Table 6. Examples of Mendelian diseases.

Inheritance pattern	Disease	Gene/region	Nature of variants	Estimated frequency
Autosomal dominant	Glut1 deficiency (De Vivo disease)	SLC2A1	Mutations reduce or eliminate function	Rare, approximately 1/90000
	Osteogenesis imperfecta (brittle bone disease)	COL1A1 or COL1A2 (90%) (also CRTAP or P3H1)	COL1A1/COL1A2 – usually missense mutations that lead to protein (collagen) of altered structure	6–7/100000
	Achondroplasia	FGFR3	Activating point mutations	1/15000 to 1/40000
Autosomal recessive	Phenylketonuria	PAH	Many different mutations, including missense, non-sense, splicing mutations	1/10000 to 1/15000
	Cystic fibrosis	CFTR	Over 2000 different variants known	1/2500 to 1/3500 in Caucasians, less common in other ethnic groups
	Sickle-cell anaemia	HBB	Various missense variants, gene deletions	1/70000 to 1/80000 in the U.S.A., more common in other countries
X-linked recessive	Haemophilia A	F8	Missense and nonsense mutations	1/4000 to 1/5000 males
	Duchenne muscular dystrophy	DMD	Usually deletions or duplications	1/3500 to 1/5000 (Duchenne and Becker muscular dystrophy together)
X-linked dominant	Fragile X syndrome	FMR1	CGG trinucleotide repeat expansion	1/4000 (males), 1/8000 (females)
	Rett syndrome	MECP2	Missense mutations, abnormal epigenetic regulation	1/8500 females
	X-linked hypophosphatemic rickets	PHEX	Deletions, insertions, missense, nonsense, splicing mutations	1/20000
Y-linked	Nonobstructive spermatogenic failure	USP9Y	Most commonly deletions	1/2000 to 1/3000

Diseases are shown together with their inheritance patterns, the affected gene, the most commonly found types of mutation, and estimated incidence rates. Note, some diseases, for example osteogenesis imperfecta (of which there are several forms), can be caused by pathogenic variants in one of a number of different genes.