Background: De novo or rare transmitted mutations in the SMAD6 gene affect 7 percent of midline nonsyndromic synostosis patients. This study aimed to determine the neurocognitive sequelae of SMAD6 synostosis.
Methods: Nonsyndromic synostosis patients 6 years or older with SMAD6 mutations and non-SMAD6 nonsyndromic synostosis controls were recruited. All patients completed a double-blinded neurodevelopmental battery (i.e., Wechsler Fundamentals, Wechsler Abbreviated Scale of Intelligence, Beery-Buktenica Developmental test), and parents/guardians completed behavioral surveys (Behavior Rating Inventory of Executive Function and Behavior Rating System for Children).
Results: Twenty-eight patients participated: 10 known SMAD6 patients (average age, 10 years; 1 female; eight metopic and two sagittal; nine treated with cranial vault remodeling and one treated with strip craniectomy) and 18 non-SMAD6 controls (age, 9.5 years; three female; 12 metopic and six sagittal; 17 treated with cranial vault remodeling and one treated with strip craniectomy). There were no differences between any demographics. Testing age, surgical age, parental education, and household income correlated with cognition (p < 0.05). After controlling for these factors, SMAD6 patients performed worse on numerical operations (p = 0.046), performance intelligence quotient (p = 0.018), full-scale intelligence quotient (p = 0.010), and motor coordination (p = 0.043) compared to age/race/gender/synostosis/operation-matched controls. On behavioral surveys, SMAD6 patients scored worse on 14 assessments, including aggression, communication, and behavior.
Conclusions: This prospective double-blinded study revealed that neuropsychiatric development of nonsyndromic synostosis may be under genetic control. SMAD6 mutations led to poorer mathematics, performance intelligence quotient, full-scale intelligence quotient, and motor coordination, even after controlling for exogenous factors. Genetic testing may be critical for advocating early adjunctive neurodevelopmental therapy.
Clinical question/level of evidence: Risk, II.