Dysmorphic features in patients with complex glycerol kinase deficiency

Glycerol kinase deficiency in adults: Description of 4 novel cases, systematic review and development of a clinical diagnostic score

BACKGROUND AND AIMS

Glycerol kinase deficiency (GKD) is a rare genetic disorder characterized by hyperglycerolemia and glyceroluria, which could be misdiagnosed as a moderate to severe hypertriglyceridemia (HTG). We aimed to describe four novel cases of GKD, to complete a systematic review of all cases of isolated GKD published so far, and to develop a suspicion clinical diagnostic score for GKD.

METHODS

We reported four cases with suspicion of GKD and compared their phenotype with 584 males with triglycerides (TG) > 300 mg/dL, selected as control group (HTG non-GKD). The GK gene was sequenced in all cases. Lipoprotein particle concentrations were measured in all cases with GKD. The systematic review involved a PubMed, Cochrane and Scopus databases search to identify anthropometric and biochemical characteristics of all described cases with GKD.

RESULTS

The systematic review retrieved a total of 15 articles involving 39 subjects with GKD. GKD cases reported a history of high TG levels resistant to lipid-lowering therapy. Compared to GKD subjects (n = 43), HTG non-GKD subjects (n = 584) showed significantly higher BMI, total cholesterol, non-HDL cholesterol and gamma-glutamyltransferase, significantly lower HDL cholesterol and TG, and higher prevalence of diabetes. The proposed diagnostic score was significantly higher in GKD than in HTG non-GKD subjects.

CONCLUSIONS

This is the first systematic review that compiles all GKD cases reported to date including 4 novel cases, and examine the differential GKD phenotype compared to other types of HTG. The proposed score would have a broad utility in clinical practice to avoid unwarranted lipid lowering treatment in GKD patients.

Pseudohypertriglyceridemia: A Novel Case with Important Clinical Implications

Pseudohypertriglyceridemia is an overestimation of serum triglyceride levels that may incorrectly lead to a diagnosis of hypertriglyceridemia. Glycerol kinase deficiency is a condition in which glycerol cannot be phosphorylated to glycerol-3-phosphate, resulting in elevated levels of serum glycerol. Laboratory assays that measure triglycerides indirectly may be affected by elevated glyerol levels and incorrectly report serum tryglyceride levels. We present a case of a novel missense mutation in the GK gene leading to isolated glycerol kinase deficiency and pseudohypertriglyceridemia in a male infant of a mother with gestational diabetes. This paper reviews glycerol kinase deficiency, describes the challenges in diagnosing pseudohypertriglyceridemia, and provides suggestions on improving diagnostic accuracy. Additionally, a potential maternal-fetal interaction between gestational diabetes and glycerol kinase deficiency is discussed.

Complex Glycerol Kinase Deficiency and Adrenocortical Insufficiency in Two Neonates

Contiguous gene deletions of chromosome Xp21 can lead to glycerol kinase deficiency and severe adrenocortical insufficiency (AI) in a male newborn among other problems. We describe our experience with two such patients who presented with dysmorphic facies, AI, and pseudo-hypertriglyceridemia. Both infants had normal serum 17-hidroxyprogesterone levels, and adrenal glands could not be observed with ultrasonography. Creatine kinase and triglyceride levels were measured to elucidate the etiology of adrenal hypoplasia and were above normal limits in both cases. Both patients required steroid and salt supplementation. They were both found to have Xp21.2 deletions (DMD, NR0B1, GK, IL1RAPL1). We conclude that AI in the context of other genetic abnormalities should prompt chromosomal investigations in the absence of another unifying explanation.

A young boy with diffuse hyperpigmentation and delayed puberty

An 18-year-old male patient had presented with diffuse hyperpigmentation after birth and with adrenal insufficiency syndrome since childhood. After puberty, no secondary sexual signs developed. Laboratory examination showed an extremely high concentration of serum triglycerides (9.14 mmol/L) and plasma adrenocorticotropic hormone (>275 pmol/L), however, a low concentration of plasma free cortisone (<25.1-67.6 nmol/L). Abdomen computed tomography detected atrophy of both adrenals glands.

Conserved family of glycerol kinase loci in Drosophila melanogaster

Glycerol kinase (GK) is an enzyme that catalyzes the formation of glycerol 3-phosphate from ATP and glycerol, the rate-limiting step in glycerol utilization. We analyzed the genome of the model organism Drosophila melanogaster and identified five GK orthologs, including two loci with sequence homology to the mammalian Xp21 GK protein. Using a combination of sequence analysis and evolutionary comparisons of orthologs between species, we characterized functional domains in the protein required for GK activity. Our findings include additional conserved domains that suggest novel nuclear and mitochondrial functions for glycerol kinase in apoptosis and transcriptional regulation. Investigation of GK function in Drosophila will inform us about the role of this enzyme in development and will provide us with a tool to examine genetic modifiers of human metabolic disorders.

