Legius Syndrome

Legius syndrome, also known as NF1-like syndrome, is a rare, genetic skin pigmentation disorder characterized by multiple café-au-lait macules with or without axillary or inguinal freckling.

Epidemiology

The prevalence of Legius syndrome is not known. Fewer than 200 cases have been reported to date. Prevalence may be higher than expected due to misdiagnosis of cases as neurofibromatosis type 1 (NF1, see this term). The incidence of NF1 is reported to be 1/3000, and about 2% of patients fulfilling diagnostic criteria for NF1 are found to have the genetic mutation underlying Legius syndrome (SPRED1).

Clinical description

The clinical presentation of Legius syndrome is very similar to that of NF1. Patients typically present with multiple café-au-lait spots sometimes associated with intertriginous freckling, but lack Lisch nodules, optic pathway gliomas, bone abnormalities, neurofibromas or other tumor manifestations. The number of café-au-lait macules tends to increase with age during childhood. Other less common manifestations include short stature, macrocephaly, Noonan-like facies, pectus excavatum/carinatum, lipomas, hypopigmented macules, vascular lesions, learning disabilities, attention deficit/hyperactivity disorder (ADHD), and developmental delay.

Etiology

Legius syndrome is caused by heterozygous inactivating mutations in the SPRED1 gene (15q14), involved in regulation of the RAS-MAPK signal transduction pathway. Nearly 100 different mutations in this gene have been identified. The proportion of cases related to de novo mutations is not yet known. No genotype-phenotype correlations have been found.

Diagnostic methods

About 50% of patients with Legius syndrome fulfill the diagnostic criteria for NF1, but they have a far milder phenotype compared to NF1 patients. Diagnosis based solely on the presence of clinical features is difficult, given the overlap with other disorders characterized by multiple café-au-lait spots. The presence of characteristic clinical signs in parents of affected individuals is supportive of diagnosis. However, molecular genetic testing is required to confirm the diagnosis and testing is available on a clinical basis.

Differential diagnosis

Legius syndrome is differentiated from NF1 by the absence of the non-pigmentary clinical manifestations seen in this disorder (i.e. Lisch nodules, neurofibromas, optic glioma, bone abnormalities). Correct diagnosis is essential because of the differences in prognosis and long-term monitoring between Legius syndrome and NF1. Other disorders to consider include Noonan syndrome, Noonan syndrome with lentigines (LEOPARD syndrome), and McCune-Albright syndrome (see these terms).

Antenatal diagnosis

Prenatal diagnosis is possible and requires prior identification of the disease-causing mutation in the family.

Genetic counseling

Legius syndrome follows an autosomal dominant pattern of inheritance. Genetic counseling should be provided to affected families.

Management and treatment

Drug therapy should be considered for the behavioral manifestations of the disorder (ADHD). Physical, speech, and occupational therapy is recommended for those with developmental delay and educational support for those with learning difficulties.

Prognosis

Given the current knowledge of disease manifestations and complications, the prognosis for patients with Legius syndrome is considered to be very good.