Legius syndrome: case report and review of literature

Legius Syndrome and Inflammatory Bowel Disease: A Pediatric Case Report

Legius syndrome (LS) is a rare and underrecognized disorder that is often misdiagnosed as neurofibromatosis type 1 (NF1). It is characterized by café-au-lait macules without the tumoral manifestations of NF1. We report the case of an 11-year-old patient with multiple café-au-lait macules and intertriginous freckling who was admitted for bloody stools, joint pain, and weight loss. His clinical and endoscopic findings were consistent with inflammatory bowel disease (IBD). He also met the clinical diagnostic criteria for NF1 but not for LS. Genetic testing played a pivotal role in the differential diagnosis and revealed a loss-of-function mutation in the SPRED1 gene, confirming the diagnosis of LS. This is the first reported case of a patient with IBD and LS. The subtle manifestations of LS make it an underdiagnosed disease, which reduces the likelihood of it being diagnosed in association with other diseases, such as IBD. There are, however, 10 published case reports linking IBD and NF1, and some pathophysiological mechanisms have been proposed. Continued reporting will help clarify the relationship between IBD and RASopathies such as NF1 and LS.

RASopathies: Dermatologists’ viewpoints

Ras/mitogen-activated protein kinase pathway dysregulation results in a group of disorders, collectively termed as RASopathies. Neurofibromatosis type 1, Noonan syndrome, Noonan syndrome with multiple lentigines, Noonan syndrome/loose anagen hair, Legius syndrome, Costello syndrome, cardio-facio-cutaneous syndrome and capillary malformation-arteriovenous malformation are the well-recognized RASopathies. These are characterized by multi-organ tumours and hamartomas. Some other features in common are facial dysmorphism, skeletal abnormalities, congenital heart disease, neurocognitive abnormalities and risk of various solid-organ and haematological malignancies. Some of the RASopathies are heterogeneous, caused by several gene mutations resulting in variations in phenotypes and severity ranging from mild to fatal. Significant phenotypic overlaps among different disorders, often makes it difficult to pinpoint a clinical diagnosis. Specific cutaneous manifestations are present in some of the RASopathies and are often the earliest clinical signs/symptoms. Hence, dermatologists contribute significantly as primary care physicians by identifying disorder-specific cutaneous lesions. However, diagnostic work-up and management of these disorders are often multidisciplinary. Confirmation of diagnosis is possible only by genetic mapping in each case. Genetic counseling of the patients and the affected families is an important component of the management. The aim of this review is description of cutaneous manifestations of RASopathies in the background of multi-system involvement to enable dermatologists a comprehensive and logical approach to work up and diagnose such patients in the absence of facility for specific molecular testing.

MEK inhibition ameliorates social behavior phenotypes in a Spred1 knockout mouse model for RASopathy disorders

BACKGROUND

RASopathies are a group of disorders that result from mutations in genes coding for proteins involved in regulating the Ras-MAPK signaling pathway, and have an increased incidence of autism spectrum disorder (ASD). Legius syndrome is a rare RASopathy caused by loss-of-function mutations in the SPRED1 gene. The patient phenotype is similar to, but milder than, Neurofibromatosis type 1-another RASopathy caused by loss-of-function mutations in the NF1 gene. RASopathies exhibit increased activation of Ras-MAPK signaling and commonly manifest with cognitive impairments and ASD. Here, we investigated if a Spred1-/- mouse model for Legius syndrome recapitulates ASD-like symptoms, and whether targeting the Ras-MAPK pathway has therapeutic potential in this RASopathy mouse model.

METHODS

We investigated social and communicative behaviors in Spred1-/- mice and probed therapeutic mechanisms underlying the observed behavioral phenotypes by pharmacological targeting of the Ras-MAPK pathway with the MEK inhibitor PD325901.

RESULTS

Spred1-/- mice have robust increases in social dominance in the automated tube test and reduced adult ultrasonic vocalizations during social communication. Neonatal ultrasonic vocalization was also altered, with significant differences in spectral properties. Spred1-/- mice also exhibit impaired nesting behavior. Acute MEK inhibitor treatment in adulthood with PD325901 reversed the enhanced social dominance in Spred1-/- mice to normal levels, and improved nesting behavior in adult Spred1-/- mice.

LIMITATIONS

This study used an acute treatment protocol to administer the drug. It is not known what the effects of longer-term treatment would be on behavior. Further studies titrating the lowest dose of this drug that is required to alter Spred1-/- social behavior are still required. Finally, our findings are in a homozygous mouse model, whereas patients carry heterozygous mutations. These factors should be considered before any translational conclusions are drawn.

CONCLUSIONS

These results demonstrate for the first time that social behavior phenotypes in a mouse model for RASopathies (Spred1-/-) can be acutely reversed. This highlights a key role for Ras-MAPK dysregulation in mediating social behavior phenotypes in mouse models for ASD, suggesting that proper regulation of Ras-MAPK signaling is important for social behavior.

Central precocious puberty in a girl with LEGIUS syndrome: an accidental association?

BACKGROUND

Central precocious puberty is a condition characterized by precocious activation of the hypothalamic-pituitary-gonadal axis. It may be idiopathic or secondary to organic causes, including syndromes such as Neurofibromatosis type 1 (NF1).

