Definition and research guide
This page combines a MeSH definition, publication statistics and selected research abstracts. It is a starting point for reading the literature, not a medical textbook or a systematic evidence review.
Content available: 4 complete abstracts (951 words), 10 references. Full article text is not stored or reproduced here; follow the PMID, DOI or PMC links to read the original sources and their access terms.
Definition
Congenital defect in the upper lip where the maxillary prominence fails to merge with the merged medial nasal prominences. It is thought to be caused by faulty migration of the mesoderm in the head region.
Definition: NLM Medical Subject Headings (MeSH) scope note (Public domain (U.S. National Library of Medicine); attribution requested). View the MeSH record.
Also known as: Cleft Lips; Lip, Cleft; Lips, Cleft; Harelip; Harelips.
Where it fits in the MeSH classification
- Broader topics
- Lip Diseases; Mouth Abnormalities
Research landscape
PubMed indexes 19,035 records tagged with the MeSH heading “Cleft Lip” (counts retrieved 2026-10-29). 4,006 of them (21.0%) were published from 2020 onward, and the busiest period so far is through 1999 with 7,425 records.
Reviews account for 1,558 records (8.2%) and meta-analyses for 241. Randomized controlled trials number 217 (1.1%) as a share of all records on the topic. Randomized trials make up only a small share of this literature, so much of what is known comes from laboratory, observational or descriptive work.
Show the data
| Period | Records |
|---|---|
| through 1999 | 7,425 |
| 2000-2009 | 2,887 |
| 2010-2019 | 4,717 |
| 2020 onward | 4,006 |
Publication-type chart data
| Type | Records | Share |
|---|---|---|
| Reviews | 1,558 | 8.2% |
| Meta-analyses | 241 | 1.3% |
| Randomized controlled trials | 217 | 1.1% |
Method: PubMed query "Cleft Lip"[MeSH Terms] with publication-type and date filters, retrieved 2026-10-29.
Reading the evidence in rare and inherited diseases
Rare conditions are difficult to study: few patients means small studies, case reports and registries are common, and randomized trials are the exception. Small samples limit precision and can exaggerate effects, and cases reported in the literature may be the most severe or unusual. Evidence from many small studies is best read together. Check how patients were identified, how many were included and how long they were followed.
Evidence from open-access studies
These open-access studies come from PubMed’s best-match results for this heading (papers whose main topic it is), ranked here by citation count, with one recent addition. Each abstract is reproduced in full under its recorded open licence so that you can read the authors’ own words. They illustrate the literature; they are not a systematic summary of it. Citation counts measure attention, not reliability or clinical benefit.
Valproic Acid in Pregnancy Revisited: Neurobehavioral, Biochemical and Molecular Changes Affecting the Embryo and Fetus in Humans and in Animals: A Narrative Review [1]
Abstract reading summary — source excerpts
- Opening excerpt
- Valproic acid (VPA) is a very effective anticonvulsant and mood stabilizer with relatively few side effects.
- Closing excerpt
- Animal studies generally recapitulate human data.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (239 words)
Valproic acid (VPA) is a very effective anticonvulsant and mood stabilizer with relatively few side effects. Being an epigenetic modulator, it undergoes clinical trials for the treatment of advanced prostatic and breast cancer. However, in pregnancy, it seems to be the most teratogenic antiepileptic drug. Among the proven effects are congenital malformations in about 10%. The more common congenital malformations are neural tube defects, cardiac anomalies, urogenital malformations including hypospadias, skeletal malformations and orofacial clefts. These effects are dose related; daily doses below 600 mg have a limited teratogenic potential. VPA, when added to other anti-seizure medications, increases the malformations rate. It induces malformations even when taken for indications other than epilepsy, adding to the data that epilepsy is not responsible for the teratogenic effects. VPA increases the rate of neurodevelopmental problems causing reduced cognitive abilities and language impairment. It also increases the prevalence of specific neurodevelopmental syndromes like autism (ASD) and Attention Deficit Hyperactivity Disorder (ADHD). High doses of folic acid administered prior to and during pregnancy might alleviate some of the teratogenic effect of VPA and other AEDs. Several teratogenic mechanisms are proposed for VPA, but the most important mechanisms seem to be its effects on the metabolism of folate, SAMe and histones, thus affecting DNA methylation. VPA crosses the human placenta and was found at higher concentrations in fetal blood. Its concentrations in milk are low, therefore nursing is permitted. Animal studies generally recapitulate human data.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 38203562 · DOI · PMC10779436
The Cleft Collective: protocol for a longitudinal prospective cohort study [2]
Abstract reading summary — source excerpts
- Opening excerpt
- IntroductionCleft lip and/or palate (CL/P) affects 1 in 700 live births globally.
