HIDEA syndrome (MIM: #618493) is a rare autosomal recessive disorder characterized by hypotonia, hypoventilation, intellectual disability, dysautonomia, epilepsy, and eye anomalies. We present the case of a Turkish female with developmental and epileptic encephalopathy, highlighting a novel compound heterozygous variation in the P4HTM gene. A 6-year and 11-month-old girl with early infantile epileptic encephalopathy and abnormal eye movements since the neonatal period has been presented to our clinic. Despite severe developmental delays and a happy demeanor, she showed significant hypotonia and autistic behaviors. Genetic testing revealed a novel heterozygous splice-site variant (c.436+1G>T) in intron 2 and a previously reported missense variant (c.934G>A; p.E312 K) in exon 6 of the P4HTM gene. Imaging showed cortical atrophy and thin corpus callosum, but no dystonia was observed. The patient's phenotype aligns with most reported cases of HIDEA syndrome, yet developmental epileptic encephalopathy had not been documented previously in such patients, emphasizing the uniqueness of this case. This case is the first to associate P4HTM gene variants with epileptic encephalopathy, expanding the phenotypic spectrum of HIDEA syndrome. It underscores the importance of genetic testing and reanalysis in undiagnosed developmental and epileptic encephalopathies. The novel genetic variations identified in this study underscore the necessity for continuous genetic exploration and personalized clinical management to improve outcomes for patients with this rare but impactful syndrome. Finally, the association between developmental epileptic encephalopathy, the patient's clinical presentation, and EEG findings suggests a compelling link to the P4HTM gene.

The P4HTM gene encodes a transmembrane prolyl 4-hydroxylase, which is responsible for the degradation of hypoxia-inducible transcription factors (HIF) under normoxia. Clinically, biallelic P4HTM variants have been identified in patients with hypotonia, hypoventilation, intellectual disabilities, dysautonomia, epilepsy, and eye abnormalities (HIDEA syndrome). Seizure was one of the most prominent symptoms. However, the clinical features of patients with epilepsy associated with P4HTM variants remain unclear. In this report, we describe a one-month-old infant with HIDEA syndrome caused by compound heterozygous P4HTM variants (c.300dupG/p.Gly103Argfs*22 and c.488C > T/p.Ala163Val). The infant presented with clonic seizures of focal onset that responded well to valproate, but with profound intellectual disability and global developmental delay at the last follow-up at 3 years old. A review of the existing literature indicates that seizures in this population typically begin early in infancy, manifest in multiple types, and are relatively well controlled. Epilepsy seemed unrelated to developmental outcomes or disease progression. Valproate, which has HIF-1α inhibiting properties, may be a promising treatment avenue for this population.

Autism spectrum disorder is a neurodevelopmental condition that involves limitations in social communication and various stereotypical repetitive behaviors. Genetic and environmental factors both play a role in the etiology. Numerous genetic syndromes accompanying autism spectrum disorders have been reported. Hypoventilation, hypotonia, intellectual disability, epilepsy, eye abnormality (HIDEA) syndrome is a rare genetic condition consisting of a combination of features such as hypoventilation, hypotonia, intellectual disability, eye abnormalities, and epilepsy. Very few cases of HIDEA syndrome have been reported in the literature to date. To the best of our knowledge, no cases of comorbid autism spectrum disorder and HIDEA syndrome have previously been reported. This report describes two brothers with a pathogenic P4HTM gene variant and autism spectrum disorder. One was diagnosed with HIDEA syndrome, while the other was a healthy carrier.

Transmembrane prolyl 4-hydroxylase (P4H-TM) is an enigmatic enzyme whose cellular function and primary substrate remain to be identified. Its loss-of-function mutations cause a severe neurological HIDEA syndrome with hypotonia, intellectual disability, dysautonomia and hypoventilation. Previously, P4H-TM deficiency in mice was associated with reduced atherogenesis and lower serum triglyceride levels. Here, we characterized the glucose and lipid metabolism of P4h-tm-/- mice in physiological and tissue analyses. P4h-tm-/- mice showed variations in 24-h oscillations of energy expenditure, VO2 and VCO2 and locomotor activity compared to wild-type (WT) mice. Their rearing activity was reduced, and they showed significant muscle weakness and compromised coordination. Sedated P4h-tm-/- mice had better glucose tolerance, lower fasting insulin levels, higher fasting lactate levels and lower fasting free fatty acid levels compared to WT. These alterations were not present in conscious P4h-tm-/- mice. Fasted P4h-tm-/- mice presented with faster hepatic glycogenolysis. The respiratory rate of conscious P4h-tm-/- mice was significantly lower compared to the WT, the decrease being further exacerbated by sedation and associated with acidosis and a reduced ventilatory response to both hypoxia and hypercapnia. P4H-TM deficiency in mice is associated with alterations in whole-body energy metabolism, day-night rhythm of activity, glucose homeostasis and neuromuscular and respiratory functions. Although the underlying mechanism(s) are not yet fully understood, the phenotype appears to have neurological origins, controlled by brain and central nervous system circuits. The phenotype of P4h-tm-/- mice recapitulates some of the symptoms of HIDEA patients, making this mouse model a valuable tool to study and develop tailored therapies.

Context: ROHHAD syndrome presents a significant resemblance to HIDEA syndrome. The latter is caused by biallelic loss-of-function variants in the P4HTM gene and encompasses hypotonia, intellectual disabilities, eye abnormalities, hypoventilation, and dysautonomia. We report the first patient identified with HIDEA syndrome from our ROHHAD cohort. Clinical case: Our patient was a 21-month-old girl who had a history of severe respiratory infections requiring intensive care, hypotonia, abnormal eye movements, and rapid weight gain. Polysomnography identified severe central hypoventilation. During her follow-up, a significant psychomotor delay and the absence of language were gradually observed. The prolactin levels were initially increased. Hypothermia was reported at 4 years. Exome sequencing identified a new homozygous truncating P4HTM variant. Discussion: Our patient met the diagnosis criteria for ROHHAD, which included rapid weight gain, central hypoventilation appearing after 1.5 years of age, hyperprolactinemia suggesting hypothalamic dysfunction, and autonomic dysfunction manifesting as strabismus and hypothermia. However, she also presented with severe neurodevelopmental delay, which is not a classic feature of ROHHAD syndrome. HIDEA syndrome presents similarities with ROHHAD, including hypoventilation, obesity, and dysautonomia. To date, only 14% of endocrinological disturbances have been reported in HIDEA patients. Better delineation of both syndromes is required to investigate the eventual involvement of P4HTM, a regulator of calcium dynamics and gliotransmission, in ROHHAD patients. Conclusion: In the case of clinical evidence of ROHHAD in a child with abnormal neurological development or eye abnormalities, we suggest that the P4HTM gene be systematically interrogated in addition to the analysis of the PHOX2B gene. A better delineation of the natural history of HIDEA is required to allow further comparisons between features of HIDEA and ROHHAD. The clinical similarities could potentially orient some molecular hypotheses in the field of ROHHAD research.