Spectrum of Schwartz-Jampel syndrome includes micromelic chondrodysplasia, kyphomelic dysplasia, and Burton disease

Clinical overview and outcome of the Stuve-Wiedemann syndrome: a systematic review

BACKGROUND

Stuve-Wiedemann syndrome (SWS) is a rare and severe genetic disease characterized by skeletal anomalies and dysautonomic disturbances requiring appropriate care. Peer support is mandatory to fill the lack of clinical recommendations in such rare diseases. We report a new case and provide the first systematic review of all previous published cases.

OBJECTIVE

To better describe the timeline of SWS and to improve paediatric management.

DATA SOURCES

SWS English publications available on Pubmed until 31/03/2021.

STUDY SELECTION

Case description combining typical osteo-articular and dysautonomic involvement (with 2 items by categories required for children < 2 years and 3 items > 2 years).

DATA EXTRACTION

Demographic, clinical, genetics and outcome data.

RESULTS

In our cohort of 69 patients, the median age at report was 32 months. Only 46% presented antenatal signs. Mortality rate is higher during the first 2 years (42% < 2 years; 10% > 2 years) mainly due to respiratory failure, pulmonary arterial hypertension appearing to be a poor prognosis factor (mortality rate 63%). After 2 years, orthopaedic symptoms significantly increase including joint mobility restriction (81%), spinal deformations (77%) and fractures (61%).

CONCLUSIONS

Natural history of SWS is marked by a high mortality rate before 2 years due to dysautonomic disturbances. A specialized multidisciplinary approach is needed to address these early mortality risks and then adapt to the specific, mainly orthopaedic, needs of patients after 2 years of age. Further research is required to provide clinical guidelines and improve pre-natal counselling.

De novo heterozygous variants in KIF5B cause kyphomelic dysplasia

Kyphomelic dysplasia is a heterogeneous group of skeletal dysplasias characterized by severe bowing of the limbs associated with other variable findings, such as narrow thorax and abnormal facies. We searched for the genetic etiology of this disorder. Four individuals diagnosed with kyphomelic dysplasia were enrolled. We performed whole-exome sequencing and evaluated the pathogenicity of the identified variants. All individuals had de novo heterozygous variants in KIF5B encoding kinesin-1 heavy chain: two with c.272A>G:p.(Lys91Arg), one with c.584C>A:p.(Thr195Lys), and the other with c.701G>T:p.(Gly234Val). All variants involved conserved amino acids in or close to the ATPase activity-related motifs in the catalytic motor domain of the KIF5B protein. All individuals had sharp angulation of the femora and humeri, distinctive facial features, and neonatal respiratory distress. Short stature was observed in three individuals. Three developed postnatal osteoporosis with subsequent fractures, two showed brachycephaly, and two were diagnosed with optic atrophy. Our findings suggest that heterozygous KIF5B deleterious variants cause a specific form of kyphomelic dysplasia. Furthermore, alterations in kinesins cause various symptoms known as kinesinopathies, and our findings also extend the phenotypic spectrum of kinesinopathies. This article is protected by copyright. All rights reserved.

A Novel Pathogenic HSPG2 Mutation in Schwartz-Jampel Syndrome

Schwartz–Jampel syndrome is a rare autosomal recessive disease caused by mutation in the heparan sulfate proteoglycan 2 (HSPG2) gene. Its cardinal symptoms are skeletal dysplasia and neuromuscular hyperactivity. Herein, we identified a new pathogenic mutation site (NM_005529.6:c.1125C>G; p.Cys375Trp) of HSPG2 leading to Schwartz–Jampel syndrome by whole-exome sequencing. This mutation carried by the asymptomatic parents was previously registered in a single-nucleotide polymorphism database of the National Institutes of Health as a coding sequence variant rs543805444. The pathogenic nature of this missense mutation was demonstrated by in silico pathogenicity assessment, clinical presentations, and cellular function of primary fibroblast derived from patients. Various in silico software applications predicted the mutation to be pathogenic [Sorting Intolerant From Tolerant (SIFT), 0; Polyphen-2, 1; CADD (Combined Annotation Dependent Depletion), 23.7; MutationTaster, 1; DANN (deleterious annotation of genetic variants using neural networks); 0.9]. Needle electromyography revealed extensive complex repetitive discharges and multiple polyphasic motor unit action potentials in axial and limb muscles at rest. Short exercise test for myotonia showed Fournier pattern I. At cellular levels, mutant primary fibroblasts had reduced levels of secreted perlecan and impaired migration ability but normal capability of proliferation. Patients with this mutation showed more neuromuscular instability and relatively mild skeletal abnormality comparing with previously reported cases.

