CRADD-related thin lissencephaly (TLIS) is an autosomal recessive malformation of cortical development that is mechanistically distinct from the classical microtubule/neuronal-migration lissencephalies. It is caused by biallelic loss-of-function missense variants in CRADD (RAIDD), a caspase-recruitment-domain and death-domain (DD) adaptor protein that oligomerizes with PIDD1 and caspase-2 to form the apoptosis-initiating PIDDosome. Rather than arresting neuronal migration, the pathogenic variants cluster in the CRADD death domain and abolish CRADD's ability to activate caspase-2, reducing caspase-2-mediated programmed cell death in the developing neocortex. The resulting failure to appropriately prune neurons and neuropil produces a characteristic "thin" lissencephaly: an anterior-predominant pachygyria with shallow, unusually wide sulci and only a mildly thick cortex (5-7 mm, versus 10-20 mm in classical lissencephaly), often with megalencephaly, intellectual disability, and seizures, and without non-cortical brain malformations. CRADD-TLIS is therefore the exemplar of a reduced-apoptosis (rather than impaired-migration) cortical malformation mechanism, and was identified through review of more than 1,400 individuals with lissencephaly. Notably, Cradd-null mice reproduce the megalencephaly and seizures but not the human cortical lamination defect, highlighting a possible species difference in the developmental importance of caspase-2 signaling.
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name: CRADD-Related Thin Lissencephaly
creation_date: "2026-06-10T12:00:00Z"
category: Mendelian
disease_term:
preferred_term: CRADD-related thin lissencephaly
term:
id: MONDO:0013785
label: intellectual disability, autosomal recessive 34
parents:
- Lissencephaly Spectrum Disorders
description: >-
CRADD-related thin lissencephaly (TLIS) is an autosomal recessive malformation
of cortical development that is mechanistically distinct from the classical
microtubule/neuronal-migration lissencephalies. It is caused by biallelic
loss-of-function missense variants in CRADD (RAIDD), a caspase-recruitment-domain
and death-domain (DD) adaptor protein that oligomerizes with PIDD1 and caspase-2
to form the apoptosis-initiating PIDDosome. Rather than arresting neuronal
migration, the pathogenic variants cluster in the CRADD death domain and abolish
CRADD's ability to activate caspase-2, reducing caspase-2-mediated programmed
cell death in the developing neocortex. The resulting failure to appropriately
prune neurons and neuropil produces a characteristic "thin" lissencephaly: an
anterior-predominant pachygyria with shallow, unusually wide sulci and only a
mildly thick cortex (5-7 mm, versus 10-20 mm in classical lissencephaly), often
with megalencephaly, intellectual disability, and seizures, and without
non-cortical brain malformations. CRADD-TLIS is therefore the exemplar of a
reduced-apoptosis (rather than impaired-migration) cortical malformation
mechanism, and was identified through review of more than 1,400 individuals
with lissencephaly. Notably, Cradd-null mice reproduce the megalencephaly and
seizures but not the human cortical lamination defect, highlighting a possible
species difference in the developmental importance of caspase-2 signaling.
pathophysiology:
- name: Loss of CRADD Death-Domain Function and PIDDosome Signaling
description: >-
CRADD (RAIDD) is a death-domain adaptor that bridges PIDD1 and caspase-2 to
assemble the apoptosis-promoting PIDDosome. The recessive TLIS-associated
missense variants cluster within the CRADD death domain. In
co-immunoprecipitation assays these variants still bind caspase-2 and PIDD,
so they do not disrupt complex partnering per se, but they abrogate the
adaptor's ability to drive caspase-2 activation, producing a functional
loss of pro-apoptotic signaling.
cell_types:
- preferred_term: Neuron
term:
id: CL:0000540
label: neuron
biological_processes:
- preferred_term: Regulation of neuron apoptotic process
term:
id: GO:0043523
label: regulation of neuron apoptotic process
modifier: DECREASED
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "CRADD (also known as RAIDD) is a death-domain-containing adaptor protein that oligomerizes with PIDD and caspase-2 to initiate apoptosis."
explanation: Establishes CRADD's normal molecular role as the PIDDosome death-domain adaptor that initiates caspase-2-dependent apoptosis.
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "TLIS variants cluster in the CRADD death domain, a platform for interaction with other death-domain-containing proteins including PIDD."
explanation: Localizes the pathogenic variants to the death domain, the functional interaction surface of CRADD.
