DONSON is required for CMG helicase assembly in the mammalian cell cycle.

DONSON is one of 13 genes mutated in a form of primordial microcephalic dwarfism known as Meier-Gorlin syndrome. The other 12 encode components of the CDC45-MCM-GINS helicase, around which the eukaryotic replisome forms, or are factors required for helicase assembly during DNA replication initiation. A role for DONSON in CDC45-MCM-GINS assembly was unanticipated, since DNA replication initiation can be reconstituted in vitro with purified proteins from budding yeast, which lacks DONSON. Using mouse embryonic stem cells as a model for the mammalian helicase, we show that DONSON binds directly but transiently to CDC45-MCM-GINS during S-phase and is essential for chromosome duplication. Rapid depletion of DONSON leads to the disappearance of the CDC45-MCM-GINS helicase from S-phase cells and our data indicate that DONSON is dispensable for loading of the MCM2-7 helicase core onto chromatin during G1-phase, but instead is essential for CDC45-MCM-GINS assembly during S-phase. These data identify DONSON as a missing link in our understanding of mammalian chromosome duplication and provide a molecular explanation for why mutations in human DONSON are associated with Meier-Gorlin syndrome.

Functional studies in yeast confirm the pathogenicity of a new GINS3 Meier-Gorlin syndrome variant.

Meier-Gorlin syndrome (MGORS) is an autosomal recessive disorder characterized by short stature, microtia, and patellar hypoplasia, and is caused by pathogenic variants of cellular factors involved in the initiation of DNA replication. We previously reported that biallelic variants in GINS3 leading to amino acid changes at position 24 (p.Asp24) cause MGORS. Here, we describe the phenotype of a new individual homozygous for the Asp24Asn variant. We also report the clinical characteristics of an individual harboring a novel homozygous GINS3 variant (Ile25Phe) and features suggestive of MGORS. Modification of the corresponding residue in yeast Psf3 (Val9Phe) compromised S phase progression compared to a humanized Psf3 Val9Ile variant. Expression of Psf3 Val9Phe in yeast also caused sensitivity to elevated temperature and the replicative stress-inducing drug hydroxyurea, confirming partial loss of function of this variant in vivo and allowing us to upgrade the classification of this variant. Taken together, these data validate the critical importance of the GINS DNA replication complex in the molecular etiology of MGORS.

Germline PTCH1: c.361_362insAlu alteration identified by comprehensive exome and RNA sequencing in a patient with Gorlin syndrome.

Gorlin syndrome can be caused by pathogenic/likely pathogenic (P/LP) variants in the tumor suppressor gene PTCH1 (9q22.1-q31), which encodes the receptor for the sonic hedgehog (SHH) ligand. We present a 12-month-old boy clinically diagnosed with Gorlin syndrome who was found to have significantly delayed development, palmar pitting, palmar and plantar keratosis, short hands, frontal bossing, coarse face, hypertelorism, a bifid rib, misaligned and missing teeth, and SHH-activated medulloblastoma. Genetic testing, including a pediatric cancer panel and genome sequencing with peripheral blood, failed to identify any P/LP variants in PTCH1. Paired tumor/normal exome sequencing was performed, which identified a germline NM_000264.5 (PTCH1): c.361_362ins? alteration through manual review of sequencing reads. Clinical RNA sequencing further demonstrated an Alu insertion at this region (PTCH1: c.361_362insAlu), providing molecular confirmation of Gorlin syndrome. This finding exemplifies a unique mechanism for PTCH1 disruption in the germline and highlights the importance of comprehensive analysis, including manual review of DNA sequencing reads and the utility of RNA analysis to detect variant types which may not be identified by routine genetic screening techniques.

Medulloblastoma and other neoplasms in patients with heterozygous germline SUFU variants: A scoping review.