Delineation of the clinical and radiological features of Stuve-Wiedemann syndrome childhood survivors, four new cases and review of the literature

Stuve-Wiedemann syndrome (SWS; MIM 601559) is a rare autosomal recessive disease caused by mutations in the leukemia inhibitor factor receptor gene (LIFR). Common clinical and radiological findings are often observed, and high neonatal mortality occurs due to respiratory distress and hyperthermic episodes. Despite initially considered as a lethal disorder during the newborn period, in recent years, several SWS childhood survivors have been reported. We report a detailed clinical and radiological characterization of four unrelated childhood SWS molecularly confirmed patients and review 22 previously reported childhood surviving cases. We contribute to the definition of the childhood survival phenotype of SWS, emphasizing the evolving phenotype, characterized by skeletal abnormalities with typical radiological findings, distinctive dysmorphic features, and dysautonomia. Based on the typical features and clinical course, early diagnosis is possible and crucial to plan appropriate management and prevent potential complications. Genetic confirmation is advisable in order to improve genetic counseling to the patients and their families.

Novel HSPG2 mutations causing Schwartz‑Jampel syndrome type 1 in a Chinese family: A case report

Schwartz-Jampel syndrome type 1 (SJS1) is a rare autosomal recessive disease caused by mutations in the gene heparan sulfate proteoglycan 2 (HSPG2; also known as basement membrane‑specific heparin sulfate). In the present study, a 10‑year‑old female SJS1 proband from a Chinese family, who was diagnosed by X‑ray and physical examination, was recruited. The key clinical features of the patient with SJS1 included short stature, joint contractures, pigeon breast, and myotonia that led to progressive stiffness of the face and limbs; barely discernible kyphosis was also noted. Genetic testing using whole exome sequencing and Sanger sequencing was performed for the proband and family members. A total of 2 novel mutations (c.8788G>A; p.Glu2930Lys and c.11671+5G>A) in the HSPG2 gene were identified in the proband. The family members harboring 1 heterozygous mutation in HSPG2 did not exhibit any skeletal abnormalities. The results of the present study suggested that the compound heterozygous mutations in HSPG2 may be responsible the induction of SJS1, and demonstrated the genotype‑phenotype associations between mutations in the HSPG2 gene and clinical characteristics of SJS1.

Stüve-Wiedemann syndrome: LIFR and associated cytokines in clinical course and etiology

Stüve-Wiedemann syndrome (STWS; OMIM #610559) is a rare bent-bone dysplasia that includes radiologic bone anomalies, respiratory distress, feeding difficulties, and hyperthermic episodes. STWS usually results in infant mortality, yet some STWS patients survive into and, in some cases, beyond adolescence. STWS is caused by a mutation in the leukemia inhibitory factor receptor (LIFR) gene, which is inherited in an autosomally recessive pattern. Most LIFR mutations resulting in STWS are null mutations which cause instability of the mRNA and prevent the formation of LIFR, impairing the signaling pathway. LIFR signaling usually follows the JAK/STAT3 pathway, and is initiated by several interleukin-6-type cytokines. STWS is managed on a symptomatic basis since there is no treatment currently available.

Stüve-Wiedemann syndrome and related bent bone dysplasias

Stüve-Wiedemann syndrome (SWS) is a severe congenital skeletal dysplasia associated with life threatening dysautonomic manifestations. Newborns affected with this condition exhibit distinctive shortening and bowing of the long bones with reduced bone volume. The majority of affected newborns die early due to neuromuscular complications namely hyperthermia, apnea, and swallowing difficulties. In this review, we provide an overall picture on the clinical, including long-term management, molecular and cellular aspects of SWS and discuss briefly other related bent bone dysplasias.

The skeletal dysplasias

The skeletal dysplasias (osteochondrodysplasias) are a heterogeneous group of more than 350 disorders frequently associated with orthopedic complications and varying degrees of dwarfism or short stature. These disorders are diagnosed based on radiographic, clinical, and molecular criteria. The molecular mechanisms have been elucidated in many of these disorders providing for improved clinical diagnosis and reproductive choices for affected individuals and their families. An increasing variety of medical and surgical treatment options can be offered to affected individuals to try to improve their quality of life and lifespan.

