Holocarboxylase synthetase deficiency: novel clinical and molecular findings

Clinical, biochemical, and genetic analysis of 28 Chinese patients with holocarboxylase synthetase deficiency

BACKGROUND

This study aimed to describe the clinical, biochemical, and molecular characteristics of Chinese patients with holocarboxylase synthetase (HLCS) deficiency, and to investigate the mutation spectrum of HCLS deficiency as well as their potential correlation with phenotype.

METHODS

A total of 28 patients with HLCS deficiency were enrolled between 2006 and 2021. Clinical and laboratory data were reviewed retrospectively from medical records.

RESULTS

Among the 28 patients, six patients underwent newborn screening, of which only one was missed. Therefore, 23 patients were diagnosed because of disease onset. Among all the patients, 24 showed varying degrees of symptoms such as rash, vomiting, seizures, and drowsiness, while only four cases remained asymptomatic nowadays. The concentration of 3-hydroxyisovalerylcarnitine (C5-OH) in blood and pyruvate, 3-hydroxypropionate, methylcitric acid, 3-hydroxyvaleric acid, 3-methylcrotonylglycine in urine were increased greatly among affected individuals. After prompt supplement of biotin, both the clinical and biochemical symptoms were dramatically resolved and nearly all patients developed normal intelligence and physique on follow-up. DNA sequencing revealed 12 known and 6 novel variants in the HLCS gene of patients. Among them, the variant of c.1522C > T was the most common.

CONCLUSIONS

Our findings expanded the spectrum of phenotypes and genotypes for HLCS deficiency in Chinese populations and suggested that with timely biotin therapy, patients with HLCS deficiency showed low mortality and optimistic prognosis. Newborn screening is crucial for early diagnosis, treatment, and long-term outcomes.

Delayed diagnosis of holocarboxylase synthetase deficiency in three patients with prominent skin findings

Holocarboxylase deficiency (HLCSD) is caused by biallelic pathogenic variants in HLCS and is associated with poor feeding, emesis, lethargy, seizures, life-threatening metabolic acidosis, and hyperammonemia. Skin involvement in HLCSD is typically described as scaly, erythrodermic, seborrhea-like, or ichthyosiform, but there is a paucity of reports. We report three patients, including two siblings, with HLCSD and significant cutaneous manifestations including ichthyosiform dermatitis and a presentation with features of annular pustular psoriasis. In this report, we show that persistent, unexplained rash, even in the absence of other clinical findings, should warrant consideration and potential workup for HLCSD.

Clinical, biochemical, and genetic analysis of a Chinese Han pedigree with holocarboxylase synthetase deficiency: a case report

BACKGROUND

Holocarboxylase synthetase (HLCS) deficiency is a rare inborn disorder of biotin metabolism, which results in defects in several biotin-dependent carboxylases and presents with metabolic ketoacidosis and skin lesions.

CASE PRESENTATION

In this paper, we report a Chinese Han pedigree with HLCS deficiency diagnosed by using next-generation sequencing and validated with Sanger sequencing of the HLCS and BTD genes. The Chinese proband carries the common missense mutation c.1522C > T (p.Arg508Trp) in exon 9 of the HLCS gene, which generates an increased K_m value for biotin. A novel frameshift mutation c.1006_1007delGA (p.Glu336Thrfs*15) in exon 6 of the HLCS gene is predicted to be deleterious through PROVEAN and MutationTaster. A novel heterozygous mutation, c.638_642delAACAC (p.His213Profs*4), in the BTD gene is also identified.

CONCLUSIONS

The Chinese proband carries the reported Arg508Trp variant, the novel 2-bp frameshift mutation c.1006_1007delGA (p.Glu336Thrfs*15), which expands the mutational spectrum of the HLCS gene, and the novel heterozygous mutation c.638_642delAACAC (p.His213Profs*4), which expands the mutational spectrum of the BTD gene. Furthermore, reversible hearing damage is rarely reported in patients with HLCS deficiency, which deserves further discussion.

