin Song, Marek Czosnyka, Chiara Robba, Zofia Czosnyka, Jennifer Lee Summers, Hui-Jie Yu, Guo-Yi Gao, Peter Smielewski, Fang Guo, Mei-Jun Pang, and Dong Ming. Congenital hydrocephalus: a review of recent advances in genetic etiology and molecular mechanisms. Military Medical Research, Aug 2024. URL: https://doi.org/10.1186/s40779-024-00560-5, doi:10.1186/s40779-024-00560-5. This article has 16 citations and is from a peer-reviewed journal.
(OpenTargets Search: L1 syndrome-L1CAM): Open Targets Query (L1 syndrome-L1CAM, 7 results). Buniello, A. et al. (2025). Open Targets Platform: facilitating therapeutic hypotheses building in drug discovery. Nucleic Acids Research.
(silan2005anovell1cam pages 1-2): Fatma Silan, Ismail Ozdemir, and Willy Lissens. A novel l1cam mutation with l1 spectrum disorders. Prenatal Diagnosis, 25:57-59, Jan 2005. URL: https://doi.org/10.1002/pd.978, doi:10.1002/pd.978. This article has 16 citations and is from a peer-reviewed journal.
(li2020l1cammutationsin pages 1-3): Ying-Ting Li, Jing-Si Chen, Wei Jian, Yi-Duo He, Nan Li, Yi-Nong Xie, Jing Wang, Victor Wei Zhang, Wei-Ran Huang, Fu-man Jiang, Xiao-Qing Ye, Dun-Jin Chen, and Min Chen. L1cam mutations in three fetuses diagnosed by medical exome sequencing. Taiwanese journal of obstetrics & gynecology, 59 3:451-455, May 2020. URL: https://doi.org/10.1016/j.tjog.2020.03.022, doi:10.1016/j.tjog.2020.03.022. This article has 12 citations and is from a peer-reviewed journal.
(ochando2016prenataldiagnosisof pages 2-3): I. Ochando, V. Vidal, J. Gascon, M. Acién, Antonio Urbano, and J. Rueda. Prenatal diagnosis of x-linked hydrocephalus in a family with a novel mutation in l1cam gene. Journal of Obstetrics and Gynaecology, 36:403-405, Apr 2016. URL: https://doi.org/10.3109/01443615.2015.1086982, doi:10.3109/01443615.2015.1086982. This article has 14 citations and is from a peer-reviewed journal.
(jiang2024singlenucleotidepolymorphism pages 1-2): Haoyu Jiang, Anna O. Giarratana, Thomas Theis, Vini Nagaraj, Xiaofeng Zhou, Smita Thakker-Varia, Melitta Schachner, and Janet Alder. Single nucleotide polymorphism in cell adhesion molecule l1 affects learning and memory in a mouse model of traumatic brain injury. International Journal of Molecular Sciences, 25:3043, Mar 2024. URL: https://doi.org/10.3390/ijms25053043, doi:10.3390/ijms25053043. This article has 3 citations.
(silan2005anovell1cam pages 2-3): Fatma Silan, Ismail Ozdemir, and Willy Lissens. A novel l1cam mutation with l1 spectrum disorders. Prenatal Diagnosis, 25:57-59, Jan 2005. URL: https://doi.org/10.1002/pd.978, doi:10.1002/pd.978. This article has 16 citations and is from a peer-reviewed journal.
(ochando2016prenataldiagnosisof pages 1-2): I. Ochando, V. Vidal, J. Gascon, M. Acién, Antonio Urbano, and J. Rueda. Prenatal diagnosis of x-linked hydrocephalus in a family with a novel mutation in l1cam gene. Journal of Obstetrics and Gynaecology, 36:403-405, Apr 2016. URL: https://doi.org/10.3109/01443615.2015.1086982, doi:10.3109/01443615.2015.1086982. This article has 14 citations and is from a peer-reviewed journal.
(congiu2023micemutatedin pages 16-17): Ludovica Congiu, Viviana Granato, Igor Jakovcevski, Ralf Kleene, Luciana Fernandes, Sandra Freitag, Matthias Kneussel, Melitta Schachner, and Gabriele Loers. Mice mutated in the third fibronectin domain of l1 show enhanced hippocampal neuronal cell death, astrogliosis and alterations in behavior. Biomolecules, 13:776, Apr 2023. URL: https://doi.org/10.3390/biom13050776, doi:10.3390/biom13050776. This article has 2 citations.
(li2020l1cammutationsin pages 3-4): Ying-Ting Li, Jing-Si Chen, Wei Jian, Yi-Duo He, Nan Li, Yi-Nong Xie, Jing Wang, Victor Wei Zhang, Wei-Ran Huang, Fu-man Jiang, Xiao-Qing Ye, Dun-Jin Chen, and Min Chen. L1cam mutations in three fetuses diagnosed by medical exome sequencing. Taiwanese journal of obstetrics & gynecology, 59 3:451-455, May 2020. URL: https://doi.org/10.1016/j.tjog.2020.03.022, doi:10.1016/j.tjog.2020.03.022. This article has 12 citations and is from a peer-reviewed journal.
(gasser2010efnsguidelineson pages 8-9): T. Gasser, J. Finsterer, J. Baets, C. Van Broeckhoven, S. Di Donato, B. Fontaine, P. De Jonghe, A. Lossos, T. Lynch, C. Mariotti, L. Schöls, A. Spinazzola, Z. Szolnoki, S. J. Tabrizi, C.M.E. Tallaksen, M. Zeviani, J‐M. Burgunder, and H. F. Harbo. Efns guidelines on the molecular diagnosis of ataxias and spastic paraplegias. European Journal of Neurology, 17:179-188, Feb 2010. URL: https://doi.org/10.1111/j.1468-1331.2009.02873.x, doi:10.1111/j.1468-1331.2009.02873.x. This article has 74 citations and is from a domain leading peer-reviewed journal.
(varagur2022syndromichydrocephalus. pages 1-3): Kaamya Varagur, Sai Anusha Sanka, and Jennifer M. Strahle. Syndromic hydrocephalus. Neurosurgery clinics of North America, 33 1:67-79, Jan 2022. URL: https://doi.org/10.1016/j.nec.2021.09.006, doi:10.1016/j.nec.2021.09.006. This article has 38 citations and is from a peer-reviewed journal.
(varagur2022syndromichydrocephalus. pages 19-23): Kaamya Varagur, Sai Anusha Sanka, and Jennifer M. Strahle. Syndromic hydrocephalus. Neurosurgery clinics of North America, 33 1:67-79, Jan 2022. URL: https://doi.org/10.1016/j.nec.2021.09.006, doi:10.1016/j.nec.2021.09.006. This article has 38 citations and is from a peer-reviewed journal.