Electrophysiological studies in a mouse model of Schwartz-Jampel syndrome demonstrate muscle fiber hyperactivity of peripheral nerve origin

Schwartz-Jampel syndrome (SJS) is an autosomal-recessive condition characterized by muscle stiffness and chondrodysplasia. It is due to loss-of-function hypomorphic mutations in the HSPG2 gene that encodes for perlecan, a proteoglycan secreted into the basement membrane. The origin of muscle stiffness in SJS is debated. To resolve this issue, we performed an electrophysiological investigation of an SJS mouse model with a missense mutation in the HSPG2 gene. Compound muscle action potential amplitudes, distal motor latencies, repetitive nerve stimulation tests, and sensory nerve conduction velocities of SJS mice were normal. On electromyography (EMG), neuromyotonic discharges, that is, bursts of motor unit action potentials firing at high rates (120-300 HZ), were constantly observed in SJS mice in all muscles, except in the diaphragm. Neuromyotonic discharges were not influenced by general anesthesia and disappeared with curare administration. They persisted after complete motor nerve section, terminating only with Wallerian degeneration. These results demonstrate that perlecan deficiency in SJS provokes a neuromyotonic syndrome. The findings further suggest a distal axonal localization of the generator of neuromyotonic discharges. SJS should now be considered as an inherited disorder with peripheral nerve hyperexcitability.

Heparan sulfate proteoglycans: a GAGgle of skeletal-hematopoietic regulators

This review summarizes our current understanding of the presence and function of heparan sulfate proteoglycans (HSPGs) in skeletal development and hematopoiesis. Although proteoglycans (PGs) comprise a large and diverse group of cell surface and matrix molecules, we chose to focus on HSPGs owing to their many proposed functions in skeletogenesis and hematopoiesis. Specifically, we discuss how HSPGs play predominant roles in establishing and regulating niches during skeleto-hematopoietic development by participating in distinct developmental processes such as patterning, compartmentalization, growth, differentiation, and maintenance of tissues. Special emphasis is placed on our novel hypothesis that mechanistically links endochondral skeletogenesis to the establishment of the hematopoietic stem cell (HSC) niche in the marrow. HSPGs may contribute to these developmental processes through their unique abilities to establish and mediate morphogen, growth factor, and cytokine gradients; facilitate signaling; provide structural stability to tissues; and act as molecular filters and barriers.

Evidence of a dosage effect and a physiological endplate acetylcholinesterase deficiency in the first mouse models mimicking Schwartz-Jampel syndrome neuromyotonia

Schwartz-Jampel syndrome (SJS) is a recessive neuromyotonia with chondrodysplasia. It results from hypomorphic mutations of the gene encoding perlecan, leading to a decrease in the levels of this heparan sulphate proteoglycan in basement membranes (BMs). It has been suggested that SJS neuromyotonia may result from endplate acetylcholinesterase (AChE) deficiency, but this hypothesis has never been investigated in vivo due to the lack of an animal model for neuromyotonia. We used homologous recombination to generate a knock-in mouse strain with one missense substitution, corresponding to a human familial SJS mutation (p.C1532Y), in the perlecan gene. We derived two lines, one with the p.C1532Y substitution alone and one with p.C1532Y and the selectable marker Neo, to down-regulate perlecan gene activity and to test for a dosage effect of perlecan in mammals. These two lines mimicked SJS neuromyotonia with spontaneous activity on electromyogramm (EMG). An inverse correlation between disease severity and perlecan secretion in the BMs was observed at the macroscopic and microscopic levels, consistent with a dosage effect. Endplate AChE levels were low in both lines, due to synaptic perlecan deficiency rather than major myofibre or neuromuscular junction disorganization. Studies of muscle contractile properties showed muscle fatigability at low frequencies of nerve stimulation and suggested that partial endplate AChE deficiency might contribute to SJS muscle stiffness by potentiating muscle force. However, physiological endplate AChE deficiency was not associated with spontaneous activity at rest on EMG in the diaphragm, suggesting that additional changes are required to generate such activity characteristic of SJS.

