Clinical features
The clinical features depend on the specific genetic defect (see natural course and prognosis). However, common criteria for the diagnosis are (a) chronic motor and sensory neuropathy; (b) infantile onset of (motor) symptoms manifested by congenital hypotonia, delayed walking (> 18 months) or early complaints about motor performances (< 2 years); (c) median motor nerve conduction velocities (MNCV) of 12 m/s or less.

Natural course and prognosis
Gabreels-Festen et al. (2002) documented the clinical and pathological features in 25 patients with a DSS and evaluated the clinical course. In this serie 14 patients had an AD mutation and six were likely affected by an AR disorder. In three patients inheritance mode was unknown and two patients obviously suffered from an acquired disorder. Eight of the 25 patients showed a moderate handicap in adult life; walking distance was still at least one kilometre. It is concluded that DSS, although in general denoting a more serious neuropathy than CMT1, does not imply a severe disability and wheelchair dependency in adult life.

Epidemiology
Incidence: <0.1/100.000

Differential diagnosis
Dejerine-Sottas syndrome (DSS) is by definition not a classifying diagnosis but a clinical syndrome. The clinical phenotype might resemble Wernig-Hoffmann disease but the two disorders are easily differentiated by nerve conduction and EMG studies. It may be extremely difficult to distinguish CIDP starting in infancy from inherited neuropathies, as the evolution of symptoms is usually identical to HMSN and a preceding normal period cannot be established with certainty (Sladky et al., 1986; Bird & Sladky, 1991).

Ancillary investigations
Nerve conduction studies, EMG, CSF (protein) analysis, sural nerve biopsy, DNA analysis (PMP22 point mutations, 17p11.2 duplication, Pzero mutations, EGR2 gene analysis)

Genetics
Recent genetic investigations showed that several of the earlier published cases of DSS resulted from (de novo) heterogeneous dominant point mutations of the Peripheral Myelin Protein 22 gene (PMP22) (Roa et al., 1993; Gabreëls-Festen et al., 1995; Valentijn et al., 1995), or the Protein zero gene (Pzero) (Hayasaka et al., 1993; Nakagawa et al., 1999). More recently it was demonstrated that also AD mutations of the Early Growth Response protein 2 gene (EGR2) might result in DSS (Warner et al., 1998). Furthermore, an AR inherited form of DSS may result from mutations in the PRX gene (Boerkoel et al., 2001). In addition, one mutation in the inhibitory domain of EGR2 and at least one PMP22 mutation in the C-terminal intracellular domain of the protein are inherited as an AR trait. (Warner et al., 1998; Parman et al., 1999). These mutations are silent in the heterozygous parents, but cause a DSS or CHN in the homozygous children (Parman et al., 1999). Two specific mutations of Pzero are leading to a DSS phenotype in the homozygous state, but result in a mild CMT1 or CMT2 phenotype in the heterozygous state (Ikegami et al., 1996; Pareyson et al., 1999). The phenotypic expression of the few reported cases of an homozygous PMP22 duplication may range from DSS to CMT1, like in the heterozygous state (Sturtz et al., 1997; LeGuern et al., 1997). This suggests that solely the number of PMP22 gene copies does not determine disease severity.

Therapy
Therapy is symptomatic and supportive.