Complex glycerol kinase deficiency: an X-linked disorder associated with adrenal hypoplasia congenita

Complex glycerol kinase deficiency (GKD) results from the contiguous deletion on Xp21 of all or part of the gene for glycerol kinase together with that for adrenal hypoplasia congenita (AHC) and /or Duchenne muscular dystrophy (DMD). The authors present the case of a newborn whose initial issues were refractory hypoglycaemia along with hyponatremia and hyperkalemia. He also had low serum cortisol levels and raised urinary excretion of glycerol and required steroid supplementation. His creatinine phosphokinase (CPK) levels were normal. Molecular studies revealed a contiguous Xp21 deletion. Therapy in such cases must be prompt and includes correction of hypoglycaemia and dyselectrolytemia, a low fat diet and steroid replacement.

Glycerol kinase deficiency: residual activity explained by reduced transcription and enzyme conformation

Four unrelated patients with glyceroluria ranging from 7 to 170 mmol/l were studied. The activity of glycerol kinase (GK) in cultured fibroblasts was determined with a specific enzyme assay and with two indirect methods, that is, incorporation into macromolecules of [(14)C] from [(14)C]glycerol and its oxidation to [(14)C]CO(2). Exon amplification and RT-PCR were used to identify mutations. In patient 1, with low activity in all three assays, we identified a c.1194A>C (E398D) missense mutation. In patient 2 with a considerable activity of the GK enzyme (22% of reference), oxidation to [(14)C]CO(2) (37%) and a high incorporation of [(14)C] into macromolecules (92%), we identified a c.182T>C (L61P) mutation that causes the enzyme to have a higher K(m) for glycerol ( approximately 300 microM) than normals (2-8 microM). In patient 3, the GK activity estimated by the three different methods ranged from 16 to 22% of reference. Analysis of mRNA from the GK gene revealed three alternatively spliced transcripts. A mutation in intron 3 (g.16835G>A) resulted in an insertion of a cryptic exon between exon 2 or 3 and exon 4. Patient 4 with minor glyceroluria (7 mmol/l) and normal plasma glycerol concentration had normal activity with all three assay methods, thus excluding GK deficiency (GKD) as a cause of slight glyceroluria. To evaluate fully patients with glyceroluria, one needs to measure the GK activity and relate this and the clinical data to genetic findings. Residual enzyme activities in cultured fibroblasts can be found in GKD patients with severe clinical symptoms.

Complex glycerol kinase deficiency leads to psychomotor and body-growth failure

Complex glycerol kinase deficiency usually presents with Duchenne muscular dystrophy, glycerol kinase deficiency and adrenal hypoplasia congenital. We describe a follow-up patient with complex glycerol kinase deficiency who had appropriate intrauterine development, but who at 1 month of age manifested severe growth delay and psychomotor retardation. Targeted therapy did not bring about the regression of symptoms: both bodyweight and height were below the 3rd centile until 8 years of age, and his Griffith's Mental Development scale score was 71 at age 5 years.

Clinical heterogeneity and molecular findings in five Polish patients with glycerol kinase deficiency: investigation of two splice site mutations with computerized splice junction analysis and Xp21 gene-specific mRNA analysis

Five cases of glycerol kinase deficiency are presented with clinical, biochemical, and genetic results. Two had the glycerol kinase deficiency as part of an Xp21 contiguous gene deletion syndrome-complex form-and three had an isolated form of the enzyme deficiency. In these we found two splice site mutations (IVS1+4A>G, IVS9-1G>T) and one insertion (1393_1394insG). In patients with the complex form, a deletion of the DAX1, GK genes and the distal part of the DMD gene was found. A computerized study was performed to predict the effects of the splice site mutations. It showed that the IVS9-1G>T mutation substantially altered and removed the wild-type site and enhanced a cryptic site seven nucleotides downstream, and that the IVS1+4A>G diminished the strength of the wild-type donor site from strong to leaky. To verify these predictions, we developed an RT-PCR system with gene-specific primers that exclusively amplifies the Xp21 glycerol kinase gene transcript. Identification of individuals at risk is motivated by a need to avoid delay in a correct diagnosis. For reliable identification of heterozygotes for isolated glycerol kinase deficiency, knowledge of the specific mutation in the proband is required. This is easily obtained with the RT-PCR analyses developed in this study.

