17 Disorders of Glycerol Metabolism Katrina M. Dipple, Edward R.B. McCabe

17.1 Introduction

Disorders of glycerol metabolism include complex deficiency (cGKD), isolated glycerol kinase deficiency (iGKD), and glycerol intolerance syndrome (GIS) (McCabe 2001a; Dipple and McCabe 2003). Glycerol kinase deficiency (GKD), both complex and isolated, is due to deletions or mutations of the glycerol kinase (GK) gene on Xp21. GIS is less well defined and some cases are due to fructose-1,6-diphosphatase (FDP) deficiency (McCabe 2001a; Dipple and McCabe 2003; Beatty et al. 2000). The treatment of acute crises in- cludes intravenous glucose and supportive care (McCabe 2001a). The mainstay of long-term treatment remains a low-fat diet and avoidance of fasting. With cGKD, there can be associated Duchenne muscular dystrophy, adrenal hypopla- sia, congenital and mental retardation; therefore, these associated diseases must be recognized and treated, especially the adrenal insufficiency (McCabe 2001a, b; Dipple and McCabe 2003; Vilain 2001). Patients with iGKD are at risk for insulin resistance, glucose intolerance, and type II diabetes mellitus (Gaudet et al. 2000), so individuals with iGKD should be monitored carefully for dia- betes. Patients with GIS must avoid glycerol, especially in intravenous infusions (McCabe 2001a). In addition, some patients with GIS have FDP deficiency, and this must be identified and treated appropriately (McCabe 2001a; Beatty et al. 2000). Unfortunately, because disorders of glycerol metabolism are such rare and presumably underdiagnosed diseases, many patients go untreated, and we therefore do not know the efficacy of treatment (Fig. 17.1). 190 Disorders of Glycerol Metabolism

GKD GIS

Avoid glycerol Avoid fasting IV glucose for crises Low fat diet IV glucose for crises

iGKD cGKD FDP deficiency

Avoid fructose Monitor for insulin Evaluate for DMD, resistance and diabetes and developmental delay

Fig. 17.1. Management if disorders of glycerol metabolism

17.2 Nomenclature

No. Disorder (symbol) Definitions/comment Gene OMIM symbol No.

17.1 Glycerol kinase deficiency Includes complex GKD (disorder 17.1.1) and GK 307030 (GKD) isolated GKD (disorder 17.1.2 and 17.1.3) 17.1.1 Complex glycerol kinase GKD as part of a contiguous gene syndrome GK, 307030, deficiency (cGKD) NROB1, 300200, DMD 310200 17.1.2 Isolated glycerol kinase Juvenile, symptomatic form GK 307030 deficiency (iGKD) 17.1.3 Isolated glycerol kinase Adultonset,benignform GK 307030 deficiency (iGKD) Adapted from Dipple and McCabe 2003

17.3 Treatment

I 17.1 Glycerol kinase deficiency 17.1.1 Complex 17.1.2 Isolated symptomatic (juvenile) 17.1.3 Isolated benign (adult) Treatment 191

No. Age Diet Symbol

17.1 All ages Acute decompensation – start IV glucose. GKD Check pH, glucose, electrolytes, ACTH Maintenance – avoid fasting, provide low-fat GKD dieta a Treatment may lower hyperglycerolemia and , but only slightly; may reduce frequency of metabolic decompensation

G 17.1.1 Complex glycerol kinase deficiency (cGKD) Diagnose and treat adrenal crisis and DMD if associated. If adrenal crisis, initi- ate glucocorticoid and mineralocorticoid replacement (McCabe 2001b; Vilain 2001b). Patients are also at risk for developmental delay, mental retardation, and (McCabe 2001a; Dipple et al. 2001). These must be monitored for and intervention started early.

G 17.1.2 and 17.1.3 Isolated symptomatic glycerol kinase deficiency (iGKD) Like patients with complex GKD, these patients are at risk for acute, episodic metabolic (acidemia ± hypoglycemia) and central nervous system (stupor, pos- sibly progressing to coma) deterioration (McCabe 2001a; Dipple and McCabe 2003). Monitor for glucose intolerance and type II diabetes mellitus (Gaudet et al. 2000), and consider referral to an endocrinologist.

