Primary Microcephaly:
A Full Research Review

Reproducible search log.

The 58 core papers derive from a structured assembly process by the thesis author covering all confirmed MCPH loci, mechanistic frameworks, expression datasets, GWAS/MAGMA resources, and neuropsychiatric intersection papers known as of 2022–2023. Eleven additional systematic search passes were run on 2026-06-17 to identify new literature: four passes targeting 2016–2022 (to fill the gap between the curated bibliography and the 2023-onward search) and seven passes targeting 2023–2026.

How the 33-gene list was built — MCPH1 (2002) to LMNB1/2 (2021).

Primary microcephaly gene discovery proceeded almost entirely through homozygosity mapping and exome sequencing in consanguineous families. Each landmark discovery not only added a locus but opened a new functional category — first DNA damage repair, then spindle poles, then kinetochore, then ESCRT, then nuclear lamina. The biological diversity of the gene list is the field's central puzzle.

Further foundational locus discoveries in the core bibliography:

• Nicholas et al. 2010 — WDR62 (MCPH2), second most common MCPH gene; regulates mitotic spindle orientation. Nat Genet · PMID 20890278
• Kumar et al. 2009 — STIL (MCPH7), pro-centriole initiation factor; loss causes monopolar spindles and mitotic arrest. AJHG · PMID 19200525
• Leidel et al. 2005 — SAS-6/SASS6 (MCPH14), the cartwheel-forming protein establishing nine-fold centriole symmetry. Nat Cell Biol · PMID 15665853
• Yang et al. 2012 — ZNF335 (MCPH10), trithorax/REST transcription regulator for upper-layer neuron identity. Cell · PMID 23178126
• Guemez-Gamboa et al. 2015 — MFSD2A (MCPH15), LPC-DHA transporter at the blood–brain barrier; uniquely non-cell-autonomous mechanism. Nat Genet · PMID 26005868
• Camargo Ortega et al. 2019 — AKNA (MCPH33), centriolar satellite TF regulating outer radial glia delamination. Nature · PMID 30787438
• Leal et al. 2020 — ANKLE2 (MCPH16), nuclear envelope reassembly factor and direct Zika NS4B target. J Hum Genet · PMID 32636503
• Parry et al. 2021 — LMNB1 (MCPH26) and LMNB2 (MCPH27), adding nuclear lamina biology as the sixth MCPH functional class. Genet Med · PMID 33033404
• Khan et al. 2020 — PDCD6IP/ALIX (MCPH29), ESCRT adaptor for cytokinetic abscission. Clin Genet · PMID 32286682
• Farooq et al. 2020 — RRP7A (MCPH28), linking ribosome biogenesis and cilia resorption. Nat Commun · PMID 33199730
• Carvalhal et al. 2022 — BUB1 (MCPH30), spindle assembly checkpoint kinase; ~40% chromosome segregation errors in patient cells. Sci Adv · PMID 35044816

For clinical reference: Verloes, Drunat & Passemard (2020) — ASPM primary microcephaly GeneReviews entry, covering inheritance, penetrance, diagnostic criteria, and management. Jean, Stuart & Tarailo-Graovac (2020) (Front Neurol, PMID 33192989) — separates Mendelian from environmental/metabolic MCPH causes. Jayaraman, Bae & Walsh (2018) (Annu Rev Genomics Hum Genet, PMID 29799801) — master review of MCPH genetics through MCPH25.

The centrosome → spindle → MSP model, and its limits.

By 2021, a unifying model had emerged — the mitotic surveillance pathway (MSP): prolonged mitosis activates 53BP1/USP28/TP53 to trigger neural progenitor apoptosis, explaining why ubiquitously expressed centrosome genes cause specifically brain phenotypes. But MCPH1, MFSD2A, ZNF335, RRP7A, and EXOSC10 operate outside the MSP, and new work shows the centrosome plays roles far beyond spindle assembly.

