Open Journal of Genetics, 2013, 3, 46-49 OJGen
http://dx.doi.org/10.4236/ojgen.2013.32A3007 Published Online August 2013 (http://www.scirp.org/journal/ojgen/)
Diagnostic challenges in Salla disease
Jessica N. Hartley1,2, Michael S. Salman3,4, Frances A. Booth3,4, Lorne Seargeant3,5,
David A. Wenger6, Jens Wrogemann7, Aizeddin A. Mhanni1,2,3*
1Department of Biochemistry and Medical Genetics, University of Manitoba, Winnipeg, Canada
2Program of Genetics and Metabolism, Winnipeg, Canada
3Department of Pediatrics and Child Health, University of Manitoba, Winnipeg, Canada
4Section of Pediatric Neurology, University of Manitoba, Winnipeg, Canada
5Diagnostic Services Manitoba, University of Manitoba, Winnipeg, Canada
6Lysosomal Diseases Testing Laboratory, Thomas Jefferson University, Philadelphia, USA
7Department of Radiology, Section of Pediatric Radiology, University of Manitoba, Winnipeg, Canada
Received 27 October 2012; revised 16 November 2012; accepted 9 December 2012
Copyright © 2013 Jessica N. Hartley et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Sialic acid storage disease (Salla disease) is an auto-
somal recessive disorder caused by mutations in a ly-
sosomal sialic acid export protein, SLC17A5 (OMIM
#604369). This disorder was initially described in
Northern Finland but more recently has been re-
ported in patients of other ethnicities. We describe
the clinical presentation and the neuroimaging find-
ings of two non-Finnish children where a diagnosis of
Salla disease was suspected on the basis of brain mag-
netic resonance imaging. The biochemical confirma-
tion of this diagnosis posed a challenge as both pa-
tients had elevated percent free urine sialic acid but
biochemical analyses in fibroblasts were not conclu-
sive; therefore, molecular testing was necessary for
confirmation of the diagnosis. The described encoun-
ters demonstrate the importance of pursuing confir-
matory molecular diagnostic testing when a sialic acid
storage disorder is suspected.
Keywords: Sialic Acid; Salla Disease; Lysosomal;
SLC17A5
1. BACKGROUND
Free sialic acid storage disease (Salla disease) is an auto-
somal recessive disease caused by mutations in a ly-
sosomal sialic acid export protein, SLC17A5 (OMIM
#604369) which leads to lysosomal accumulation of free
sialic acid [1]. Common features of this disease include
developmental delay, ataxia, subtle coarse facial features
and brain magnetic resonance imaging (MRI) findings of
hypomyelination and hypoplastic corpus callosum [2].
Biochemical findings of a defect in the sialic acid export
protein include elevated total and free sialic acid in urine
and fibroblasts [3,4]. The mild to moderate form of this
condition was initially described in Northern Finland
with the eponym “Salla” referring to the geographically
restricted area where the first family resided [4]. Since
that time, free sialic acid storage disease has been re-
ported in patients of other ethnicities and infantile free
sialic acid storage disease (ISSD) (OMIM# 269920) has
been described to be allelic to Salla, with ISSD being as-
sociated with an infantile onset progressive disease and
extremely elevated total and free sialic acid levels [1,3,
5,6]. We describe the clinical presentation, neuroimaging
and the challenges in confirming this diagnosis in two
children of non-Finnish ancestry.
2. MATERIALS AND PATIENTS
2.1. Methods
Urine Sialic Acid Measurements: Determinations of urine
total and free sialic acid levels were conducted using a
spectrophometric method as described [7,8] and com-
pared to age-matched controls [9].
Sialic Acid Studies in Fibroblasts: A pellet of cultured
skin fibroblasts was sonicated in distilled water and the
protein concentration was determined. The total sialic
acid content were determined after heating an aliquot
containing between 100 and 150 μg protein at 80˚C in
0.1 N sulfuric acid for 1 hour. The same size aliquot in
distilled water and not heated was used to determine the
free sialic acid content. The method of Aminoff was then
followed to measure the sialic acid content [10]. After
reading the absorbance at both 549 and 532 nm, the sialic
*Corresponding author.

J. N. Hartley et al. / Open Journal of Genetics 3 (2013) 46-49 47
acid content per mg protein was calculated.
This case series has been reviewed by the University
of Manitoba Research Ethics Board to ensure that patient
identity is protected and consent processes were adhered to.
