A dyadic approach to the delineation of diagnostic entities in clinical genomics.

The delineation of disease entities is complex, yet recent advances in the molecular characterization of diseases provide opportunities to designate diseases in a biologically valid manner. Here, we have formalized an approach to the delineation of Mendelian genetic disorders that encompasses two distinct but inter-related concepts: (1) the gene that is mutated and (2) the phenotypic descriptor, preferably a recognizably distinct phenotype. We assert that only by a combinatorial or dyadic approach taking both of these attributes into account can a unitary, distinct genetic disorder be designated. We propose that all Mendelian disorders should be designated as "GENE-related phenotype descriptor" (e.g., "CFTR-related cystic fibrosis"). This approach to delineating and naming disorders reconciles the complexity of gene-to-phenotype relationships in a simple and clear manner yet communicates the complexity and nuance of these relationships.

Delphi Consensus on Diagnostic Criteria for LUMBAR Syndrome.

OBJECTIVE: To develop consensus on diagnostic criteria for LUMBAR syndrome, the association of segmental infantile hemangiomas that affect the Lower body with Urogenital anomalies, Ulceration, spinal cord Malformations, Bony defects, Anorectal malformations, Arterial anomalies and/or Renal anomalies. STUDY DESIGN: These diagnostic criteria were developed by an expert multidisciplinary and multi-institutional team based on analysis of peer-reviewed data, followed by electronic-Delphi consensus of a panel of 61 international pediatric specialists. RESULTS: After 2 Delphi rounds, a 92% or higher level of agreement was reached for each Delphi statement. 98% of panelists agreed with the diagnostic criteria, and 100% agreed the criteria would be useful in clinical practice. The diagnosis of LUMBAR requires the presence of a segmental, or patterned, infantile hemangioma of the lumbosacral, sacrococcygeal, or pelvic cutaneous regions plus one additional criterion of the urogenital, spinal, bony, anorectal, arterial, or renal organ systems. CONCLUSIONS: These diagnostic criteria will enhance clinical care by improving screening, detection, and overall awareness of this poorly understood neurocutaneous disorder. The criteria can be utilized by a wide variety of pediatric subspecialists. In addition, formal criteria will improve phenotypic uniformity among LUMBAR syndrome cohorts and a patient registry, allowing investigators to assess clinical features, long-term outcomes, and results of genetic sequencing in a standardized manner. Finally, these criteria will serve as a starting point for prospective studies to establish formal screening and management guidelines.

LUMBAR syndrome-OEIS complex overlap: A case series and review.

We present three new and six published infants with overlapping features of LUMBAR syndrome (lower body hemangioma, urogenital anomalies, spinal cord malformations, bony deformities, anorectal/arterial anomalies and renal anomalies) and OEIS complex (omphalocele, exstrophy, imperforate anus, and spinal defects), also known as cloacal exstrophy. OEIS is included under the recently proposed umbrella coined recurrent constellations of embryonic malformations (RCEMs). The RCEMs represent a phenotypically overlapping spectrum of rare disorders of caudal dysgenesis with unknown cause but likely shared pathogenesis. It has recently been proposed that LUMBAR be considered an RCEM. This report of infants with combined features of OEIS and LUMBAR is the first to demonstrate an overlap between LUMBAR and another RCEM, which supports LUMBAR's inclusion within the RCEM spectrum.

Personal journeys to and in human genetics and dysmorphology.

Genetics has become a critical component of medicine over the past five to six decades. Alongside genetics, a relatively new discipline, dysmorphology, has also begun to play an important role in providing critically important diagnoses to individuals and families. Both have become indispensable to unraveling rare diseases. Almost every medical specialty relies on individuals experienced in these specialties to provide diagnoses for patients who present themselves to other doctors. Additionally, both specialties have become reliant on molecular geneticists to identify genes associated with human disorders. Many of the medical geneticists, dysmorphologists, and molecular geneticists traveled a circuitous route before arriving at the position they occupied. The purpose of collecting the memoirs contained in this article was to convey to the reader that many of the individuals who contributed to the advancement of genetics and dysmorphology since the late 1960s/early 1970s traveled along a journey based on many chances taken, replying to the necessities they faced along the way before finding full enjoyment in the practice of medical and human genetics or dysmorphology. Additionally, and of equal importance, all exhibited an ability to evolve with their field of expertise as human genetics became human genomics with the development of novel technologies.

