MRC1 and LYVE1 expressing macrophages in vascular beds of GNAQ p.R183Q driven capillary malformations in Sturge Weber syndrome.

Sturge-Weber syndrome (SWS), a neurocutaneous disorder, is characterized by capillary malformations (CM) in the skin, brain, and eyes. Patients may suffer from seizures, strokes, and glaucoma, and only symptomatic treatment is available. CM are comprised of enlarged vessels with endothelial cells (ECs) and disorganized mural cells. Our recent finding indicated that the R183Q mutation in ECs leads to heightened signaling through phospholipase Cß3 and protein kinase C, leading to increased angiopoietin-2 (ANGPT2). Furthermore, knockdown of ANGPT2, a crucial mediator of pro-angiogenic signaling, inflammation, and vascular remodeling, in EC-R183Q rescued the enlarged vessel phenotype in vivo. This prompted us to look closer at the microenvironment in CM-affected vascular beds. We analyzed multiple brain histological sections from patients with GNAQ-R183Q CM and found enlarged vessels devoid of mural cells along with increased macrophage-like cells co-expressing MRC1 (CD206, a mannose receptor), CD163 (a scavenger receptor and marker of the monocyte/macrophage lineage), CD68 (a pan macrophage marker), and LYVE1 (a lymphatic marker expressed by some macrophages). These macrophages were not found in non-SWS control brain sections. To investigate the mechanism of increased macrophages in the perivascular environment, we examined THP1 (monocytic/macrophage cell line) cell adhesion to EC-R183Q versus EC-WT under static and laminar flow conditions. First, we observed increased THP1 cell adhesion to EC-R183Q compared to EC-WT under static conditions. Next, using live cell imaging, we found THP1 cell adhesion to EC-R183Q was dramatically increased under laminar flow conditions and could be inhibited by anti-ICAM1. ICAM1, an endothelial cell adhesion molecule required for leukocyte adhesion, was strongly expressed in the endothelium in SWS brain histological sections, suggesting a mechanism for recruitment of macrophages. In conclusion, our findings demonstrate that macrophages are an important component of the perivascular environment in CM suggesting they may contribute to the CM formation and SWS disease progression.

Sturge-Weber syndrome with massive macroglossia and anterior neck space infection- a case report and review of literature.

Sturge- Weber syndrome (SWS), is a rare neuro-cutaneous angiomatosis which affects male and females alike. The clinical manifestations include angiomas, haemangiomas of the lips, tongue and palatine region. The oral manifestations are usually unilateral and are susceptible to bleed. Patients can also present with macroglossia and maxillary bone hypertrophy which can lead to malocclusion of the oral cavity. Food accumulation due to occlusion can cause growth of bacteria which can intensify infections and can cause gingival hyperplasia. A case of a middle-aged 39 year old female was reported in the Ziauddin Hospital, Karachi on 2nd of February,2022 with the presenting complaints of intermittent fever and drowsiness for 10 days. On examination she had massive tongue enlargement, drooling, malocclusion, difficulty in eating and breathing. She was a known case of Sturgeweber syndrome. Based on the clinical and radiological findings, she was managed along the lines of prelaryngeal soft tissue and submandibular infection.

Neurological function and drug-refractory epilepsy in Sturge-Weber syndrome children: a retrospective analysis.

Epilepsy in Sturge-Weber syndrome (SWS) is common, but drug-refractory epilepsy (DRE) in SWS has rarely been studied in children. We investigated the characteristics of epilepsy and risk factors for DRE in children with SWS. A retrospective study was conducted to analyze the clinical characteristics of children with SWS with epilepsy in our hospital from January 2013 to October 2022. Univariate and multivariate logistic analyses were performed to investigate the factors influencing DRE in children with SWS. A total of 35 SWS children with epilepsy were included (51% male; mean age of presentation 3.6 ± 0.5 years), 71% of children with SWS had their first seizure within the first year of life, and the most common type of seizure was focal seizure (77%). Eleven (31%) patients developed DRE. The median age of onset for the first seizure was 1.0 years and all these cases were of SWS type I. Multivariate logistic analysis revealed that stroke-like episodes and seizure clusters were risk factors for DRE in SWS children. A poor neurological function group was observed in twenty-five children with SWS. Status epilepticus was a risk factor that affected the neurological function of SWS children with epilepsy.  Conclusion: The study explored the epileptic features of children with SWS. The results revealed that stroke-like episodes and seizure clusters are risk factors for DRE in children with SWS. The occurrence of status epilepticus impacts the neurological function of SWS children with epilepsy. Thus, long-term follow-up is necessary to monitor outcomes. What is Known: • Sturge-Weber syndrome (SWS) is a rare neurocutaneous disorder, over 75% of children with SWS experience seizures, and 30-57% develop drug-refractory epilepsy (DRE), which leads to a poor outcome. • Drug-refractory epilepsy in SWS has been rarely studied in children, and the risk factors associated with DRE are unclear. What is New: • Clinical features of SWS children with drug-refractory epilepsy. • In SWS, stroke-like episodes and seizure clusters are risk factors of DRE, the occurrence of status epilepticus impacts the neurological function.