Angulated femurs and the skeletal dysplasias: experience of the International Skeletal Dysplasia Registry (1988-2006)

Angulated or bent femur (isolated or associated with other long bone bowing) in the fetus or newborn is relatively common when evaluating patients with skeletal dysplasias. To determine the extent and heterogeneity of disorders associated with angulated or bent femurs, we analyzed cases in the radiographic database (1998-2006) of the International Skeletal Dysplasia Registry (ISDR) and determined which established skeletal dysplasias and genetic syndromes are associated with this finding. The results show that more than 40 distinct disorders with varying frequency (very rare to more commonly occurring disorders) can be associated with bowed/bent/angulated femurs. Sixty-six percent of the cases with angulated femurs belonged to three well described groups of disorders; campomelic disorders (24.4%), thanatophoric dysplasia (23.9%) and osteogenesis imperfecta (OI) (18.1%). With specific emphasis on these, this cross-sectional cohort provides discussion of data on other rare disorders associated with angulated femurs and the importance of the finding relative to its occurrence within a diagnostic group. This study aims to provide differential diagnosis of entities to be considered when a fetus or newborn is found to have congenital bowing/angulation of the femur.

Radiological manifestations of the skeleton, lungs and brain in Stueve-Wiedemann syndrome

A total of 25 patients with the rare skeletal dysplasia Stueve-Wiedemann syndrome (SWS) have been evaluated during the last 11 years. Of all patients with clinical suspicion of SWS, skeletal and chest radiographs were obtained for classification of the underlying skeletal dysplasia. In one case, CT was carried out for the first time for further investigation of the midface hypoplasia. Typical conventional radiological findings and CT features were analysed and compared with published data. Early diagnosis of SWS was made by correlating radiological and clinical findings. Follow-up radiological examinations of the skeleton and of the chest were carried out in six children surviving infancy for evaluation of progression. Clinically, they suffered from progressive orthopaedic problems, recurrent aspiration pneumonia and recurrent episodes of hyperthermia, as well as cutaneous infections. Radiologically progressive bowing of the long tubular bones and progressive metaphyseal decalcification were present on follow-up skeletal radiographs. Skeletal abnormalities in SWS are so characteristic that an early post-partum diagnosis can be made by correlation of typical clinical and radiological findings. Few cases survive infancy. First, these patients face progressive orthopaedic problems and respiratory infections.

Reduced perlecan in mice results in chondrodysplasia resembling Schwartz-Jampel syndrome

Perlecan knock-in mice were developed to model Schwartz-Jampel syndrome (SJS), a skeletal disease resulting from decreased perlecan. Two mouse strains were generated: those carrying a C-to-Y mutation at residue 1532 and the neomycin cassette (C1532Yneo) and those harboring the mutation alone (C1532Y). Immunostaining, biochemistry, size measurements, skeletal studies and histology revealed Hspg2 transcriptional changes in C1532Yneo mice, leading to reduced perlecan secretion and a skeletal disease phenotype characteristic of SJS patients. Skeletal disease features include smaller size, impaired mineralization, misshapen bones, flat face and joint dysplasias reminiscent of osteoarthritis and osteonecrosis. Moreover, C1532Yneo mice displayed transient expansion of hypertrophic cartilage in the growth plate concomitant with radial trabecular bone orientation. In contrast, C1532Y mice, harboring only the mutation associated with SJS, displayed a mild phenotype, inconsistent with SJS. These studies question the C1532Y mutation as the sole causative factor of SJS in the human family harboring this alteration and imply that transcriptional changes leading to perlecan reduction may represent the disease mechanism for SJS.

New insights in congenital bowing of the femora

The aim of this study is to review the clinical, radiological and molecular findings of the bent bone dysplasia group including Stüve-Wiedemann syndrome due to LIFR mutations, Compomelic dysplasia due to SOX9 mutations and Kyphomelic dysplasia with no known molecular bases.

