Is the transportation highway the right road for hereditary spastic paraplegia?

Abstract

The term "hereditary spastic paraplegia" (HSP) refers to a genetically and clinically diverse group of disorders whose primary feature is progressive spasticity of the lower extremities. The condition arises because of degeneration of the longest motor and sensory axons on the spinal cord, which appear to be most sensitive to the underlying mutations. The marked genetic heterogeneity in HSP, with 20 loci chromosomally mapped and eight genes now identified, suggests that a number of defective cellular processes may be shown to result in the disease. Although previous studies have suggested a mitochondrial basis for at least one form of the disease, a mechanism common to a number of the other genes mutated in HSP has remained elusive until now. The identification of the most recent genes for the condition suggests that aberrant cellular-trafficking dynamics may be a common process responsible for the specific pattern of neurodegeneration seen in HSP.

Figure 1

Multiple sequence alignment of selected members of the ESP (MIT) domain–containing proteins. Sequences are indicated using their database accession number followed by the starting and the ending residues of the domain and by the species. The consensus present in ⩾70% of the sequences is given below the alignment; residues and colors are as follows: h (hydrophobic, blue), l (aliphatic, blue), K (lysine), p (polar, yellow), and R (arginine). Plus signs (+) indicate conserved, positively charged residues (lysine and arginine), which are colored in red in the alignment; minus signs (−) indicate conserved, negatively charged residues, which are indicated in pink. The secondary structure prediction (“Sec.Str.Pred.”) at the bottom of the alignment is derived from the alignment (H = helix predicted with expected average accuracy >82%; h = helix predicted with expected average accuracy <82%). Abbreviations: Hs, Homo sapiens; Mm, Mus musculus; and Sc, Saccharomyces cerevisiae.