Determinants of Functional Outcome after Pediatric Hemispherotomy.

OBJECTIVE: We aimed to evaluate determinants of functional outcome after pediatric hemispherotomy in a large and recent multicenter cohort. METHODS: We retrospectively investigated the functional outcomes of 455 children who underwent hemispherotomy at 5 epilepsy centers in 2000-2016. We identified determinants of unaided walking, voluntary grasping with the hemiplegic hand, and speaking through Bayesian multivariable regression modeling using missing data imputation. RESULTS: Seventy-five percent of children were seizure-free, and 44% stopped antiseizure medication at a 5.1-year mean follow-up (range = 1-17.1). Seventy-seven percent of children could walk unaided, 8% could grasp voluntarily, and 68% could speak at the last follow-up. Children were unlikely to walk when they had contralateral magnetic resonance imaging (MRI) abnormalities (40/73, p = 0.04), recurrent seizures following hemispherotomy (62/109, p = 0.04), and moderately (50/61, p = 0.03) or severely impaired (127/199, p = 0.001) postsurgical intellectual functioning, but were likely to walk when they were older at outcome determination (p = 0.01). Children were unlikely to grasp voluntarily with the hand contralateral to surgery when they had Rasmussen encephalitis (0/61, p = 0.001) or Sturge-Weber syndrome (0/32, p = 0.007). Children were unlikely to speak when they had contralateral MRI abnormalities (30/69, p = 0.002) and longer epilepsy duration (p = 0.01), but likely to speak when they had Sturge-Weber syndrome (29/35, p = 0.01), were older at surgery (p = 0.04), and were older at outcome determination (p < 0.001). INTERPRETATION: Etiology and bilaterality of structural brain abnormalities were key determinants of functional outcome after hemispherotomy. Longer epilepsy duration affected language outcomes. Not surprisingly, walking and talking ability increased with older age at outcome evaluation. ANN NEUROL 2024;95:377-387.

Incidence of and Risk Factors for Fellow-Eye Involvement in Sturge-Weber Syndrome Children With Unilateral Glaucoma.

PRCIS: Among children with unilateral glaucoma associated with Sturge-Weber syndrome (SWS), 7 of 47 demonstrated involvement in the fellow eye, and that group had had earlier first-eye surgery relative to the noninvolvement group. PURPOSE: The aim of this study was to determine the incidence of and risk factors for fellow-eye involvement in children with unilateral SWS-associated glaucoma. MATERIALS AND METHODS: Children diagnosed with a unilateral facial port-wine stain and ipsilateral glaucoma before the age of 5 and followed up for at least 5 years were enrolled. The incidence rates of fellow-eye glaucoma involvement were estimated per 100 person-years, and factors associated with a higher incidence of fellow-eye involvement were investigated. RESULTS: A total of 47 children [24 (51.1%) girls] with unilateral SWS-associated glaucoma were included. All of them had facial port-wine stain involving ophthalmic division of the trigeminal nerve, and 18 (38.3%) had neurological comorbidities. The mean age at glaucoma diagnosis was 0.8±1.2 years [range, 0.08 (1 mo)-4.0 y]. Over a median follow-up of 8.4 years, glaucoma was diagnosed in the fellow eye of 7 of the children (14.9%; incidence rate of 1.8 per 100 person-years), 6 of whom were girls ( P =0.097) and 5 of whom were diagnosed before the age of 4 years ( P =0.508). The fellow-eye-involvement group showed significantly higher mean follow-up intraocular pressure in the fellow eye, older age at first-eye surgery (both P <0.005), and higher frequency of choroidal hemangioma both at first onset and in fellow eyes ( P =0.026 and 0.019, respectively). CONCLUSIONS: In this cohort of SWS children diagnosed with unilateral glaucoma, the risk of fellow-eye involvement was higher in girls, within the first 4 years, and in cases with choroidal hemangioma. The fellow-eye-involved children underwent surgery on the first eye earlier than those without fellow-eye involvement.