CASE PRESENTATION

We presented a girl of 6 years and 10 months with almost 11 café-au-lait skin macules, without other clinical or radiological signs typical of NF1, and with a central precocious puberty. Genetic analysis evidenced the new variant NM-152594.2:c.304delAp. (Thr102Argfs*19) in SPRED1 gene, which allowed to diagnose Legius syndrome.

CONCLUSIONS

We report for the first time a case of central precocious puberty in a girl with Legius syndrome. The presence of central precocious puberty in a child with characteristic café-au-lait macules should suggest pediatricians to perform genetic analysis in order to reach a definitive diagnosis. Further studies on timing of puberty in patients with RASopathies are needed to better elucidate if this clinical association is casual or secondary to their clinical condition.

Café au Lait Macules and Associated Genetic Syndromes

Café au lait macules (CALMs) are a common, isolated dermatologic finding in the general population. But when do these irregularly shaped, jagged-edged, flat, hyperpigmented birthmarks suggest something that may warrant referral? Most pediatric providers are familiar with the association of CALMs and neurofibromatosis type 1. There are, however, other genetic conditions associated with these seemingly benign skin spots. This article provides an overview of CALMs, followed by a summary of several conditions associated with CALMs ranging from the most common (neurofibromatosis type 1) to rare, ring chromosome syndromes. It reviews the associated gene(s), pattern of inheritance, incidence, presenting symptoms, diagnosis, and management for these genetic conditions.

[Pigmented macules as possible early signs of genetic syndromes]

Solitary congenital or early apparent pigmented macules are usually without relevance; however, when multiple, extensive or in a patterned arrangement, they are not uncommonly the first sign of an underlying genetic syndrome. The present article gives an overview on the clinical significance of multiple café-au-lait macules, multiple lentigines and pigmentary mosaicism and discusses the differential diagnosis of associated syndromes. Early diagnosis with the essential contribution of the dermatologist is not only important for genetic counseling but can also contribute to avoidance of sometimes life-threatening complications.

A review of craniofacial and dental findings of the RASopathies

OBJECTIVES

The RASopathies are a group of syndromes that have in common germline mutations in genes that encode components of the Ras/mitogen-activated protein kinase (MAPK) pathway and have been a focus of study to understand the role of this pathway in development and disease. These syndromes include Noonan syndrome (NS), Noonan syndrome with multiple lentigines (NSML or LEOPARD syndrome), neurofibromatosis type 1 (NF1), Costello syndrome (CS), cardio-facio-cutaneous (CFC) syndrome, neurofibromatosis type 1-like syndrome (NFLS or Legius syndrome) and capillary malformation-arteriovenous malformation syndrome (CM-AVM). These disorders affect multiple systems, including the craniofacial complex. Although the craniofacial features have been well described and can aid in clinical diagnosis, the dental phenotypes have not been analysed in detail for each of the RASopathies. In this review, we summarize the clinical features of the RASopathies, highlighting the reported craniofacial and dental findings.

METHODS

Review of the literature.

RESULTS

Each of the RASopathies reviewed, caused by mutations in genes that encode different proteins in the Ras pathway, have unique and overlapping craniofacial and dental characteristics.

CONCLUSIONS

Careful description of craniofacial and dental features of the RASopathies can provide information for dental clinicians treating these individuals and can also give insight into the role of Ras signalling in craniofacial development.

Progressive osseous heteroplasia is not a Mendelian trait but a type 2 segmental manifestation of GNAS inactivation disorders: A hypothesis

Progressive osseous heteroplasia (POH) is a segmental disorder characterized by progressive heterotopic ossification that extends from dermal and subcutaneous tissues to deeper structures. So far, it has been taken as a rarely occurring bone disease with autosomal dominant inheritance. Here, arguments are presented in favor of the alternative concept that the disorder is merely a type 2 segmental manifestation of autosomal dominant GNAS inactivation disorders. Type 2 segmental mosaicism arises, in a heterozygous embryo, from a somatic mutational event that occurs at an early developmental stage, resulting in loss of the corresponding wild-type allele and giving rise to a homozygous or hemizygous cell clone. As a characteristic feature, such type 2 segmental involvement is far more pronounced than the type 1 segmental mosaicism as noted in otherwise healthy individuals. The concept of type 2 segmental mosaicism has been proven at the molecular level in six human traits including neurofibromatosis 1, Hailey-Hailey disease, and Gorlin syndrome. In POH, molecular proof of principle is so far lacking. The following lines of reasoning, however, support the hypothesis that POH can be explained by a similar mechanism. Firstly, POH has been found to be associated with different phenotypes caused by inactivating GNAS mutations, which is why it cannot be categorized as one distinct Mendelian trait. Secondly, POH occurs as a rather rare complication of these autosomal dominant traits, which is not compatible with the assumption of a separate Mendelian disorder. Thirdly, in a case of plate-like osteoma that represents a more superficial variant of POH, molecular proof of the concept of type 2 segmental manifestation has already been provided, and the available literature suggests that POH can be best explained by a similar mechanism. Moreover, findings obtained in animal experiments support the assumption that human POH represents such superimposed segmental manifestation of GNAS inactivation disorders.