In 2002, heterozygous suppressor of fused variants (SUFU+/-) in the germline were described to have a tumor suppressor role in the development of pediatric medulloblastoma (MB). Other neoplasms associated with pathologic germline SUFU+/- variants have also been described among patients with basal cell nevus syndrome (BCNS; BCNS is also known as Gorlin syndrome, nevoid basal cell carcinoma [BCC] syndrome or Gorlin-Goltz syndrome; OMIM 109400), an autosomal-dominant cancer predisposition syndrome. The phenotype of patients with germline SUFU+/- variants is very poorly characterized due to a paucity of large studies with long-term follow-up. As such, there is a clinical need to better characterize the spectrum of neoplasms among patients with germline SUFU+/- variants so that clinicians can provide accurate counseling and optimize tumor surveillance strategies. The objective of this study is to perform a scoping review to map the evidence on the rate of medulloblastoma and to describe the spectrum of other neoplasms among patients with germline SUFU+/- variants. A review of all published literature in PubMed (MEDLINE), EMBASE, Cochrane, and Web of Science were searched from the beginning of each respective database until October 9, 2021. Studies of pediatric and adult patients with a confirmed germline SUFU+/- variant who were evaluated for the presence of any neoplasm (benign or malignant) were included. There were 176 patients (N = 30 studies) identified with a confirmed germline SUFU+/- variant who met inclusion criteria. Data were extracted from two cohort studies, two case-control studies, 18 case series, and eight case reports. The median age at diagnosis of a germline SUFU+/- variant was 4.5 years where 44.4% identified as female and 13.4% of variants were de novo. There were 34 different neoplasms (benign and malignant) documented among patients with confirmed germline SUFU+/- variants, and the most common were medulloblastoma (N = 59 patients), BCC (N = 21 patients), and meningioma (N = 19 patients). The median age at medulloblastoma diagnosis was 1.42 years (range 0.083-3; interquartile range 1.2). When data were available for these three most frequent neoplasms (N = 95 patients), 31 patients (32.6%) had neither MB, BCC nor meningioma; 51 patients (53.7%) had one of medulloblastoma or BCC or meningioma; eight patients (8.4%) had two of medulloblastoma or BCC or meningioma, and five patients (5.3%) had medulloblastoma and BCC and meningioma. This is the first study to synthesize the data on the frequency and spectrum of neoplasms specifically among patients with a confirmed germline SUFU+/- variant. This scoping review is a necessary step forward in optimizing evidence-based tumor surveillance strategies for medulloblastoma and estimating the risk of other neoplasms that could impact patient outcomes.

Oral smoothened inhibitors for Gorlin syndrome: A clinical review.

Although smoothened inhibitors (SMOi) have demonstrated efficacy in the management of basal cell carcinoma, no guidelines are available on how to utilize SMOi in the treatment of Gorlin syndrome (GS). This review's objective is to assess the clinical response to SMOi in GS, provide practical guidance for clinicians, and identify areas for future research. Through comprehensive searches of previous publications and expert opinion, this review demonstrates that intermittent dosing of SMOi and daily dosing have similar efficacy. While the adverse events of SMOi may result in their discontinuation during treatment of GS, intermittent dosing may improve compliance.

Clinicopathological and molecular spectrum of patients with germline SUFU mutations: A case series.

BACKGROUND: One of the hereditary syndromes associated with multiple early-onset basal cell carcinomas (BCCs) is basal cell nevus syndrome (BCNS), of which a minority is caused by germline SUFU mutations. Germline SUFU mutations show a spectrum of phenotypes, of which multiple hereditary infundibulocystic basal cell carcinoma syndrome (MHIBCC) is one. Patients with MHIBCC develop multiple basaloid skin tumors from middle age onwards. METHODS: Three patients presenting with an MHIBCC phenotype were tested for a germline SUFU mutation. Skin biopsies were assessed by two dermatopathologists. RESULTS: Our study adds three new pathogenic SUFU variants, including a mosaic, to the current literature. Literature suggests a spectrum of phenotypes of patients carrying the same SUFU mutation, which ranges from the MHIBCC phenotype, to BCNS, to patients that develop life-threatening brain tumors. This last risk is significantly higher in germline SUFU mutation carriers when compared to BCNS patients carrying germline PTCH1 mutations. CONCLUSIONS: Germline SUFU mutation carriers should be recognized as a distinct group of patients carrying specific health risks, independent of meeting the BCNS criteria. Phenotypic prediction based on the specific SUFU mutation seems unfeasible. It is of utmost importance that the less apparent MHIBCC phenotype is recognized, to provide (second generation) germline SUFU mutation carriers appropriate healthcare.

