Acid maltase deficiency is caused by deficiency in the enzyme Acid alpha-glucosidase. It is the only glycogen storage disease with a defect in lysosomal metabolism and was the first glycogen storage disease to be identified, in 1932.

Clinical Types of acid maltase levels:

• Infantile
• Late infantile
• Juvenile
• Adult

Infantile acid maltase deficiency (Pompe disease)

• Infantile acid maltase deficiency is the classic example of a metabolic myopathy and motor neuron disease that causes infantile hypotonic.
• This form of the disorder is the most severe and carries the worst prognosis, with death ensuing between ages 6 months and 2 years.
• Pompe disease is characterized by hypotonia, weakness, areflexia, macroglossia, massive cardiomegaly, and moderate hepatomegaly.
• Development usually is normal for the first weeks or months of life, but as the disease progresses, spontaneous movements slowly decline and the infant's cry becomes weak and struggling.
• Swallowing becomes difficult. Skeletal muscle weakness and inability to handle pooled secretions lead to respiratory difficulty.
• Cardiomegaly then results, and a soft murmur sometimes is heard over the left sternal border.
• Ultimately, hepatomegaly appears, and the tongue may become enlarged and may protrude awkwardly.

Late infantile form of acid maltase deficiency (Smith disease)

• Diflty walking usually is the first symptom to appear in the late infantile form.
• The signs and symptoms may simulate those of Duchenne muscular dystrophy but usually manifest during the first few months of life.
• The disease can progress for several years until death results from cardio respiratory decompensation.

Juvenile and adult forms of acid maltase deficiency (Engel disease)

• Motor delay and progressive myopathy are the main features of the juvenile and adult forms.
• Mental retardation may be present.
• The disease is limited to skeletal muscle and leads to progressive weakness and respiratory insufficiency.
• Because enzymatic function is not entirely affected in the juvenile and adult forms, cardiac function in these groups usually is normal.
• The legs are affected more than the arms, with proximal muscles involved earlier than distal ones, and the pelvic girdle is more involved than the shoulder.
• The heart, liver, and CNS generally are uninvolved in the juvenile and adult forms.

Tests and diagnosis

• Serum Creatine Kinase usually is elevated
• Serum aspartate aminotransferase and lactic dehydrogenase can also be elevated.
• The tissue concentration level of acid maltase helps to establish a definite diagnosis
• EMG- A myopathy is demonstrated, neuropathic findings may be revealed. Pseudomyotonia may be seen in the absence of myotonia.
• ECG findings include extremely tall and broad QRS complexes with a short PR interval
• Prenatal testing- Prenatal diagnosis using chorionic villi or amniocentesis is available for the fatal infantile form.
• Postnatal testing- Newborn screening for Pompe disease can be performed by determining the total acid alpha-glucosidase in plasma or dried blood spots. The sensitivity of these tests is 82-95%, and the specificity is 100%.

Complications

• Cardio-respiratory failure
• Lung infections like bronchitis or pneumonia
• Severe muscle weakness

Treatment

Treatment for this fatal disorder is limited

Enzyme replacement therapy

Alglucosidase alfa (Myozyme)- Recombinant human enzyme alpha-glucosidase (rhGAA) indicated as an orphan drug for treatment of Pompe disease. Replaces rhGAA, which is deficient or lacking in persons with Pompe disease.

Physical therapy

The use of assistive devices and orthoses may prove beneficial in patients with AMD who develop ambulatory difficulties. The use of intermittent positive pressure ventilation in Pompe disease would seem appropriate;

Prognosis

The infantile form of acid maltase deficiency has a very unfavorable prognosis.

Death usually occurs between ages 6 months and 2 years. A less severe infantile form that exhibits a better prognosis and improved survival has been identified.

Patients with the late infantile form may survive for several years.

Patient’s education

Educating patients and family members thoroughly about this condition is important. Parents and caregivers need to be instructed in all aspects of taking care of an infant or child with acid maltase deficiency