SPATCCM explained

Spastic tetraplegia, thin corpus callosum, and progressive microcephaly (often referred to by its acronym SPATCCM) is a rare autosomal recessive disease caused by mutations in the SLC1A4 gene encoding the ASCT1 protein. The ASCT1 protein is primarily found in astrocytes in the brain where its main role is to import L-serine, a non-essential amino acid.

Symptoms and diagnosis

Clinically, patients present with microcephaly and significant developmental delay. While some patients may be able to walk, others may not due to spasticity of limbs and hypotonic muscle tone, with progressive degeneration over time. Patients may also present with seizures, ranging from single febrile seizure to intractable epilepsy. Following brain MRI, patients may present with thin corpus callosum, decreased myelination, and/or brain atrophy.^[1] These symptoms mimic that of other L-serine deficiencies^[2]

Diagnosis of SPATCCM generally relies on whole exome sequencing and the identification of a mutation in the SLC1A4 gene, while also lacking any other potential pathogenic mutations.

Cause

There have so far been several identified mutations in the SLC1A4 gene that are linked to SPATCCM, including several frameshift (L314Hfs*42, N324Tfs*29^[3]), nonsense (Y191*,^[4] W453*^[5]), duplication (L86_M88dup^[6]), and missense mutations (E256K,^[7] R457W, G374R,^[8] G381R,^[9] S181F). These mutations interrupt the transport of serine from astrocytes to neurones, and across the blood brain barrier^[10]

L-serine is important in brain development as it is a vital component in protein synthesis, as well as being the precursor to several essential compounds, including phosphatidylserine, sphingomyelin, glycine, and D-serine.

Epidemiology

Although most of the reported cases of SPATCCM are in people of Ashkenazi Jewish ancestry, it has also been reported in Irish, Hispanic, South Asian, Italian, Czech, Palestinian, and Pakistani ethnicities.

SPATCCM has a carrier frequency of 0.7% in the Ashkenazi Jewish population.

Treatment

SPATCCM is an incurable genetic disease, however patients are often treated with anti-epileptics including vigabatrin, topiramate or clobazam, to reduce associated seizures. Supplementation of L-serine has also been proposed as a treatment. and has shown effective in a knock-in mouse model of the disease if administered prenatal and early postnatal.

Notes and References

1. Damseh N, Simonin A, Jalas C, Picoraro JA, Shaag A, Cho MT, Yaacov B, Neidich J, Al-Ashhab M, Juusola J, Bale S, Telegrafi A, Retterer K, Pappas JG, Moran E, Cappell J, Anyane Yeboa K, Abu-Libdeh B, Hediger MA, Chung WK, Elpeleg O, Edvardson S . Mutations in SLC1A4, encoding the brain serine transporter, are associated with developmental delay, microcephaly and hypomyelination . Journal of Medical Genetics . 52 . 8 . 541–547 . August 2015 . 26041762 . 10.1136/jmedgenet-2015-103104 .
2. El-Hattab AW . Serine biosynthesis and transport defects . Molecular Genetics and Metabolism . 118 . 3 . 153–159 . July 2016 . 27161889 . 10.1016/j.ymgme.2016.04.010 .
3. Mohamed FE, Ghattas MA, Almansoori TM, Tabouni M, Baydoun I, Kizhakkedath P, John A, Alblooshi H, Shaukat Q, Al-Jasmi F . Novel compound heterozygous variants (c.971delA/c.542C > T) in SLC1A4 causes spastic tetraplegia, thin corpus callosum, and progressive microcephaly: a case report and mutational analysis . Frontiers in Pediatrics . 11 . 1183574 . 2023-07-12 . 37502193 . 10369183 . 10.3389/fped.2023.1183574 . free .
4. Abdelrahman HA, Al-Shamsi A, John A, Ali BR, Al-Gazali L . A Novel SLC1A4 Mutation (p.Y191*) Causes Spastic Tetraplegia, Thin Corpus Callosum, and Progressive Microcephaly (SPATCCM) With Seizure Disorder . Child Neurology Open . 6 . 2329048X19880647 . 2019-01-01 . 31763347 . 6852354 . 10.1177/2329048X19880647 .
5. Conroy J, Allen NM, Gorman K, O'Halloran E, Shahwan A, Lynch B, Lynch SA, Ennis S, King MD . Novel European SLC1A4 variant: infantile spasms and population ancestry analysis . Journal of Human Genetics . 61 . 8 . 761–764 . August 2016 . 27193218 . 10.1038/jhg.2016.44 .
6. Pujol-Giménez J, Mirzaa G, Blue EE, Albano G, Miller DE, Allworth A, Bennett JT, Byers PH, Chanprasert S, Chen J, Doherty D, Folta AB, Gillentine MA, Glass I, Hing A, Horike-Pyne M, Leppig KA, Parhin A, Ranchalis J, Raskind WH, Rosenthal EA, Schwarze U, Sheppeard S, Strohbehn S, Sybert VP, Timms A, Wener M, Bamshad MJ, Hisama FM, Jarvik GP, Dipple KM, Hediger MA, Stergachis AB . Dominant-negative variant in SLC1A4 causes an autosomal dominant epilepsy syndrome . Annals of Clinical and Translational Neurology . 10 . 6 . 1046–1053 . June 2023 . 37194416 . 10270265 . 10.1002/acn3.51786 .
7. Srour M, Hamdan FF, Gan-Or Z, Labuda D, Nassif C, Oskoui M, Gana-Weisz M, Orr-Urtreger A, Rouleau GA, Michaud JL . A homozygous mutation in SLC1A4 in siblings with severe intellectual disability and microcephaly . Clinical Genetics . 88 . 1 . e1–e4 . July 2015 . 25930971 . 10.1111/cge.12605 .
8. Sarigecili E, Bulut FD, Anlas O . A rare cause of microcephaly, thin corpus callosum and refractory epilepsy due to a novel SLC1A4 gene mutation . Clinical Neurology and Neurosurgery . 218 . 107283 . July 2022 . 35605507 . 10.1016/j.clineuro.2022.107283 .
9. Pironti E, Salpietro V, Cucinotta F, Granata F, Mormina E, Efthymiou S, Scuderi C, Gagliano A, Houlden H, Di Rosa G . A novel SLC1A4 homozygous mutation causing congenital microcephaly, epileptic encephalopathy and spastic tetraparesis: a video-EEG and tractography - case study . Journal of Neurogenetics . 32 . 4 . 316–321 . December 2018 . 29989513 . 10.1080/01677063.2018.1476510 .
10. Odeh M, Sajrawi C, Majcher A, Zubedat S, Shaulov L, Radzishevsky A, Mizrahi L, Chung WK, Avital A, Hornemann T, Liebl DJ, Radzishevsky I, Wolosker H . A new type of blood-brain barrier aminoacidopathy underlies metabolic microcephaly associated with SLC1A4 mutations . Brain . April 2024 . 38662784 . 10.1093/brain/awae134 .