Hypothalamic-pituitary dysfunction in Sturge-Weber syndrome: case report and review of the literature.

OBJECTIVES: Sturge-Weber syndrome (SWS) is a rare neurocutaneous disorder that is characterized by a segmental dermatomal facial port-wine stain birthmark and is frequently accompanied by ipsilateral brain and eye abnormalities. We present a case of a patient with SWS who exhibited hypogonadotropic hypogonadism, growth hormone (GH) deficiency, and central hypothyroidism at the age of 20 despite the absence of radiographic findings in the pituitary and hypothalamus. CASE PRESENTATION: A 20-year-old male with SWS with epilepsy and Klippel-Trenaunay syndrome presents with delayed pubertal development, short stature, and obesity. Upon further examination, he was found to have biochemical and clinical evidence of hypogonadism, hypothyroidism, and GH deficiency. A pituitary MRI displayed no abnormalities of the pituitary or hypothalamus. Treatment with testosterone cypionate and levothyroxine was initiated. Despite successful pubertal induction, IGF-1 levels have remained low and treatment with recombinant human growth hormone (rhGH) is now being considered for metabolic benefits. CONCLUSIONS: This case emphasizes the importance of endocrine evaluation and treatment of hormonal deficiencies in patients with SWS despite the absence of radiographic findings.

Parkes Weber syndrome: a rare cause of foot drop.

This case report describes a patient in her late 60s, previously diagnosed with Klippel-Trenaunay syndrome who presented with difficulty walking. A year prior to her presentation she had a fall which made her notice a painless foot drop on the right. Her right leg was profoundly hypertrophied compared with the left, and a port-wine stain was present on the lateral side, extending from the hip to the mid-shin. The patient's differential diagnosis based on clinical examination and investigations is discussed leading to a final diagnosis of sciatic neuropathy secondary to an arteriovenous malformation due to Parkes Weber syndrome.

Arterial spin-labeled (ASL) perfusion in children with Sturge-Weber syndrome: a retrospective cross-sectional study.

PURPOSE: Sturge-Weber syndrome (SWS) is a developmental disorder with venous hypertension and associated tissue responses including pial angiomatosis, cortical calcifications, and cerebral atrophy. Arterial spin-labeled (ASL) perfusion is an advanced MR sequence which can assess perfusion, without the need for contrast. We systematically evaluated the potential benefits of using ASL in Sturge-Weber syndrome, to determine the extent of intracranial perfusion abnormality and stage of disease, relevant for prognostication and surgical planning. METHODS: Two pediatric neuroradiologists retrospectively evaluated ASL perfusion imaging of 31 children with confirmed SWS and recorded the presence of hyper-perfusion, hypo-perfusion, or normal perfusion. The presence and distribution of ASL abnormality were compared against the presence and side of atrophy/calcification and pial angiomatosis on standard MR sequences. RESULTS: Thirty-one children (52% female, median age 16.7 months) with SWS had ASL imaging. Seven (23%) had hyper-perfusion, 15 (48%) had hypo-perfusion, and 9 (29%) had no perfusion abnormalities. ASL perfusion abnormality matched the location of SWS findings on conventional imaging in 86% (19/22). ASL demonstrated statistically significant increased perfusion in the early stage of the disease and decreased perfusion when there was atrophy. The parietal lobe was involved in 86% of cases. CONCLUSION: ASL perfusion imaging is an advanced technique which may contribute to earlier diagnosis and more accurate prognostication of Sturge-Weber syndrome, helping guide management and potential surgical planning.

[Medium-term efficacy and safety analysis of Ex-PRESS shunt implantation for the treatment of secondary glaucoma in Sturge-Weber syndrome].