Phenotypes, Genetics, and Estimated Prevalence of Focal Dermal Hypoplasia (Goltz Syndrome): A Single-Center Report.

BACKGROUND: Focal dermal hypoplasia (FDH), also known as Goltz syndrome, is a rare ectodermal dysplasia that primarily affects the skin, skeleton, and eyes. It is an X-linked dominant disorder, predominantly seen in females, caused by pathogenic variants in PORCN. METHODS: We characterized a case series of four genetically confirmed FDH patients (three females, one male) at Aarhus University Hospital, Denmark. We estimated the FDH prevalence from our local cohort and nationwide registry data. RESULTS: Three patients had characteristic dermatological findings suspicious for FDH and confirmed by targeted PORCN analysis. One patient had an atypical presentation with several malformations but only subtle skin changes and was diagnosed following trio exome-sequencing analysis. Skin atrophy with fat herniations and telangiectasias were typical cutaneous findings. Limb malformations included oligodactyly (cleft foot), syndactyly, and polydactyly. Eye abnormalities included coloboma and microphthalmos. Facial dysmorphology was defined by asymmetry, thin upper lip, and malformed ears. One patient developed a giant cell bone tumor, which is a rare feature of FDH. Dental findings included enamel hypoplasia with vertical grooving and irregular crowns. Four PORCN variants were identified, including three not previously reported in the literature.We estimated a regional point prevalence in Western Denmark of 1.6 cases per million population (95% confidence intervals (CI): 0.7-3.7 per million) and a nationwide registry-based point prevalence of 1.2 cases per million population (95% CI: 0.6-2.4 per million). CONCLUSIONS: FDH is an extremely rare and complex multisystem disorder of variable presentation, which requires close multidisciplinary collaboration for diagnosis and patient care.

Whole-Exome Sequencing Identified Two Novel Pathogenic Mutations in the PTCH1 Gene in BCNS.

Basal cell nevus syndrome (BCNS, OMIM 109400) is a familial cancer syndrome characterized by the development of numerous basal cell cancers and various other developmental abnormalities, including epidermal cysts of the skin, calcified dural folds, keratocysts of the jaw, palmar and plantar pits, ovarian fibromas, medulloblastomas, lymphomesenteric cysts, and fetal rhabdomyomas. BCNS shows autosomal dominant inheritance and is caused by mutations in the patched 1 (PTCH1) gene and the suppressor of the fused homolog (SUFU) gene. In a few cases, variants of patched 2 (PTCH2) have been found in patients who met the criteria for BCNS. In an investigation of 11 Hungarian families who fulfilled the diagnostic criteria for BCNS, whole-exome sequencing (WES) and multiplex ligation-dependent probe amplification (MLPA) identified two novel pathogenic variants (c.2994C>A; p.Cys998Ter and c.814_818del; p.Asn272SerfsTer11), one recently identified variant (c.1737_1745del p.Val580_Val582del), and three recurrent disease-causing variants of the PTCH1 gene with a diagnosis rate of 63.6%. Disease-causing variants were not found for the SUFU and PTCH2 genes. These applied methods could not fully elucidate the genetic background of all the BCNS cases that we investigated. To uncover the missing heritability of BCNS, whole-genome sequencing or an epigenetic approach might be considered in the future.

Isolated frontosphenoidal craniosynostosis: An argument for genetic testing.

Isolated frontosphenoidal craniosynostosis (IFSC) is a rare congenital defect defined as premature fusion of the frontosphenoidal suture in the absence of other suture fusion. Until now, IFSC was regarded as a phenomenon with an unclear genetic etiology. We have identified three cases with IFSC with underlying syndromic diagnoses that were attributable to pathogenic mutations involving FGFR3 and MN1, as well as 22q11.2 deletion syndrome. These findings suggest a genetic predisposition to IFSC may exist, thereby justifying the recommendation for genetic evaluation and testing in this population. Furthermore, due to improved imaging resolution, cases of IFSC are now readily identified. With the identification of IFSC with underlying genetic diagnoses, in combination with significant improvements in imaging resolution, we recommend genetic evaluation in children with IFSC.

