Schinzel-Giedion Syndrome

Excerpt

Clinical characteristics: Classic Schinzel-Giedion syndrome (SGS), an ultra-rare multisystem disorder caused by gain-of-function pathogenic variants in a SETBP1 mutational hot spot, is characterized by global neurodevelopmental impairment leading to moderate-to-profound intellectual disability, epilepsy (often refractory to treatment), hypotonia, spasticity, dysautonomia, hearing loss, and cerebral visual impairment. Other findings can include poor weight gain often associated with gastroesophageal reflux disease, chronic vomiting, constipation, gastroparesis, and/or feeding intolerance. Structural malformations can involve the heart, skeleton, kidney and urinary tract, genitalia, and brain. Anomalies of the liver, spleen, and/or pancreas are less common. Other features may include neuroepithelial neoplasia, severely disrupted sleep, choanal stenosis, inguinal hernia, sensitive skin, and increased risk of infection.

To date, more than 50 individuals have been reported with molecularly confirmed classic SGS.

Atypical SGS, reported in five individuals to date, is caused by pathogenic SETBP1 variants in proximity to – but not within – the mutational hot spot. The broad spectrum of clinical features of variable severity partially overlaps with classic SGS; however, this spectrum does not include risk for neuroepithelial neoplasia to date.

Diagnosis/testing: The diagnosis of classic SGS can be established in a proband based on published clinical diagnostic criteria, or the molecular diagnosis can be established in a proband with suggestive findings and a heterozygous SETBP1 pathogenic gain-of-function variant within the mutational hot spot (i.e., a 12-base-pair region in exon 4 encoding a canonical degron). The diagnosis of atypical SGS syndrome is established in a proband with suggestive findings and a heterozygous SETBP1 pathogenic variant adjacent to – but not within – the mutational hot spot.

Management: Treatment of manifestations: There is no cure for classic or atypical SGS. Supportive treatment to improve quality of life, maximize function, and reduce complications can include multidisciplinary care by specialists in pediatrics, neurology, physiatry, occupational and physical therapy, speech-language pathology, psychiatry, ophthalmology, ENT, surgery, pulmonology, oncology, urology, nephrology, audiology, gastroenterology, orthopedics, cardiology, and medical genetics.

Surveillance: At each visit, evaluate for feeding issues (including nutritional status and safety of oral intake), gastrointestinal issues, respiratory issues, neurologic manifestations (including seizures, changes in tone, movement disorders, mood, irritability, and alertness), kidney and urinary tract manifestations, and musculoskeletal manifestations. In individuals with classic SGS, age-related surveillance for occurrence of neoplasia includes liver ultrasound and serum alpha-fetoprotein levels, renal ultrasound examination, pelvic MRI for sacrococcygeal teratoma, and monitoring for clinical signs of leukemia.

Agents/circumstances to avoid: Nephrotoxic drugs such as nonsteroidal anti-inflammatory drugs and vancomycin should be used with caution due to high frequency of chronic renal impairment from recurrent pyelonephritis and structural renal anomalies.

Genetic counseling: Classic and atypical SGS are autosomal dominant disorders typically caused by a de novo SETBP1 pathogenic variant. Rarely, individuals diagnosed with SGS have the disorder as the result of a pathogenic variant inherited from a parent. Sib recurrence of clinically defined classic SGS, presumed to be due to parental germline mosaicism, has been reported in two families. Transmission of a SETBP1 pathogenic missense variant from an unaffected parent to a child with atypical SGS has been reported in one family (of note, the possibility of mosaicism in the unaffected parent was not excluded). Once the SETBP1 pathogenic variant has been identified in an affected family member, prenatal and preimplantation genetic testing are possible.