Objective: To evaluate the medium-term efficacy and safety of Ex-PRESS shunt implantation in the treatment of secondary glaucoma associated with Sturge-Weber Syndrome (SWS). Methods: This was a retrospective case series study. Medical records of patients diagnosed with secondary glaucoma due to SWS who underwent Ex-PRESS shunt implantation at Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, between January 2013 and February 2020 were collected. Only the right eye were included in the analysis when both eyes were affected. Follow-up visits were scheduled at postoperative week 1, 3 months, 6 months, 1 year, 2 years, and 3 years. Clinical data including intraocular pressure (IOP), vertical cup-to-disc (C/D) ratio, corneal horizontal diameter, visual field, anterior chamber condition, anti-glaucoma medication usage, and additional surgeries were evaluated and analyzed before and after the procedure. Surgical success rates and procedure-related complications at each follow-up time point were assessed. Statistical analyses were performed using t-test, Mann-Whitney U test, and χ2 test. Results: A total of 21 patients (21 eyes) were included in the study, comprising 10 females and 11 males. Among them, 15 eyes were on the right side, and 6 eyes were on the left side. The patients' ages ranged from 3 to 51 years, with a median age of 8.1 (6.3, 11.9) years. The follow-up period ranged from 3 to 53 months, with a median of 11 (6, 24) months. Preoperatively, the IOP in the 21 operated eyes was (32.9±9.1) mmHg (1 mmHg=0.133 kPa), significantly higher than the IOP in the 19 healthy eyes, which was (17.1±4.3) mmHg (t=5.80, P<0.001). The C/D ratio in the operated eyes was (0.75±0.13), also significantly higher than that in the healthy eyes, which was (0.32±0.10) (t=11.22, P<0.001). At the 1-year, 2-year, and 3-year follow-up, 8 eyes out of 16 operated eyes, 6 eyes out of 9 operated eyes, and 7 eyes out of 10 operated eyes achieved overall surgical success (complete success+conditional success), respectively. The number of eyes with complete success at the three follow-up time points was 3, 2, and 4, respectively. The IOP in the operated eyes was significantly reduced at all follow-up time points compared to preoperative values (all P<0.05), while there was no statistically significant difference in C/D ratio before and after surgery (all P>0.05). Two operated eyes experienced retinal detachment or choroidal leakage postoperatively, both of which recovered after conservative treatment. One eye developed postoperative degree Ⅰ shallow anterior chamber, and it resolved spontaneously on the third day after surgery. No serious surgical complications, such as bleb-related complications, malignant glaucoma, expulsive choroidal hemorrhage, or endophthalmitis, were observed postoperatively. Conclusions: Ex-PRESS shunt implantation for the treatment of secondary glaucoma in SWS demonstrated a relatively high level of safety. The medium-term IOP in the operated eyes significantly decreased compared to preoperative values. However, the majority of operated eyes did not achieve complete surgical success.

GNAQ R183Q somatic mutation contributes to aberrant arteriovenous specification in Sturge-Weber syndrome through Notch signaling.

Episcleral vasculature malformation is a significant feature of Sturge-Weber syndrome (SWS) secondary glaucoma, the density and diameter of which are correlated with increased intraocular pressure. We previously reported that the GNAQ R183Q somatic mutation was located in the SWS episclera. However, the mechanism by which GNAQ R183Q leads to episcleral vascular malformation remains poorly understood. In this study, we investigated the correlation between GNAQ R183Q and episcleral vascular malformation via surgical specimens, human umbilical vein endothelial cells (HUVECs), and the HUVEC cell line EA.hy926. Our findings demonstrated a positive correlation between episcleral vessel diameter and the frequency of the GNAQ R183Q variant. Furthermore, the upregulation of genes from the Notch signaling pathway and abnormal coexpression of the arterial marker EphrinB2 and venous marker EphB4 were demonstrated in the scleral vasculature of SWS. Analysis of HUVECs overexpressing GNAQ R183Q in vitro confirmed the upregulation of Notch signaling and arterial markers. In addition, knocking down of Notch1 diminished the upregulation of arterial markers induced by GNAQ R183Q. Our findings strongly suggest that GNAQ R183Q leads to malformed episcleral vasculatures through Notch-induced aberrant arteriovenous specification. These insights into the molecular basis of episcleral vascular malformation will provide new pathways for the development of effective treatments for SWS secondary glaucoma.

Isolated diffuse choroidal hemangioma without systemic symptoms: a case report.