Variants in CLDN5 cause a syndrome characterized by seizures, microcephaly and brain calcifications.

The blood-brain barrier ensures CNS homeostasis and protection from injury. Claudin-5 (CLDN5), an important component of tight junctions, is critical for the integrity of the blood-brain barrier. We have identified de novo heterozygous missense variants in CLDN5 in 15 unrelated patients who presented with a shared constellation of features including developmental delay, seizures (primarily infantile onset focal epilepsy), microcephaly and a recognizable pattern of pontine atrophy and brain calcifications. All variants clustered in one subregion/domain of the CLDN5 gene and the recurrent variants demonstrate genotype-phenotype correlations. We modelled both patient variants and loss of function alleles in the zebrafish to show that the variants analogous to those in patients probably result in a novel aberrant function in CLDN5. In total, human patient and zebrafish data provide parallel evidence that pathogenic sequence variants in CLDN5 cause a novel neurodevelopmental disorder involving disruption of the blood-brain barrier and impaired neuronal function.

Pharmacodynamic Study of Miransertib in Individuals with Proteus Syndrome.

Proteus syndrome is a life-threatening segmental overgrowth syndrome caused by a mosaic gain-of-function AKT1 variant. There are no effective treatments for Proteus syndrome. Miransertib is an AKT1 inhibitor that, prior to this study, has been evaluated only in adult oncology trials. We designed a non-randomized, phase 0/1 pilot study of miransertib in adults and children with Proteus syndrome to identify an appropriate dosage starting point for a future efficacy trial using a pharmacodynamic endpoint. The primary endpoint was a 50% reduction in the tissue levels of AKT phosphorylation from biopsies in affected individuals. We also evaluated secondary efficacy endpoints. We found that a dose of 5 mg/m2/day (1/7 the typical dose used in oncology) led to a 50% reduction in phosphorylated AKT (pAKT) in affected tissues from five of six individuals. This dose was well tolerated. Two of the six efficacy endpoints (secondary objectives) suggested that this agent may be efficacious. We observed a decrease in a cerebriform connective tissue nevus and a reduction in pain in children. We conclude that 5 mg/m2/day of miransertib is an appropriate starting point for future efficacy trials and that this agent shows promise of therapeutic efficacy in children with Proteus syndrome.

A standard of care for individuals with PIK3CA-related disorders: An international expert consensus statement.

Growth promoting variants in PIK3CA cause a spectrum of developmental disorders, depending on the developmental timing of the mutation and tissues involved. These phenotypically heterogeneous entities have been grouped as PIK3CA-Related Overgrowth Spectrum disorders (PROS). Deep sequencing technologies have facilitated detection of low-level mosaic, often necessitating testing of tissues other than blood. Since clinical management practices vary considerably among healthcare professionals and services across different countries, a consensus on management guidelines is needed. Clinical heterogeneity within this spectrum leads to challenges in establishing management recommendations, which must be based on patient-specific considerations. Moreover, as most of these conditions are rare, affected families may lack access to the medical expertise that is needed to help address the multi-system and often complex medical issues seen with PROS. In March 2019, macrocephaly-capillary malformation (M-CM) patient organizations hosted an expert meeting in Manchester, United Kingdom, to help address these challenges with regards to M-CM syndrome. We have expanded the scope of this project to cover PROS and developed this consensus statement on the preferred approach for managing affected individuals based on our current knowledge.

A mouse model of Proteus syndrome.

Proteus syndrome is a mosaic, progressive overgrowth disorder caused by a somatic activating variant c.49G > A p.(E17K) in AKT1. The presentation in affected individuals is variable, with a diversity of tissues demonstrating abnormalities. Common manifestations include skin and bony overgrowth, vascular malformations (VMs), cysts and benign tumors. We used two methods to create mouse models that had endogenously-regulated mosaic expression of the Proteus syndrome variant. Variant allele fractions (VAFs) ranged from 0% to 50% across numerous tissues in 44 Proteus syndrome mice. Mice were phenotypically heterogeneous with lesions rarely observed before 12 months of age. VMs were the most frequent finding with a total of 69 found in 29 of 44 Proteus syndrome mice. Twenty-eight cysts and ectasia, frequently biliary, were seen in 22 of 44 Proteus syndrome mice. Varying levels of mammary hyperplasia were seen in 10 of 16 female Proteus syndrome mice with other localized regions of hyperplasia and stromal expansion noted in several additional animals. Interestingly, 27 of 31 Proteus syndrome animals had non-zero blood VAF that is in contrast to the human disorder where it is rarely seen in peripheral blood. Identification of variant-positive cells by green fluorescent protein (GFP) staining in chimeric Proteus syndrome mice showed that in some lesions, hyperplastic cells were predominantly GFP/Akt1E17K-positive and showed increased pAKT signal compared to GFP-negative cells. However, hyperplastic mammary epithelium was a mixture of GFP/Akt1E17K-positive and negative cells with some GFP/Akt1E17K-negative cells also having increased pAKT signal suggesting that the variant-positive cells can induce lesion formation in a non-cell autonomous manner.

