Multisystem developmental disorder (MSDD) is a term used by Stanley Greenspan to describe children under age 3 who exhibit signs of impaired communication as in autism, but with strong emotional attachments atypical of autism.^{[citation needed]} It is described in the DC:0-3R manual as an optional diagnosis for children under two years of age.^[1][2]

The term multisystem developmental disorder has also been used to describe various developmental disorders. These include:

• Alagille syndrome,^[3] an autosomal dominant disorder with a wide range of features and manifestations. Its five most significant features are chronic cholestasis, a condition where bile cannot flow from the liver to the duodenum, occurring in 95% of cases; heart abnormalities (over 90%); butterfly vertebrae; posterior embryotoxon and a distinctive face (prominent forehead, deep-set eyes, and a pointed chin).^[4]
• Rubinstein-Taybi syndrome,^[5][6] a syndrome characterized by broad thumbs, facial abnormalities, and big toes alongside moderate to severe intellectual disability.^[7]
• Williams syndrome,^[8][9] a neurodevelopmental disorder characterized by a unique profile of strengths and deficits; most with the condition have mild intellectual disability but have grammatical and lexical abilities above what would be expected from their IQs.^[10] They are hypersocial and empathetic, but social isolation is commonly experienced.^[11]
• Proteus syndrome,^[12] a congenital disorder causing disproportionate growth of skin, bone, and other tissues.^[13]
• Asphyxiating thoracic dysplasia,^[14] an autosomal recessive skeletal disorder with an estimated prevalence of between 1 in 100,000 and 1 in 130,000 live births.^[15]

• Toe walking^[16]
• Pragmatic speech problems^[16]
• Clumsiness^[16]
• Obsessions and rituals^[16]
• Sensory issues^[16]
• Disinterest in social interaction^[16]
• Autistic characteristics^[16]

• Scheeringa, MS (2001). "The differential diagnosis of impaired reciprocal social interaction in children: A review of disorders". Child Psychiatry and Human Development. 32 (1): 71–89. doi:10.1023/A:1017511714145. PMID 11579660. S2CID 43311652.
• Increasing Interaction with Children with Multisystem Developmental Disorder (MSDD), Developmental Delay Resources
• Wieder, S (1996). "Integrated treatment approaches for young children with multisystem developmental disorder". Infants & Young Children. 8 (3): 24–34. doi:10.1097/00001163-199601000-00005. S2CID 145177134.