Cancer in Patients With Familial Adenomatous Polyposis: A Nationwide Danish Cohort Study With Matched Controls.

BACKGROUND & AIMS: Familial adenomatous polyposis (FAP) is a hereditary disorder that predisposes patients to colorectal cancer (CRC). Prophylactic colectomy has greatly reduced the risk of CRC. However, new associations between FAP and the risk of other cancers have subsequently emerged. In this study, we assessed the risk of specific primary and secondary cancers among patients with FAP compared with matched controls. METHODS: All known patients with FAP up until April 2021 were identified in the nationwide Danish Polyposis Register and paired with 4 unique controls matched by birth year, sex, and postal code. The risk of overall cancers, specific cancer types, and risk of a second primary cancer was assessed and compared with controls. RESULTS: The analysis included 565 patients with FAP and 1890 controls. The overall risk of cancer was significantly higher for patients with FAP than for controls (hazard ratio [HR], 4.12; 95% confidence interval [CI], 3.28-5.17; P < .001). The increased risk was mainly due to CRC (HR, 4.61; 95% CI, 2.58-8.22; P < .001), pancreatic cancer (HR, 6.45; 95% CI, 2.02-20.64; P = .002), and duodenal/small-bowel cancer (HR, 14.49; 95% CI, 1.76-119.47; P = .013), whereas no significant difference was observed for gastric cancer (HR, 3.29; 95% CI, 0.53-20.23; P = .20). Furthermore, the risk of a second primary cancer was significantly higher for patients with FAP (HR, 1.89; 95% CI, 1.02-3.50; P = .042). Between 1980 and 2020, the risk of cancer among patients with FAP decreased by ∼50%. CONCLUSIONS: Despite an absolute reduction in the risk of developing cancer among patients with FAP, the risk remained significantly higher than for the background population due to colorectal, pancreatic, and duodenal/small-bowel cancers.

Psychiatric and Educational Aspects of Familial Adenomatous Polyposis: A Nationwide Danish Cohort Study With Matched Nonexposed Individuals.

INTRODUCTION: Familial adenomatous polyposis (FAP) is an autosomal, dominantly inherited disorder that predisposes to colorectal cancer. An increased risk of cancer may affect mental health, but the magnitude of this effect remains unknown. We assessed the psychosocial functioning, including the educational level attained and risk of psychiatric comorbidity, of patients with FAP by comparing them with matched nonexposed individuals. METHODS: All Danish patients with FAP diagnosed before April 2021 were identified in the Danish Polyposis Register and paired with 4 matched nonexposed individuals. Educational history, psychiatric contacts or diagnoses ( International Classification of Disease, 10th Revision ), and treatment with antidepressants, anxiolytics, or antipsychotics were compared between patients with FAP and nonexposed individuals. RESULTS: The analysis included 445 patients with FAP and 1,538 nonexposed individuals. The highest educational level reached was significantly lower for patients with FAP ( P < 0.001). When comparing patients with FAP and nonexposed and adjusting for a cancer diagnosis, an increased risk was observed for a psychiatric contact (1.69, 95% confidence interval [CI] 1.25-2.29, P < 0.001), any psychiatric prescription (1.39, 95% CI 1.17-1.66, P < 0.001), a psychiatric diagnosis (1.64, 95% CI 1.19-2.26, P = 0.002), and experiencing any psychiatric event (hazard ratio 1.42, 95% CI 1.20-1.68, P < 0.001). An increased risk was specifically seen for mood (affective) disorders (1.76, 95% CI 1.09-2.83, P = 0.02) and behavioral and emotional disorders (2.01, 95% CI 1.10-3.69, P = 0.02) and the need for antidepressants (1.59, 95% CI 1.24-2.03, P < 0.001) and antipsychotics (1.85, 95% CI 1.26-2.70, P = 0.002). DISCUSSION: Compared with nonexposed individuals, patients with had significantly less education and an increased risk of developing mood and behavioral disorders, with an increased likelihood of needing antidepressants and antipsychotics.

Cancer Risks in Attenuated and Classical Familial Adenomatous Polyposis: A Nationwide Cohort with Matched, Non-Exposed Individuals: Cancer and surgery in AFAP and FAP patients.

