**3.14 Cystic fibrosis**

Cystic fibrosis is a common autosomal recessive genetic disease caused by mutations of cystic fibrosis transmembrane conductance regulator (CFTR) gene on chromosome 7 in Caucasian population (Kerem et al., 1989; Riordan et al., 1989; Rommens et al., 1989). CFTR is a cAMP-regulated chloride channel; the CFTR gene mutations lead to the cAMP-induced chloride channel dysfunction, thereby alter the transport of chloride and associated liquid, cause problems in several organ systems including respiratory system, sweat glands, pancreas, intestine, liver and gallbladder. There are more than 1800 CFTR gene mutations in the world. Cystic fibrosis affacts more than 70, 000 individuals worldwide. In 2006, the median survival age for a person with cystic fibrosis was 37 (M. Anderson et al., 1991; Collaco & Cutting, 2008; Collins, 1992; Cutting, 2010; Lee et al., 2005; Rowntree & Harris, 2003; G. Wang et al., 2005; Zielenski, 2000).

#### **3.15 Duchenne muscular dystrophy**

Duchenne muscular dystrophy (DMD) is the most common form of muscular dystrophy, it affacts about one of every 3500 males. DMD is an X-linked recessive muscle degenerative disease caused by the mutations of dystrophin. As the above stated, the DMD gene is the largest human gene (>2.4 million bp on chromosome X), its cDNA is 14 kb long. DMD gene encodes a single 427 kDa protein-dystrophin. Patient's muscle fibers do not have the 427 kDa dystrophin (Burghes et al., 1987; Campeau et al., 2001; Hoffmanet al., 1987; Koenig et al., 1987, 1988; Kunkel, 2004; Monaco et al., 1986; Nelson et al., 2009).

#### **3.16 Huntington's disease**

Huntington's disease (HD) was first described by George Huntington in 1872. HD is an autosomal dominant neurodegenerative disease caused by the mutation of the huntingtin (HTT) gene. HTT gene located at 4p16.3; it has longer CAG trinucletide repeats (more than 40 CAG repeats) in the first exon of the HTT gene than the normal gene. There are transgenic mouse, sheep and monkey models available for conducting animal experiments currently (Bates et al., 1997; Beilby, 2007; S. Davies & Ramsden, 2001; Jacobsen et al., 2010; MacDonald et al., 1993; Yang et al., 2008).
