Clinical characteristics: While the majority of individuals with Costello syndrome share characteristic findings affecting multiple organ systems, the phenotypic spectrum is wide, ranging from a milder or attenuated phenotype to a severe phenotype with early lethal complications. Costello syndrome is typically characterized by failure to thrive in infancy as a result of severe postnatal feeding difficulties; short stature; developmental delay or intellectual disability; coarse facial features (full lips, large mouth, full nasal tip); curly or sparse, fine hair; loose, soft skin with deep palmar and plantar creases; papillomata of the face and perianal region; diffuse hypotonia and joint laxity with ulnar deviation of the wrists and fingers; tight Achilles tendons; and cardiac involvement including: cardiac hypertrophy (usually typical hypertrophic cardiomyopathy), congenital heart defect (usually valvar pulmonic stenosis), and arrhythmia (usually supraventricular tachycardia, especially chaotic atrial rhythm/multifocal atrial tachycardia or ectopic atrial tachycardia). Relative or absolute macrocephaly is typical, and postnatal cerebellar overgrowth can result in the development of a Chiari I malformation with associated anomalies including hydrocephalus or syringomyelia. Individuals with Costello syndrome have an approximately 15% lifetime risk for malignant tumors including rhabdomyosarcoma and neuroblastoma in young children and transitional cell carcinoma of the bladder in adolescents and young adults.
Diagnosis/testing: The diagnosis of Costello syndrome is established in a proband with suggestive clinical findings and a heterozygous HRAS pathogenic variant identified by molecular genetic testing.
Management: Treatment of manifestations: Failure to thrive is the most common and challenging clinical problem; most infants require nasogastric or gastrostomy feeding; many require Nissen fundoplication. Treatment of cardiac manifestations and malignancy is routine. Ulnar deviation of the wrists and fingers often requires early bracing and occupational and/or physical therapy; tight Achilles tendons may require surgical tendon lengthening. Developmental delay requires early-intervention programs and individualized education strategies. Recurrent facial papillomata may require routine removal with dry ice. Hemodynamically significant valvar stenoses require antibiotic prophylaxis for subacute bacterial endocarditis; anesthesia may pose a risk to those with hypertrophic cardiomyopathy or those predisposed to some types of atrial tachycardia.
Surveillance: Monitoring for neonatal hypoglycemia; echocardiography with electrocardiogram at diagnosis with subsequent follow up by a cardiologist who is aware of the spectrum of cardiac disease and its natural history; abdominal and pelvic ultrasound examinations to screen for rhabdomyosarcoma and neuroblastoma every three to six months until age eight to ten years may be considered; annual urinalysis for evidence of hematuria to screen for bladder cancer beginning at age ten years.
Genetic counseling: Costello syndrome is inherited in an autosomal dominant manner. To date, most probands with Costello syndrome have the disorder as the result of a de novo pathogenic variant; although parents of probands are not affected, vertical transmission has been reported in two families with the rare, attenuated phenotype. Because Costello syndrome is typically caused by a de novo pathogenic variant, the risk to the sibs of a proband is presumed to be small; however, recurrence in sibs has been reported and is suspected to be the result of germline mosaicism in a parent. Individuals with Costello syndrome typically do not reproduce. Once an HRAS pathogenic variant has been identified in an affected family member, prenatal testing for a pregnancy at increased risk and preimplantation genetic testing are possible.
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