Case report of holocarboxylase synthetase deficiency (late-onset) in 2 Chinese patients

RATIONALE

Holocarboxylase synthetase (HCLS) deficiency, especially the late-onset type, is a rare disease. Affected patients can present with irreversible metabolic acidosis and may be misdiagnosed with a glucose metabolic disorder. Prompt and correct diagnosis and treatment can reduce mortality to a great extent.

PATIENT CONCERNS

We report 2 Chinese patients who were diagnosed with late-onset HCLS deficiency. The age of onset of the 2 patients was approximately 8 months. The 2 patients had skin lesions, severe profound metabolic acidosis, dyspnea, and hyperglycemia.

DIAGNOSES

The results of urinary and blood organic acid analysis with gas chromatography/mass spectrometry revealed multiple carboxylase deficiency. Maple syrup urine disease and diabetic ketoacidosis could not be excluded. This finding is different from those of hypoglycemic complications reported in previous reports. Human genetic analysis eventually provided a definite diagnosis.

INTERVENTIONS

Prompt oral treatment with biotin dramatically corrected the metabolic imbalances of the 2 patients, and continued oral biotin therapy was essential to the improvement of their prognoses.

OUTCOMES

Their metabolic disorders were corrected within 48 hours. During long-term follow-up, the patients achieved developmental milestones.

LESSONS

Late-onset HCLS deficiency may present with obvious hyperglycemia. Human genetic analysis eventually provided a definite diagnosis. Prompt treatment with biotin is vital to correct metabolic imbalances, and continued therapy is essential to the improving long-term prognoses. Their mutations were p.R508W and c.1088T > A, and these mutations might represent hot-spot genes in Chinese populations with HCLS deficiency. The variants c.1484T > G(p.L495*) and c.835G > T(p.E279x) are likely pathogenic, and more studies are needed to confirm these results.

Guidance for assessment of erythroderma in neonates and infants for the pediatric immunologist

Neonatal and infantile erythroderma (NIE) represents the common clinical phenotype of heterogeneous diseases ranging from benign and transient skin conditions to fatal multiorgan disorders. NIE regularly demands a comprehensive diagnostic workup in a multiprofessional setting, especially if newborns and young infants with the disease develop a failure to thrive and concomitant infectious, neurologic, or metabolic complications. By obtaining a detailed medical history and performing a thorough clinical examination, targeted diagnostic steps can be scheduled for most affected children. If NIE occurs in the early neonatal period, lesional skin biopsy and histology are often indicated. Likewise, if monogenic skin or immunologic diseases are suspected, genetic testing with customized panels of potentially underlying genes is mandatory. Of note, if acute symptoms such as severe infections, metabolic acidosis, or seizures occur, rapid microbiologic and metabolic investigations are warranted to rule out immunodeficiency and inborn errors of metabolism.

Paracentric Inversion of Chromosome 21 Leading to Disruption of the HLCS Gene in a Family with Holocarboxylase Synthetase Deficiency

Holocarboxylase synthetase (HLCS) deficiency is a rare autosomal recessive disorder that presents with multiple life-threatening metabolic derangements including metabolic acidosis, ketosis, and hyperammonemia. A majority of HLCS deficiency patients respond to biotin therapy; however, some patients show only a partial or no response to biotin therapy. Here, we report a neonatal presentation of HLCS deficiency with partial response to biotin therapy. Sequencing of HLCS showed a novel heterozygous mutation in exon 5, c.996G>C (p.Gln332His), which likely abolishes the normal intron 6 splice donor site. Cytogenetic analysis revealed that the defect of the other allele is a paracentric inversion on chromosome 21 that disrupts HLCS. This case illustrates that in addition to facilitating necessary family testing, a molecular diagnosis can optimize management by providing a better explanation of the enzyme's underlying defect. It also emphasizes the potential benefit of a karyotype in cases in which molecular genetic testing fails to provide an explanation.

