Incidence and patterns of inborn errors of metabolism in the Eastern Province of Saudi Arabia, 1983-2008

BACKGROUND AND OBJECTIVES

Individual inborn errors of metabolism (IEM) are rare disorders, but may not be that uncommon in our patient population. We report the incidence of IEM in a defined cohort of births at the Saudi Aramco medical facilities in the Eastern Province of Saudi Arabia over 25 years.

METHODS

The records of all patients diagnosed with IEM from 1 January 1983 to 31 December 2008 were reviewed and categorized according to accumulated or deficient metabolites into small-molecule disorders (aminoacidemia, organic acidopathies [OA], urea cycle defects, fatty acid oxidation, and carbohydrate metabolic disorders) and other disorders, including glycogen and lysosomal storage disorders (LSDs), and organelle disorders.

RESULTS

During the study period, 165,530 Saudi Arabian infants were born at Saudi Aramco and 248 were diagnosed with an IEM, corresponding to a cumulative incidence of 150 cases per 100,000 live births. Small-molecule disorders were diagnosed in 134/248 patients (54%). OA were the most common (48/248 patients; 19%), and methylmalonic aciduria was the most frequently observed OA (13/48 patients; 27%). LSDs were diagnosed in 74/248 patients (30%), and mucopolysaccharidosis was the most frequently observed LSD (28/74; 38%).

CONCLUSION

We believe that our data underestimate the true incidence of IEM in the region. Regional and national newborn screening programs will provide a better estimation of the incidence of IEM. We recommend a centralized newborn screening program that employs tandem mass spectrometry.

Acrodermatitis enteropathica-like skin eruption in a case of short bowel syndrome following jejuno-transverse colon anastomosis

Acrodermatitis enteropathica is a rare autosomal recessive disorder of zinc deficiency. Zinc is an essential trace element in human metabolism and acquired zinc deficiency may manifest with skin eruptions simulating acrodermatitis enteropathica. We report an unusual case of acrodermatitis enteropathica-like skin eruption due to deficiency of zinc and other nutritional factors in a patient who has undergone extensive small bowel resection and jejuno-transverse colon anastomosis for mesenteric ischemia.

Incidence and features of galactosaemia in Saudi Arabs

Over a 12-year period (1983 to 1994), 11 cases of classical galactosaemia were identified in the Saudi Aramco Medical Services Organization (SAMSO). This yields an incidence of 12 cases per 100,000 live births in the Easter Province of Saudi Arabia. A higher proportion of infants presented with infections compared to reports in the literature. Screening for galactosaemia is highly recommended in this high-risk population.

Arterialisation of transcutaneous oxygen and carbon dioxide

We compared previously calculated global correction factors for oxygen and carbon dioxide arterial/transcutaneous ratios with individual in vivo calibrations from the first arterial sample. In infants beyond the neonatal period and older children in vivo calibration confers little benefit over the use of a global calibration correction factor for transcutaneous carbon dioxide, and may reduce the precision with which arterial oxygen can be estimated from transcutaneous oxygen.

Transcutaneous oxygen monitoring beyond the neonatal period

Transcutaneous O2 (PtcO2) tensions were compared with PaO2 measurements in 57 infants and children (age range 2 wk to 15.5 yr) using electrode temperatures of 43 degrees and 44 degrees C. At both temperatures, the relationships between PtcO2 and PaO2 were linear over the whole range of data (PaO2 39.75 to 120 torr) although mean PtcO2/PaO2 fell from 44 degrees to 43 degrees C. Skin stripping by repeated applications of adhesive tape immediately before electrode placement did not improve these relationships. In an additional 20 children with a mean age of 2.4 yr (range 0.08 to 15.85) who were being investigated for sleep-disordered breathing, the mean PaO2/PtcO2 ratio of 1.22 at 44 degrees C was used as a correction factor during air calibration for PtcO2. This resulted in a mean PtcO2/PaO2 of 0.99 (range 0.83 to 1.15) provided blood flow is not impaired. Extending the monitoring period from 4 to 8 h between site changes did not result in any burns or persisting erythema. In hemodynamically stable infants and children, and at electrode temperatures of 44 degrees C and 43 degrees C, PtcO2 is linearly related to PaO2 over a wide range of PaO2 values. At an electrode temperature of 44 degrees C, PtcO2 can be arterialized effectively by allowing for transepidermal O2 loss during air calibration; at this electrode temperature, intervals between site changes can be extended safely up to 8 h.

Transcutaneous estimation of arterial carbon dioxide in intensive care. Which electrode temperature?

Transcutaneous and arterial carbon dioxide were measured simultaneously in 57 children (age range 10 days to 14.3 years) undergoing intensive care. All were haemodynamically stable at the time of study. Mean calibration time with 5 and 10% carbon dioxide was 43 (range 38-58) minutes and mean arterialisation time was 10.5 (range 3-30) minutes. Duplicate hourly arterial samples over a four hour period showed that transcutaneous: arterial carbon dioxide correlation was independent of electrode temperatures over the range 42-44 degrees C and was independent of child age. One and a half hours after electrode placement transcutaneous carbon dioxide (kPa) = arterial carbon dioxide X 1.41 + 0.02. Use of a simple ratio (arterial carbon dioxide = transcutaneous carbon dioxide/1.40) resulted in a mean estimate of arterial carbon dioxide within 3% of the actual value with coefficients of variation of 11 and 15% at 1.5 and 4.5 hours, respectively. For prediction of arterial carbon dioxide 95% confidence limits around the regression mean rose from +/- 1.04 kPa (7.8 mm Hg) at 1.5 hours to +/- 1.56 (11.7 mm Hg) at 4.5 hours. Baseline drift was more than +/- 0.67 kPa (5 mm Hg) during 22% of the studies. For a drift of less than 0.67 kPa 95% confidence limits were 0.87 and 1.12 kPa, respectively. Arterial carbon dioxide can be estimated with clinically acceptable tolerances from surface electrodes operating at temperatures between 42-44 degrees C. Improved electrode stability and speed of calibration should make this a valuable monitoring technique.

[Transcutaneous oxygen and carbon dioxide measurement in pediatric intensive care patients]

Transcutaneous partial pressures of oxygen (PtcO2) and carbon dioxide (PtcCO2) were measured in 16 haemodynamically stable patients of a paediatric intensive care unit and were compared with simultaneously measured arterial partial pressures (PaO2 and PaCO2). For the transcutaneous measurement a sensor temperature of 44 degrees C was chosen, blood gas analysis was performed on 2 different automatic blood gas analysers. Comparisons of 82 pairs of oxygen and 60 pairs of carbon dioxide partial pressures were made. Our data show a tight linear correlation between cutaneous and arterial partial pressures of oxygen and carbon dioxide, defined by regression equations and correlation coefficients: PtcO2 = 1.22 + 0.8 X PaO2 (r = 0.93) and PtcCO2 = 5.52 + 1.26 X PaCO2 (r = 0.88). We conclude that transcutaneous measurements of oxygen and carbon dioxide partial pressures are reliable noninvasive techniques for monitoring arterial gas tensions in haemodynamically stable paediatric patients.