Malan syndrome and Marshall Smith syndrome are multisystem disorders characterised by accelerated bone maturation, developmental delay, and intellectual disability, characteristic facial dysmorphism. Spinal deformities are common in both. Marfanoid habitus is characteristic feature of Malan syndrome.
Failure to thrive and early death is seen in Marshal Smith syndrome.
Around 80 cases reported worldwide for Malan syndrome. Marshall–Smith syndrome has a prevalence of <1/1000000 and less than 60 cases reported worldwide.
Both these disorders are causes by de novo monoallelic variations in NFIX gene with a high penetrance.
NFIX