INTRODUCTION: Familial adenomatous polyposis (FAP) is caused by pathogenic variants in the APC gene. FAP is usually categorized according to phenotype: classical FAP (CFAP) and attenuated FAP (AFAP); the latter is considered to have a milder disease course. We aimed to assess the risk of overall and specific cancers in CFAP and AFAP patients compared to matched, non-exposed individuals. METHODS: All known Danish FAP patients were classified as either CFAP or AFAP and assigned four matched, non-exposed individuals. The risk of overall and specific cancers, and mortality were analyzed. RESULTS: The analysis included 311 CFAP patients, 134 AFAP patients, and 1,600 non-exposed individuals. The overall cancer risk was significantly higher for both CFAP and AFAP patients than for non-exposed individuals, with hazard ratios (HR) of 4.77 (95% confidence interval (CI), 3.61-6.32; P<0.001) for CFAP and 3.22 (95% CI, 2.16-4.80; P<0.001) for AFAP. No significant difference was observed when comparing CFAP and AFAP (HR=1.48; 95% CI, 0.98-2.25; P=0.0646). The HR of colonic cancer was 2.16 (95% CI, 0.99-7.72; P=0.0522) and 2.72 (95% CI, 1.19-6.22; P=0.0177 for CFAP and AFAP), respectively compared to non-exposed and did not differ between CFAP and AFAP patients (HR=0.80; 95% CI, 0.32-2.00; P=0.6278). Mortality was significantly higher in CFAP (HR=2.96; 95% CI, 2.04-4.28; P<0.001), but not in AFAP (HR=1.40; 95% CI, 0.73-2.69; P=0.311). CONCLUSION: Nationwide data reveal differing risk profiles for specific cancers and mortality in AFAP and CFAP compared to non-exposed individuals. The cancer burden of AFAP necessitates consistent monitoring of these patients.

Expanding the understanding of telomere biology disorder with reports from two families harboring variants in ZCCHC8 and TERC.

Telomere biology disorder (TBD) can present within a wide spectrum of symptoms ranging from severe congenital malformations to isolated organ dysfunction in adulthood. Diagnosing TBD can be challenging given the substantial variation in symptoms and age of onset across generations. In this report, we present two families, one with a pathogenic variant in ZCCHC8 and another with a novel variant in TERC. In the literature, only one family has previously been reported with a ZCCHC8 variant and TBD symptoms. This family had multiple occurrences of pulmonary fibrosis and one case of bone marrow failure. In this paper, we present a second family with the same ZCCHC8 variant (p.Pro186Leu) and symptoms of TBD including pulmonary fibrosis, hematological disease, and elevated liver enzymes. The suspicion of TBD was confirmed with the measurement of short telomeres in the proband. In another family, we report a novel likely pathogenic variant in TERC. Our comprehensive description encompasses hematological manifestations, as well as pulmonary and hepatic fibrosis. Notably, there are no other reports which associate this variant to disease. The families expand our understanding of the clinical implications and genetic causes of TBD.

Hereditary haemorrhagic telangiectasia in Danish patients with pathogenic variants in SMAD4: a nationwide study.

BACKGROUND AND AIMS: Hereditary haemorrhagic telangiectasia (HHT) is an autosomal dominant condition characterised by recurrent epistaxis, telangiectatic lesions in the skin and mucosal membranes, and arteriovenous malformations (AVMs) in various organs. In 3%-5% of patients, HHT is caused by pathogenic germline variants (PVs) in SMAD4, and these patients often have additional symptoms of juvenile polyposis syndrome and thoracic aneurysms. The phenotypic spectrum of SMAD4-associated HHT is less known, including the penetrance and severity of HHT. We aimed to investigate the phenotypic spectrum of HHT manifestations in Danish patients with PVs in SMAD4 and compare the findings with current literature. METHODS: The study is a retrospective nationwide study with all known Danish patients with PVs in SMAD4. In total, 35 patients were included. The patients were identified by collecting data from genetic laboratories, various databases and clinical genetic departments across the country. Clinical information was mainly collected from the Danish HHT-Centre at Odense University Hospital. RESULTS: Twenty-nine patients with PVs in SMAD4 (83%) were seen at the HHT-Centre. Seventy-six per cent of these fulfilled the Curaçao criteria, 86% experienced recurrent epistaxis and 83% presented with telangiectatic lesions at different anatomical localisations. Almost 60% had AVMs, mainly pulmonary and hepatic, while none was found to have cerebral AVMs. Fifteen per cent had thoracic aortic abnormalities. CONCLUSION: We present a nationwide study of one of the largest populations of patients with PVs in SMAD4 that has systematically been examined for HHT manifestations. The patients presented the full spectrum of HHT-related manifestations and the majority fulfilled the Curaçao criteria.