BACKGROUND: Sturge-Weber syndrome is a nonhereditary congenital neurocutaneous syndrome characterized by a distinctive facial capillary malformation,neurological abnormalities, and ocular abnormalities such as glaucoma and choroidal hemangioma.It can be divided into different subtypes according to different clinical manifestations. It is rare for a patient to present with isolated difuse choroidal hemangioma and ipsilateral abnormal conjunctival and episcleral vessels without other systemic symptoms. CASE PRESENTATION: We report a 30-year-old man with isolated diffuse choroidal hemangioma in his right eye without systemic symptoms, such as vascular malformations in the skin or leptomeningeal angiomatosis. The only additional ophthalmic finding was ipsilateral abnormal conjunctival and episcleral vessels without glaucoma. However, there was no evidence of leptomeningeal angiomatosis or port-wine stain on the right side of the face, or glaucoma, which are common clinical manifestations of the Sturge-Weber syndrome (SWS).The absence of these characteristic symptoms did not preclude the diagnosis, and the patient could be diagnosed with a particular subtype of SWS. CONCLUSIONS: This is a rare case of documented isolated difuse choroidal hemangioma with ipsilateral abnormal conjunctival and episcleral vessels without glaucoma which we think it is belonging to a particular subtype of SWS.In addition to the traditional clinical manifestations, more and more atypical clinical manifestations are also accompanied by SWS, which requires our clinicians to continuously discover and report, so as to help more clinicians understand this disease.

Posterior sclerectomy for persistent serous retinal detachment with secondary glaucoma in Sturge-Weber syndrome: A case report.

INTRODUCTION: A serous retinal detachment is one of the most likely ocular manifestation of Sturge-Weber syndrome (SWS). This finding can frequently occur as a complication after filtering surgery to maintain the intraocular pressure (IOP). Proper treatment has been approached with choroidal hemangioma as an organ target. To the best of our knowledge, various treatments for SRD are associated with diffuse choroidal hemangioma has been approached. However, a second retinal detachment following radiation therapy has worsened the situation. Here, we report an unexpected serous retina and choroidal detachment after non penetrating trabeculectomy. Although radiation therapy has been proposed for previous detachment to the ipsilateral eye in this case, repetition radiation therapy was not suggested concerning the health and quality of life especially in for young subjects. However, the kissing choroidal detachment in this case necessitated immediate intervention. Thus, posterior sclerectomy was performed for the recurrent retinal detachment. We believe that an intervention for a SWS case related complication will remain a significant and important to share as a public health contribution. CASE PRESENTATION: A 20 year-old male confirmed with SWS with no known family history was diagnosed with SWS. He was gain from another hospital for glaucoma therapy. On the left brain MRI showed severe hemiatrophy in the frontal and parietal lobes and leptomeningeal angioma. Although his right (RE) eye had 3 gonio surgeries, 2 Baerveldt tube shunts and Micropulse trans-scleral cyclophotocoagulation, his IOP remained uncontrollable when he was 20 years old. RE IOP was in controlled after non-penetrating filtering surgery hence, his RE developed a recurrent serous retinal detachment. A posterior sclerectomy was performed in 1 quadrant of the globe to drain subretinal fluid. CONCLUSION: Sclerectomies to the inferotemporal quadrant of the globe for serous retinal detachment associated with SWS are considered efficient for optimal drain subretinal fluid, resulting in complete regression of detachment.

Combined Trabeculotomy-Non-Penetrating Deep Sclerectomy for Glaucoma in Sturge-Weber Syndrome.

INTRODUCTION: The aim of the study was to evaluate the efficacy and safety of combined trabeculotomy-non-penetrating deep sclerectomy (CTNS) in the treatment of Sturge-Weber syndrome (SWS) secondary glaucoma. METHODS: This retrospective study reviewed cases that underwent CTNS as initial surgery for SWS secondary glaucoma at our Ophthalmology Department center from April 2019 to August 2020. Surgical success was defined as an intraocular pressure (IOP) ≤ 21 mm Hg with (qualified success) or without (complete success) the use of anti-glaucoma medications. IOP >21 mm Hg or <5 mm Hg despite 3 or more applications of anti-glaucoma medications on 2 consecutive follow-up visits or at the last follow-up, performance of additional glaucoma (IOP-lowering) surgery, or with vision-threatening complications were classified as failure. RESULTS: A total of 22 eyes of 21 patients were included. Twenty-one eyes were of early-onset type and 1 eye was of adulthood onset. For Kaplan-Meier survival analysis, the overall success rates at 1st and 2nd years were 95.2% and 84.9%, while the complete success rates at 1st and 2nd years were 42.9% and 36.7%. At the last follow-up (22.3 ± 4.0 months, range: 11.2∼31.2), overall success was achieved in 19 (85.7%) eyes and complete success in 12 (52.4%) eyes. Postoperative complications included transient hyphema (11/22, 50.0%) and transient Ⅰ degree shallow anterior chamber (1/22, 4.5%), and retinal detachment (1/22, 4.5%). No other severe com plications were detected during the follow-up. CONCLUSION: CTNS significantly reduces IOP in SWS secondary glaucoma patients who have serious episcleral vascular malformation. CTNS in SWS secondary glaucoma patients is safe and effective for short and medium periods. A randomized controlled study comparing the long-term prognosis of SWS early-onset and late-onset glaucoma underwent CTNS is worth conducting.

