Callosome
Gene: HYLS1
ClinGen classification: Moderate
Absent corpus callosum seen as brain anomaly
HYLS1 was first reported in relation to autosomal recessive hydrolethalus in 2005 (Mee et al., PMID: 15843405). This is often a fatal fetal condition that results in stillbirth, or death shortly after birth. Prenatal features have been identified as early as the first trimester, and phenotypes include FGR (fetal growth restriction), brain anomalies, skeletal features (like femoral bowing and polydactyly/syndactyly), congenital heart disease, and genital anomalies. The most frequent features of this condition in probands with the founder missense mutation include hydrocephalus, small mandible, polydactyly, congenital heart defects, and respiratory anomalies. Affected probands compound heterozygous for the recurrent missense variant and another missense or nonsense variant have also been reported. Three variants (missense, nonsense) that have been reported in over 40 probands in 3 publications (PMIDs: 15843405, 18648327, 34212369) are included in this curation. The mechanism of pathogenicity appears to be loss-of-function. There were also two homozygous stop loss variants reported in 2 probands from 2 publications (PMID: 26830932, 36580738), but these were not scored because the phenotype does not fully match that of the other cases and and their disease mechanism similarity cannot be confirmed. This gene-disease relationship is also supported by experimental evidence (mouse model, drosophila model, expression-level data, interaction evidence, cell culture evidence, functional alteration evidence; PMIDs: 15843405, 19656802, 32509774, 40009365). Homozygous mutant mice exhibit perinatal lethality, brain anomaly, polydactyly, and kidney complications. The drosophila model showed ciliary dysfunction and atypical spermatogenesis in mutants. The gene is widely expressed in mice, including in specific brain regions such as the medulla. HYLS1 interacts with SAS-4 (CENPJ), which is definitively associated with autosomal recessive microcephaly 6 with/without short stature. Other experimental evidence indicates the key role of HYLS1 in centriole stability and ciliogenesis. In summary, there is moderate evidence to support this gene-disease relationship. While more evidence is needed to establish this relationship definitively, no convincing contradictory evidence has emerged. This classification was approved by the ClinGen Prenatal GCEP on the meeting date 8/06/2025 (SOP Version 11).Created: 14 Aug 2025, 11:28 p.m. | Last Modified: 14 Aug 2025, 11:28 p.m.
Panel Version: 0.547
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Hydrolethalus syndrome MONDO:0006037
A recurring homozygous missense variant p.Asp211Gly has been identified in at least 64 cases of hydrolethalus syndrome, described as a Finnish founder mutation (PMID: 15843405, PMID: 18648327). Functional studies in human and patient cells have shown mislocalisation of the protein to the nucleus (PMID: 15843405, PMID: 19400947). Functional studies in c. elegans showed that this variant impaired ciliogenesis (PMID: 19656802). Functional studies in drosophila showed that deletion of HYLS1 led to cilia dysfunction (PMID: 32509774). 2 homozygous living siblings (stop-loss, extension variant p.Ter300TyrextTer11) both diagnosed with Joubert syndrome. Patients had molar tooth signs and dysplasia of cerebellar vermis (PMID: 26830932). No other variants have been reported as pathogenic in this gene. Amber rating on this panel as only the hydrolethalus phenotype has been reported in association with absent corpus callosum in the setting of very severe brain malformation.Created: 7 Aug 2020, 12:06 a.m. | Last Modified: 7 Aug 2020, 12:06 a.m.
Panel Version: 0.179
Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal
Phenotypes
Hydrolethalus syndrome (MIM#236680)
Publications
Gene: hyls1 has been classified as Green List (High Evidence).
Gene: hyls1 has been classified as Amber List (Moderate Evidence).
Phenotypes for gene: HYLS1 were changed from to Hydrolethalus syndrome (MIM#236680)
Publications for gene: HYLS1 were set to
Mode of inheritance for gene: HYLS1 was changed from Unknown to BIALLELIC, autosomal or pseudoautosomal
Gene: hyls1 has been classified as Amber List (Moderate Evidence).
gene: HYLS1 was added gene: HYLS1 was added to Corpus callosum agenesis, Callosome_VCGS. Sources: Expert Review Green,Victorian Clinical Genetics Services Mode of inheritance for gene: HYLS1 was set to Unknown