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "TLIS-associated CRADD variants do not disrupt interactions with caspase-2 or PIDD in co-immunoprecipitation assays, but still abolish CRADD's ability to activate caspase-2, resulting in reduced neuronal apoptosis in vitro."
explanation: Shows the variants retain binding to caspase-2/PIDD yet lose the ability to activate caspase-2, defining a functional (not interaction-disrupting) loss of function.
downstream:
- target: Reduced Caspase-2-Mediated Developmental Neuronal Apoptosis
- name: Reduced Caspase-2-Mediated Developmental Neuronal Apoptosis
conforms_to: "neural_progenitor_centrosome_spindle_dysfunction#Programmed Cell Death Imbalance Branch"
description: >-
Loss of CRADD-dependent caspase-2 activation reduces programmed cell death
in the developing cortex. In vitro, wild-type CRADD drives apoptosis of
PC12 cells and CRADD-null neurons, whereas the TLIS variants fail to do so,
confirming that the variants reduce neuronal apoptosis. This places
deficient developmental apoptosis — rather than the migration arrest of
classical lissencephaly — at the center of the CRADD pathomechanism.
cell_types:
- preferred_term: Neuron
term:
id: CL:0000540
label: neuron
- preferred_term: Cerebral cortex neuron
term:
id: CL:0010012
label: cerebral cortex neuron
biological_processes:
- preferred_term: Neuron apoptotic process
term:
id: GO:0051402
label: neuron apoptotic process
modifier: DECREASED
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: IN_VITRO
snippet: "Only WT CRADD import induced apoptosis in PC12 cells."
explanation: Demonstrates that TLIS variants, unlike wild-type CRADD, fail to induce apoptosis, directly supporting reduced caspase-2-mediated cell death.
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Megalencephaly and lissencephaly associated with defective programmed cell death from loss of CRADD function in humans implicate reduced apoptosis as an important pathophysiological mechanism of cortical malformation."
explanation: States the authors' central conclusion that reduced developmental apoptosis is the pathophysiological mechanism of the human cortical malformation.
downstream:
- target: Impaired Cortical Sculpting with Megalencephaly and Thin Lissencephaly
- name: Impaired Cortical Sculpting with Megalencephaly and Thin Lissencephaly
description: >-
Deficient developmental apoptosis impairs the normal "sculpting" of the
neocortex — the elimination of excess neurons and neuropil that shapes
cortical size and gyration. The proposed consequence is megalencephaly with
a thin lissencephaly pattern (anterior-predominant pachygyria, wide shallow
sulci, mildly thickened cortex) together with intellectual disability,
reflecting a failure to prune inappropriate neurons rather than a neuronal
migration arrest.
cell_types:
- preferred_term: Cerebral cortex neuron
term:
id: CL:0010012
label: cerebral cortex neuron
biological_processes:
- preferred_term: Cerebral cortex development
term:
id: GO:0021987
label: cerebral cortex development
modifier: ABNORMAL
- preferred_term: Synapse pruning
term:
id: GO:0098883
label: synapse pruning
modifier: DECREASED
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "loss of CRADD function results in reduction of caspase-2-mediated apoptosis, resulting in megalencephaly and TLIS from failure to prune inappropriate neurons and/or neuropil."
explanation: Articulates the proposed link from reduced apoptosis to megalencephaly and thin lissencephaly via failed pruning of neurons/neuropil.
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Our data suggest that CRADD/caspase-2 signaling is critical for normal gyration of the developing human neocortex and for normal cognitive ability."
explanation: Connects CRADD/caspase-2 signaling to normal human cortical gyration and cognition, the functions disrupted in TLIS.
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: PARTIAL
evidence_source: MODEL_ORGANISM
snippet: "seizures without obvious changes in cortical thickness or lamination"
explanation: Cradd-null mice reproduce megalencephaly and seizures but not the cortical lamination defect, so the mouse only partially recapitulates the human cortical malformation (see HUMAN_MODEL_MISMATCH discussion).
downstream:
- target: Thin Lissencephaly (Anterior-Predominant Pachygyria)
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Failed developmental pruning produces the characteristic anterior-predominant thin lissencephaly pattern.
