Paediatric or syndromic cardiomyopathy

Gene: FBXL4

Green List (high evidence)

Comment on list classification: There are >90 patients reported with biallelic FBXL4 variants and mitochondrial DNA depletion syndrome 13 (encephalomyopathic type) (MIM #615471). Of these, ~20% of patients are reported with early-onset hypertrophic cardiomyopathy. As there are >15 patients reported with cardiomyopathy, this gene can be promoted to green rating in the next GMS update.

Created: 21 Aug 2025, 2:48 p.m. | Last Modified: 21 Aug 2025, 2:48 p.m.

Panel Version: 7.17

PMID:23993193 (2013) reported three consanguineous families of Arab descent with homozygous FBXL4 loss-of-function mutations causing a lethal neonatal encephalopathy. The proband from family 2 presented in the first month of life with severe hypotonia, encephalopathy, cardiomyopathy, and lactic acidosis, leading to death at age 4 months. Three older siblings presented with a similar fatal, early-onset phenotype, and the proband’s mother has also suffered three miscarriages. Exome sequencing identified nonsense variant in FBXL4 (c.1303C>T/ p.(Arg435Ter)), predicting an earlier truncation of the protein than that observed in family 1.

PMID:23993194 (2013) reported nine patients from seven unrelated families with FBXL4 variants causing early-onset mitochondrial encephalomyopathy. Two of these patients were reported with cardiac phenotypes: Prenatal ultrasound revealing growth retardation and dilated lateral ventricles in patient S7 (of Bahrain Arab descent) and echocardiography revealing left ventricular heart hypertrophy in patient S8 (of European descent). Patient S7 harboured homozygous missense variant (c.1652T>A/ p.(Ile551Asn)), while patient S8 harboured compound heterozygous variants – a nonsense and a missense variant in FBXL4 gene (c.614T>C; c.106A>T/ p.(Ile205Thr); p.(Arg36Ter].

PMID:25868664 (2015) reported 21 individuals from 19 different families of various ethnic backgrounds with biallelic FBXL4 variants and early-onset encephalopathic mitochondrial DNA depletion syndrome, of which three cases were previously reported in PMID:23993194 and one case was reported in PMID:23993193. Cardiac disease was observed at first presentation in seven individuals and evolved in another patient during the course and these patients included one from PMID:23993194. Cardiomyopathy (non-progressive or hypertrophic) was reported in four of these patients, while one other patient was reported with Borderline left-ventricular hypertrophy and hyperdynamic left ventricular function.

PMID:26404457 (2016) reported a female neonate born to a French-Canadian mother with severe multisystem disease including lactic acidosis, cystic white matter lesions, cardiomyopathy, arrhythmias, and immunodeficiency. This patient was identified with homozygous frameshift variant in FBXL4 gene (c.1641_1642delTG; c.141del/ p.(Cys547Ter); p.(Asn48MetfsTer4)).

PMID:28940506 (2017) reported 37 unreported individuals and 11 previously unreported pathogenic variants in addition to review of 36 FBXL4 variants from 50 affected individuals with a total of 87 patients and 47 variants. Hypertrophic cardiomyopathy, congenital heart disease and arrhythmia were reported in 20% (15/74), 19% (14/74) and 12% (9/78) patients respectively.

PMID:39472908 (2024) reported paediatric and adult probands with diverse cardiomyopathies from the 100,000 genomes project, of which one patient was identified with compound heterozygous variants in FBXL4 variants (c.1641_1642del/ p.Cys547Ter).

There is also functional evidence available from mice model, where transfection of FBXL4 rescued the cardiac geometry and the mitochondrial integrity with altered mitochondrial dynamics in the adult mice model of the heart failure with preserved ejection fraction (PMID: 38359748).
Sources: Literature

Created: 21 Aug 2025, 2:41 p.m. | Last Modified: 25 Aug 2025, 5:51 p.m.

Panel Version: 7.17

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
Mitochondrial DNA depletion syndrome 13 (encephalomyopathic type), OMIM:615471

Publications

• 23993193
• 23993194
• 25868664
• 26404457
• 28940506
• 38359748
• 39472908