Identification of a novel pathogenic deep intronic variant in PTEN resulting in pseudoexon inclusion in a patient with juvenile polyps.

Colorectal, hamartomatous juvenile polyps occur as part of different hereditary syndromes, including Juvenile polyposis syndrome and PTEN-hamartoma tumour syndrome. However, based on clinical manifestations alone, it is difficult to differentiate between the syndromes, and genetic analysis with an NGS-panel is often used to aid diagnostics. We report a 59-year-old male with colorectal juvenile polyps, who had been referred to genetic testing but had normal genetic analysis. He did not fulfil the clinical criteria of PTEN- hamartoma tumour syndrome, but the clinical criteria of Juvenile polyposis syndrome. With Whole Genome Sequencing we detected a novel intronic variant of unknown significance in PTEN (NC_000010.11:g.89687361 A > G(chr10, hg19), NM_000314.8:c.209 + 2047 A > G). RNA analysis classified the variant as likely pathogenic as it results in a pseudoexon inclusion introducing a frameshift and a premature stop codon. The patient was then diagnosed with PTEN-hamartoma Tumour syndrome. To our knowledge this is the first report of a variant resulting in pseudoexon inclusion in PTEN.

Survival, surveillance, and genetics in patients with Peutz-Jeghers syndrome: A nationwide study.

Peutz-Jeghers syndrome (PJS) is an autosomal dominant hereditary polyposis syndrome causing increased morbidity and mortality due to complications of polyposis and the development of cancer. STK11 is the only gene known to be associated with PJS, although in 10%-15% of patients fulfilling the diagnostic criteria no pathogenic variant (PV) is identified. The primary aim of this study was to identify the genetic etiology in all known PJS patients in Denmark and to estimate the risk of cancer, effect of surveillance and overall survival. We identified 56 patients (2-83 years old) with PJS. The detection rate of PVs was 96%, including three cases of mosaicism (6%). In two patients a variant was not detected. At the age of 40 years, the probabilities of cancer and death were 21% and 16%, respectively; at the age of 70 years these probabilities were 71% and 69%. Most cases of cancer (92%) were identified between the scheduled examinations in the surveillance program. These observations emphasize that PJS should be regarded as a general cancer predisposition syndrome, where improvement of clinical care is needed.

Preimplantation genetic testing in two Danish couples affected by Peutz-Jeghers syndrome.

BACKGROUND: Guidelines from the European Hereditary Tumor Group as well as The Danish National Guidelines for Peutz-Jeghers Syndrome (PJS) state that both prenatal diagnosis and preimplantation genetic testing for monogenic disorders (PGT-M) should be offered to patients with PJS. However, only a few cases resulting in viable pregnancies have been published. OBJECTIVE: We present two cases of PJS patients going through PGT-M for PJS. We highlight the awareness of this possibility and discuss the technical and ethical challenges of performing PGT-M for PJS. METHODS AND RESULTS: Case 1: A 36-year-old male with PJS and his partner were referred for genetic counseling. The patient carried a pathogenic de novo variant in STK11. After a terminated pregnancy of a fetus carrying the same pathogenic variant, microsatellite polymorphic marker analysis was established, and the patient was offered PGT-M. The female partner of the patient gave birth to a healthy boy after five years of fertility treatment. Case 2: A 35-year-old female with PJS and her partner were referred for genetic counseling. She carried an inherited pathogenic STK11 variant. The couple was offered PGT-M. Genetic testing of the embryos was performed using microsatellite polymorphic markers. After two rounds of oocyte extraction a blastocyst predicted not to be affected by PJS was identified. The blastocyst was transferred; however, this did not result in a viable pregnancy. CONCLUSIONS: PGT-M can be offered to patients with PJS. The process may be long and filled with ethical dilemmas requiring patients to be motivated and persistent.

Size matters in telomere biology disorders ‒ expanding phenotypic spectrum in patients with long or short telomeres.

