Homozygous NADH-methemoglobin reductase and aspartylglucosaminidase deficiencies in a moderately retarded Sicilian child

Aspartylglucosaminuria: Clinical Presentation and Potential Therapies

Aspartylglucosaminuria (AGU) is a recessively inherited neurodegenerative lysosomal storage disease characterized by progressive intellectual disability, skeletal abnormalities, connective tissue overgrowth, gait disturbance, and seizures followed by premature death. AGU is caused by pathogenic variants in the aspartylglucosaminidase (AGA) gene, leading to glycoasparagine accumulation and cellular dysfunction. Although more prevalent in the Finnish population, more than 30 AGA variants have been identified worldwide. Owing to its rarity, AGU may be largely underdiagnosed. Recognition of the following early clinical features may aid in AGU diagnosis: developmental delays, hyperactivity, early growth spurt, inguinal and abdominal hernias, clumsiness, characteristic facial features, recurring upper respiratory and ear infections, tonsillectomy, multiple sets of tympanostomy tube placement, and sleep problems. Although no curative therapies currently exist, early diagnosis may provide benefit through the provision of anticipatory guidance, management of expectations, early interventions, and prophylaxis; it will also be crucial for increased clinical benefits of future AGU disease-modifying therapies.

Early clinical symptoms and incidence of aspartylglucosaminuria in Finland

Early clinical symptoms were analyzed from all known 43 children with aspartylglucosaminuria, born during 1974-1989 in Finland. Pre- and perinatal histories appeared normal for all children, except for muscular hypotonia and weak sucking in some babies. Three infants had abduction stiffness in the hips, needing follow-up. Other abnormalities found in infancy were umbilical or inguinal hernias and unusual susceptibility to respiratory and ear infections. This susceptibility diminished clearly in most patients after six years of age. Episodic diarrhea, described earlier, appeared to be a rather infrequent symptom and a less valuable diagnostic clue. New clinical phenomena were talipes planovalgus or clubfoot, needing surgical treatment, and aggressive behavior, needing, occasionally, child psychiatric consultation or treatment. In addition, angiokeratoma of the skin, not an infrequent phenomenon among adult patients, was found in one child. The main indications for further studies were delayed speech, attention deficit and clumsy or delayed motor functions. The disease is easily misdiagnosed and, universally, probably underdiagnosed. Its incidence in Finland was recalculated and appeared to be at least 1 in 18,500 live-born babies in this country.

Spectrum of mutations in aspartylglucosaminuria

Aspartylglucosaminuria (AGU) is an inherited lysosomal storage disorder caused by the deficiency of aspartylglucosaminidase. We have earlier reported a single missense mutation (Cys163----Ser) to be responsible for 98% of the AGU alleles in the isolated Finnish population, which contains about 90% of the reported AGU patients. Here we describe the spectrum of 10 AGU mutations found in unrelated patients of non-Finnish origin. Since 11 out of 12 AGU patients were homozygotes, consanguinity has to be a common denominator in most AGU families. The mutations were distributed over the entire coding region of the aspartylglucosaminidase cDNA, except in the carboxyl-terminal 17-kDa subunit in which they were clustered within a 46-amino acid region. Based on the character of the mutations, most of them are prone to affect the folding and stability and not to directly affect the active site of the aspartylglucosaminidase enzyme.