- Closing excerpt
- Findings from the Cleft Collective are disseminated through peer-reviewed publications, conference presentations, newsletters and social media.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (296 words)
IntroductionCleft lip and/or palate (CL/P) affects 1 in 700 live births globally. Children born with CL/P and their families face various challenges throughout the child's development. Extant research is often limited by small numbers and single-centre data. The Cleft Collective, a national cohort study in the UK, aims to build a resource, available to collaborators across the globe, to understand causes, best treatments and long-term outcomes for those born with CL/P, ultimately seeking to enhance their quality of life through improved understanding and care.Methods and analysisA longitudinal prospective cohort study of children born with CL/P and their families. Recruitment occurs across the UK and started in November 2013. Recruitment will continue until September 2027 with an estimated final sample of 4822 children born with CL/P (1157 cleft lip including/excluding the alveolus; 2112 cleft palate only; 1042 unilateral cleft lip and palate and 511 bilateral cleft lip and palate). Biological samples are collected from all recruited members of the family. Parental and child questionnaires are collected at key time points throughout the child's development. Surgical data are collected at the time of surgical repair of the child's cleft. Consent is obtained to link to external data sources. Nested substudies can be hosted within the cohort. Regular engagement with participants takes place through birthday cards for the children, social media posts and newsletters. Patient and Public Involvement is conducted through the Cleft Lip And Palate Association and Cleft Collective Patient Consultation Group who provide insightful and essential guidance to the Cleft Collective throughout planning and conducting research.Ethics and disseminationThe Cleft Collective was ethically approved by the National Research Ethics Service committee South West-Central Bristol (REC13/SW/0064). Parental informed consent is required for participation. Findings from the Cleft Collective are disseminated through peer-reviewed publications, conference presentations, newsletters and social media.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 38969383 · DOI · PMC11227803
A distant global control region is essential for normal expression of anterior HOXA genes during mouse and human craniofacial development [3]
Abstract reading summary — source excerpts
- Opening excerpt
- Craniofacial abnormalities account for approximately one third of birth defects.
- Closing excerpt
- This evidence suggests we have identified a critical noncoding locus control region that specifically regulates anterior HOXA genes and copy number changes are pathogenic in human patients.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (182 words)
Craniofacial abnormalities account for approximately one third of birth defects. The regulatory programs that build the face require precisely controlled spatiotemporal gene expression, achieved through tissue-specific enhancers. Clusters of coactivated enhancers and their target genes, known as superenhancers, are important in determining cell identity but have been largely unexplored in development. In this study we identified superenhancer regions unique to human embryonic craniofacial tissue. To demonstrate the importance of such regions in craniofacial development and disease, we focused on an ~600 kb noncoding region located between NPVF and NFE2L3. We identified long range interactions with this region in both human and mouse embryonic craniofacial tissue with the anterior portion of the HOXA gene cluster. Mice lacking this superenhancer exhibit perinatal lethality, and present with highly penetrant skull defects and orofacial clefts phenocopying Hoxa2-/- mice. Moreover, we identified two cases of de novo copy number changes of the superenhancer in humans both with severe craniofacial abnormalities. This evidence suggests we have identified a critical noncoding locus control region that specifically regulates anterior HOXA genes and copy number changes are pathogenic in human patients.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 38167838 · DOI · PMC10762089
The Psychosocial Impact of Cleft Lip and/or Palate on Caregivers and Individuals in Low- and Middle-Income Countries: A Narrative Review [4]
Abstract reading summary — source excerpts
- Opening excerpt
- Low- and middle-income countries (LMICs) represent the highest incidence, morbidity, and Disability Adjusted Life Years for cleft lip and/or palate (CL/P) globally.
- Closing excerpt
- Building practice-relevant research capacity in LMICs to develop the evidence-base is essential.
- Interpretation limits
- Verbatim excerpts from the authors’ abstract; the closing excerpt may describe a finding, limitation or recommendation. Design, population, effect size and uncertainty have not been independently extracted or appraised. Read the complete abstract and linked paper before interpreting the findings.