Novel findings and expansion of phenotype in a mosaic RASopathy caused by somatic KRAS variants.

Mosaic KRAS variants and other RASopathy genes cause oculoectodermal, encephalo-cranio-cutaneous lipomatosis, and Schimmelpenning-Feuerstein-Mims syndromes, and a spectrum of vascular malformations, overgrowth and other associated anomalies, the latter of which are only recently being characterized. We describe eight individuals in total (six unreported cases and two previously reported cases) with somatic KRAS variants and variably associated features. Given the findings of somatic overgrowth (in seven individuals) and vascular or lymphatic malformations (in eight individuals), we suggest mosaic RASopathies (mosaic KRAS variants) be considered in the differential diagnosis for individuals presenting with asymmetric overgrowth and lymphatic or vascular anomalies. We expand the association with embryonal tumors, including the third report of embryonal rhabdomyosarcoma, as well as novel findings of Wilms tumor and nephroblastomatosis in two individuals. Rare or novel findings in our series include the presence of epilepsy, polycystic kidneys, and T-cell deficiency in one individual, and multifocal lytic bone lesions in two individuals. Finally, we describe the first use of targeted therapy with a MEK inhibitor for an individual with a mosaic KRAS variant. The purposes of this report are to expand the phenotypic spectrum of mosaic KRAS-related disorders, and to propose possible mechanisms of pathogenesis, and surveillance of its associated findings.

Recurrent constellations of embryonic malformations re-conceptualized as an overlapping group of disorders with shared pathogenesis.

Several recurrent malformation associations affecting the development of the embryo have been described in which a genetic etiology has not been found, including LBWC, MURCS, OAVS, OEIS, POC, VACTERL, referred to here as "recurrent constellations of embryonic malformations" (RCEM). All are characterized by an excess of reported monozygotic discordant twins and lack of familial recurrence. We performed a comprehensive review of published twin data across all six phenotypes to allow a more robust assessment of the association with twinning and potential embryologic timing of a disruptive event. We recorded the type of twinning, any overlapping features of another RCEM, maternal characteristics, and the use of ART. Statistically significant associations included an excess of monozygotic twins and 80% discordance rate for the phenotype across all twins. There was an 18.5% rate of ART and no consistently reported maternal adverse events during pregnancy. We found 24 instances of co-occurrence of two RCEM, suggesting a shared pathogenesis across all RCEM phenotypes. We hypothesize the following timing for RCEM phenotypes from the earliest perturbation in development to the latest: LBWC, POC, OEIS, VACTERL, OAVS, then MURCS. The RCEM group of conditions should be considered a spectrum that could be studied as a group.

A dyadic genotype-phenotype approach to diagnostic criteria for Proteus syndrome.

Phenotype-based diagnostic criteria were developed for Proteus syndrome in 1999 and updated in 2006. Subsequently, the causative mosaic gene alteration was discovered, the c.49G>A p.E17K variant in AKT1. As well, a number of overlapping overgrowth disorders attributable to mosaic PIK3CA variants have now been characterized, leading to the designation of PIK3CA-related overgrowth spectrum (PROS). Finally, ongoing work to better characterize Proteus syndrome has led to identification of additional features of that disorder that could be useful in diagnostic criteria. We have taken the opportunity of these discoveries to re-evaluate the Proteus syndrome diagnostic criteria. Here we propose a new set of diagnostic criteria that establishes a weighted, point-based system for the phenotypic attributes and then integrates that with the potential molecular test results to result in one of two designations: AKT1-related Proteus syndrome or AKT1-related overgrowth spectrum. A patient whose only manifestation is an AKT1 c.49G>A-positive tumor would receive neither of these designations. Here we review the rational basis of diagnostic criteria and argue that a unitary diagnostic entity is a distinct gene-phenotype dyad and that this should be the model for all mendelian disorders. The gene-alone or phenotype-alone approach is inadequate to rigorously delineate a unitary diagnostic entity.

