Lakhasly

Patients’ recruitment and data collection
Patients were recruited through the nationwide German
SCD registry (NCT03327428) which collects prospective
and retrospective data on patients with SCD in Germany.
The study was performed according to the Declaration of
Helsinki and approved by the institutional review board of
the Medical Faculty of Heidelberg University (S416/2014).
Written informed consent was obtained from patients or
legal guardians.
The data collected included demographic information, di-
agnosis and genotype, treatment, laboratory parameters
and clinical events. At the time of the data cutoff, May 13,
2020, 425 patients with homozygous SCD from 28 different
institutions were enrolled in the registry. Data were ana-
lyzed by PA, JK, NA and AK-S. All co-authors had access to
all registry data.
Treatment guidelines implemented in 2014 recommend
parental education, the use of penicillin prophylaxis at
least until the age of 5 years, and annual screening with
transcranial Doppler ultrasound starting from 2 until 18
years of age. The use of hydroxyurea is encouraged in all
patients with SCD who have ever experienced a painful
vaso-occlusive crisis, including mild ones. The recom-
mended starting dose of hydroxyurea is 15 mg/kg/day for
adults and 20 mg/kg/day for children. In the case of insuf-
ficient efficacy, a dose escalation up to the maximum tol-
erated dose or to 35 mg/kg/day is recommended.
For the analysis of the frequency and distribution of genetic
modifiers, patients with homozygous SCD of all ages and ir-
respective of treatment were included. Patients with com-
pound heterozygous SCD (HbSC, HbS/β-thalassemia, others)
were excluded. For the analysis of laboratory parameters
and complications of SCD, only patients at least 2 years of
age and with ongoing treatment with hydroxyurea were con-
sidered. Patients’ data collected after stem cell transplan-
tation were excluded. Data on complications and treatment
of SCD were documented annually, together with routine
laboratory parameters (hemoglobin, mean corpuscular vol-
ume [MCV], reticulocytes, lactate dehydrogenase [LDH], bili-
rubin and HbF) (Table 1). The laboratory parameters were
only considered if the patient had not received red blood
cell transfusions within 100 days before the assessment. All
laboratory parameters were determined while the patient
was on hydroxyurea and followed for clinical complications.
If more than one laboratory data point fulfilled these criteria,
we used the average of all available data.
Patients registered by May 13, 2020 were included in the
analysis. For the correlation of HbF with laboratory par-
ameters and clinical course, all patients with available data
were analyzed (n=193 to n=202) (Figures 1 and 2). All patients
for whom the complete set of genetic traits of interest (a-
thalassemia, HBG2-polymorphism rs7482144, BCL11A poly-
morphisms rs1427407 and rs7606173, HMIP polymorphism
rs66650371) was available in combination with the respect-
ive laboratory parameter (n=121 for HbF to n=164 for MCV)
(Table 2) were included in the analyses that correlated gen-
etics with laboratory parameters and clinical course.
In order to investigate geographic and ethnic differences in
the phenotypic expression of SCD, we categorized patients
according to the origins of their parents from one of the
three regions Mediterranean Sea, Sub-Saharan Africa and
“rest of the world”. The last included mainly patients from
Iraq (n=13), all other countries contributed at most two pa-
tients.
Pain crises were defined as pain requiring pharmacological
treatment and hospitalization with no other obvious cause
besides SCD. This definition does not include visits in the
emergency department that did not result in hospital ad-
mission. Clinical events were considered from the first
dose of hydroxy urea until last follow-up (median/mean
observation period per patient 1.8/1.1 years; range, 0.5-5.3
years), independently of changes in the hydroxyurea dose.
In 313 patients with at least 1 year of follow-up on hy-
droxyurea, the severity of SCD was graded as “severe”
(n=83) if 1.5 or more pain crises requiring hospitalization
per year or 0.5 or more episodes of acute chest syndrome
(ACS) per year were documented. In addition, any stroke,
sepsis, chronic pain or need of chronic red blood cell
transfusions occurring on hydroxyurea defined a severe
course.