Proximal spinal muscular atrophy (SMA) is classified into three main subtypes (I–III), defined by age at onset and achieved motor milestones. As age at onset can be very early in SMA II and III (IIIa, onset <3 years) and does not necessarily correlate with prognosis, the question arises whether the child can be correctly assigned to a specific SMA type at the time of presentation based on the assessment of motor function. Therefore we studied the motor milestones in 175 SMA type II and 266 SMA type III patients. In SMA II, 73% of the patients sat within the normal age range (up to 9 months), the remainder learned to do so at ages between 10 and 30 months. In SMA III, the walking milestone was passed with delay (given an upper normal limit of 18 months) in 10% of all and 16% of SMA IIIa patients (median age 13 months, range 9–53 months). There was a correlation between late sitting and walking in SMA III, since those who sat after 9 months were responsible for the majority of delayed walkers. The median age when becoming chairbound did not differ between early-onset SMA III patients who walked with delay and those who walked within the normal age range (10.2 versus 10.5 years). In conclusion, a significant proportion of patients with early-onset SMA classified as SMA II on the basis of achieved motor function turned out to be SMA III at later follow-up. It is important to reassess a child in the first 2–4 years, to determine whether walking can be achieved with or without aids, as children who start to walk late have a similar favourable outcome for ambulation compared to earlier walkers.

Keywords:
Proximal spinal muscular atrophy, Motor milestones, Prognosis
1.
Lefebvre S, Bürglen S, Reboullet O, Burlet P, Viollet L, Benichou B, Cruaud C, Millasseau P, Zeviani M, Le Paslier D, Frézal J, Cohen D, Weissenbach J, Munnich A, Melki J: Identification and characterization of a spinal muscular atrophy determining gene. Cell 1995;80:155–165.
2.
Hahnen E, Forkert R, Marke C, Rudnik-Schöneborn S, Schönling J, Zerres K, Wirth B: Molecular analysis of candidate genes on 5q13 in autosomal recessive spinal muscular atrophy: Evidence of homozygous deletions of the SMN gene in unaffected individuals. Hum Mol Genet 1995;4:1927–1933.
3.
International SMA Consortium: Meeting report. Neuromuscul Disord 1992;2:423–428.
4.
International SMA Consortium: Workshop report. Neuromuscul Disord 1999;9:272–278.
5.
Wirth B, Herz M, Wetter A, Hahnen E, Moskau S, Rudnik-Schöneborn S, Wienker T, Zerres K: Quantitative analysis of SMN copies: Identification of subtle SMN mutations in SMA patients, genotype-phenotype correlation and implications for genetic counseling. Am J Hum Genet 1999;64:1340–1356.
6.
Zerres K, Rudnik-Schöneborn S, Forrest E, Lusakowska A, Borkowska J, Hausmanowa-Petrusewicz I: A collaborative study on the natural history of childhood and juvenile onset proximal spinal muscular atrophy (type II and III SMA): 569 patients. J Neurol Sci 1997;146:67–72.
7.
Tonali P, Servidei S, Uncini A, Restuccia D, Galluzzi G: Clinical study of proximal spinal muscular atrophy. Report on 89 cases. Ital J Neurol Sci 1984;5:423–432.
8.
Bayley N: Manual for the Bayley Scales of Infant Development. Berkeley, Institute of Human Development, University of California, 1969.
9.
Dalton FD, Forman MA, Muller BA: Growth and development; in Behrmann RE (ed): Nelson Textbook of Paediatrics. Philadelphia, Saunders, 1992, pp 21–22.
10.
Pearn J: The use of motor milestones to determine retrospectively the clinical onset of disease. Aust Paediatr J 1974;10:147–153.
11.
Neligan G, Prudham D: Norms for four standard developmental milestones by sex, social class and place in family. Dev Med Child Neurol 1969;11:413–422.
12.
Bono R, Inverno M, Botteon G, Iotti E, Estienne M, Berardinelli A, Lanzi G, Fedrizzi E: Prospective study of gross motor development in children with SMA type II. Ital J Neurol Sci 1995;16:223–230.
13.
Russman BS, Iannaccone ST, Buncher CR, Samaha FJ, White M, Perkins B, Zimmerman L, Smith C, Burhans K, Barker L: Spinal muscular atrophy: New thoughts on the pathogenesis and classification scheme. J Child Neurol 1992;7:347–353.
14.
Souchon F, Simard LR, Lebrun S, Rochette C, Lambert J, Vanasse M: Clinical and genetic study of chronic (types II and III) childhood onset spinal muscular atrophy. Neuromuscul Disord 1996;6:419–424.
15.
Carter GR, Abresch RT, Fowler WM, Johnson ER, Kilmer DD, McDonald CM: Profiles of neuromuscular diseases. Am J Phys Med Rehabil 1995;74:S150–S159.
16.
Robinson D, Galasko CSB, Delaney C, Wiliiamson JB, Barrie JL: Scoliosis and lung function in spinal muscular atrophy. Eur Spine J 1995;4:268–273.
17.
Iannaccone ST, Russman BS, Browne RH, Buncher CR, White M, Samaha FJ: Prospective analysis of strength in spinal muscular atrophy. J Child Neurol 2000;15:97–101.
18.
Dubowitz V: Chaos in the classification of SMA: A possible resolution. Neuromuscul Disord 1995;5:3–5.
© 2001 S. Karger AG, Basel
2001
Copyright / Drug Dosage / Disclaimer
Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher.
Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug.
Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.
You do not currently have access to this content.