Clinical, biochemical and genetic spectrum of 70 patients with ACAD9 deficiency: is riboflavin supplementation effective?

BACKGROUND: Mitochondrial acyl-CoA dehydrogenase family member 9 (ACAD9) is essential for the assembly of mitochondrial respiratory chain complex I. Disease causing biallelic variants in ACAD9 have been reported in individuals presenting with lactic acidosis and cardiomyopathy. RESULTS: We describe the genetic, clinical and biochemical findings in a cohort of 70 patients, of whom 29 previously unpublished. We found 34 known and 18 previously unreported variants in ACAD9. No patients harbored biallelic loss of function mutations, indicating that this combination is unlikely to be compatible with life. Causal pathogenic variants were distributed throughout the entire gene, and there was no obvious genotype-phenotype correlation. Most of the patients presented in the first year of life. For this subgroup the survival was poor (50% not surviving the first 2 years) comparing to patients with a later presentation (more than 90% surviving 10 years). The most common clinical findings were cardiomyopathy (85%), muscular weakness (75%) and exercise intolerance (72%). Interestingly, severe intellectual deficits were only reported in one patient and severe developmental delays in four patients. More than 70% of the patients were able to perform the same activities of daily living when compared to peers. CONCLUSIONS: Our data show that riboflavin treatment improves complex I activity in the majority of patient-derived fibroblasts tested. This effect was also reported for most of the treated patients and is mirrored in the survival data. In the patient group with disease-onset below 1 year of age, we observed a statistically-significant better survival for patients treated with riboflavin.

Biallelic mutations in CYP24A1 or SLC34A1 as a cause of infantile idiopathic hypercalcemia (IIH) with vitamin D hypersensitivity: molecular study of 11 historical IIH cases.

Idiopathic infantile hypercalcemia (IIH) is a mineral metabolism disorder characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis. The periodical increase in incidence of IIH, which occurred in the twentieth century in the United Kingdom, Poland, and West Germany, turned out to be a side effect of rickets over-prophylaxis. It was recently discovered that the condition is linked to two genes, CYP24A1 and SLC34A1. The aim of the study was to search for pathogenic variants of the genes in adult persons who were shortlisted in infancy as IIH caused by "hypersensitivity to vit. D". All persons were found to carry mutations in CYP24A1 or SLC34A1, nine and two persons respectively. The changes were biallelic, with one exception. Incidence of IIH in Polish population estimated on the basis of allele frequency of recurrent p.R396W CYP24A1 variant, is 1:32,465 births. It indicates that at least a thousand homozygotes and compound heterozygotes with risk of IIH live in the country. Differences in mechanism of developing hypercalcemia indicate that its prevention may vary in both IIH defects. Theoretically, vit. D restriction is a first indication for CYP24A1 defect (which disturbs 1,25(OH)2D degradation) and phosphate supplementation for SLC34A1 defect (which impairs renal phosphate transport). In conclusion, we suggest that molecular testing for CYP24A1 and SLC34A1 mutations should be performed in each case of idiopathic hypercalcemia/hypercalciuria, both in children and adults, to determine the proper way for acute treatment and complications prevention.

NAXE Mutations Disrupt the Cellular NAD(P)HX Repair System and Cause a Lethal Neurometabolic Disorder of Early Childhood.

To safeguard the cell from the accumulation of potentially harmful metabolic intermediates, specific repair mechanisms have evolved. APOA1BP, now renamed NAXE, encodes an epimerase essential in the cellular metabolite repair for NADHX and NADPHX. The enzyme catalyzes the epimerization of NAD(P)HX, thereby avoiding the accumulation of toxic metabolites. The clinical importance of the NAD(P)HX repair system has been unknown. Exome sequencing revealed pathogenic biallelic mutations in NAXE in children from four families with (sub-) acute-onset ataxia, cerebellar edema, spinal myelopathy, and skin lesions. Lactate was elevated in cerebrospinal fluid of all affected individuals. Disease onset was during the second year of life and clinical signs as well as episodes of deterioration were triggered by febrile infections. Disease course was rapidly progressive, leading to coma, global brain atrophy, and finally to death in all affected individuals. NAXE levels were undetectable in fibroblasts from affected individuals of two families. In these fibroblasts we measured highly elevated concentrations of the toxic metabolite cyclic-NADHX, confirming a deficiency of the mitochondrial NAD(P)HX repair system. Finally, NAD or nicotinic acid (vitamin B3) supplementation might have therapeutic implications for this fatal disorder.

Autosomal-Recessive Mutations in SLC34A1 Encoding Sodium-Phosphate Cotransporter 2A Cause Idiopathic Infantile Hypercalcemia.

