Correlating phenotype and genotype in the periodic paralyses.
BACKGROUND
Periodic paralyses and paramyotonia congenita are rare disorders causing disabling weakness and myotonia. Mutations in sodium, calcium, and potassium channels have been recognized as causing disease.


OBJECTIVE
To analyze the clinical phenotype of patients with and without discernible genotype and to identify other mutations in ion channel genes associated with disease.


METHODS
The authors have reviewed clinical data in patients with a diagnosis of hypokalemic periodic paralysis (56 kindreds, 71 patients), hyperkalemic periodic paralysis (47 kindreds, 99 patients), and paramyotonia congenita (24 kindreds, 56 patients). For those patients without one of the classically known mutations, the authors analyzed the entire coding region of the SCN4A, KCNE3, and KCNJ2 genes and portions of the coding region of the CACNA1S gene in order to identify new mutations.


RESULTS
Mutations were identified in approximately two thirds of kindreds with periodic paralysis or paramyotonia congenita. The authors found differences between the disorders and between those with and without identified mutations in terms of age at onset, frequency of attacks, duration of attacks, fixed proximal weakness, precipitants of attacks, myotonia, electrophysiologic studies, serum potassium levels, muscle biopsy, response to potassium administration, and response to treatment with acetazolamide.


CONCLUSIONS
Hypokalemic periodic paralysis, hyperkalemic periodic paralysis, and paramyotonia congenita may be distinguished based on clinical data. This series of 226 patients (127 kindreds) confirms some clinical features of this disorder with notable exceptions: In this series, patients without mutations had a less typical clinical presentation including an older age at onset, no changes in diet as a precipitant, and absence of vacuolar myopathy on muscle biopsy.
Miller
T M
TM
Department of Neurology, University of California San Francisco 94143-2922, USA.
Dias da Silva
M R
MR
Miller
H A
HA
Kwiecinski
H
H
Mendell
J R
JR
Tawil
R
R
McManis
P
P
Griggs
R C
RC
Angelini
C
C
Servidei
S
S
Petajan
J
J
Dalakas
M C
MC
Ranum
L P W
LP
Fu
Y H
YH
Ptácek
L J
LJ
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005260:Female; D005838:Genotype; D006801:Humans; D020514:Hypokalemic Periodic Paralysis / Q000175:diagnosis* / Q000235:genetics; D008297:Male; D008875:Middle Aged; D020967:Myotonic Disorders / Q000175:diagnosis* / Q000235:genetics; D062553:NAV1.4 Voltage-Gated Sodium Channel; D020513:Paralysis, Hyperkalemic Periodic / Q000175:diagnosis* / Q000235:genetics; D010641:Phenotype; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics; D015222:Sodium Channels / Q000235:genetics
C418492:KCNE3 protein, human; C489457:KCNJ2 protein, human; D062553:NAV1.4 Voltage-Gated Sodium Channel; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated; C106251:SCN4A protein, human; D015222:Sodium Channels