2.2. Patients
Patient 1 presented at age twenty-two months with a his-
tory of global developmental delay. The family history
was unremarkable for neurodegenerative disease and
there was no history of consanguinity. The family was of
Irish, English, Ukrainian and Dutch descent (non-Fin-
nish). The pregnancy history was unremarkable with no
history of exposure to known teratogens. The perinatal
and neonatal histories were unremarkable. His birth
weight was 3.486 kg (75th percentile). His Apgar scores
were 5 and 8 at 1 and 5 minutes respectively. His ex-
amination at twenty-two months of age was remarkable
for subtle coarse facial features, a depressed nasal bridge,
a high arched palate and a high forehead. His weight was
12.8 kg (50th - 75th percentile), height was 84.5 cm
(25th - 50th percentile) and OFC was 50.5 cm (90th -
97th percenttile). Hepatomegaly was noted with a palpa-
ble liver edge 3 cm below the right costal margin in the
midclavicular line. His neurologic examination revealed
normal visual behaviour and extraocular movements and
generalized hypotonia (central and peripheral) with nor-
mal muscle strength. His deep tendon reflexes were nor-
mal and symmetric in the upper limbs and slightly in-
creased in the lower limbs. Ataxia was noted in the lower
but not the upper limbs. A formal developmental assess-
ment using the Yale Developmental Schedules at twenty-
seven months of age revealed a developmental quotient
of 65%. The child’s ophthalmologic and echocardiogra-
phic assessments were unrevealing. An electroencepha-
logram revealed left-sided slowing in background activ-
ity and right-sided epileptiform discharges; however there
was no history of clinical seizures. Brain MRI at age
twenty-one months showed abnormalities suggestive of
Salla disease (Figure 1).
Patient 2 presented at age thirty-one months with a
history of ataxia and developmental delay. The preg-
nancy, perinatal, neonatal and family histories were un-
remarkable. No consanguinity was reported and the fam-
ily was not of Finnish ancestry. The child’s examination
at thirty-one months of age was remarkable for subtle
coarse facial features and significant ataxia. The weight
was 14 kg (75th percentile), height was 93.5 cm (50th
percentile) and OFC was 48.8 cm (75th - 90th percentile).
Cranial nerve examination was remarkable for excessive
drooling with an intact gag response. Muscle strength
and tone were normal. The child had prominent truncal
and limb ataxia affecting all four extremities and walked
only with support with a broad-based gait. The child had
a bilateral pincer grasp but had difficulty with fine finger
Figure 1. Coronal T2-weighted MRI in patient 1 at age twenty-
one months showing complete lack of normal myelin signal
and white matter volume loss throughout the cerebral hemi-
spheres (horizontal arrow). Hypomyelination and volume loss
of the cerebellar white matter was also present (vertical arrow).
The cortical gray matter and deep gray matter (not shown) were
preserved.
movements and finger-to-nose testing. Deep tendon re-
flexes were normal and symmetric with down-going
plantar responses. A formal developmental assessment
using the Yale Developmental Schedules at thirty-one
months of age revealed a developmental quotient of 65%.
Follow-up assessment using the Revised Gesell Devel-
opmental Schedules at sixty-nine months of age (five
years) suggested a gross motor developmental quotient
of 26%, a fine motor developmental quotient of 50% and
a language developmental quotient of 35%. An electro-
encephalogram revealed localized epileptiform abnorma-
lities. Brain MRI at age forty months also showed ab-
normalities suggestive of Salla disease (Figure 2).
3. RESULTS
A summary of the results of the laboratory investigations
undertaken in both patients to investigate the possibility
of Salla disease in provided in Table 1.
In patient 1, urine total and free sialic acid were ele-
vated above age-matched control values on two occa-
sions, with the percent free urine sialic acid and skin
electron microscopy being suggestive of a free sialic acid
storage disorder (data not shown). Fibroblast assay re-
vealed elevations of free sialic acid in the diagnostic
range, however total sialic acid values were only mildly
elevated as compared to controls. Molecular analysis of
the SLC17A5 gene revealed compound heterozygosity

J. N. Hartley et al. / Open Journal of Genetics 3 (2013) 46-49 48
Table 1. Pertinent laboratory investigations for Salla disease.
