Ataxia and cerebellar anomalies - narrow panel

Gene: SLC25A46

Green List (high evidence)

The rating of this gene has been updated to green following NHS Genomic Medicine Service approval.

Created: 11 Oct 2023, 10:01 a.m. | Last Modified: 11 Oct 2023, 10:01 a.m.

Panel Version: 4.37

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Green List (high evidence)

Comment on classification of this gene:

The rating for this gene should be GREEN, as this gene has been identified to be implicated in cerebellar ataxia (MONDO:0000437) from biallelic loss-of-function variants from at least 8 unrelated individuals/ families and in pontocerebellar hypoplasia, type 1E (MIM# 619303) from biallelic loss-of-function variants from at least 6 unrelated individuals/ families. These cases were from multiple ethnicities and were supported by results from animal models.

In addition, this gene has also been identified to be implicated in cerebellar hypoplasia from monoallelic loss-of-function variants from a family of three siblings. As we currently do not have three unrelated cases for monoallelic inheritance, this gene is assigned only to biallelic MOI.

Cerebellar ataxia:

Two brothers of consanguineous parents of Pakistani origin were identified with homozygous variant in SLC25A46 (c.413T>G./ p.Leu138Arg). The younger of the two brothers was presented with balancing difficulties in infancy, prominent myoclonus, cerebellar ataxia, profound visual loss, rod cone dysfunction, exotropia, difficulty initiating saccades, mild spasticity, and axonal sensory-motor neuropathy leading to trophic changes. He also developed scoliosis and had cerebellar atrophy as well as T2/FLAIR (fluid-attenuated inversion recovery) hyperintensities and cavitations in the cerebellum. The older brother was mildly affected with similar clinical manifestations (PMID:27430653).

A study on patients from three North African families (Two siblings from Tunisian family and two unrelated Algerians) showed that the previously reported variant c.1018C>T/ p.Arg340Cys (displayed in Tunisian siblings and one Algerian patient) was associated with childhood onset, optic atrophy, gait and speech difficulties and wasting of the lower limbs, and the Algerian patient with the novel variant p.Trp160Ser did not present with optic atrophy, while all patients were presented with ataxia (PMID:28558379). Similarly, ataxia was also observed in Sardinian (p.Arg340Cys) and Palestinian (c.1005A>T/ p.Glu335Asp) patients from Abrams et al, 2015 (PMID:26168012).

A six year old boy with homozygous missense variant c.770G>A (p.Arg257Gln) was reported with optic atrophy, peripheral neuropathy, ataxia, but not cerebellar atrophy (PMID:30178502). p.Arg340Cys variant was also identified in the eleven year old male patient and in other unaffected family members, and the patient was presented with insidious onset, progressive vision loss and swaying since 8 years of age. The other presentations were gait ataxia, torticollis to left and tilt to right, head tremors and myoclonus (PMID:33816684).

Cerebellar hypoplasia:

Four infants from two different families with homozygous variants (family 1: c.1022T>C/ p.Leu341Pro; family 2: deletion of exon 1) were reported to have died soon after birth with a profound neurodevelopmental disorder associated with congenital pontocerebellar hypoplasia (PMID:27543974). The phenotypes are similar to a female infant from the United States with pontocerebellar atrophy who died at age 15 weeks. This infant reported by Abram et al (2015) exhibited compound heterozygous variants (c.882_885dupTTAC/ p.Asn296fs*297 & c.998C>T/ p.Pro333Leu) (PMID:26168012).

Four infants from two unrelated families of German and Italian descent were reported with PCH1E. All died in the first days or weeks of life. The German infants were identified with homozygous variant c.736A>T (p.Arg246Ter) and the Italian infants were identified with compound heterozygous variants c.42C>G (p.Tyr14Ter) & 462+ 1G>A (PMID:28653766).

Two siblings with bi-allelic compound heterozygous variants (a splicing variant - c.385-1G > A and a deletion) had a fulminant neonatal course. The mother of these siblings exhibited a heterozygous c.385-1G > A allele and the father had an 80-kb deletion spanning SLC25A46 and TMEM232 genes. Pontocerebellar hypoplasia was reported by postmortem brain CT imaging in one of the siblings (PMID:35012485).

Barth (1993) reported a Dutch family in which three siblings died within the first day of life due to lack of spontaneous respiration and profound muscle weakness (PMID:8147499). Although these infants displayed similarities to the clinical indications described by Wan et al, 2016 (PMID:27543974), they were identified to possess heterozygous variant leading to a premature stop codon (c.691C>T/ p.Arg231Ter) in exon 8 of the SLC25A46 gene (PMID:28637197).

Functional studies:

Mouse models with loss-of-function mutation or lacking SLC25A46 gene manifest the main clinical features identified in patients such as ataxia, optic atrophy, cerebellar hypoplasia and peripheral neuropathy which were completely rescued by expression of human ortholog (PMID:28376086; PMID:28934388). The results suggest that the gene loss causes degeneration in neurons by affecting mitochondrial dynamics and energy production.

Loss-of-function in cultured cells and in zebrafish also led to increased mitochondrial connectivity, while severely affecting the development and maintenance of neurons in the zebrafish (PMID:26168012).

SLC25A46 has been associated with neuropathy, hereditary motor and sensory, type VIB in OMIM and Gene2Phenotype and with pontocerebellar hypoplasia, type 1E in OMIM.

Created: 11 Dec 2022, 8:30 a.m. | Last Modified: 11 Dec 2022, 9:31 a.m.

Panel Version: 3.11

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
Cerebellar ataxia, MONDO:0000437; Pontocerebellar hypoplasia, type 1E, MIM# 619303, MONDO:0030260; Neuropathy, hereditary motor and sensory, type VIB, MIM# 616505

Publications

• 26168012
• 27430653
• 28376086
• 28558379
• 28934388
• 30178502
• 33816684

Green List (high evidence)

Hereditary motor and sensory neuropathy type VIB is an autosomal recessive complex progressive neurologic disorder characterized mainly by early-onset optic atrophy resulting in progressive visual loss and peripheral axonal sensorimotor neuropathy with highly variable age at onset and severity. Affected individuals also have cerebellar or pontocerebellar atrophy on brain imaging, and they show abnormal movements, such as ataxia, dysmetria, and myoclonus.

At least 10 unrelated families reported, supportive functional data.
Sources: Expert list

Created: 13 Sep 2020, 6:18 a.m.

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
Neuropathy, hereditary motor and sensory, type VIB, MIM# 616505

Publications

• 30178502
• 26168012
• 27543974
• 27430653
• 27390132
• 28934388
• 28558379

Variants in this GENE are reported as part of current diagnostic practice