Table I.

Fibroblast cell lines tested with their respective mutations in HEXA (TSD variant), HEXB (SD variant) genes, phenotype and residual Hex A activities.

Patient cell line numberA	Mutation 1	Phenotype	Mutation 2	Phenotype	% residual Hex A
TSD variants
27991	R178H	Juvenile	c.1510delC	Infantile	1.7
27986	R178H	Juvenile	R178H	Juvenile	3.0
27985	R178H	Juvenile	Y277XB	InfantileD	2.3
28236	R178H	Juvenile	R499C	Juvenile	2.2
27989	G269S	Adult	c.1278insTATC	Infantile	5.3
32540	G269S	Adult	IVS6+1G>A	Juvenile	6.4
32664	R499H	Juvenile	c.1278insTACT	Infantile	3.3
7638	R499H	Juvenile	IVS9+1G>A	Infantile	2.4
28237	R499H	Juvenile	IVS11+1G>A	Infantile	2.0
26649	IVS9+1G>A	Infantile	IVS8-7G>AB	AdultD	3.7
SD variants
1303	C137YB	JuvenileD	C137YB	JuvenileD	1.3
32429	T150LB,C	InfantileD	P417L	Adult	2.6
30037	G353RB	InfantileD	IVS12-26G>A	Juvenile	3.5
3585	P417L	Adult	Δ16kbE	Infantile	3.6
2400	P504S	Adult	Δ16kbE	Infantile	12.7F
32045	R505Q	Adult	IVS11+5G>AB	InfantileD	4.2
39997	R505Q	Adult	Δ16kbE	Infantile	5.32

^APatients’ cell lines are labeled according to the storage number from our Tissue Culture Laboratory.

^BNovel mutations.

^CThis specific mutation was originally identified by Dr. John O’Brien.

^DPredicted phenotype of novel mutations based on clinical data and residual Hex A activity levels.

^ELarge deletion of promoter-exon5 previously described (48).

^FThe residual Hex A activity is apparently above the critical threshold, because this mutation was shown to specifically decrease the ability of the residual Hex A to bind and thus, hydrolyze the GM2 ganglioside/Activator complex by ~3-fold (natural substrate assay) (23).