Neurology

SLC35A2-CDG: A Patient Guide

At a Glance

SLC35A2-CDG is a rare genetic disorder that often causes early seizures, low muscle tone, and developmental delays. Routine blood screening may be normal, so diagnosis often depends on genetic testing, while care combines seizure treatment, therapies, and specialist support.

SLC35A2-CDG is an ultra-rare metabolic condition that primarily affects the brain’s development and electrical activity. It belongs to a group of diseases called Congenital Disorders of Glycosylation (CDG), which are caused by the body’s inability to properly attach sugar chains to proteins and fats ^[1]. In this specific type, a genetic change—often occurring randomly at conception (de novo) rather than being inherited, though recurrence counseling is important—disrupts the transport of an activated sugar called UDP-galactose into the cell’s “packaging center,” the Golgi apparatus ^[2]^[3]. Without enough UDP-galactose in the right place, the brain cannot build particular glycoproteins and glycolipids it needs to function correctly, often leading to a pattern of early-onset seizures and developmental challenges known as Developmental and Epileptic Encephalopathy ^[4]^[5].

The condition is often difficult to identify because it does not follow the “rules” of many other metabolic disorders. Most children with SLC35A2-CDG have normal results on standard blood screening tests, such as serum transferrin glycosylation, which can lead to significant diagnostic delays ^[2]^[6]. Confirmation usually requires advanced genetic testing, like Whole Exome Sequencing, to find the specific variant in the SLC35A2 gene ^[7]. In some cases, the diagnosis is even more elusive because the genetic change may only be present in certain cells, a phenomenon called mosaicism, which sometimes affects only the brain tissue and may not appear in a standard blood sample ^[8]^[9].

Living with this diagnosis means managing a complex range of neurological symptoms, including infantile spasms, low muscle tone (hypotonia), and global developmental delays ^[4]. Brain imaging often reveals variable reported findings, such as delayed myelination (the protective coating on nerves) or a thin corpus callosum ^[4]^[10]. Because the condition affects so many systems, care requires a coordinated team of specialists, including neurologists to manage seizures and biochemical geneticists to oversee metabolic health ^[2].

While the diagnosis is serious, there is an active and targeted approach to investigating treatments. Some children in a small study showed developmental changes with a specialized investigational dietary supplement of D-galactose, which aims to increase substrate for the cells to function better, though response is unpredictable and seizure efficacy is not yet established ^[11]. When combined with intensive physical, occupational, and speech therapies, this targeted therapy may offer a path forward for supporting developmental outcomes ^[11]^[3]. Understanding the biology of this condition empowers you to advocate for the multidisciplinary care your child needs.

In this guide

6 chapters

Navigating an SLC35A2-CDG Diagnosis

Learn how SLC35A2-CDG affects development and seizures, why transferrin tests may be normal, and what genetic testing and D-galactose research may involve.

Symptoms, Seizures, and Brain Development

Learn how SLC35A2-CDG affects seizures, development, muscle tone, vision, and brain MRI findings, including infantile spasms and hypsarrhythmia on EEG.

Confirming the Diagnosis and Genetics

Learn how SLC35A2-CDG is confirmed when blood screening is normal, including WES, WGS, mosaicism, variant allele fraction, and tissue testing for your child.

Investigational Therapies and Epilepsy Care

Learn about SLC35A2-CDG treatment research, including D-galactose, seizure care, infantile spasms, side effects, and supportive care options for families.

Building Your Care Team

Learn how to build a care team for a child with SLC35A2-CDG, including metabolic specialists, neurology, therapies, records, seizure tracking, and coordination.

Daily Management and Emergency Care

Learn how to manage SLC35A2-CDG with routine health monitoring, feeding safety, seizure first aid, and clear signs that require emergency medical care.

Common questions in this guide

What is SLC35A2-CDG?

SLC35A2-CDG is a rare genetic condition that affects how cells transport UDP-galactose and build certain proteins and fats. It mainly affects the brain and can lead to early seizures, low muscle tone, and developmental delays.

What symptoms can SLC35A2-CDG cause in children?

Children may have early-onset seizures, including infantile spasms, along with low muscle tone and global developmental delays. Brain imaging may also show delayed myelination or a thin corpus callosum, although findings can vary.

Can routine blood tests miss SLC35A2-CDG?

Yes. Standard tests such as serum transferrin glycosylation are often normal in children with SLC35A2-CDG, so a normal blood screen does not rule it out.

How is SLC35A2-CDG diagnosed?

Diagnosis usually involves advanced genetic testing, such as whole exome sequencing, to identify a disease-causing change in the SLC35A2 gene. If the change is mosaic and present in only some cells, it may not be detected in a blood sample.

Is SLC35A2-CDG inherited?