MSP origins — the founding 2016 papers & key 2019–2021 evidence

• Zaqout & Kaindl 2022 — MCPH is "not just a small brain": pachygyria, lissencephaly, corpus callosum dysgenesis, PV interneuron reduction, seizures in 3–75% of patients by gene. Front Cell Dev Biol · PMID 35111754
• Kiyomitsu, Obuse & Yanagida 2007 — Early characterisation of KNL1 (Blinkin/AF15q14) showing direct BUB1/BUBR1 interaction; mechanistic basis for why KNL1 loss causes mitotic failure. Dev Cell · PMID 17981135
• Cheeseman et al. 2006 — KMN network as the conserved core microtubule-binding site of the outer kinetochore; biochemical foundation for KNL1 structural role. Cell · PMID 17129783
• Caldas & DeLuca 2014 — Best single review of KNL1 molecular architecture: SILK/RVSF PP1 docking motifs, MELT repeats, phosphorylation switch. Chromosoma · PMID 24346128
• Saadi et al. 2016 — KNL1/CASC5 phenotypic expansion with brain MRI showing simplified gyral pattern. Neurogenetics · PMID 26446437
• Szczepanski et al. 2016 — KNL1 splice-disruption variant in large consanguineous family. Hum Genet · PMID 26800779
• Gurkaslar HK et al. 2020 — CCDC57 cooperates with microcephaly protein CEP63 to regulate centriole duplication; dual centrosomal roles reveal non-redundant functions within the CEP63 proximity network. Cell Rep · PMID 32402286

Why MCPH genes matter for understanding primate brain expansion.

ASPM, CDK5RAP2, CENPJ, and MCPH1 all show signatures of positive selection in anthropoid primates correlated with brain size, establishing the evolutionary rationale for studying MCPH genes as molecular candidates for the brain expansion event. KNL1 was subsequently identified as one of the top positively selected genes in the hominin lineage specifically — directly motivating this thesis.

• Montgomery, Mundy & Barton 2014 — Reviews whether MCPH evolution correlates are driven by direct selection on brain size or linked selection; evolutionary biology framework for KNL1 adaptive variant interpretation. Proc R Soc B · PMID 24452022
• Finlay & Darlington 1995 — Brain regions scale predictably with total brain size across mammals; quantitative basis for why MCPH progenitor perturbations produce macroscopically visible brain size reduction. Science · PMID 7777856

The same biology at different doses — microcephaly to autism to schizophrenia.

The central hypothesis of the MCPH atlas heatmap: complete loss of MCPH genes causes microcephaly, but partial disruption of the same pathways contributes to autism, schizophrenia, and cognitive variation. Evidence now exists at five levels: (1) mouse behavioural phenotypes in MCPH-gene models independent of brain size; (2) MCPH coding variants in psychiatric case-control studies; (3) GWAS/MAGMA statistical overlap; (4) centrosome proteins encoded by GWAS-confirmed psychiatric risk genes; (5) polygenic risk scores predicting neonatal brain volume.

• Garrett et al. 2020 — Aspm truncating mice: impaired cognition, corpus callosum dysgenesis, reduced parvalbumin+ interneurons in hippocampus and thalamic reticular nucleus — PV interneuron deficits are replicated across both autism and schizophrenia. Transl Psychiatry · PMID 32066665
• Al Eissa et al. 2019 — MCPH1 missense p.Asp61Gly associates with bipolar disorder (P=0.0009) and schizophrenia (P=0.037) in ~4,000 cases — first coding MCPH variant linked to adult-onset psychiatric illness. Am J Med Genet B · PMID 30957974
• Kaplanis et al. 2020 — 31,058 parent–offspring trios confirming de novo centrosome/spindle pathway variant burden across the NDD spectrum; MCPH genes sit within a rare-variant NDD continuum. Nature · PMID 33057194
• Yoon et al. 2025 — Korean NDD cohort; 418 patients with microcephaly; 142 causative genes; de novo dominant predominate; CRISPR validation of RTF1 and ASAP2 in organoids. Genome Med · PMID 40770811