Thrombosis risk factors in PIK3CA-related overgrowth spectrum and Proteus syndrome.

Increased risk of thromboembolism has been recognized in individuals with mosaic overgrowth disorders, Proteus syndrome (PS) and PIK3CA-related overgrowth spectrum (PROS), including Klippel-Trenaunay syndrome and CLOVES syndrome. PS and PROS have distinct, yet overlapping clinical findings and are caused by somatic pathogenic variants in the PI3K/AKT gene signaling pathway. PS is caused by a single somatic activating AKT1 c.49G > A p.E17K variant while PROS can be caused one of multiple variants in PIK3CA. The role of prothrombotic factors, endothelial cell adhesion molecules, and vascular malformations in both PS and PROS have not been previously investigated. A pilot study of prospective clinical and laboratory evaluations with the purposes of identifying potential risk factors for thrombosis was conducted. Doppler ultrasounds and magnetic resonance angiogram/ venography (MRA/MRV) scans identified vascular malformations in PS and PROS that were not appreciated on physical examination. Abnormal D-dimers (0.60-2.0 mcg/ml) occurred in half of individuals, many having vascular malformations, but no thromboses. Soluble vascular endothelial markers, including thrombomodulin, soluble vascular adhesion molecule (sVCAM), soluble intercellular adhesion molecule (sICAM), E-selectin, and P-selectin were significantly higher in PS and PROS compared to controls. However, no single attribute was identified that explained the risk of thrombosis. Predisposition to thrombosis is likely multifactorial with risk factors including chronic stasis within vascular malformations, stasis from impaired mobility (e.g., following surgery), decreased anticoagulant proteins, and effects of AKT1 and PIK3CA variants on vascular endothelium. Based on our findings, we propose clinical recommendations for surveillance of thrombosis in PS and PROS.

Safety and efficacy of low-dose sirolimus in the PIK3CA-related overgrowth spectrum.

PURPOSE: PIK3CA-related overgrowth spectrum (PROS) encompasses a range of debilitating conditions defined by asymmetric overgrowth caused by mosaic activating PIK3CA variants. PIK3CA encodes the p110α catalytic subunit of phosphatidylinositol-3-kinase (PI3K), a critical transducer of growth factor signaling. As mTOR mediates the growth-promoting actions of PI3K, we hypothesized that the mTOR inhibitor sirolimus would slow pathological overgrowth. METHODS: Thirty-nine participants with PROS and progressive overgrowth were enrolled into open-label studies across three centers, and results were pooled. For the primary outcome, tissue volumes at affected and unaffected sites were measured by dual energy X-ray absorptiometry during 26 weeks of untreated run-in and 26 weeks of sirolimus therapy. RESULTS: Thirty participants completed the study. Sirolimus led to a change in mean percentage total tissue volume of -7.2% (SD 16.0, p = 0.04) at affected sites, but not at unaffected sites (+1.7%, SD 11.5, p = 0.48) (n = 23 evaluable). Twenty-eight of 39 (72%) participants had ≥1 adverse event related to sirolimus of which 37% were grade 3 or 4 in severity and 7/39 (18%) participants were withdrawn consequently. CONCLUSION: This study suggests that low-dose sirolimus can modestly reduce overgrowth, but cautions that the side-effect profile is significant, mandating individualized risk-benefit evaluations for sirolimus treatment in PROS.

A Point Mutation in PDGFRB Causes Autosomal-Dominant Penttinen Syndrome.