The natural history of epilepsy and nonepileptic seizures in Sturge-Weber syndrome: A retrospective case-note review.

OBJECTIVE: Patients with Sturge-Weber Syndrome (SWS) experience varying degrees of neurological problems - including epilepsy, hemiparesis, learning disability (LD), and stroke-like episodes. While the range of clinical problems experienced by children with SWS is well recognized, the spectrum of clinical presentation and its treatment during adulthood has been relatively neglected in the literature to date. This study explored the natural history of epileptic and nonepileptic seizures into adulthood in patients with SWS, and their treatment, and investigated whether any clinical factors predict which symptoms a patient will experience during adulthood. METHODS: A retrospective case-note review of a cohort of 26 adults with SWS at the National Hospital for Neurology and Neurosurgery (NHNN). Childhood data were also recorded, where available, to enable review of change/development of symptoms over time. RESULTS: The course of epilepsy showed some improvement in adulthood - seventeen adults continued to have seizures, while six patients gained seizure freedom, and no one had adult-onset seizures. However, seizures did worsen for some patients. Although no factors reached statistical significance regarding predicting continued epilepsy in adulthood, being male, more severe LD, having required epilepsy surgery, and bilateral cortical involvement may be important. Nonepileptic seizures (NES) also began during adulthood for four patients. SIGNIFICANCE: By adulthood, there is some degree of improvement in epilepsy overall; while NES may occur for the first time. While the majority of the results did not survive adjustments for multiple comparisons, some interesting trends appeared, which require further investigation in a multicenter national audit. Patients with more neurologically severe presentations during childhood may continue to experience seizures. Careful monitoring and screening are needed during adulthood, to detect changes and newly developing symptoms such as NES, and target treatment promptly.

Developmental expression of the Sturge-Weber syndrome-associated genetic mutation in Gnaq: a formal test of Happle's paradominant inheritance hypothesis.

Sturge-Weber Syndrome (SWS) is a sporadic (non-inherited) syndrome characterized by capillary vascular malformations in the facial skin, leptomeninges, or the choroid. A hallmark feature is the mosaic nature of the phenotype. SWS is caused by a somatic mosaic mutation in the GNAQ gene (p.R183Q), leading to activation of the G protein, Gαq. Decades ago, Rudolf Happle hypothesized SWS as an example of "paradominant inheritance", that is, a "lethal gene (mutation) surviving by mosaicism". He predicted that the "presence of the mutation in the zygote will lead to death of the embryo at an early stage of development". We have created a mouse model for SWS using gene targeting to conditionally express the GNAQ p.R183Q mutation. We have employed two different Cre-drivers to examine the phenotypic effects of expression of this mutation at different levels and stages of development. As predicted by Happle, global, ubiquitous expression of this mutation in the blastocyst stage results in 100% embryonic death. The majority of these developing embryos show vascular defects consistent with the human vascular phenotype. By contrast, global but mosaic expression of the mutation enables a fraction of the embryos to survive, but those that survive to birth and beyond do not exhibit obvious vascular defects. These data validate Happle's paradominant inheritance hypothesis for SWS and suggest the requirement of a tight temporal and developmental window of mutation expression for the generation of the vascular phenotype. Furthermore, these engineered murine alleles provide the template for the development of a mouse model of SWS that acquires the somatic mutation during embryonic development, but permits the embryo to progress to live birth and beyond, so that postnatal phenotypes can also be investigated. These mice could then also be employed in pre-clinical studies of novel therapies.