We read with interest the excellent review article by Dr Fink on hereditary spastic paraplegias (HSPs).1 The author refers to 3 different X-linked HSP disorders. We would like to point out that there is a fourth X-linked disorder, Allan-Herndon- Dudley (AHD) syndrome, which is similar to these 3.2 Although originally described almost 60 years ago, to our knowledge AHD has not been cited in any standard neurology textbook or journal. Like the other 3 X-linked HSP disorders, AHD is of relatively early onset, has limited worsening across time, and is complicated by mental retardation. Neck drop, or limber neck, is a characteristic finding in patients with AHD syndrome. This feature apparently has not been reported in other forms of HSP, so it may well be pathognomonic for AHD. Limited molecular studies show linkage to chromosome Xq213 in 2 different American families with AHD. Three men from England with similar features have been described,4 and 1 of us (P.A.) has observed the features of AHD syndrome in 19 men from 5 Iranian families, 2 with definite X-linked inheritance. All 19 had neck drop or limber neck similar to that reported in AHD.
Bohan TP, Azizi P. Allan-Herndon-Dudley Syndrome: Should the Locus for This Hereditary Spastic Paraplegia Be Designated SPG 22?. Arch Neurol. 2004;61(9):1470-1471. doi:10.1001/archneur.61.9.1470-c