The genetic change is often new in the child rather than inherited from a parent. Families should still receive genetic counseling because recurrence considerations depend on the specific genetic findings and family circumstances.

Could D-galactose help treat SLC35A2-CDG?

D-galactose supplementation is an investigational approach that has shown developmental changes in some children in a small study. Responses are unpredictable, and its ability to control seizures has not been established, so families should discuss it with the child’s specialists.

What care does a child with SLC35A2-CDG need?

Care may include a neurologist for seizure management and a biochemical geneticist for metabolic care. Physical, occupational, and speech therapies can support motor, daily-living, and communication skills as part of a coordinated care plan.

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Curated prompts to bring to your next appointment.

1.Given the rarity of SLC35A2-CDG, how can we ensure our child's care team is connected with national experts in glycosylation disorders?
2.If our child's initial blood tests were normal, what specific genetic findings confirmed the diagnosis?
3.Is our child a candidate for a trial of D-galactose therapy, and how would we measure its effectiveness?
4.How do we balance seizure management with therapies meant to improve our child's motor and communication skills?

References (11)

1
Glycosphingolipid synthesis is impaired in SLC35A2-CDG and improves with galactose supplementation.
Jáñez Pedrayes A, De Craemer S, Idkowiak J, et al.
Cellular and molecular life sciences : CMLS 2025; (82(1)):257 doi:10.1007/s00018-025-05759-w.
PMID: 40576648
2
SLC35A2-CDG: Functional characterization, expanded molecular, clinical, and biochemical phenotypes of 30 unreported Individuals.
Ng BG, Sosicka P, Agadi S, et al.
Human mutation 2019; (40(7)):908-925 doi:10.1002/humu.23731.
PMID: 30817854
3
D-galactose Supplementation for the Treatment of Mild Malformation of Cortical Development with Oligodendroglial Hyperplasia in Epilepsy (MOGHE): A Pilot Trial of Precision Medicine After Epilepsy Surgery.
Aledo-Serrano Á, Valls-Carbó A, Fenger CD, et al.
Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 2023; (20(5)):1294-1304 doi:10.1007/s13311-023-01395-z.
PMID: 37278968
4
Clinical, neuroradiological, and biochemical features of SLC35A2-CDG patients.
Vals MA, Ashikov A, Ilves P, et al.
Journal of inherited metabolic disease 2019; (42(3)):553-564 doi:10.1002/jimd.12055.
PMID: 30746764
5
SLC35A2-related congenital disorder of glycosylation: Defining the phenotype.
Yates TM, Suri M, Desurkar A, et al.
European journal of paediatric neurology : EJPN : official journal of the European Paediatric Neurology Society 2018; (22(6)):1095-1102 doi:10.1016/j.ejpn.2018.08.002.
PMID: 30194038
6
Mosaicism of the UDP-Galactose transporter SLC35A2 in a female causing a congenital disorder of glycosylation: a case report.
Westenfield K, Sarafoglou K, Speltz LC, et al.
BMC medical genetics 2018; (19(1)):100 doi:10.1186/s12881-018-0617-6.
PMID: 29907092
7
A case of de novo splice site variant in SLC35A2 showing developmental delays, spastic paraplegia, and delayed myelination.
Miyamoto S, Nakashima M, Ohashi T, et al.
Molecular genetics & genomic medicine 2019; (7(8)):e814 doi:10.1002/mgg3.814.
PMID: 31231989
8
Frequent SLC35A2 brain mosaicism in mild malformation of cortical development with oligodendroglial hyperplasia in epilepsy (MOGHE).
Bonduelle T, Hartlieb T, Baldassari S, et al.
Acta neuropathologica communications 2021; (9(1)):3 doi:10.1186/s40478-020-01085-3.
PMID: 33407896
9
Brain somatic mutations in SLC35A2 cause intractable epilepsy with aberrant N-glycosylation.
Sim NS, Seo Y, Lim JS, et al.
Neurology. Genetics 2018; (4(6)):e294 doi:10.1212/NXG.0000000000000294.
PMID: 30584598
10
A case of early onset epileptic encephalopathy with de novo mutation in SLC35A2: Clinical features and treatment for epilepsy.
Kimizu T, Takahashi Y, Oboshi T, et al.
Brain & development 2017; (39(3)):256-260 doi:10.1016/j.braindev.2016.09.009.
PMID: 27743886
11
Clinical and biochemical improvement with galactose supplementation in SLC35A2-CDG.
Witters P, Tahata S, Barone R, et al.
Genetics in medicine : official journal of the American College of Medical Genetics 2020; (22(6)):1102-1107 doi:10.1038/s41436-020-0767-8.
PMID: 32103184

This page provides educational information about SLC35A2-CDG and does not replace medical advice. A metabolic geneticist and neurologist can help interpret your child’s testing and plan care.

Guide Contents