Glycerol: a neglected variable in metabolic processes?

Glycerol is a small and simple molecule produced in the breakdown of glucose, proteins, pyruvate, triacylglycerols and other glycerolipid, as well as release from dietary fats. An increasing number of observations show that glycerol is probably involved in a surprising variety of physiopathologic mechanisms. Glycerol has long been known to play fundamental roles in several vital physiological processes, in prokaryotes and eukaryotes, and is an important intermediate of energy metabolism. Despite some differences in the details of their operation, many of these mechanisms have been preserved throughout evolution, demonstrating their fundamental importance. In particular, glycerol can control osmotic activity and crystal formation and then act as a cryoprotective agent. Furthermore, its properties make it useful in numerous industrial, therapeutic and diagnostic applications. Few studies have focussed directly on glycerol, however, and while its metabolism is increasingly well documented, much of the details remain unknown. Considering the importance of glycerol in multiple vital physiological processes, its study could help unlock important physiopathological mechanisms.

Isolated and contiguous glycerol kinase gene disorders: a review

Glycerol kinase deficiency (GKD) is an X-linked recessive disorder. There are two types. an isolated form and a complex form. We review the clinical, biochemical and molecular genetic features of GKD. The clinical and biochemical phenotype of isolated GKD may vary from a life-threatening childhood metabolic crisis to asymptomatic adult 'pseudohypertriglyceridaemia', resulting from hyperglycerolaemia. To date 38 patients from 24 families with isolated GKD have been reported. At least 7 of these patients had a metabolic crisis during a catabolic condition. The complex GKD is an Xp21 contiguous gene syndrome involving the glycerol kinase locus together with the adrenal hypoplasia congenita (AHC) or Duchenne muscular dystrophy (DMD) loci or both. Clinical features of a patient with complex GKD depend on the loci that are involved. Approximately 100 patients from 78 families with a complex GKD have been reported. Seventeen patients with complex GKD (AHC-GKD-DMD or AHC-GKD) died in the neonatal period or early childhood because of unrecognized or inappropriate management of adrenal dysfunction. Since the outcome of the crisis in GKD is highly dependent on the physicians' knowledge of the disease, we devised an algorithmic approach to the diagnosis. From molecular genetic investigations of isolated GKD, 7 missense mutations, 2 splice site mutations, I nonsense mutation, 1 Alu Sx insertion and 2 small deletions were reported for isolated GKD in 13 unrelated families. In 4 families consisting of more than one patient with the same biochemical and genetic defect, the phenotypic variability of the isolated GKD was remarkable. The clinical variability in isolated GKD cannot be explained by biochemical or by molecular heterogeneity. Isolated GKD patients showed a tendency towards hypoglycaemia with hyperketonaemia; whether the clinical symptoms of GKD are caused by dysfunction of gluconeogenesis and/or ketolysis needs to be investigated further.

Clinical heterogeneity and novel mutations in the glycerol kinase gene in three families with isolated glycerol kinase deficiency

Isolated glycerol kinase deficiency (GKD) is an X linked recessive disorder. The clinical and biochemical picture may vary from a childhood metabolic crisis to asymptomatic adult "pseudohypertriglyceridaemia", the result of hyperglycerolaemia. We performed glycerol kinase (GK) gene analysis to study the molecular heterogeneity and genotype-phenotype correlation in eight males from three families with isolated GKD. All patients had hyperglycerolaemia and glyceroluria. Four patients from two families were essentially free of symptoms. Three patients had gastrointestinal symptoms with ketoacidosis or hypoglycaemia or both. One patient had recurrent convulsions as the only acute sign, without evidence that it was correlated with a catabolic state. Fasting tests in two symptomatic patients of family 1 showed hyperketotic states, together with a tendency to hypoglycaemia. The diagnosis was confirmed by a defective 14C-glycerol incorporation into trichloroacetic acid precipitable macromolecules in intact skin fibroblasts. Mutation screening of the GK gene was performed by amplification and direct sequencing of exons using PCR. Three novel mutations were identified: (1) a deletion starting downstream of exon 9, extending to the 3' end of the gene; (2) a nonsense mutation R413X caused by a C1351T transition; and (3) a missense mutation W503R caused by a T1651C transition. In addition, we found differences from the reported sequence: (1) exon 9 actually consists of two exons, which consequently will change the number of GK gene exons from 19 to 20 exons, and (2) nucleotide differences in exon 19. So far, no genotype-phenotype correlation can be established in these GKD families.