Siblings of hyaline fibromatosis syndrome with accumulation of sulfatide and <scp> G _M3 </scp> ganglioside in addition to ceramide

Hyaline fibromatosis syndrome (HFS) is characterized by the accumulation of hyaline material in body tissues, manifesting multiple subcutaneous nodules, gingival hypertrophy, joint stiffness and deformities, and villous atrophy, resulting in severe diarrhea.1 We present a case series of siblings diagnosed with HFS, who exhibited an accumulation of several types of sphingolipids. This finding has not been previously reported in the extant literature. The patients were the second and fourth children (a boy and a girl) of unrelated Japanese parents. The first and third siblings of the subject were healthy males. Both patients were born at term via vaginal delivery and were appropriate-for-dates neonates. In a previous report, the elder brother was documented to have a variant form of Farber disease (FD).2 The subject presented with a shrill voice, joint ankylosis, and bilateral foot deformity at birth. Subsequently, recurrent subcutaneous nodules in the perianal region, intractable diarrhea, and cholelithiasis were observed. The subject expired from bronchopneumonia at 2 years and 1 month of age. His younger sister exhibited limited hip abduction at 2 days of age and later developed multiple joint contractures, intractable diarrhea, and congestive heart failure, eventually dying of circulatory failure at 3 years of age. A substantial quantity of material was identified through pathological observations, which was found to be positive for PAS and resistant to diastase digestion. This material was detected in the cytoplasm of subcutaneous nodules and in the intercellular space of subcutaneous and periarticular fatty tissue.3 This histochemical finding was consistent with the accumulation of hyaline components. Acid ceramidase activity was not reduced in either patient. The lipid analysis of the elder brother's autopsy tissues4, 5 and the younger sister's cultured fibroblasts6 revealed an accumulation of ceramide, sulfatide, and GM3 ganglioside (Table 1). In the younger sister, no pathogenic variants were detected in either the ASAH1 gene, which is the causative gene for FD, or the PSAP gene, which encodes the precursor of sphingolipid activator protein (prosaposin). Trio-based whole-genome sequencing and whole-exome sequencing (WES) was performed in the elder brother and the younger sister, respectively. The Human All Exon V6 kit (Agilent Technologies, CA, USA) and a NovaSeq were used for library enrichment in WES and sequencing of 150-bp paired-end, respectively. Sequence reads were aligned to GRCh38 and annotated using CompStor NOVOS and CompStor Insight (OmniTier, CA, USA). Variants were narrowed down based on the allele frequency and assumed modes of inheritance. We identified a homozygous frameshift variant in ANTXR2, [NM_058172.6:c.1073dup,p.(Ala359CysfsTer13)], in both affected siblings. Both parents were carriers. This variant was registered in ClinVar as pathogenic for several cases of hyaline fibromatosis syndrome (Variation ID:2604). The MutationTaster and FATHMMMKL in silico prediction programs predicted that this variant is deleterious. According to the guidelines of the American College of Medical Genetics and Genomics (ACMG), the variant was classified as pathogenic (PVS1, PS1, PM2, PP3). We made a definitive diagnosis of the affected siblings as lethal-grade HFS. HFS is an autosomal recessive disorder that is caused by ANTXR2 mutations. As of December 10, 2024, a total of 61 genetically confirmed patients and 80 associated variants have been documented in the Human Gene Mutation Database. The clinical diagnosis of FD in these subjects was revised to HFS based on genetic testing. The presence of phenotypic overlap between HFS and FD has been acknowledged. Cozma et al. reported on five patients initially suspected of FD but genetically diagnosed with HFS.1 Furthermore, a high degree of metabolomic similarity was demonstrated, including ceramide accumulation, between HFS and FD. However, to the best of our knowledge, there have been no reports of the accumulation of other sphingolipids, such as sulfatide and GM3 ganglioside, in HFS. The primary pathological mechanism of HFS is thought to involve impaired transport of extracellular matrix components, including type VI collagen, into lysosomes. A subsequent investigation must be conducted to determine the impact of the ANTXR2 loss-of-function on sphingolipids transport to lysosomes and lysosomal dysfunction. This case report makes a significant contribution to the field of HFS pathophysiology. T.F. drafted the initial manuscript. H.A. provided the valuable information of ANTXR2. K.I. conducted an investigation on acid ceramidase. J.M. and K.K. conducted an investigation on prosaposin. K.Y. and T.K. provided molecular genetic data. All authors read and approved the final manuscript. Written informed consent was obtained from the parents for the genetic analysis and for publication of this report. This work was supported by grants for the Initiative on Rare and Undiagnosed Diseases (IRUD) (15gk0110012h0101, 23ek0109549s2503, 25ek0109760s0201) from the Japanese Agency for Medical Research and Development (AMED). The authors declare no conflict of interest. Research data are not shared.