- target: Megalencephaly
causal_link_type: DIRECT
description: Reduced developmental neuronal apoptosis expands brain size, producing megalencephaly.
- target: Intellectual Disability
causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
description: Abnormal cortical sculpting disrupts cognitive development.
- target: Seizures
causal_link_type: INDIRECT_UNKNOWN_INTERMEDIATES
description: Malformed cortical architecture and altered neuronal pruning increase seizure susceptibility.
genetic:
- name: CRADD
gene_term:
preferred_term: CRADD
term:
id: hgnc:2340
label: CRADD
association: Causal
notes: >-
CRADD (RAIDD) encodes the caspase-recruitment-domain/death-domain adaptor of
the PIDDosome. Biallelic missense variants clustered in the death domain
cause autosomal recessive thin lissencephaly (MONDO:0013785 / OMIM:614499,
"intellectual developmental disorder, autosomal recessive 34, with variant
lissencephaly"). The variants act through loss of caspase-2 activation rather
than disruption of complex assembly.
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "Trio-based whole-exome sequencing and targeted re-sequencing identified recessive mutations of CRADD in six individuals with TLIS from four unrelated families of diverse ethnic backgrounds."
explanation: Establishes CRADD as the causal gene through recessive variants identified across four unrelated TLIS families.
inheritance:
- name: Autosomal recessive
inheritance_term:
preferred_term: Autosomal recessive inheritance
term:
id: HP:0000007
label: Autosomal recessive inheritance
description: >-
CRADD-related thin lissencephaly follows autosomal recessive inheritance.
Biallelic (homozygous or compound heterozygous) loss-of-function variants
in CRADD are required for disease expression.
phenotypes:
- category: Neurologic
name: Thin Lissencephaly (Anterior-Predominant Pachygyria)
description: >-
Anterior-predominant pachygyria with shallow, unusually wide sulci and a
mildly thick cortex (5-7 mm), without non-cortical brain malformations — the
"thin" lissencephaly pattern that distinguishes CRADD-TLIS from classical
lissencephaly.
phenotype_term:
preferred_term: Thin lissencephaly (anterior-predominant pachygyria)
term:
id: HP:0020188
label: Anterior predominant pachygyria with 5-10 mm cortical thickness
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "lissencephaly (TLIS) variant characterized by megalencephaly, frontal predominant pachygyria, intellectual disability, and seizures."
explanation: Defines the core TLIS phenotype, including the frontal-predominant pachygyria pattern.
- category: Neurologic
name: Megalencephaly
description: >-
Enlarged brain size (megalencephaly), frequently with a large occipitofrontal
circumference, accompanying the thin lissencephaly.
phenotype_term:
preferred_term: Megalencephaly
term:
id: HP:0001355
label: Megalencephaly
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "lissencephaly (TLIS) variant characterized by megalencephaly, frontal predominant pachygyria, intellectual disability, and seizures."
explanation: Megalencephaly is a defining feature of the CRADD-TLIS phenotype.
- category: Neurologic
name: Intellectual Disability
description: >-
Mild-to-moderate intellectual disability accompanies the cortical
malformation in affected individuals.
phenotype_term:
preferred_term: Intellectual disability
term:
id: HP:0001249
label: Intellectual disability
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "lissencephaly (TLIS) variant characterized by megalencephaly, frontal predominant pachygyria, intellectual disability, and seizures."
explanation: Intellectual disability is part of the defining TLIS phenotype.
- category: Neurologic
name: Seizures
description: >-
Seizures occur in a subset of affected individuals.
phenotype_term:
preferred_term: Seizure
term:
id: HP:0001250
label: Seizure
evidence:
- reference: PMID:27773430
reference_title: "Mutations in CRADD Result in Reduced Caspase-2-Mediated Neuronal Apoptosis and Cause Megalencephaly with a Rare Lissencephaly Variant."
supports: SUPPORT
evidence_source: HUMAN_CLINICAL
snippet: "lissencephaly (TLIS) variant characterized by megalencephaly, frontal predominant pachygyria, intellectual disability, and seizures."
explanation: Seizures are listed among the defining clinical features of TLIS.
treatments:
- name: Antiseizure Pharmacotherapy
description: >-
Symptomatic management of seizures with antiseizure medication, guided by
seizure type and clinical course. No disease-modifying therapy exists.
