Which condition is characterized by development delay and abnormal myelin, alongside urine arylsulfatase being decreased?

The condition characterized by developmental delay, abnormal myelin, and decreased urine arylsulfatase is Metachromatic leukodystrophy. This is a genetic disorder related to the deficiency of the enzyme arylsulfatase A, which is essential for the breakdown of sulfatides. The accumulation of these lipids in the nervous system results in demyelination, leading to neurological decline and developmental delays.

In Metachromatic leukodystrophy, the abnormal myelin observed is a direct consequence of this accumulation, disrupting normal nerve conduction and causing various neurological symptoms. The measurement of arylsulfatase A in urine can provide a diagnostic clue, as its level is decreased in individuals with the condition.

The other conditions mentioned involve different metabolic derangements, primarily affecting other pathways or enzymes. For instance, Gaucher's Disease pertains to glucocerebrosidase deficiency, Tay-Sachs Disease involves hexosaminidase A deficiency leading to GM2 ganglioside accumulation, and Niemann-Pick Disease is associated with sphingomyelinase deficiency. While these diseases can also present with neurological symptoms, they do not share the specific combination of findings that define Metachromatic leukodystrophy.