Penttinen syndrome is a distinctive disorder characterized by a prematurely aged appearance with lipoatrophy, epidermal and dermal atrophy along with hypertrophic lesions that resemble scars, thin hair, proptosis, underdeveloped cheekbones, and marked acro-osteolysis. All individuals have been simplex cases. Exome sequencing of an affected individual identified a de novo c.1994T>C p.Val665Ala variant in PDGFRB, which encodes the platelet-derived growth factor receptor ß. Three additional unrelated individuals with this condition were shown to have the identical variant in PDGFRB. Distinct mutations in PDGFRB have been shown to cause infantile myofibromatosis, idiopathic basal ganglia calcification, and an overgrowth disorder with dysmorphic facies and psychosis, none of which overlaps with the clinical findings in Penttinen syndrome. We evaluated the functional consequence of this causative variant on the PDGFRB signaling pathway by transfecting mutant and wild-type cDNA into HeLa cells, and transfection showed ligand-independent constitutive signaling through STAT3 and PLCγ. Penttinen syndrome is a clinically distinct genetic condition caused by a PDGFRB gain-of-function mutation that is associated with a specific and unusual perturbation of receptor function.

Urine cell-free DNA is a biomarker for nephroblastomatosis or Wilms tumor in PIK3CA-related overgrowth spectrum (PROS).

PURPOSE: We set out to facilitate the molecular diagnosis of patients with PIK3CA-related overgrowth spectrum (PROS), a heterogeneous somatic disorder characterized by variable presentations of segmental overgrowth, vascular malformations, skin lesions, and nephroblastomatosis, rare precursor lesions to Wilms tumor. Molecular diagnosis of PROS is challenging due to its mosaic nature, often requiring invasive biopsies. METHODS: Digital droplet polymerase chain reaction (ddPCR) was used to analyze tissues including urine, saliva, buccal cells, and blood, from eight patients with PROS. Further analyses were performed on plasma and urine cell-free DNA (cfDNA). RESULTS: PIK3CA variants were detected in plasma cfDNA at levels up to 0.5% in 50% of tested samples. In addition, high levels of PIK3CA variants in urine cfDNA correlated with a history of nephroblastomatosis compared with patients without renal involvement (P < 0.05). CONCLUSION: Digital droplet PCR is a sensitive molecular tool that enables low-level variant detection of PIK3CA in various tissue types, providing an alternative diagnostic method. Furthermore, urine cfDNA is a candidate biomarker for nephroblastomatosis in PROS, which may be useful to refine screening guidelines for tumor risk in these patients.

Characterization of the hepatosplenic and portal venous findings in patients with Proteus syndrome.

Proteus syndrome (PS) is a rare disorder caused by a mosaic AKT1 variant that comprises patchy overgrowth of tissues derived from all three germinal layers affecting multiple viscera. We sought to delineate the extent of hepatoportal manifestations in patients with PS. We identified patients with PS who had abdominal imaging from 1989 to 2015 in a natural history study. Imaging was characterized for evidence of focal findings in the liver, spleen, and portal vasculature and for organomegaly. Relevant clinical and laboratory data were compared among those with or without organomegaly. Abdominal imaging was available on 38 patients including 20 who had serial studies. Nine patients had focal hepatic lesions including vascular malformations (VMs). Focal splenic abnormalities were noted in seven patients. Patients without cutaneous VMs did not have visceral VMs. Nine patients had splenomegaly, 12 had portal vein dilation, and 4 had hepatomegaly. There was a weak correlation of portal vein dilation to spleen height ratio (r2 = 0.18, p < .05). On laboratory evaluation, hepatic function was normal but there was thrombocytopenia in those with splenomegaly; platelet counts were 179 ± 87K/µL compared to those with normal spleen size at 253 ± 57K/µL (p < .05). Overall, focal hepatosplenic abnormalities occurred in 11 of 38 (29%) patients with PS. Splenomegaly and portal venous dilation were both found in 8 of 38 (21%) patients; however, other than relative thrombocytopenia, there was no evidence of portal hypertension. Although the AKT1-E17K somatic variant is a suspected oncogene, there were no malignant lesions identified in this study.

Pathogenetic insights from quantification of the cerebriform connective tissue nevus in Proteus syndrome.

BACKGROUND: The plantar cerebriform connective tissue nevus (CCTN) is the most common and problematic cutaneous manifestation of Proteus syndrome. OBJECTIVE: To gain insights into CCTN pathogenesis and natural history. METHODS: The size and location of plantar CCTN was measured on 152 images from 22 individuals with Proteus syndrome by 2 independent, blinded reviewers. Average measures of plantar CCTN were transformed into a linear mixed model to estimate proportionate change in size with age. RESULTS: Median patient age was 6.9 years at study onset. The intraclass correlation coefficient between 2 blinded reviewers was 0.946 for CCTN single measures. The CCTN relative area increased with age in children (n = 18, P < .0001) by 5.6% per year. Confluent papules and nodules extending beyond the boundaries of CCTNs were gradually replaced by typical CCTN over time. The location of CCTN in different individuals overlapped near the ball of the foot. A positive relationship between CCTN growth rate and AKT1 mutant allele frequency was observed (0.62, P = .10, n = 8). LIMITATIONS: This was a retrospective review using photographs. CONCLUSION: CCTN growth is affected by age and extent of the CCTN precursor lesion. Monitoring of CCTN size might prove useful for evaluating drug response in the treatment of Proteus syndrome.

