Chromosome locus: 19p13.13
Gene: NFIX (nuclear factor I X; encodes a transcription factor involved in brain development)
Mechanism: splice site or frameshift variants
Inheritance: autosomal dominant
Clinical manifestations:
(1) absence of macrocephaly
(2) relative failure to thrive with growth parameters below the 3rd percentile postnatally
(3) accelerated skeletal maturation with dysostosis in the lower extremities
(4) facial features: proptosis (shallow orbits), underdeveloped midface, small chin, prominent forehead, depressed nasal bridge with anteverted nares, everted lower lip, blue sclera, retrognathia/micrognathia
(5) scoliosis
(6) variable hypertrichosis
(7) osteopenia with multiple fractures
(8) intellectual disability
(9) respiratory problems with upper airway obstruction
(10) feeding problems