Brain and/or Spinal Cord Tumors Accompanied with Other Diseases or Syndromes.

Several medical conditions that interest both the brain and the spinal cord have been described throughout the history of medicine. Formerly grouped under the term Phacomatosis because lesions of the eye were frequently encountered or genodermatosis when typical skin lesions were present, these terms have been progressively discarded. Although originally reported centuries ago, they still represent a challenge for their complexity of cure. Nowadays, with the introduction of advanced genetics and the consequent opportunity of whole-genome sequencing, new single cancer susceptibility genes have been identified or better characterized; although there is evidence that the predisposition to a few specific tumor syndromes should be accounted to a group of mutations in different genes while certain syndromes appeared to be manifestations of different mutations in the same gene adding supplementary problems in their characterization and establishing the diagnosis. Noteworthy, many syndromes have been genetically determined and well-characterized, accordingly in the near future, we expect that new targeted therapies will be available for the definitive cure of these syndromes and other gliomas (Pour-Rashidi et al. in World Neurosurgery, 2021). The most common CNS syndromes that will be discussed in this chapter include neurofibromatosis (NF) types 1 and 2, von Hippel-Lindau (VHL) disease, and tuberous sclerosis complex (TSC), as well as syndromes having mostly extra-neural manifestations such as Cowden, Li-Fraumeni, Turcot, and Gorlin syndromes.

Hedgehog-Related Mutation Causes Bone Malformations with or without Hereditary Gene Mutations.

The hedgehog (Hh) family consists of numerous signaling mediators that play important roles at various stages of development. Thus, the Hh pathway is essential for bone tissue development and tumorigenesis. Gorlin syndrome is a skeletal and tumorigenic disorder caused by gain-of-function mutations in Hh signaling. In this review, we first present the phenotype of Gorlin syndrome and the relationship between genotype and phenotype in bone and craniofacial tissues, including the causative gene as well as other Hh-related genes. Next, the importance of new diagnostic methods using next-generation sequencing and multiple gene panels will be discussed. We summarize Hh-related genetic disorders, including cilia disease, and the genetics of Hh-related bone diseases.

Microcephalic primordial dwarfism with predominant Meier-Gorlin phenotype, ichthyosis, and multiple joint deformities-Further expansion of DONSON Cell Cycle-opathy phenotypic spectrum.

We report a patient with microcephalic primordial dwarfism with predominant Meier-Gorlin syndrome phenotype with ichthyosis and disabling multiple joint deformities in addition to classic features of the syndrome. The patient was a 10.5-year-old girl referred in view of short stature, joint deformities, and facial dysmorphism. There was history of intrauterine growth restriction and collodion like skin abnormality at birth. She had normal developmental milestones and intellect. On clinical evaluation, anthropometry was suggestive of proportionate short stature and microcephaly. There was abnormal posture due to spine and peripheral joint deformities, along with ichthyosis, facial, and digital dysmorphism. Skeletal radiographs showed radial subluxation, acetabular dysplasia and hip dislocation, bilateral knee joint dislocation, absent patellae, slender long bones with delayed bone age, and subluxation of small joints of hands and feet. Work up for metabolic bone disease and peripheral blood karyotype was normal. Whole exome sequencing revealed a pathogenic homozygous variant c.C1297T (p.Pro433Ser) in the exon 8 of DONSON gene. This report further expands the genotypic-phenotypic spectrum of the group of disorders known as Cell Cycle-opathies.

Novel uses of laser therapy in Goltz syndrome.

Goltz syndrome is an X-linked dominant, multisystem birth defect due to PORCN mutation. The skin findings follow Blaschko's lines and often show epidermal atrophy and herniation of subcutaneous fatty tissue. Regarding treatment, light sources can offer a good therapeutic option for some manifestations of this rare disease and improve the aesthetic appearance of the skin lesions. We report two new cases of Goltz syndrome in which the cutaneous findings remarkably improved with pulsed dye laser and carbon dioxide laser.