The end of each chromosome consists of a DNA region termed the telomeres. The telomeres serve as a protective shield against degradation of the coding DNA sequence, as the DNA strand inevitably ‒ with each cell division ‒ is shortened. Inherited genetic variants cause telomere biology disorders when located in genes (e.g. DKC1, RTEL1, TERC, TERT) playing a role in the function and maintenance of the telomeres. Subsequently patients with telomere biology disorders associated with both too short or too long telomeres have been recognized. Patients with telomere biology disorders associated with short telomeres are at increased risk of dyskeratosis congenita (nail dystrophy, oral leukoplakia, and hyper- or hypo-pigmentation of the skin), pulmonary fibrosis, hematologic disease (ranging from cytopenia to leukemia) and in rare cases very severe multiorgan manifestations and early death. Patients with telomere biology disorders associated with too long telomeres have in recent years been found to confer an increased risk of melanoma and chronic lymphocytic leukemia. Despite this, many patients have an apparently isolated manifestation rendering telomere biology disorders most likely underdiagnosed. The complexity of telomere biology disorders and many causative genes makes it difficult to design a surveillance program which will ensure identification of early onset disease manifestation without overtreatment.

Danish guidelines for management of non-APC-associated hereditary polyposis syndromes.

Hereditary Polyposis Syndromes are a group of rare, inherited syndromes characterized by the presence of histopathologically specific or numerous intestinal polyps and an increased risk of cancer. Some polyposis syndromes have been known for decades, but the development in genetic technologies has allowed the identification of new syndromes.. The diagnosis entails surveillance from an early age, but universal guideline on how to manage and surveille these new syndromes are lacking. This paper represents a condensed version of the recent guideline (2020) from a working group appointed by the Danish Society of Medical Genetics and the Danish Society of Surgery on recommendations for the surveillance of patients with hereditary polyposis syndromes, including rare polyposis syndromes.

Juvenile Polyps in Denmark From 1995 to 2014.

BACKGROUND: Juvenile polyps in the large bowel are rare but the most common type of polyp in children. The prevalence and incidence are unknown, and few studies exist on the occurrence in adults. They are considered not to harbor any malignant potential unless they are part of the hereditary juvenile polyposis syndrome. OBJECTIVE: We aimed to study the demographics of juvenile polyps in Denmark in a 20-year period from 1995 to 2015 in both adults and children. This is the first report on the occurrence, anatomic localization, and reoccurrence of these polyps in a whole population. DESIGN: Data from all of the patients who had been diagnosed with 1 or more juvenile polyp from January 1, 1995, until December 31, 2014, were obtained. SETTINGS: The study was conducted based on patients registered in the nationwide pathological register in Denmark, the Danish Pathology Data Bank. PATIENTS: We detected a total of 1772 patients who had 2108 juvenile polyps removed (male = 946; female = 826). MAIN OUTCOME MEASURES: We noted the sex, age, number, reoccurrence, and localization of polyps. RESULTS: Of the detected juvenile polyps ≈75% were detected in adults and ≈25% in children. Approximately 96% of the patients had a single juvenile polyp without reoccurrence, 1% fulfilled the diagnostic criteria for juvenile polyposis syndrome (more than 5 polyps), and 5% had multiple juvenile polyps (2-5 polyps). The incidence in the Danish population can be estimated to be between 1:45,000 and 1:65,000. LIMITATIONS: Miscoding or misclassification in the register cannot be ruled out. We only have data for the 20-year period, limiting the evaluation of reoccurrence, and no data for the endoscopic removal procedures. CONCLUSIONS: We conclude that juvenile polyps are rare, with the majority found in adults, and most often found as a single juvenile polyp. A subgroup of patients have juvenile polyposis syndrome, which requires follow-up.

Germline variants in Hamartomatous Polyposis Syndrome-associated genes from patients with one or few hamartomatous polyps.

OBJECTIVE: A subgroup of patients with hamartomatous polyps in the GI tract has a hereditary Hamartomatous Polyposis Syndrome with an increased risk of cancer. The distinction between patients with one or few polyps and patients with a syndrome can be difficult. A pathogenic germline mutation can be detected in a majority of HPS patients. This study investigates whether patients with one or few hamartomatous polyps could have a syndrome based on genetic screening of relevant genes. METHODS: We designed a gene panel including 26 hamartomatous polyposis-associated genes. Using targeted Next Generation Sequencing, DNA samples from 77 patients with 84 hamartomatous polyps were sequenced. The detected germline variants were classified into pathogenicity classes. RESULTS: We detected several germline variants, among them three in ENG, two in BMPR1A, one in PTEN, and one in SMAD4. Although some of the detected variants have been reported previously none could be definitely pathogenic or likely pathogenic. CONCLUSIONS: Our study points towards that genetic testing for the Hamartomatous Polyposis Syndromes in patients with one or few polyps does not improve diagnostics, however we illustrate that the clinical significance of genetic variants can be difficult to interpret. A family history of polyps, cancer, or extraintestinal findings or a minimum of 3-5 polyps seems to be relevant information to include before genetic testing.

