Table 1 Clinically identified patients with a pathogenic/likely pathogenic null variant in PHKA1

ID	Sex	Location of care	Age at onset	Age at last follow up	GSD IXα1-related chief complaints	PHKA1 allele			Genetic testing	CK	EMG
ID	Sex	Location of care	Age at onset	Age at last follow up	GSD IXα1-related chief complaints	Variant	Location	Type	Genetic testing	CK	EMG
1	M	Netherlands	Early childhood^a	68	Delayed developmental milestones delay, myalgia, dysphagia	c.2806C>T (p.Arg936Ter)	Exon 25	Nonsense	WES	1.2 N	N/A
2	M	USA	5.5	11.3	Exercise intolerance, myalgia, fatigue	c.3334G>T (p.Glu1112Ter)^b	Exon 31	Nonsense	WES^c	N	N/A
3	M	Netherlands	9	15	Exercise intolerance, myalgia	c.2806C>T (p.Arg936Ter)	Exon 25	Nonsense	WES	N	N/A
4	M	USA	10	12.2	Exercise intolerance, myalgia, fatigue	c.2215C>T (p.Arg739Ter)	Exon 20	Nonsense	WES	N	N/A
5	M	USA	30	38	Myalgia, cramps, weakness	c.3334G>T (p.Glu1112Ter)^a	Exon 31	Nonsense	WGS^d	17.8 N	High frequency discharges
6	M	USA	31	34	Myalgia, cramps	c.892C>T (p.Arg298Ter)	Exon 9	Nonsense	Rhabdomyolysis and Metabolic Myopathy Panel^e	4 N	N/A
7	M	UK	49	60	Exercise intolerance, cramps, muscle wasting	c.1152T>A (p.Tyr384Ter)	Exon 12	Nonsense	WGS	2 N	N/A
8	M	USA	0.5	1.2	Failure to thrive, hypotonia, dysphagia	c.1531dup (p.Tyr511LeufsTer2)	Exon 15	Insertion/ Frameshift	Rhabdomyolysis and Metabolic Myopathy Panel	N	N/A
9	M	USA	20	33	Exercise intolerance, myalgia, cramps, weakness	c.3244-155_3620del	Exons 30-32	Deletion	Rhabdomyolysis and Metabolic Myopathy Panel	2.7 N	N/A
10	F	Germany	13	35	Exercise intolerance, myalgia, cramps	c.2029del (p.Leu677Ter)	Exon 19	Deletion/ Nonsense	WGS	N	N/A

Patients are ordered by sex, age at which symptoms first presented, and type of PHKA1 variant. Ages are provided in years. The highest creatine kinase (CK) level detected since presentation is reported and the upper limit of normal (N) was considered 310 U/L.
N/A not applicable/assessed, WES whole exome sequencing, WGS whole genome sequencing.
^aAn exact age of onset was not available. The patient endorsed symptoms starting in early childhood (i.e., prior to age 8 years). See the case description for more details.
^bVariant in PHKA1 was previously reported in the literature.
^cA homozygous nonsense mutation in FLG at c.1501C>T (p.Arg501Ter), associated with ichthyosis vulgaris, was also identified and considered to be unrelated to his myopathic symptoms.
^dA variant of uncertain significance in RYR1 at c.1735G>A (p.Glu579Lys) was also identified and has been associated with autosomal dominant central core myopathy and congenital myopathy with fiber type disproportion.
^eVariants of uncertain significance in AMPD1 at c.133C>T (p.Gln45Ter) and PYGM at c.160T>G (p.Phe54Val) were also identified.

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