Idiopathic infantile hypercalcemia (IIH) is characterized by severe hypercalcemia with failure to thrive, vomiting, dehydration, and nephrocalcinosis. Recently, mutations in the vitamin D catabolizing enzyme 25-hydroxyvitamin D3-24-hydroxylase (CYP24A1) were described that lead to increased sensitivity to vitamin D due to accumulation of the active metabolite 1,25-(OH)2D3. In a subgroup of patients who presented in early infancy with renal phosphate wasting and symptomatic hypercalcemia, mutations in CYP24A1 were excluded. Four patients from families with parental consanguinity were subjected to homozygosity mapping that identified a second IIH gene locus on chromosome 5q35 with a maximum logarithm of odds (LOD) score of 6.79. The sequence analysis of the most promising candidate gene, SLC34A1 encoding renal sodium-phosphate cotransporter 2A (NaPi-IIa), revealed autosomal-recessive mutations in the four index cases and in 12 patients with sporadic IIH. Functional studies of mutant NaPi-IIa in Xenopus oocytes and opossum kidney (OK) cells demonstrated disturbed trafficking to the plasma membrane and loss of phosphate transport activity. Analysis of calcium and phosphate metabolism in Slc34a1-knockout mice highlighted the effect of phosphate depletion and fibroblast growth factor-23 suppression on the development of the IIH phenotype. The human and mice data together demonstrate that primary renal phosphate wasting caused by defective NaPi-IIa function induces inappropriate production of 1,25-(OH)2D3 with subsequent symptomatic hypercalcemia. Clinical and laboratory findings persist despite cessation of vitamin D prophylaxis but rapidly respond to phosphate supplementation. Therefore, early differentiation between SLC34A1 (NaPi-IIa) and CYP24A1 (24-hydroxylase) defects appears critical for targeted therapy in patients with IIH.

[Recommendations of prophylaxis of vitamin D deficiency in Poland (2009)]. / Zalecenia dotyczace profilaktyki niedoborów witaminy D w polsce (2009).

Adequate vitamin D intake and its status as well outdoor physical activity are important not only for normal bone development and Ca-P metabolism, but for optimal function of many organs and tissues throughout the body. Due to documented changes in dietary habits and physical activity level, both observed in growing children and adults, the prevalence of vitamin D insufficiency is continuously increasing. National Consultants and experts in this field established the Polish recommendations for prophylactic vitamin D supplementation in infants, toddlers, children and adolescents as well as in adults, including pregnant and lactating women based on current literature review. Taking into consideration pleyotropic vitamin D action and safety aspects serum 25-hydroxyvitamin D (25-OHD) level of 20-60 ng/ml (50-750 nmol/l) in children and 30-80 ng/ml (75-200 nmol/I) in adults is considered as optimal. Sunlight exposure inducing vitamin D production in the skin is main endogen source of vitamin D in the body but sunscreens may reduce skin synthesis by 90%. In Poland, skin synthesis is effective only from April to September so other sources of vitamin D such as diet and supplements play an important role. All newborns should be supplemented with 400 IU/d of vitamin D beginning from the first few days of life and continue during infancy. In formula fed infants vitamin D intake from the diet should be taken into account. In preterm infants higher total vitamin D intake (400-800 IU/day) is recommended till 40 weeks post conception. Total vitamin D intake in children and adolescents required from all sources (diet and/or supplements) should be 400 IU/d between October and March and throughout the whole year in case of inadequate vitamin D skin synthesis during the summer months. In overweight/obese children supplementation with higher dosage of vitamin D up to 800-1000 IU/d should be considered. Adults require 800-1000 IU/d of vitamin D. In pregnant and lactating women such supplementation is recommended in case of inadequate intake from diet and/or skin synthesis supplementation. Monitoring of serum 25-OHD level to define optimal dosage should be considered.

[Prophylaxis of vitamin D deficiency--Polish recommendations 2009]. / Polskie zalecenia dotyczace profilaktyki niedoborów witaminy D--2009.

Appropriate state procurement system for vitamin D is important not only for the proper functioning of the skeletal, maintaining calcium and phosphorus homeostasis, but also for a number of other organs and tissues in our body. In connection with the change in lifestyle including dietary habits change, the widespread use of UV filters and less outdoor activity, observed an increase in the percentage of vitamin D deficiency, both in population and developmental age and adults. Based on the results of recent scientific research team of experts provides recommendations for preventive Polish supply of vitamin D in infants, children, adolescents and adults, including pregnant women and nursing mothers.

[Prophylaxis of vitamin D deficiency--Polish recommendation 2009]. / Stanowisko Zespolu Ekspertów. Polskie zalecenia dotyczace profilaktyki niedoborów witaminy D - 2009.

Adequate vitamin D intake and its status are important not only for bone health and Ca-P metabolism, but for optimal function of many organs and tissues throughout the body. Due to documented changes in dietary habits and physical activity level, both observed in growing children and adults, the prevalence of vitamin D insufficiency is continuously increasing. Basing on current literature review and opinions of National Consultants and experts in the field, polish recommendations for prophylactic vitamin D supplementation in infants, toddlers, children and adolescents as well as in adults, including pregnant and lactating women have been established.