GWAS & MAGMA resources

• Savage et al. 2018 — IQ GWAS (N=269,867); the IQ MAGMA heatmap column. Nat Genet · PMID 29942086
• Grove et al. 2019 — ASD GWAS (N~18 k cases); the ASD MAGMA column. Nat Genet · PMID 30804558
• Grasby et al. 2020 — Cortical surface area and thickness GWAS (N~52 k); not yet in bundle — adding it would directly test MCPH genes against brain size variation. Science · PMID 32193296
• Okbay et al. 2022 — Educational attainment GWAS EA4 (N~3 M); loci enriched in fetal brain regulatory regions. Nat Genet · PMID 35361970
• Darnell et al. 2011 — HITS-CLIP of ~800 brain mRNAs bound by FMRP; source of FMRP column in atlas. Cell · PMID 21784246
• Sugathan et al. 2014 — CHD8 ChIP-seq in human NPCs; CDK5RAP2 and ASPM are direct CHD8 targets. PNAS · PMID 25273099
• Abrahams et al. 2013 — SFARI Gene 2.0 curation system; source of SFARI columns in atlas. Mol Autism · PMID 24090431

New cross-condition evidence 2024–2026

From mouse to human organoids — why the model system matters.

MCPH research has gone through three model-system generations: patient fibroblasts and mouse knockouts (2000s–2010s), iPSC-derived NPCs (2010s), and human brain organoids (2013 onward). A 2024 paper shows the transition is sometimes necessary: CIT kinase mouse models failed to phenocopy the disease where human organoids succeeded.

• Takahashi & Yamanaka 2006 — iPSC reprogramming (Cell, Nobel Prize). Foundation of the patient-derived cell modelling pipeline. PMID 16904174
• Ran et al. 2013 — CRISPR-Cas9 genome engineering protocol (Nat Protoc). Used to validate guide RNAs for KNL1 variants in HEK293T cells in this thesis. PMID 24157548
• Anzalone et al. 2020 — CRISPR toolkit review including base editors (Nat Biotechnol). For introducing specific KNL1 adaptive substitutions without DSBs, base editing is the appropriate tool. PMID 32572269
• Yoon et al. 2025 — Korean NDD cohort; CRISPR KO of RTF1 and ASAP2 in human NPCs and organoids; current state of the art for variant-to-mechanism pipeline. Genome Med · PMID 40770811
• Xu et al. 2025 — CETN3 KO organoids smaller with excess neuronal differentiation; dual mechanism through centrosome assembly and RNA splicing. EMBO Mol Med · PMID 40926052
• Turkalj et al. 2025 (preprint) — METTL5 KO organoids; delayed NSC proliferation via mitochondrial CHCHD2. bioRxiv · PMID 40672170

Single-cell expression datasets underlying the atlas

• Telley et al. 2019 — scRNA-seq of mouse cortical progenitors E12–E15; source of Telley slope columns in the heatmap; temporal patterning at the progenitor birth cohort level. Science · PMID 31073041
• Pollen et al. 2015 — First comprehensive transcriptomic characterisation of outer radial glia (oRG/bRG), the human-enriched progenitor subtype. Cell · PMID 26406371
• Lui, Hansen & Kriegstein 2011 — Three-tier progenitor hierarchy (apical RG → IPC → oRG) as context for interpreting CoGAPS developmental stages. Cell · PMID 21729779

Large-scale exome sequencing — diagnostic yields and the allelic series.

Consanguineous families from Turkey, Pakistan, Iran, and Korea continue to be the primary resource for MCPH gene discovery. Diagnostic yields have risen to 50–53% with modern exome sequencing. The mechanistic split between true MCPH (mitotic division pathway) and syndromic microcephaly (transcription regulation, trafficking) is now visible at cohort scale.