treatment_term:
preferred_term: Pharmacotherapy
term:
id: NCIT:C15986
label: Pharmacotherapy
- name: Supportive and Developmental Care
description: >-
Multidisciplinary supportive care including developmental support, physical
and occupational therapy, and management of intellectual disability.
treatment_term:
preferred_term: supportive care
term:
id: MAXO:0000950
label: supportive care
- name: Genetic Counseling
description: >-
Counseling for families given the autosomal recessive inheritance and
recurrence risk; relevant in populations with consanguinity or founder
variants.
treatment_term:
preferred_term: Genetic Counseling
term:
id: NCIT:C15240
label: Genetic Counseling
discussions:
- discussion_id: gap_cradd_mouse_model_lamination_mismatch
prompt: >-
Does the Cradd-null mouse faithfully model the human CRADD-TLIS cortical
malformation, or does the absence of a cortical lamination/gyration defect in
the mouse — which has megalencephaly and seizures but cytoarchitecturally
normal cortex — indicate that caspase-2-dependent developmental apoptosis is
more critical for human than for mouse neocortical sculpting?
kind: HUMAN_MODEL_MISMATCH
status: OPEN
attaches_to:
- pathophysiology#Reduced Caspase-2-Mediated Developmental Neuronal Apoptosis
- pathophysiology#Impaired Cortical Sculpting with Megalencephaly and Thin Lissencephaly
rationale: >-
Homozygous Cradd-knockout mice reproduce the megalencephaly and (handling-
induced) seizures seen in affected humans but show normal cortical thickness
and lamination, in contrast to the pachygyria/thin lissencephaly and
intellectual disability of CRADD-TLIS individuals. The authors note that
caspase-2 activity may be less important in development of the mouse brain
than the human brain. Because the human neocortex undergoes far more
extensive gyrification and a longer, larger neurogenic and pruning program
than the lissencephalic mouse cortex, a quantitatively or qualitatively
greater dependence on caspase-2-mediated apoptosis in humans is a plausible
explanation for the mismatch. The mismatch matters because the in vivo
mechanistic evidence for the cortical malformation rests substantially on a
mouse model that does not reproduce the defining human cortical phenotype.
proposed_experiments:
- experiment_id: exp_cradd_human_organoid_apoptosis
name: CRADD-null / CRADD-TLIS human cortical organoid apoptosis and lamination assay
description: >-
Generate CRADD-null and patient-variant (e.g., p.Gly128Arg) iPSC-derived
cortical organoids and quantify caspase-2 activation, developmental
neuronal apoptosis, neuron number, cortical-plate thickness, and lamination
relative to isogenic controls, to test whether reduced caspase-2-mediated
apoptosis produces a human cortical-architecture phenotype not seen in
mouse.
experiment_type:
preferred_term: iPSC organoid perturbation assay
model_systems:
- name: Human iPSC-derived cortical organoid
description: >-
Cortical organoid differentiated from patient-derived or gene-edited
human iPSCs carrying CRADD loss-of-function variants.
experimental_model_type: ORGANOID
- experiment_id: exp_cradd_gyrencephalic_model
name: CRADD loss in a gyrencephalic model
description: >-
Evaluate cortical lamination, gyration, and brain size after CRADD
loss-of-function in a gyrencephalic species (e.g., ferret) that, unlike the
mouse, normally gyrifies, to test whether the human-like cortical phenotype
emerges when a gyrencephalic developmental program is present.
experiment_type:
preferred_term: in vivo gene perturbation
model_systems:
- name: Gyrencephalic mammalian model
description: >-
A gyrencephalic species with an outer subventricular zone and cortical
folding, contrasting with the lissencephalic mouse.
experimental_model_type: OTHER
notes: >-
CRADD-TLIS is anchored to MONDO:0013785 (OMIM:614499; "intellectual
developmental disorder, autosomal recessive 34, with variant lissencephaly").
It is modeled as a distinct entry from the classical microtubule/migration
lissencephalies (see Lissencephaly Spectrum Disorders) because its
pathomechanism is reduced caspase-2-mediated developmental apoptosis rather
than impaired neuronal migration. This entry was seeded from the cortical
malformation curation epic (Romero, Bahi-Buisson & Francis, Semin Cell Dev
Biol 2018, section 3) but all evidence is drawn from and verified against the
primary report (Di Donato et al., Am J Hum Genet 2016, PMID:27773430).