(kutlubaeva2024hereditaryspasticparaplegias pages 1-2): R. F. Kutlubaeva, M. Kutlubaev, R. V. Magzhanov, E. V. Sayfullina, and I. Khidiyatova. Hereditary spastic paraplegias. Neuromuscular Diseases, Jan 2024. URL: https://doi.org/10.17650/2222-8721-2023-13-4-74-82, doi:10.17650/2222-8721-2023-13-4-74-82. This article has 5 citations.
(awuah2024hereditaryspasticparaplegia pages 1-2): Wireko Andrew Awuah, Joecelyn Kirani Tan, Anastasiia D Shkodina, Tomas Ferreira, Favour Tope Adebusoye, Adele Mazzoleni, Jack Wellington, Lian David, Ellie Chilcott, Helen Huang, Toufik Abdul-Rahman, Vallabh Shet, Oday Atallah, Jacob Kalmanovich, Riaz Jiffry, Divine Elizabeth Madhu, Kateryna Sikora, Oleksii Kmyta, and Mykhailo Yu Delva. Hereditary spastic paraplegia: novel insights into the pathogenesis and management. SAGE Open Medicine, Dec 2024. URL: https://doi.org/10.1177/20503121231221941, doi:10.1177/20503121231221941. This article has 31 citations.
(awuah2024hereditaryspasticparaplegia pages 8-10): Wireko Andrew Awuah, Joecelyn Kirani Tan, Anastasiia D Shkodina, Tomas Ferreira, Favour Tope Adebusoye, Adele Mazzoleni, Jack Wellington, Lian David, Ellie Chilcott, Helen Huang, Toufik Abdul-Rahman, Vallabh Shet, Oday Atallah, Jacob Kalmanovich, Riaz Jiffry, Divine Elizabeth Madhu, Kateryna Sikora, Oleksii Kmyta, and Mykhailo Yu Delva. Hereditary spastic paraplegia: novel insights into the pathogenesis and management. SAGE Open Medicine, Dec 2024. URL: https://doi.org/10.1177/20503121231221941, doi:10.1177/20503121231221941. This article has 31 citations.
(xie2018twonovelpathogenic pages 1-2): Bobo Xie, Jingsi Luo, Yaqin Lei, Qi Yang, Mengting Li, Shang Yi, Shiyu Luo, Jin Wang, Zailong Qin, Zuojian Yang, Hongwei Wei, and Xin Fan. Two novel pathogenic variants of l1cam gene in two fetuses with isolated x‑linked hydrocephaly: a case report. Molecular Medicine Reports, 18 6:5760-5764, Oct 2018. URL: https://doi.org/10.3892/mmr.2018.9583, doi:10.3892/mmr.2018.9583. This article has 6 citations and is from a peer-reviewed journal.
(weller2001geneticandclinical pages 10-11): Sabine Weller and Jutta Gärtner. Genetic and clinical aspects of x‐linked hydrocephalus (l1 disease): mutations in the l1cam gene. Human Mutation, 18:1-12, Jul 2001. URL: https://doi.org/10.1002/humu.1144, doi:10.1002/humu.1144. This article has 241 citations and is from a domain leading peer-reviewed journal.
(sato2020hemizygousmutationsin pages 1-6): Mitra S. Sato, Marinos Kyriakopoulos, Anthony James, Susanne Marwedel, Clare Borsay, Armandina Almanza Gutierrez, Alexandra I. Blakemore, and Anna C. Need. Hemizygous mutations in l1cam in two unrelated male probands with childhood onset psychosis. Psychiatric Genetics, 30:73-82, Jun 2020. URL: https://doi.org/10.1097/ypg.0000000000000253, doi:10.1097/ypg.0000000000000253. This article has 7 citations and is from a peer-reviewed journal.
(loers2023interactionofl1cam pages 1-2): Gabriele Loers, Ralf Kleene, Viviana Granato, Ute Bork, and Melitta Schachner. Interaction of l1cam with lc3 is required for l1-dependent neurite outgrowth and neuronal survival. International Journal of Molecular Sciences, 24:12531, Aug 2023. URL: https://doi.org/10.3390/ijms241512531, doi:10.3390/ijms241512531. This article has 9 citations.
(congiu2023micemutatedin pages 1-2): Ludovica Congiu, Viviana Granato, Igor Jakovcevski, Ralf Kleene, Luciana Fernandes, Sandra Freitag, Matthias Kneussel, Melitta Schachner, and Gabriele Loers. Mice mutated in the third fibronectin domain of l1 show enhanced hippocampal neuronal cell death, astrogliosis and alterations in behavior. Biomolecules, 13:776, Apr 2023. URL: https://doi.org/10.3390/biom13050776, doi:10.3390/biom13050776. This article has 2 citations.
(congiu2023micemutatedin pages 2-4): Ludovica Congiu, Viviana Granato, Igor Jakovcevski, Ralf Kleene, Luciana Fernandes, Sandra Freitag, Matthias Kneussel, Melitta Schachner, and Gabriele Loers. Mice mutated in the third fibronectin domain of l1 show enhanced hippocampal neuronal cell death, astrogliosis and alterations in behavior. Biomolecules, 13:776, Apr 2023. URL: https://doi.org/10.3390/biom13050776, doi:10.3390/biom13050776. This article has 2 citations.
(weller2001geneticandclinical pages 9-10): Sabine Weller and Jutta Gärtner. Genetic and clinical aspects of x‐linked hydrocephalus (l1 disease): mutations in the l1cam gene. Human Mutation, 18:1-12, Jul 2001. URL: https://doi.org/10.1002/humu.1144, doi:10.1002/humu.1144. This article has 241 citations and is from a domain leading peer-reviewed journal.
(loers2023interactionofl1cam pages 16-17): Gabriele Loers, Ralf Kleene, Viviana Granato, Ute Bork, and Melitta Schachner. Interaction of l1cam with lc3 is required for l1-dependent neurite outgrowth and neuronal survival. International Journal of Molecular Sciences, 24:12531, Aug 2023. URL: https://doi.org/10.3390/ijms241512531, doi:10.3390/ijms241512531. This article has 9 citations.
(congiu2023micemutatedin pages 20-21): Ludovica Congiu, Viviana Granato, Igor Jakovcevski, Ralf Kleene, Luciana Fernandes, Sandra Freitag, Matthias Kneussel, Melitta Schachner, and Gabriele Loers. Mice mutated in the third fibronectin domain of l1 show enhanced hippocampal neuronal cell death, astrogliosis and alterations in behavior. Biomolecules, 13:776, Apr 2023. URL: https://doi.org/10.3390/biom13050776, doi:10.3390/biom13050776. This article has 2 citations.

