. Author manuscript; available in PMC: 2018 Jun 1.

Published in final edited form as: Obstet Gynecol Clin North Am. 2018 Jun;45(2):249–265. doi: 10.1016/j.ogc.2018.01.010

Table 3.

Genotype-phenotype correlations in myotonic dystrophy type 1

Phenotype	Clinical Features^a	CTG Repeat Length
Normal (unaffected)	None	5–34

Premutation	None	35–49

Mild	Cataracts	50–150
Mild	Mild myotonia	50–150

Classic	Weakness	100–1000
	Myotonia
	Cataracts
	Cardiac arrhythmia

Congenital	Infantile hypotonia	>1000
	Respiratory difficulties
	Intellectual disability

There is significant overlap of phenotypes and CTG repeats, making predictions of age of onset and severity for individual patients challenging.

Data from The International Myotonic Dystrophy Consortium (IDMC). New nomenclature and DNA testing guidelines for myotonic dystrophy type 1 (DM1). Neurology 2000;54(6):1218–1221.