An investigation of metabolic disturbances, including urinary stone disease, hypothyroidism, and osteoporosis in basal cell nevus syndrome.

BACKGROUND/OBJECTIVES: Basal cell nevus syndrome (BCNS) is an autosomal dominant skin cancer predisposition syndrome associated with abnormal mineral metabolism, a risk factor for urinary stone disease (USD). However, no research investigating the association between BCNS and USD or other manifestations of abnormal mineral metabolism has been conducted. The objective of this study is to investigate the association between BCNS and conditions associated with disordered mineral metabolism including USD, hypothyroidism, and osteoporosis and compare them to prevalence in the general population to elucidate potential unknown manifestations of the condition. METHODS: This retrospective study examined medical records of adult and pediatric patients with confirmed BCNS from the Mayo Clinic database from 1 January 1995 to 12 January 2020. Records were surveyed for evidence of USD and other comorbidities potentially related to BCNS. The studied cohort included 100 adult patients and 5 pediatric patients. RESULTS: A total of 105 patients were included in this analysis, 10 of whom experienced confirmed USD, representing a prevalence of 10%. Six adult patients were identified with a diagnosis of osteoporosis, representing a prevalence of 6%. Thirteen adult patients were identified with a diagnosis of hypothyroidism, representing a prevalence of 13%. CONCLUSIONS: This study identified a prevalence of USD in BCNS patients comparable to estimates of national prevalence, indicating that known abnormalities in mineral metabolism likely do not increase the incidence of USD in BCNS patients. Additional findings included increased prevalence of hypothyroidism and decreased prevalence of osteoporosis in the BCNS cohort compared to national averages.

Patient and caregiver perspectives on delayed childhood Gorlin syndrome diagnoses.

The diagnostic trends of Gorlin syndrome (GS) in the pediatric population are not well understood. In an international survey conducted by the Gorlin Syndrome Alliance, 118 individuals who were diagnosed with GS when aged 18 years and under provided information about their diagnosis. Oral surgeons and dermatologists were the most commonly reported physicians involved in diagnosis for 48.3% and 28% of cases, respectively. For 50% of children, the diagnosis was made within a year from presenting sign(s), while 27% report over 4 years to receive GS diagnosis. Of individuals who reported >4 years between presenting signs and diagnosis, 81.3% attributed the delay to insufficient medical team knowledge and 65.6% attributed to lack of personal awareness that presenting signs were related to GS, emphasizing the need for patient and physician education of GS for prompt diagnosis.

Utility of optical coherence tomography in basal cell naevus syndrome: A case report.

Optical Coherence Tomography (OCT) is a useful non-invasive diagnostic tool for diagnosing and monitoring treatment of basal cell carcinomas. We describe the use of OCT in a patient with Basal Cell Naevus Syndrome. Through measuring tumour depth on OCT, management of individual tumours was triaged accordingly using 0.4 mm tumour depth as a cut-off for surgical and non-surgical management. OCT has potential to reduce unnecessary excisions and associated morbidity in this population of patients.

Meier-Gorlin Syndrome: Clinical Misdiagnosis, Genetic Testing and Functional Analysis of ORC6 Mutations and the Development of a Prenatal Test.

Meier−Gorlin syndrome (MGS) is a rare genetic developmental disorder that causes primordial proportional dwarfism, microtia, the absence of or hypoplastic patellae and other skeletal anomalies. Skeletal symptoms overlapping with other syndromes make MGS difficult to diagnose clinically. We describe a 3-year-old boy with short stature, recurrent respiratory infections, short-rib dysplasia, tower head and facial dysmorphisms who was admitted to the Tomsk Genetic Clinic to verify a clinical diagnosis of Jeune syndrome. Clinical exome sequencing revealed two variants (compound heterozygosity) in the ORC6 gene: c.2T>C(p.Met1Thr) and c.449+5G>A. In silico analysis showed the pathogenicity of these two mutations and predicted a decrease in donor splicing site strength for c.449+5G>A. An in vitro minigene assay indicated that variant c.449+5G>A causes complete skipping of exon 4 in the ORC6 gene. The parents requested urgent prenatal testing for MGS for the next pregnancy, but it ended in a miscarriage. Our results may help prevent MGS misdiagnosis in the future. We also performed in silico and functional analyses of ORC6 mutations and developed a restriction fragment length polymorphism and haplotype-based short-tandem-repeat assay for prenatal genetic testing for MGS. These findings should elucidate MGS etiology and improve the quality of genetic counselling for affected families.