Progress report: Peutz-Jeghers syndrome.

Peutz-Jeghers syndrome is a rare, autosomal dominant polyposis syndrome. Presenting with a remarkable phenotype including development of characteristic gastrointestinal polyps, mucocutaneous pigmentations, and an increased risk of cancer, the syndrome has been subject to many studies concerning the natural course of disease. In most patients, pathogenic germline variants are detected in the STK11 gene including cases of mosaicism and structural variants. Yet, studies assessing the effect of surveillance, understanding of cancer development, as well as clinical studies evaluating chemoprevention are lacking. In addition, the impact of Peutz-Jeghers syndrome on mental health, education, and family planning are insufficiently addressed. In this progress report, we describe current knowledge, clinical phenotype, surveillance strategies, and future areas of research.

Re-evaluating the genotypes of patients with adenomatous polyposis of unknown etiology: a nationwide study.

In the Danish Polyposis Register, patients with over 100 cumulative colorectal adenomas of unknown genetic etiology, named in this study colorectal polyposis (CP), is registered and treated as familial adenomatous polyposis (FAP). In this study, we performed genetic analyses, including whole genome sequencing (WGS), of all Danish patients registered with CP and estimated the detection rate of pathogenic variants (PV). We identified 231 families in the Polyposis Register, 31 of which had CP. A polyposis-associated gene panel was performed and, if negative, patients were offered WGS and screening for mosaicism in blood and/or adenomas. Next-generation sequencing (NGS) was carried out for 27 of the families (four declined). PVs were detected in 11 families, and WGS revealed three additional structural variants in APC. Mosaicism of a PV in APC was detected in two families. As the variant detection rate of eligible families was 60%, 93% of families in the register now have a known genetic etiology.

Hereditary polyposis syndromes remain a challenging disease entity: Old dilemmas and new insights.

In this editorial we present an overview and insights of the management of hereditary polyposis syndromes. The primary focus was on familial adenomatous polyposis, juvenile polyposis syndrome and Peutz-Jegher syndrome. Genetic testing has become increasingly available and is easier than ever to integrate into clinical practice. Furthermore, several genes have been added to the expanding list of genes associated with hereditary polyposis syndromes, allowing for precise diagnostics and tailored follow-up. Endoscopic evaluation of patients with hereditary polyposis syndromes is paramount in the surveillance strategies. Current endoscopic procedures include both diagnostic procedures and surveillance as well as therapeutic interventions. Recommendations for endoscopic procedures in the upper and lower gastrointestinal canal were described. Surgery is still a key component in the management of patients with hereditary polyposis syndromes. The increased cancer risk in these patients often render prophylactic procedures or intended curative procedures in the case of cancer development. Surgical interventions in the upper and lower gastrointestinal canal were described with relevant considerations. Development of chemopreventive medications is ongoing. Few drugs have been investigated, including nonsteroidal anti-inflammatory drugs. It has been demonstrated that cyclooxygenase-2 inhibitors may lower the number of polyps. Other medications are currently under investigation, but none have, to date, consistently been able to prevent development of disease.

Cancer risk and mortality in patients with solitary juvenile polyps-A nationwide cohort study with matched controls.

INTRODUCTION: The risk of cancer in patients with solitary colorectal juvenile polyps (JPs) is poorly investigated and several studies have reported polyps with dysplastic and adenomatous alterations. We aimed to investigate the long-term risk of cancer and mortality in these patients by merging data from national registers and comparing them to a matched control cohort. MATERIALS AND METHODS: Patients with a solitary JP were identified in The Danish National Pathology Register and Data Bank (DNPR). The included patients were matched on sex, age, and place of birth with 50 controls. The groups were then analyzed for risk of cancer using the Danish Cancer Registry and mortality using the Danish Cause of Death Registry. RESULTS: We identified 1781 patients with solitary JPs and matched them with 83,713 controls. The mean follow-up time was 7.65 years for cases and 7.36 years for controls. The risk of cancer, including colorectal cancer, did not differ for the two groups and when adjusting for sex and year of birth, the hazard ratio (HR) was 1.15 (confidence interval [CI] 95% 0.94-1.41, p = 0.162). There was no increased risk of death (HR: 1.07, CI 95% 0.88-1.30, p = 0.486). The risk did not differ for different age groups or sex. CONCLUSION: There is no increased risk of cancer or mortality for patients with solitary colorectal JPs. Thus, endoscopic follow-up may be safely omitted in these patients.

