Marshall Smith Syndrome is rare genetic disorder that is allelic to the Malan Syndrome (Sotos Syndrome 2).
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
(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
(6) variable hypertrichosis
(7) osteopenia with multiple fractures
(8) intellectual disability
(9) respiratory problems with upper airway obstruction
(10) feeding problems
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