Patient 1 Patient 2
Urine Average Free Sialic Acid (umol/mmol creatinine) 313* 93.5
Urine Average Total Sialic Acid (umol/mmol creatinine) 387* 146
% Urine Free Sialic Acid
(Salla > 80%)
(Control < 60%) 80.9%* 63.8%*
Fibroblast Sialic Acid (nmol/mg protein)
Free SA
(Salla 10.0 +/− 2.9 SD)**
(Control 1.0 +/− 0.6 SD)
10.4* 2.1
Total SA
(Control 18.0 +/− 4.6 SD) 20 15.3
Skin Electron Microscopy Lysosomal storage of fine fibrillar materialEnlarged lysosomes with fine fibrillar
structures
Molecular Pat c. 250 del C
Mat c. 115C > T Homozygous c. 115C > T
*Diagnostic laboratory values; **Case/control values from Seppala et al. 1991.
Figure 2. Coronal T2-weighted MRI in patient 2 at age forty
months showing marked volume loss and increased T2 signal
intensity of the cerebral hemispheric white matter (horizontal
arrow) and corpus callosum (oblique arrow), reflecting a lack
of myelin. The cortical gray matter and deep gray matter were
preserved. There was no evidence of volume loss or signal
abnormality in the posterior limbs of the internal capsule, cere-
bellum, and brainstem (not shown).
for the common Finnish mutation, 115C > T (R39C), and
another mutation, 250delC, previously described in a
French patient [11] confirming the diagnosis of Salla dis-
ease.
In patient 2, four independent urine samples revealed
borderline elevations of free and total sialic acid. Urine
percent free sialic acid was mildly elevated compared to
age-matched control values, but not in the diagnostic
range for Salla disease. Skin electron microscopy was
consistent with a free sialic acid storage disorder (data
not shown). Fibroblast assay showed normal total and
free sialic acid. Molecular analysis of the SLC17A5 gene
revealed homozygosity for the common Finnish mutation,
115C > T (R39C), confirming a diagnosis of Salla dis-
ease.
4. DISCUSSION
The clinical phenotype of both patients is consistent with
Salla disease, rather than infantile free sialic acid storage
disease (ISSD) given that symptoms developed during
the first year of life and that both patients continued to
make developmental progress, albeit slowly, without any
evidence of developmental regression [5]. The elevated
total but not free sialic acid in fibroblast culture in pa-
tient one and the normal total and free sialic acid in fi-
broblast culture for patient two posed a diagnostic chal-
lenge. The more severe ISSD is associated with ex-
tremely high total and free sialic acid levels in cultured
fibroblasts, leukocytes and urine as compared to the
milder Salla disease [3]. To our knowledge, there are no
published reports of individuals with phenotypic Salla
disease with normal fibroblast free sialic acid, even
among the Finnish population where the condition was
originally described. A pair of siblings with a Salla phe-
notype and homozygosity for a different mutation, K136E,
also had non-diagnostic biochemical findings, with nor-
mal urine free sialic acid (percent free sialic acid not
reported), elevated sialic acid in cerebrospinal fluid and
mildly elevated free sialic acid in fibroblasts [12]. Nor-
mal leukocyte total and free sialic acid levels in mildly
affected children of Mennonite descent, who are homo-
zygous for the R39C Finnish mutation, like patient 2,
have been noted. In the urine of these patients, the total
sialic acid content was noted to be normal, however the
percent free was elevated above normal (greater than
80% free versus less than 60% in non-Salla individuals)

J. N. Hartley et al. / Open Journal of Genetics 3 (2013) 46-49 49
(Wenger, personal communication 2012). Our patient
two was comparable, with mildly elevated urine free si-
alic acid, however, 63% free sialic acid is not consid-
ered to be in the diagnostic range.
Molecular diagnostic testing was required for confir-
mation of the diagnosis in both our patients as well as
those noted by Wenger (personal communication 2012)
and reported by Mochel [12]. Patient 2 was homozygous
for the Finnish mutation associated with the Salla disease
phenotype. It is interesting to note that neither of our
patients is of Finnish ancestry but the R39C mutation is
present in both. Salla disease due to the originally de-
scribed R39C mutation appears to be pan-ethnic; homo-
zygosity for this mutation has been reported in individu-
als of other ethnicities, including those of Old Order
Mennonite extraction [1].
Our report demonstrates the importance not only by
considering the diagnosis of Salla disease in children
with subtle coarse facial features, developmental delay
and hypomyelination on brain MRI who are not of Fin-
nish ancestry, but also of the importance of pursuing
molecular testing for Salla disease for confirmation of
the diagnosis in the face of non-diagnostic biochemical
analyses.
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ONLINE DATABASES CITED
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http://omim.org/
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