Successful pregnancies in an adult with Meier-Gorlin syndrome harboring biallelic CDT1 variants.

Meier-Gorlin syndrome is an autosomal recessively inherited disorder of growth retardation, accompanied by microtia and patellae a/hypoplasia and characteristic facies. Pathogenic variants in genes associated with the initiation of DNA replication underlie the condition, with biallelic variants in CDT1 the most common cause. Using 10× Chromium genome sequencing, we report CDT1 variants in an adult female, with an inframe amino acid deletion inherited in trans with a deep intronic variant which likely serves as the branchpoint site in Intron 8. Splicing defects arising from this variant were confirmed through in vitro analysis. At 49 years, she represents the oldest patient with a molecular diagnosis described in the literature and is the first reported patient with Meier-Gorlin syndrome to have carried a successful pregnancy to term. Both of her pregnancies were complicated by postpartum hemorrhage and upon subsequent necessary hysterectomy, revealed uterine abnormalities. There is scant knowledge on reproductive ability and success in patients with Meier-Gorlin syndrome. Successful pregnancies among other clinically recognizable forms of primordial dwarfism have also not been described previously. This case is therefore of clinical interest for many forms of inherited growth retardation, and will assist in providing more information and clinical guidance for females of reproductive age.

Microdeletion of 9q22.3: A patient with minimal deletion size associated with a severe phenotype.

Basal cell nevus syndrome (also known as Gorlin Syndrome; MIM109400) is an autosomal dominant disorder characterized by recurrent pathological features such as basal cell carcinomas and odontogenic keratocysts as well as skeletal abnormalities. Most affected individuals have point mutations or small insertions or deletions within the PTCH1 gene on human chromosome 9, but there are some cases with more extensive deletion of the region, usually including the neighboring FANCC and/or ERCC6L2 genes. We report a 16-year-old patient with a deletion of approximately 400,000 bases which removes only PTCH1 and some non-coding RNA genes but leaves FANCC and ERCC6L2 intact. In spite of the small amount of DNA for which he is haploid, his phenotype is more extreme than many individuals with longer deletions in the region. This includes early presentation with a large number of basal cell nevi and other skin lesions, multiple jaw keratocysts, and macrosomia. We found that the deletion was in the paternal chromosome, in common with other macrosomia cases. Using public databases, we have examined possible interactions between sequences within and outside the deletion and speculate that a regulatory relationship exists with flanking genes, which is unbalanced by the deletion, resulting in abnormal activation or repression of the target genes and hence the severity of the phenotype.

Retrospective analysis of the histopathologic features of basal cell carcinomas in pediatric patients with basal cell nevus syndrome.

Basal cell nevus syndrome (BCNS) is an autosomal dominant condition caused most often by a loss-of-function mutation in the Patched-1 (PTCH1) gene. It is characterized by the development of varied benign and malignant tumors, including numerous cutaneous basal cell carcinomas (BCCs). The PTCH1 gene is integral in hair follicle development and loss of function mutation may lead to BCCs with an infundibulocystic histopathology in BCNS patients. Few studies have described the histopathological features of BCCs in BCNS. The recognition of these histopathologic features by dermatologists, dermatopathologists, and others caring for children will allow earlier and more effective identification of BCNS. We performed a retrospective analysis of 25 BCCs in 11 patients aged 5 to 19 years with BCNS and evaluated the histopathologic features on hematoxylin-eosin-stained sections. Our study found that 80% of BCCs in BCNS patients occurred on the head and neck with 64% of the specimens demonstrating infundibulocystic differentiation. Infundibulocystic differentiation is a common finding in BCCs found in BCNS. The finding of cutaneous neoplasms consistent with BCC with infundibulocystic differentiation in children is common in pediatric patients with BCNS and can be considered to be an early marker of the disorder, prompting further clinical investigation.