TINF2 is a major susceptibility gene in Danish patients with multiple primary melanoma.

TINF2 encodes the TINF2 protein, which is a subunit in the shelterin complex critical for telomere regulation. Three recent studies have associated six truncating germline variants in TINF2 that have previously been associated with a cancer predisposition syndrome (CPS) caused by elongation of the telomeres. This has added TINF2 to the long telomere syndrome genes, together with other telomere maintenance genes such as ACD, POT1, TERF2IP, and TERT. We report a clinical study of 102 Danish patients with multiple primary melanoma (MPM) in which a germline truncating variant in TINF2 (p.(Arg265Ter)) was identified in four unrelated participants. The telomere lengths of three variant carriers were >90% percentile. In a routine diagnostic setting, the variant was identified in two more families, including an additional MPM patient and monozygotic twins with thyroid cancer and other cancer types. A total of 10 individuals from six independent families were confirmed carriers, all with cancer history, predominantly melanoma. Our findings suggest a major role of TINF2 in Danish patients with MPM. In addition to melanoma, other cancers in the six families include thyroid, renal, breast, and sarcoma, supporting a CPS in which melanoma, thyroid cancer, and sarcoma predominate. Further studies are needed to establish the full spectrum of associated cancer types and characterize lifetime cancer risk in carriers.

Whole genome sequencing and disease pattern in patients with juvenile polyposis syndrome: a nationwide study.

Juvenile polyposis syndrome (JPS) is a hereditary hamartomatous polyposis syndrome characterized by gastrointestinal juvenile polyps and increased risk of gastrointestinal cancer. Germline pathogenic variants are detected in SMAD4 or BMPR1A, however in a significant number of patients with JPS, the etiology is unknown. From Danish registers, and genetic department and laboratories, we identified all patients in Denmark with a clinical diagnosis of JPS and/or a pathogenic variant in BMPR1A or SMAD4. In patients where no variant had been detected, we performed genetic analysis, including whole genome sequencing. We collected clinical information on all patients to investigate the phenotypic spectrum. Sixty-six patients (mean age 40 years) were included of whom the pathogenic variant was unknown in seven patients. We detected a pathogenic variant in SMAD4 or PTEN in additional three patients and thus ≈ 95% of patients had a pathogenic germline variant. Endoscopic information was available in fifty-two patients (79%) and of these 31 (60%) fulfilled the clinical criteria of JPS. In 41 patients (79%), other types of polyps than juvenile had been removed. Our results suggest that almost all patients with a clinical diagnosis of JPS has a pathogenic variant in mainly BMPR1A, SMAD4, and more rarely PTEN. However, not all patients with a pathogenic variant fulfil the clinical criteria of JPS. We also demonstrated a wide clinical spectrum, and that the histopathology of removed polyps varied.

CUX1-related neurodevelopmental disorder: deep insights into phenotype-genotype spectrum and underlying pathology.

Heterozygous, pathogenic CUX1 variants are associated with global developmental delay or intellectual disability. This study delineates the clinical presentation in an extended cohort and investigates the molecular mechanism underlying the disorder in a Cux1+/- mouse model. Through international collaboration, we assembled the phenotypic and molecular information for 34 individuals (23 unpublished individuals). We analyze brain CUX1 expression and susceptibility to epilepsy in Cux1+/- mice. We describe 34 individuals, from which 30 were unrelated, with 26 different null and four missense variants. The leading symptoms were mild to moderate delayed speech and motor development and borderline to moderate intellectual disability. Additional symptoms were muscular hypotonia, seizures, joint laxity, and abnormalities of the forehead. In Cux1+/- mice, we found delayed growth, histologically normal brains, and increased susceptibility to seizures. In Cux1+/- brains, the expression of Cux1 transcripts was half of WT animals. Expression of CUX1 proteins was reduced, although in early postnatal animals significantly more than in adults. In summary, disease-causing CUX1 variants result in a non-syndromic phenotype of developmental delay and intellectual disability. In some individuals, this phenotype ameliorates with age, resulting in a clinical catch-up and normal IQ in adulthood. The post-transcriptional balance of CUX1 expression in the heterozygous brain at late developmental stages appears important for this favorable clinical course.