Double child burial from sunghir (Russia): Pathology and inferences for upper paleolithic funerary practices

The double child burial from Sunghir (Russia) is a spectacular Mid Upper Palaeolithic funerary example dated to about 24,000 BP. A boy (Sunghir 2) and a girl (Sunghir 3), about 12-13 and 9-10 years old, respectively, were buried at the same time, head to head, covered by red ocher and ornamented with extraordinarily rich grave goods. Examination of the two skeletons reveals that the Sunghir 3 femora are short and exhibit marked antero-posterior bowing. The two femora do not show any asymmetry in the degree of shortening and bowing. Bowing affects the whole diaphysis and shows a regularly incurved profile, with the highest point at midshaft. Pathology is confined to the femora, and no other part of this well-preserved specimen shows abnormality. The isolated nature of the Sunghir 3 anomalies points to cases reported in the medical literature under the label of "congenital bowing of long bones" (CBLB). These are a group of rare conditions exhibiting localized, sometimes bilateral, bowing and shortening which are nonspecific and may result from different causes, including abnormalities of the primary cartilaginous anlage (i.e., the aggregation of cells representing the first trace of an organ). Localized ossification disturbances, possibly linked to a diabetic maternal condition, might explain the shortening and the coincidence of maximum midshaft curvature with the position of the primary ossification center, as well as the lack of involvement of other skeletal parts. This scenario, rather than other possibilities (early bilateral midshaft fracture, acute plastic bowing deformities, or faulty fetal posture), provides the most likely explanation for the Sunghir 3 femoral deformities. The intriguing combination of a pathological condition apparent since birth with a spectacular burial of unusually positioned young individuals of different sexes recalls significant aspects of the triple burial from the contemporary site of Dolní Vestonice (Moravia), evoking a patterned relationship between physical abnormality and extraordinary Upper Paleolithic funerary behavior.

Prenatal diagnosis of isolated femoral bent bone skeletal dysplasia: problems in differential diagnosis and genetic counseling

Severe localized and symmetric bowing of the femora, in the absence of other significant skeletal or nonskeletal abnormalities, is a rare prenatal ultrasound finding. A 38-year-old woman was referred at 19 weeks gestation and ultrasound of the fetus showed severe shortening, and marked symmetric bowing of the femora. A provisional diagnosis of kyphomelic dysplasia (KD) was made. The patient elected termination of pregnancy and post mortem assessments were most consistent with kyphomelic dysplasia. KD is bent-bone skeletal dysplasia that, in contrast to campomelic dysplasia, involves principally the femora with relative sparing of the remainder of the skeleton. KD can be difficult to distinguish, particularly from symmetric cases of femoral hypoplasia unusual facies syndrome (FH-UFS), and few prenatal diagnoses have been reported. Because KD is thought to an be autosomal recessive disorder, the possibility that definitive diagnosis may not be possible prenatally, and even by postmortem assessment in cases choosing to abort, is an important counseling consideration.

Stüve-Wiedemann syndrome in children surviving infancy: clinical and radiological features

We report three children from two inbred Arab families with Stüve-Wiedemann syndrome who have survived the first year of life (ages are 6 years, 2.8 years and 2 years). All exhibited a characteristic phenotype resembling that described by Chen et al.[(2001). Am J Med Genet 101:240-245]. In all three children the skeletal abnormalities progressed to severe bowing of the long bones with prominent joints and severe spinal deformity. Neurological symptoms were present in all of them. These included temperature instability with excessive sweating, reduced pain sensation with repeated injury to the tongue and limbs, absent corneal reflexes and a smooth tongue. Mentality was normal in all of them. Radiological changes included under tubulation of the diaphyses, rarefaction and striation of metaphyses, destruction of the femoral heads and spinal deformity. We confirm that survival in this syndrome is possible and that the prognosis improves after the first year of life. This should be taken into consideration when counselling parents of affected children. This report further supports the existence of a characteristic phenotype in Stüve-Wiedemann syndrome survivors which include, in addition to the skeletal abnormalities and distinctive radiological features, neurological symptoms reminiscent of dysautonomia.

Schwartz-jampel syndrome: report of five cases

We describe five patients with Schwartz-Jampel syndrome (SJS) examined at the outpatient service for neuromuscular disorders at our Institution from 1996 to 1999 with the objective of emphasizing the characteristic dysmorphic phenotype of SJS and its different clinical forms. Two cases presented SJS-type 1A, two had SJS-type 1B and one manifested SJS-type 2. Two boys with 3 and 13 years of age had generalized stiffness and the characteristic facial as well as osteoarticular changes from birth. Other two boys with 11 and 7 years had less marked dysmorphic changes at birth and manifested myotonia, as a limiting factor, during the second year of age. A girl with two months of age had severe myotonia from birth leading to feeding diffuculties. In all cases the diagnosis was based on dysmorphic features, and on electromyographic changes showing continuous electrical activity of muscle fibers. All were treated with carbamazepine, 20-30 mg/Kg since diagnosis. The four boys (all with normal intelligence) improved of myotonia in daily activities, markedly in three, and moderately in one. The girl did not improve and showed global development delay: by the last follow-up (at 20 months of age) she did not sit unsupported, and had mental retardation. Carbamazepine in SJS-type 1 improves general daily performance and psychological status of the patients.