Read complete abstract (234 words)
Low- and middle-income countries (LMICs) represent the highest incidence, morbidity, and Disability Adjusted Life Years for cleft lip and/or palate (CL/P) globally. Most cleft care models now include psychosocial support, yet the psychosocial impacts of CL/P in LMICs are understudied. This narrative review aimed to synthesize published literature to provide a foundation for future research and evidence-based psychosocial support. Seventy-one peer-reviewed articles published between September 2003 and July 2024 were included. Themes pertaining to caregivers included Social Experiences, Emotional Well-Being, Treatment Experiences, and overall Quality of Life. Themes regarding individuals with CL/P included Developmental Trajectory, Social Integration, Emotional Health, Satisfaction with Treatment, and Health-Related Quality of Life. Most articles focused on upper-middle-income countries. East Asia and Pacific was the most studied geographical region in LMICs, while Europe and Central Asia was the least studied. Only 28 of 135 LMICs (20.7%) were represented in the included psychosocial literature. Most studies (69%) utilized a quantitative design. Sample sizes ranged from 2 to 295, with 73% of studies recruiting from a single site. Few studies (28%) compared their data to reference or control groups. Just over half of studies used standardized, validated measures. Most studies were led by LMIC teams. This review calls for ongoing monitoring of psychological health in individuals with CL/P and their caregivers and coordinated investment into multifaceted psychosocial program in LMICs. Building practice-relevant research capacity in LMICs to develop the evidence-base is essential.
Abstract reproduced from the open-access article under the recorded cc by licence; © the authors. PMID 40518838 · DOI · PMC13176505
Key reviews and meta-analyses
The most cited review-type papers among PubMed’s best-match results for this heading, listed with bibliographic details only. Follow the links for the full text and access terms.
- Research article The psychosocial effects of cleft lip and palate: a systematic review [5]
- Research article Global prevalence of cleft palate, cleft lip and cleft palate and lip: A comprehensive systematic review and meta-analysis [6]
- Research article Tobacco smoking and oral clefts: a meta-analysis [7]
- Research article A meta-analysis of cleft maxillary osteotomy and distraction osteogenesis [8]
- Research article Revisiting the embryogenesis of lip and palate development [9]
- Research article Passive smoking in the etiology of non-syndromic orofacial clefts: a systematic review and meta-analysis [10]
References
- Ornoy A, Echefu B, Becker M. Valproic Acid in Pregnancy Revisited: Neurobehavioral, Biochemical and Molecular Changes Affecting the Embryo and Fetus in Humans and in Animals: A Narrative Review. . 2023. PMID 38203562 · DOI · PMC10779436
- Davies AJV, Humphries K, Lewis SJ, Ho K, Sandy JR, Wren Y. The Cleft Collective: protocol for a longitudinal prospective cohort study. . 2024. PMID 38969383 · DOI · PMC11227803
- Wilderman A, D'haene E, Baetens M, Yankee TN, Winchester EW, Glidden N, et al.. A distant global control region is essential for normal expression of anterior HOXA genes during mouse and human craniofacial development. . 2024. PMID 38167838 · DOI · PMC10762089
- Stock NM, Costa B, Zarola A, Auslander A, Brewster H, Swift P, et al.. The Psychosocial Impact of Cleft Lip and/or Palate on Caregivers and Individuals in Low- and Middle-Income Countries: A Narrative Review. . 2026. PMID 40518838 · DOI · PMC13176505
- Hunt O, Burden D, Hepper P, Johnston C. The psychosocial effects of cleft lip and palate: a systematic review. Eur J Orthod. 2005. PMID 15947228 · DOI
- Salari N, Darvishi N, Heydari M, Bokaee S, Darvishi F, Mohammadi M. Global prevalence of cleft palate, cleft lip and cleft palate and lip: A comprehensive systematic review and meta-analysis. J Stomatol Oral Maxillofac Surg. 2022. PMID 34033944 · DOI
- Little J, Cardy A, Munger RG. Tobacco smoking and oral clefts: a meta-analysis. Bull World Health Organ. 2004. PMID 15112010 · PMC2585921
- Cheung LK, Chua HD. A meta-analysis of cleft maxillary osteotomy and distraction osteogenesis. Int J Oral Maxillofac Surg. 2006. PMID 16154316 · DOI
- Hammond NL, Dixon MJ. Revisiting the embryogenesis of lip and palate development. Oral Dis. 2022. PMID 35226783 · DOI · PMC10234451
- Sabbagh HJ, Hassan MH, Innes NP, Elkodary HM, Little J, Mossey PA. Passive smoking in the etiology of non-syndromic orofacial clefts: a systematic review and meta-analysis. PLoS One. 2015. PMID 25760440 · DOI · PMC4356514
About this article
- Sources
- NLM Medical Subject Headings (definition, synonyms); NCBI PubMed (counts, identifiers); Europe PMC (open-access abstracts and citation counts).
- Verification
- Every reference was resolved against PubMed on 2026-10-31; title, year and DOI matched.
- Review state
- automated source verified; no human expert review has been recorded yet.
- Version
- 1, last updated 2026-10-29.
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Evidence strength
EvidenceHelix's computed view of the study designs behind this topic: how common meta-analyses, randomized trials and reviews are, how recent the literature is, and a plain-language reading. It describes the design mix of the literature. It is not a quality appraisal of any study, and it is not medical advice.