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Inheritance

Subtypes

Pathophysiology

Pathograph

Phenotypes

Genetic Associations

Medical Actions

Experimental Models

Source YAML

References & Deep Research

References

Deep Research

L1 Syndrome (L1CAM-related disorder) — Disease Characteristics Research Report

Executive summary

Target disease

1. Disease Information

1.1 Definition and overview

1.2 Key identifiers and synonyms

1.3 Evidence type

2. Etiology

2.1 Disease causal factors

2.2 Risk factors

2.3 Protective factors and gene–environment interaction

3. Phenotypes

3.1 Core phenotype spectrum (clinical)

3.2 Prenatal imaging phenotypes

3.3 HPO mapping

3.4 Quality of life impact

4. Genetic / Molecular Information

4.1 Causal gene

4.2 Pathogenic variant spectrum

4.3 Genotype–phenotype correlations (current understanding)

4.4 Allele frequency and constraint notes

4.5 Modifier genes / epigenetics / chromosomal abnormalities

5. Environmental Information

6. Mechanism / Pathophysiology

6.1 Causal chain (high-level)

6.2 2023 mechanistic advance: L1–LC3 (autophagy-related) coupling

6.3 2024 congenital hydrocephalus genetics synthesis

6.4 Anatomy and cell types implicated

6.5 Molecular profiling / omics

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

9.1 Inheritance pattern

9.2 Epidemiology (statistics)

10. Diagnostics

10.1 Clinical/imaging

10.2 Genetic testing approaches (real-world)

10.3 Differential diagnosis (prenatal hydrocephalus)

11. Outcome / Prognosis

12. Treatment

12.1 Surgical/interventional management (hydrocephalus)

12.2 Pharmacotherapy / disease-modifying therapies

12.3 Experimental/advanced therapeutics

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Key knowledge-base summary table

Visual evidence (recent review)

Notes on limitations of this report

Artifacts