Dangers/Pitfalls Patients are at increased risk for metabolic crisis when ill with febrile illness.

17.4 Treatment

I Glycerol Intolerance Syndrome Avoid glycerol ingestions and infusions. Some cases of glycerol intolerance syndrome (GIS) are secondary to FDP deficiency (McCabe 2001a; Beatty et al. 2000), in that case, treatment is based on FDP (see Chap. 15). These patients are at risk for acute, episodic metabolic and central nervous system deteri- oration (McCabe 2001a; Dipple and McCabe 2003). If patient has associated hypoglycemia, acidosis and ketosis, these should be treated using standard treatment protocols (see Part I: Initial Approaches). 192 References

17.5 Alternative Therapies/Experimental Trials

17.1 (disorders 17.1.1, 17.1.2, and 17.1.3). None.

17.6 Follow-up/Monitoring

G 17.1.1 cGKD

Age Biochemical Clinical Developmental glycerol assessment

0–3 months + Respond rapidly + to intercurrent illnesses 4–12 months Respond rapidly + to intercurrent illnesses 1–2 years Respond rapidly + to intercurrent illnesses 2–3 years Respond rapidly to intercurrent illnesses 4–6 years Respond rapidly + to intercurrent illnesses 7–9 years Respond rapidly to intercurrent illnesses 10–12 years Respond rapidly to intercurrent illnesses 13–15 years Monitor for insulin resistance Adolescents/ Monitor adults for insulin resistance

Standard protocol for intercurrent illness • Intravenous fluids (glucose) without glycerol. No added fat. • Treatment of acidosis, hypoglycemia, electrolyte abnormalities, and adrenal crisis (stress-dose steroids).

References

1. Beatty ME, Zhang YH, McCabe ERB, Steiner RD (2000) Fructose-1,6-diphosphatase deficiency and glyceroluria: one possible etiology for GIS. Molec Genet Metab 69:338– 340 2. Dipple KM, Zhang YH, Huang BL, McCabe LL, Dallongeville J, Inokuchi T, Kimura M, Marx H, Roederer C, Shih V,Yamaguchi S, Yoshida I, McCabe ERB (2001) Glycerol kinase deficiency: evidence for complexity in a single gene disorder. Hum Genet 109:55–62 3. Dipple KM, McCabe ERB (2003) Disorders of glycerol metabolism. In: Blau N, Du- ran M, Blaskovics ME, Gibson KM (eds) Physician’s guide to the laboratory diagnosis of metabolic diseases, 2nd edn. Springer, Berlin Heidelberg New York, pp 369–376 References 193

4. Gaudet D, Arsenault S, P´erusse L, Vohl MC, St.-Pierre J, Bergeron J, Després JP,Dewar K, Daly MJ, Hudson T, Rious JD (2000) Glycerol as a correlate of impaired glucose tolerance: dissection of a complex system by use of a simple genetic trait. Am J Hum Genet 66:1558– 1568 5. McCabe ERB (2001a) Disorders of glycerol metabolism. In: Scriver CR, Beaudet AL, Sly WS, Valle D, Childs B, Vogelstein B (eds) The metabolic and molecular bases of inherited disease, 8th edn. McGraw-Hill, New York, pp 2217–2237 6. McCabe ERB (2001b) Adrenal hypoplasias and aplasias. In: Scriver CR, Beaudet AL, Sly WS, Valle D, Childs B, Vogelstein B (eds) The metabolic and molecular bases of inherited disease, 8th edn. McGraw-Hill, New York, pp 4263–4274 7. Vilain E (2001) X-linked adrenal hypoplasia congenita. In: GeneReviews: genetic disease online reviews at genetests-geneclinics [database online]. University of Washington, Seattle. http://www.geneclinics.org