Mutations in kelch-like 3 and cullin 3 cause hypertension and electrolyte abnormalities.

Hypertension affects one billion people and is a principal reversible risk factor for cardiovascular disease. Pseudohypoaldosteronism type II (PHAII), a rare Mendelian syndrome featuring hypertension, hyperkalaemia and metabolic acidosis, has revealed previously unrecognized physiology orchestrating the balance between renal salt reabsorption and K(+) and H(+) excretion. Here we used exome sequencing to identify mutations in kelch-like 3 (KLHL3) or cullin 3 (CUL3) in PHAII patients from 41 unrelated families. KLHL3 mutations are either recessive or dominant, whereas CUL3 mutations are dominant and predominantly de novo. CUL3 and BTB-domain-containing kelch proteins such as KLHL3 are components of cullin-RING E3 ligase complexes that ubiquitinate substrates bound to kelch propeller domains. Dominant KLHL3 mutations are clustered in short segments within the kelch propeller and BTB domains implicated in substrate and cullin binding, respectively. Diverse CUL3 mutations all result in skipping of exon 9, producing an in-frame deletion. Because dominant KLHL3 and CUL3 mutations both phenocopy recessive loss-of-function KLHL3 mutations, they may abrogate ubiquitination of KLHL3 substrates. Disease features are reversed by thiazide diuretics, which inhibit the Na-Cl cotransporter in the distal nephron of the kidney; KLHL3 and CUL3 are expressed in this location, suggesting a mechanistic link between KLHL3 and CUL3 mutations, increased Na-Cl reabsorption, and disease pathogenesis. These findings demonstrate the utility of exome sequencing in disease gene identification despite the combined complexities of locus heterogeneity, mixed models of transmission and frequent de novo mutation, and establish a fundamental role for KLHL3 and CUL3 in blood pressure, K(+) and pH homeostasis.

Orthopaedic Management of Leg-length Discrepancy in Proteus Syndrome: A Case Series.

INTRODUCTION: Proteus syndrome (PS) is a rare mosaic disorder comprising asymmetric bony and soft tissue overgrowth leading to significant morbidity. Placement of growth inhibition hardware with subsequent epiphyseal arrest improves leg-length and angular deformities in pediatric patients without PS. The purpose of this study was to review the surgical approach and present outcomes, complications, and recommendations in 8 patients with PS and leg-length discrepancy (LLD). METHODS: We conducted a retrospective chart review of 8 patients with PS whose primary reason for surgery was LLD. Patients were eligible if they met clinical diagnostic criteria for PS and if the National Institutes of Health team performed at least 1 of their surgical interventions between 2005 and 2015. Surgical techniques included growth inhibition, with tension band plates, applied ≥1 times, and epiphyseal arrest. RESULTS: Eight patients, followed for an average of 4.6 years (range, 1.0 to 7.1 y) after the index procedure, were included in this analysis. Average age at first LLD surgery was 9.4 years (range, 6.1 to 13.6 y); the average LLD was 3.4 cm (range, 0.4 to 7.0 cm) at presentation, and 5.0 cm (range, 1.8 to 10.0 cm) at the time of the first LLD surgery. Participants underwent 23 total surgeries (range, 1 to 5 per patient) and 7 patients have completed surgical intervention. For the 7 patients who did not require overcorrection the average LLD at the last clinical encounter was 2.6 cm (range, 0.6 to 7.2 cm). We encountered 2 complications: 2 patients developed mild knee valgus, which responded to standard guided growth techniques. CONCLUSIONS: This case series suggests that growth inhibition and epiphyseal arrest in children with PS can reduce LLD with few complications. Careful monitoring, rapid mobilization, deep venous thrombosis prophylaxis, and sequential compression devices were also integral elements of our surgical protocol. LEVEL OF EVIDENCE: Level IV.