Antenatal and postnatal radiologic diagnosis of holocarboxylase synthetase deficiency: a systematic review

BACKGROUND

Holocarboxylase synthetase deficiency results in impaired activation of enzymes implicated in glucose, fatty acid and amino acid metabolism. Antenatal imaging and postnatal imaging are useful in making the diagnosis. Untreated holocarboxylase synthetase deficiency is fatal, while antenatal and postnatal biotin supplementation is associated with good clinical outcomes. Although biochemical assays are required for definitive diagnosis, certain radiologic features assist in the diagnosis of holocarboxylase synthetase deficiency.

OBJECTIVE

To review evidence regarding radiologic diagnostic features of holocarboxylase synthetase deficiency in the antenatal and postnatal period.

MATERIALS AND METHODS

A systematic review of all published cases of holocarboxylase synthetase deficiency identified by a search of Pubmed, Scopus and Web of Science.

RESULTS

A total of 75 patients with holocarboxylase synthetase deficiency were identified from the systematic review, which screened 687 manuscripts. Most patients with imaging (19/22, 86%) had abnormal findings, the most common being subependymal cysts, ventriculomegaly and intraventricular hemorrhage.

CONCLUSION

Although the radiologic features of subependymal cysts, ventriculomegaly, intraventricular hemorrhage and intrauterine growth restriction may be found in the setting of other pathologies, these findings should prompt consideration of holocarboxylase synthetase deficiency in at-risk children.

Treatable inborn errors of metabolism causing intellectual disability: a systematic literature review

BACKGROUND

Intellectual disability ('developmental delay' at age<5 years) affects 2.5% of population worldwide. Recommendations to investigate genetic causes of intellectual disability are based on frequencies of single conditions and on the yield of diagnostic methods, rather than availability of causal therapy. Inborn errors of metabolism constitute a subgroup of rare genetic conditions for which an increasing number of treatments has become available. To identify all currently treatable inborn errors of metabolism presenting with predominantly intellectual disability, we performed a systematic literature review.

METHODS

We applied Cochrane Collaboration guidelines in formulation of PICO and definitions, and searched in Pubmed (1960-2011) and relevant (online) textbooks to identify 'all inborn errors of metabolism presenting with intellectual disability as major feature'. We assessed levels of evidence of treatments and characterised the effect of treatments on IQ/development and related outcomes.

RESULTS

We identified a total of 81 'treatable inborn errors of metabolism' presenting with intellectual disability as a major feature, including disorders of amino acids (n=12), cholesterol and bile acid (n=2), creatine (n=3), fatty aldehydes (n=1); glucose homeostasis and transport (n=2); hyperhomocysteinemia (n=7); lysosomes (n=12), metals (n=3), mitochondria (n=2), neurotransmission (n=7); organic acids (n=19), peroxisomes (n=1), pyrimidines (n=2), urea cycle (n=7), and vitamins/co-factors (n=8). 62% (n=50) of all disorders are identified by metabolic screening tests in blood (plasma amino acids, homocysteine) and urine (creatine metabolites, glycosaminoglycans, oligosaccharides, organic acids, pyrimidines). For the remaining disorders (n=31) a 'single test per single disease' approach including primary molecular analysis is required. Therapeutic modalities include: sick-day management, diet, co-factor/vitamin supplements, substrate inhibition, stemcell transplant, gene therapy. Therapeutic effects include improvement and/or stabilisation of psychomotor/cognitive development, behaviour/psychiatric disturbances, seizures, neurologic and systemic manifestations. The levels of available evidence for the various treatments range from Level 1b,c (n=5); Level 2a,b,c (n=14); Level 4 (n=45), Level 4-5 (n=27). In clinical practice more than 60% of treatments with evidence level 4-5 is internationally accepted as 'standard of care'.

CONCLUSION

This literature review generated the evidence to prioritise treatability in the diagnostic evaluation of intellectual disability. Our results were translated into digital information tools for the clinician (www.treatable-id.org), which are part of a diagnostic protocol, currently implemented for evaluation of effectiveness in our institution. Treatments for these disorders are relatively accessible, affordable and with acceptable side-effects. Evidence for the majority of the therapies is limited however; international collaborations, patient registries, and novel trial methodologies are key in turning the tide for rare diseases such as these.