• Ahmad et al. 2026 (Bicknell/Baple labs) — Pakistani families; novel ASPM, CDK5RAP2, VPS13B variants; extends VPS13B beyond Cohen syndrome. BMC Neurology · PMID 42249392
• Fellows et al. 2024 (Bicknell lab) — Novel KNL1 intronic variant causing exon 23 skipping; important new allele for KNL1 functional work. Am J Med Genet A · PMID 37937525 · DOI 10.1002/ajmg.a.63468
• Saima et al. 2024 — Five centrosomal genes (CENPJ, STIL, CDK5RAP2, RBBP8, CEP135) in South Asian cohort with microcephaly + intellectual disability. Neurogenetics · PMID 38795246
• Farooq et al. 2026 — Pakistani cohort extending the ASPM allelic series. Front Genet · PMID 41555927
• Lee J et al. 2021 — 40 Korean patients; 47.5% diagnostic yield with WES; CDK5RAP2 and CENPJ most common; includes functional GFP-centrosome assays validating novel alleles. Temporal precursor to Yoon 2025. Front Genet · PMID 33584783
• Rasool S et al. 2020 — 32 consanguineous Pakistani families; 15 novel pathogenic variants across 6 MCPH genes (ASPM, CDK5RAP2, CENPJ, KNL1, CEP135, MCPH1); extends known allelic series for each locus. Mol Genet Genomic Med · PMID 32677750
• Boonsawat P et al. 2019 — 62-patient European cohort; 48.4% molecular diagnostic yield by WES; centrosome/kinetochore pathway variants were specific to primary (non-syndromic) MCPH. Key data point supporting the centrosome pathway–primary MCPH specificity. Genet Med · PMID 30842647

New genes, new pathways, and the limits of the mouse model.

Since 2023, six new MCPH gene candidates have been reported and two mechanistic paradigm shifts have emerged: RNA processing as a genuine MCPH functional class, and DNA replication fork speed as a developmental clock that bridges microcephaly biology to adult psychiatric phenotypes.

• Isik et al. 2026 — CDK4/CDK6 biallelic variants; mitochondrial ROS and mitochondria-induced apoptosis as a novel MCPH apoptotic arm parallel to MSP. J Med Genet · PMID 41856556
• Wang et al. 2026 — DIAPH1 mutations; microcephaly with visual impairment via Wnt/β-catenin activation. BMC Med Genomics · PMID 41963888
• Liao et al. 2026 — CEP170 as novel MCPH locus; centrosome subdistal appendage protein regulating microtubule anchoring. J Biomed Sci · PMID 41888776
• Li et al. 2024 — CEP295 biallelic variants causing Seckel-like syndrome with microcephaly; centriole elongation factor. EBioMedicine · PMID 38154379
• Tshuva et al. 2025 (preprint) — NDE1 loss drives caudal identity shift in neural progenitors via aberrant ERK; "wrong-identity divisions" model extends the field beyond simple cell number reduction. bioRxiv · PMID 40832186 · DOI 10.1101/2025.08.12.669854
• Sterling et al. 2023 — BubR1 microcephaly via p53-independent apoptotic pathways; expands the MSP model. Front Cell Dev Biol · PMID 37900274
• Wang et al. 2024 — PRMT5-mediated HR in neural progenitors; arginine methylation as epigenetic regulator of DNA damage response. Cell Mol Life Sci · PMID 38459149
• Zhi et al. 2025 — WDR62 post-mitotic role in radial migration and callosal projections; explains ASD-like behaviour in Xu 2023. Neurobiol Dis · PMID 40349858

The researchers shaping the field — past contributions and what to follow.

These researchers have published key papers in this atlas bibliography or in the 2023–2026 update search. Designed as a living watch-list: if you want to monitor new MCPH developments, these are the authors and labs whose outputs most directly affect the atlas.

Where the field stands, and what it means for the atlas.