Dyssegmental dysplasia, Silverman-Handmaker type: unexpected role of perlecan in cartilage development

Dyssegmental dysplasia, Silverman-Handmaker type (DDSH), is a lethal autosomal recessive form of dwarfism with characteristic anisospondylic micromelia. The remarkable similarities in the radiographic, clinical, and chondroosseous morphology of DDSH patients to those of perlecan-null mice led to the identification of mutations in the perlecan gene (HSPG2) of DDSH. Perlecan, a large heparan sulfate proteoglycan, is expressed in various tissues and is a component of all basement membrane extracellular matrices. A chondrodysplasia phenotype caused by the loss of perlecan was unexpected, because cartilage does not have basement membranes. Insertion and splicing mutations in HSPG2 of DDSH were found that were predicted to create a premature termination codon. Immunostaining and biochemical analysis revealed that the mutant perlecan molecules were unstable and not secreted into the extracellular matrix. These results indicate that DDSH is caused by functional null mutations of HSPG2 and that perlecan is essential for cartilage development. Published 2002 Wiley-Liss, Inc.

Role of perlecan in skeletal development and diseases

Perlecan, a large heparan sulfate proteoglycan (HSPG), is present in the basement membrane and other extracellular matrices. Its protein core is 400 kDa in size and consists of five distinct structural domains. A number of in vitro studies suggest multiple functions of perlecan in cell growth and differentiation and tissue organization. Recent studies with gene knockout mice and human diseases revealed critical in vivo roles of perlecan in cartilage development and neuromuscular junction activity.

Structural and functional mutations of the perlecan gene cause Schwartz-Jampel syndrome, with myotonic myopathy and chondrodysplasia

Perlecan, a large heparan sulfate proteoglycan, is a component of the basement membrane and other extracellular matrices and has been implicated in multiple biological functions. Mutations in the perlecan gene (HSPG2) cause two classes of skeletal disorders: the relatively mild Schwartz-Jampel syndrome (SJS) and severe neonatal lethal dyssegmental dysplasia, Silverman-Handmaker type (DDSH). SJS is an autosomal recessive skeletal dysplasia characterized by varying degrees of myotonia and chondrodysplasia, and patients with SJS survive. The molecular mechanism underlying the chondrodystrophic myotonia phenotype of SJS is unknown. In the present report, we identify five different mutations that resulted in various forms of perlecan in three unrelated patients with SJS. Heterozygous mutations in two patients with SJS either produced truncated perlecan that lacked domain V or significantly reduced levels of wild-type perlecan. The third patient had a homozygous 7-kb deletion that resulted in reduced amounts of nearly full-length perlecan. Unlike DDSH, the SJS mutations result in different forms of perlecan in reduced levels that are secreted to the extracellular matrix and are likely partially functional. These findings suggest that perlecan has an important role in neuromuscular function and cartilage formation, and they define the molecular basis involved in the difference in the phenotypic severity between DDSH and SJS.

Characterization of a long-term survivor with Stüve-Wiedemann syndrome and mosaicism of a supernumerary marker chromosome

Stüve-Wiedemann syndrome (SWS) is typically lethal in the neonatal period; only two patients have been reported with a longer survival. We report a new patient with SWS, who at 9 years of age is one of the longest survivors with this disorder. In addition to the characteristic features of SWS, she has a number of unique clinical signs, including lack of corneal and patellar reflexes, a smooth tongue with no fungiform papillae, chronic gingival abscesses, mottled, poor dentition, blotchy pigmentation of the skin, unusual infections, multiple fractures, and progressive scoliosis. Cytogenetic analysis identified mosaicism for a supernumerary marker chromosome (SMC), seen in the majority of amniocytes, blood, and skin fibroblasts. The SMC was shown to be derived from chromosome 5 and contains euchromatin. The significance of the SMC to the etiology of SWS is unknown. This patient further demonstrates that SWS is not universally lethal.